diff options
Diffstat (limited to 'net/ipv4/tcp_input.c')
| -rw-r--r-- | net/ipv4/tcp_input.c | 6989 |
1 files changed, 6989 insertions, 0 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c new file mode 100644 index 000000000..0f9fe5eda --- /dev/null +++ b/net/ipv4/tcp_input.c @@ -0,0 +1,6989 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * INET An implementation of the TCP/IP protocol suite for the LINUX + * operating system. INET is implemented using the BSD Socket + * interface as the means of communication with the user level. + * + * Implementation of the Transmission Control Protocol(TCP). + * + * Authors: Ross Biro + * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG> + * Mark Evans, <evansmp@uhura.aston.ac.uk> + * Corey Minyard <wf-rch!minyard@relay.EU.net> + * Florian La Roche, <flla@stud.uni-sb.de> + * Charles Hedrick, <hedrick@klinzhai.rutgers.edu> + * Linus Torvalds, <torvalds@cs.helsinki.fi> + * Alan Cox, <gw4pts@gw4pts.ampr.org> + * Matthew Dillon, <dillon@apollo.west.oic.com> + * Arnt Gulbrandsen, <agulbra@nvg.unit.no> + * Jorge Cwik, <jorge@laser.satlink.net> + */ + +/* + * Changes: + * Pedro Roque : Fast Retransmit/Recovery. + * Two receive queues. + * Retransmit queue handled by TCP. + * Better retransmit timer handling. + * New congestion avoidance. + * Header prediction. + * Variable renaming. + * + * Eric : Fast Retransmit. + * Randy Scott : MSS option defines. + * Eric Schenk : Fixes to slow start algorithm. + * Eric Schenk : Yet another double ACK bug. + * Eric Schenk : Delayed ACK bug fixes. + * Eric Schenk : Floyd style fast retrans war avoidance. + * David S. Miller : Don't allow zero congestion window. + * Eric Schenk : Fix retransmitter so that it sends + * next packet on ack of previous packet. + * Andi Kleen : Moved open_request checking here + * and process RSTs for open_requests. + * Andi Kleen : Better prune_queue, and other fixes. + * Andrey Savochkin: Fix RTT measurements in the presence of + * timestamps. + * Andrey Savochkin: Check sequence numbers correctly when + * removing SACKs due to in sequence incoming + * data segments. + * Andi Kleen: Make sure we never ack data there is not + * enough room for. Also make this condition + * a fatal error if it might still happen. + * Andi Kleen: Add tcp_measure_rcv_mss to make + * connections with MSS<min(MTU,ann. MSS) + * work without delayed acks. + * Andi Kleen: Process packets with PSH set in the + * fast path. + * J Hadi Salim: ECN support + * Andrei Gurtov, + * Pasi Sarolahti, + * Panu Kuhlberg: Experimental audit of TCP (re)transmission + * engine. Lots of bugs are found. + * Pasi Sarolahti: F-RTO for dealing with spurious RTOs + */ + +#define pr_fmt(fmt) "TCP: " fmt + +#include <linux/mm.h> +#include <linux/slab.h> +#include <linux/module.h> +#include <linux/sysctl.h> +#include <linux/kernel.h> +#include <linux/prefetch.h> +#include <net/dst.h> +#include <net/tcp.h> +#include <net/inet_common.h> +#include <linux/ipsec.h> +#include <asm/unaligned.h> +#include <linux/errqueue.h> +#include <trace/events/tcp.h> +#include <linux/jump_label_ratelimit.h> +#include <net/busy_poll.h> +#include <net/mptcp.h> + +int sysctl_tcp_max_orphans __read_mostly = NR_FILE; + +#define FLAG_DATA 0x01 /* Incoming frame contained data. */ +#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */ +#define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */ +#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */ +#define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */ +#define FLAG_DATA_SACKED 0x20 /* New SACK. */ +#define FLAG_ECE 0x40 /* ECE in this ACK */ +#define FLAG_LOST_RETRANS 0x80 /* This ACK marks some retransmission lost */ +#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/ +#define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */ +#define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */ +#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */ +#define FLAG_SET_XMIT_TIMER 0x1000 /* Set TLP or RTO timer */ +#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */ +#define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */ +#define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */ +#define FLAG_ACK_MAYBE_DELAYED 0x10000 /* Likely a delayed ACK */ + +#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED) +#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED) +#define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK) +#define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED) + +#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH) +#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH)) + +#define REXMIT_NONE 0 /* no loss recovery to do */ +#define REXMIT_LOST 1 /* retransmit packets marked lost */ +#define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */ + +#if IS_ENABLED(CONFIG_TLS_DEVICE) +static DEFINE_STATIC_KEY_DEFERRED_FALSE(clean_acked_data_enabled, HZ); + +void clean_acked_data_enable(struct inet_connection_sock *icsk, + void (*cad)(struct sock *sk, u32 ack_seq)) +{ + icsk->icsk_clean_acked = cad; + static_branch_deferred_inc(&clean_acked_data_enabled); +} +EXPORT_SYMBOL_GPL(clean_acked_data_enable); + +void clean_acked_data_disable(struct inet_connection_sock *icsk) +{ + static_branch_slow_dec_deferred(&clean_acked_data_enabled); + icsk->icsk_clean_acked = NULL; +} +EXPORT_SYMBOL_GPL(clean_acked_data_disable); + +void clean_acked_data_flush(void) +{ + static_key_deferred_flush(&clean_acked_data_enabled); +} +EXPORT_SYMBOL_GPL(clean_acked_data_flush); +#endif + +#ifdef CONFIG_CGROUP_BPF +static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb) +{ + bool unknown_opt = tcp_sk(sk)->rx_opt.saw_unknown && + BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk), + BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG); + bool parse_all_opt = BPF_SOCK_OPS_TEST_FLAG(tcp_sk(sk), + BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG); + struct bpf_sock_ops_kern sock_ops; + + if (likely(!unknown_opt && !parse_all_opt)) + return; + + /* The skb will be handled in the + * bpf_skops_established() or + * bpf_skops_write_hdr_opt(). + */ + switch (sk->sk_state) { + case TCP_SYN_RECV: + case TCP_SYN_SENT: + case TCP_LISTEN: + return; + } + + sock_owned_by_me(sk); + + memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp)); + sock_ops.op = BPF_SOCK_OPS_PARSE_HDR_OPT_CB; + sock_ops.is_fullsock = 1; + sock_ops.sk = sk; + bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb)); + + BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops); +} + +static void bpf_skops_established(struct sock *sk, int bpf_op, + struct sk_buff *skb) +{ + struct bpf_sock_ops_kern sock_ops; + + sock_owned_by_me(sk); + + memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp)); + sock_ops.op = bpf_op; + sock_ops.is_fullsock = 1; + sock_ops.sk = sk; + /* sk with TCP_REPAIR_ON does not have skb in tcp_finish_connect */ + if (skb) + bpf_skops_init_skb(&sock_ops, skb, tcp_hdrlen(skb)); + + BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops); +} +#else +static void bpf_skops_parse_hdr(struct sock *sk, struct sk_buff *skb) +{ +} + +static void bpf_skops_established(struct sock *sk, int bpf_op, + struct sk_buff *skb) +{ +} +#endif + +static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb, + unsigned int len) +{ + static bool __once __read_mostly; + + if (!__once) { + struct net_device *dev; + + __once = true; + + rcu_read_lock(); + dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif); + if (!dev || len >= dev->mtu) + pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n", + dev ? dev->name : "Unknown driver"); + rcu_read_unlock(); + } +} + +/* Adapt the MSS value used to make delayed ack decision to the + * real world. + */ +static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + const unsigned int lss = icsk->icsk_ack.last_seg_size; + unsigned int len; + + icsk->icsk_ack.last_seg_size = 0; + + /* skb->len may jitter because of SACKs, even if peer + * sends good full-sized frames. + */ + len = skb_shinfo(skb)->gso_size ? : skb->len; + if (len >= icsk->icsk_ack.rcv_mss) { + icsk->icsk_ack.rcv_mss = min_t(unsigned int, len, + tcp_sk(sk)->advmss); + /* Account for possibly-removed options */ + if (unlikely(len > icsk->icsk_ack.rcv_mss + + MAX_TCP_OPTION_SPACE)) + tcp_gro_dev_warn(sk, skb, len); + /* If the skb has a len of exactly 1*MSS and has the PSH bit + * set then it is likely the end of an application write. So + * more data may not be arriving soon, and yet the data sender + * may be waiting for an ACK if cwnd-bound or using TX zero + * copy. So we set ICSK_ACK_PUSHED here so that + * tcp_cleanup_rbuf() will send an ACK immediately if the app + * reads all of the data and is not ping-pong. If len > MSS + * then this logic does not matter (and does not hurt) because + * tcp_cleanup_rbuf() will always ACK immediately if the app + * reads data and there is more than an MSS of unACKed data. + */ + if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_PSH) + icsk->icsk_ack.pending |= ICSK_ACK_PUSHED; + } else { + /* Otherwise, we make more careful check taking into account, + * that SACKs block is variable. + * + * "len" is invariant segment length, including TCP header. + */ + len += skb->data - skb_transport_header(skb); + if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) || + /* If PSH is not set, packet should be + * full sized, provided peer TCP is not badly broken. + * This observation (if it is correct 8)) allows + * to handle super-low mtu links fairly. + */ + (len >= TCP_MIN_MSS + sizeof(struct tcphdr) && + !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) { + /* Subtract also invariant (if peer is RFC compliant), + * tcp header plus fixed timestamp option length. + * Resulting "len" is MSS free of SACK jitter. + */ + len -= tcp_sk(sk)->tcp_header_len; + icsk->icsk_ack.last_seg_size = len; + if (len == lss) { + icsk->icsk_ack.rcv_mss = len; + return; + } + } + if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED) + icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2; + icsk->icsk_ack.pending |= ICSK_ACK_PUSHED; + } +} + +static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss); + + if (quickacks == 0) + quickacks = 2; + quickacks = min(quickacks, max_quickacks); + if (quickacks > icsk->icsk_ack.quick) + icsk->icsk_ack.quick = quickacks; +} + +static void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + + tcp_incr_quickack(sk, max_quickacks); + inet_csk_exit_pingpong_mode(sk); + icsk->icsk_ack.ato = TCP_ATO_MIN; +} + +/* Send ACKs quickly, if "quick" count is not exhausted + * and the session is not interactive. + */ + +static bool tcp_in_quickack_mode(struct sock *sk) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + const struct dst_entry *dst = __sk_dst_get(sk); + + return (dst && dst_metric(dst, RTAX_QUICKACK)) || + (icsk->icsk_ack.quick && !inet_csk_in_pingpong_mode(sk)); +} + +static void tcp_ecn_queue_cwr(struct tcp_sock *tp) +{ + if (tp->ecn_flags & TCP_ECN_OK) + tp->ecn_flags |= TCP_ECN_QUEUE_CWR; +} + +static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb) +{ + if (tcp_hdr(skb)->cwr) { + tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR; + + /* If the sender is telling us it has entered CWR, then its + * cwnd may be very low (even just 1 packet), so we should ACK + * immediately. + */ + if (TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) + inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW; + } +} + +static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp) +{ + tp->ecn_flags &= ~TCP_ECN_QUEUE_CWR; +} + +static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + + switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) { + case INET_ECN_NOT_ECT: + /* Funny extension: if ECT is not set on a segment, + * and we already seen ECT on a previous segment, + * it is probably a retransmit. + */ + if (tp->ecn_flags & TCP_ECN_SEEN) + tcp_enter_quickack_mode(sk, 2); + break; + case INET_ECN_CE: + if (tcp_ca_needs_ecn(sk)) + tcp_ca_event(sk, CA_EVENT_ECN_IS_CE); + + if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) { + /* Better not delay acks, sender can have a very low cwnd */ + tcp_enter_quickack_mode(sk, 2); + tp->ecn_flags |= TCP_ECN_DEMAND_CWR; + } + tp->ecn_flags |= TCP_ECN_SEEN; + break; + default: + if (tcp_ca_needs_ecn(sk)) + tcp_ca_event(sk, CA_EVENT_ECN_NO_CE); + tp->ecn_flags |= TCP_ECN_SEEN; + break; + } +} + +static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb) +{ + if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK) + __tcp_ecn_check_ce(sk, skb); +} + +static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th) +{ + if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr)) + tp->ecn_flags &= ~TCP_ECN_OK; +} + +static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th) +{ + if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr)) + tp->ecn_flags &= ~TCP_ECN_OK; +} + +static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th) +{ + if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK)) + return true; + return false; +} + +/* Buffer size and advertised window tuning. + * + * 1. Tuning sk->sk_sndbuf, when connection enters established state. + */ + +static void tcp_sndbuf_expand(struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops; + int sndmem, per_mss; + u32 nr_segs; + + /* Worst case is non GSO/TSO : each frame consumes one skb + * and skb->head is kmalloced using power of two area of memory + */ + per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) + + MAX_TCP_HEADER + + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); + + per_mss = roundup_pow_of_two(per_mss) + + SKB_DATA_ALIGN(sizeof(struct sk_buff)); + + nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd); + nr_segs = max_t(u32, nr_segs, tp->reordering + 1); + + /* Fast Recovery (RFC 5681 3.2) : + * Cubic needs 1.7 factor, rounded to 2 to include + * extra cushion (application might react slowly to EPOLLOUT) + */ + sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2; + sndmem *= nr_segs * per_mss; + + if (sk->sk_sndbuf < sndmem) + WRITE_ONCE(sk->sk_sndbuf, + min(sndmem, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_wmem[2]))); +} + +/* 2. Tuning advertised window (window_clamp, rcv_ssthresh) + * + * All tcp_full_space() is split to two parts: "network" buffer, allocated + * forward and advertised in receiver window (tp->rcv_wnd) and + * "application buffer", required to isolate scheduling/application + * latencies from network. + * window_clamp is maximal advertised window. It can be less than + * tcp_full_space(), in this case tcp_full_space() - window_clamp + * is reserved for "application" buffer. The less window_clamp is + * the smoother our behaviour from viewpoint of network, but the lower + * throughput and the higher sensitivity of the connection to losses. 8) + * + * rcv_ssthresh is more strict window_clamp used at "slow start" + * phase to predict further behaviour of this connection. + * It is used for two goals: + * - to enforce header prediction at sender, even when application + * requires some significant "application buffer". It is check #1. + * - to prevent pruning of receive queue because of misprediction + * of receiver window. Check #2. + * + * The scheme does not work when sender sends good segments opening + * window and then starts to feed us spaghetti. But it should work + * in common situations. Otherwise, we have to rely on queue collapsing. + */ + +/* Slow part of check#2. */ +static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb, + unsigned int skbtruesize) +{ + struct tcp_sock *tp = tcp_sk(sk); + /* Optimize this! */ + int truesize = tcp_win_from_space(sk, skbtruesize) >> 1; + int window = tcp_win_from_space(sk, READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])) >> 1; + + while (tp->rcv_ssthresh <= window) { + if (truesize <= skb->len) + return 2 * inet_csk(sk)->icsk_ack.rcv_mss; + + truesize >>= 1; + window >>= 1; + } + return 0; +} + +/* Even if skb appears to have a bad len/truesize ratio, TCP coalescing + * can play nice with us, as sk_buff and skb->head might be either + * freed or shared with up to MAX_SKB_FRAGS segments. + * Only give a boost to drivers using page frag(s) to hold the frame(s), + * and if no payload was pulled in skb->head before reaching us. + */ +static u32 truesize_adjust(bool adjust, const struct sk_buff *skb) +{ + u32 truesize = skb->truesize; + + if (adjust && !skb_headlen(skb)) { + truesize -= SKB_TRUESIZE(skb_end_offset(skb)); + /* paranoid check, some drivers might be buggy */ + if (unlikely((int)truesize < (int)skb->len)) + truesize = skb->truesize; + } + return truesize; +} + +static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb, + bool adjust) +{ + struct tcp_sock *tp = tcp_sk(sk); + int room; + + room = min_t(int, tp->window_clamp, tcp_space(sk)) - tp->rcv_ssthresh; + + /* Check #1 */ + if (room > 0 && !tcp_under_memory_pressure(sk)) { + unsigned int truesize = truesize_adjust(adjust, skb); + int incr; + + /* Check #2. Increase window, if skb with such overhead + * will fit to rcvbuf in future. + */ + if (tcp_win_from_space(sk, truesize) <= skb->len) + incr = 2 * tp->advmss; + else + incr = __tcp_grow_window(sk, skb, truesize); + + if (incr) { + incr = max_t(int, incr, 2 * skb->len); + tp->rcv_ssthresh += min(room, incr); + inet_csk(sk)->icsk_ack.quick |= 1; + } + } +} + +/* 3. Try to fixup all. It is made immediately after connection enters + * established state. + */ +static void tcp_init_buffer_space(struct sock *sk) +{ + int tcp_app_win = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_app_win); + struct tcp_sock *tp = tcp_sk(sk); + int maxwin; + + if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) + tcp_sndbuf_expand(sk); + + tcp_mstamp_refresh(tp); + tp->rcvq_space.time = tp->tcp_mstamp; + tp->rcvq_space.seq = tp->copied_seq; + + maxwin = tcp_full_space(sk); + + if (tp->window_clamp >= maxwin) { + tp->window_clamp = maxwin; + + if (tcp_app_win && maxwin > 4 * tp->advmss) + tp->window_clamp = max(maxwin - + (maxwin >> tcp_app_win), + 4 * tp->advmss); + } + + /* Force reservation of one segment. */ + if (tcp_app_win && + tp->window_clamp > 2 * tp->advmss && + tp->window_clamp + tp->advmss > maxwin) + tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss); + + tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp); + tp->snd_cwnd_stamp = tcp_jiffies32; + tp->rcvq_space.space = min3(tp->rcv_ssthresh, tp->rcv_wnd, + (u32)TCP_INIT_CWND * tp->advmss); +} + +/* 4. Recalculate window clamp after socket hit its memory bounds. */ +static void tcp_clamp_window(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + struct net *net = sock_net(sk); + int rmem2; + + icsk->icsk_ack.quick = 0; + rmem2 = READ_ONCE(net->ipv4.sysctl_tcp_rmem[2]); + + if (sk->sk_rcvbuf < rmem2 && + !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) && + !tcp_under_memory_pressure(sk) && + sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) { + WRITE_ONCE(sk->sk_rcvbuf, + min(atomic_read(&sk->sk_rmem_alloc), rmem2)); + } + if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf) + tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss); +} + +/* Initialize RCV_MSS value. + * RCV_MSS is an our guess about MSS used by the peer. + * We haven't any direct information about the MSS. + * It's better to underestimate the RCV_MSS rather than overestimate. + * Overestimations make us ACKing less frequently than needed. + * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss(). + */ +void tcp_initialize_rcv_mss(struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache); + + hint = min(hint, tp->rcv_wnd / 2); + hint = min(hint, TCP_MSS_DEFAULT); + hint = max(hint, TCP_MIN_MSS); + + inet_csk(sk)->icsk_ack.rcv_mss = hint; +} +EXPORT_SYMBOL(tcp_initialize_rcv_mss); + +/* Receiver "autotuning" code. + * + * The algorithm for RTT estimation w/o timestamps is based on + * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL. + * <https://public.lanl.gov/radiant/pubs.html#DRS> + * + * More detail on this code can be found at + * <http://staff.psc.edu/jheffner/>, + * though this reference is out of date. A new paper + * is pending. + */ +static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep) +{ + u32 new_sample = tp->rcv_rtt_est.rtt_us; + long m = sample; + + if (new_sample != 0) { + /* If we sample in larger samples in the non-timestamp + * case, we could grossly overestimate the RTT especially + * with chatty applications or bulk transfer apps which + * are stalled on filesystem I/O. + * + * Also, since we are only going for a minimum in the + * non-timestamp case, we do not smooth things out + * else with timestamps disabled convergence takes too + * long. + */ + if (!win_dep) { + m -= (new_sample >> 3); + new_sample += m; + } else { + m <<= 3; + if (m < new_sample) + new_sample = m; + } + } else { + /* No previous measure. */ + new_sample = m << 3; + } + + tp->rcv_rtt_est.rtt_us = new_sample; +} + +static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp) +{ + u32 delta_us; + + if (tp->rcv_rtt_est.time == 0) + goto new_measure; + if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq)) + return; + delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time); + if (!delta_us) + delta_us = 1; + tcp_rcv_rtt_update(tp, delta_us, 1); + +new_measure: + tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd; + tp->rcv_rtt_est.time = tp->tcp_mstamp; +} + +static inline void tcp_rcv_rtt_measure_ts(struct sock *sk, + const struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr) + return; + tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr; + + if (TCP_SKB_CB(skb)->end_seq - + TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) { + u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr; + u32 delta_us; + + if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) { + if (!delta) + delta = 1; + delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ); + tcp_rcv_rtt_update(tp, delta_us, 0); + } + } +} + +/* + * This function should be called every time data is copied to user space. + * It calculates the appropriate TCP receive buffer space. + */ +void tcp_rcv_space_adjust(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 copied; + int time; + + trace_tcp_rcv_space_adjust(sk); + + tcp_mstamp_refresh(tp); + time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time); + if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0) + return; + + /* Number of bytes copied to user in last RTT */ + copied = tp->copied_seq - tp->rcvq_space.seq; + if (copied <= tp->rcvq_space.space) + goto new_measure; + + /* A bit of theory : + * copied = bytes received in previous RTT, our base window + * To cope with packet losses, we need a 2x factor + * To cope with slow start, and sender growing its cwin by 100 % + * every RTT, we need a 4x factor, because the ACK we are sending + * now is for the next RTT, not the current one : + * <prev RTT . ><current RTT .. ><next RTT .... > + */ + + if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) && + !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) { + int rcvmem, rcvbuf; + u64 rcvwin, grow; + + /* minimal window to cope with packet losses, assuming + * steady state. Add some cushion because of small variations. + */ + rcvwin = ((u64)copied << 1) + 16 * tp->advmss; + + /* Accommodate for sender rate increase (eg. slow start) */ + grow = rcvwin * (copied - tp->rcvq_space.space); + do_div(grow, tp->rcvq_space.space); + rcvwin += (grow << 1); + + rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER); + while (tcp_win_from_space(sk, rcvmem) < tp->advmss) + rcvmem += 128; + + do_div(rcvwin, tp->advmss); + rcvbuf = min_t(u64, rcvwin * rcvmem, + READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])); + if (rcvbuf > sk->sk_rcvbuf) { + WRITE_ONCE(sk->sk_rcvbuf, rcvbuf); + + /* Make the window clamp follow along. */ + tp->window_clamp = tcp_win_from_space(sk, rcvbuf); + } + } + tp->rcvq_space.space = copied; + +new_measure: + tp->rcvq_space.seq = tp->copied_seq; + tp->rcvq_space.time = tp->tcp_mstamp; +} + +/* There is something which you must keep in mind when you analyze the + * behavior of the tp->ato delayed ack timeout interval. When a + * connection starts up, we want to ack as quickly as possible. The + * problem is that "good" TCP's do slow start at the beginning of data + * transmission. The means that until we send the first few ACK's the + * sender will sit on his end and only queue most of his data, because + * he can only send snd_cwnd unacked packets at any given time. For + * each ACK we send, he increments snd_cwnd and transmits more of his + * queue. -DaveM + */ +static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + u32 now; + + inet_csk_schedule_ack(sk); + + tcp_measure_rcv_mss(sk, skb); + + tcp_rcv_rtt_measure(tp); + + now = tcp_jiffies32; + + if (!icsk->icsk_ack.ato) { + /* The _first_ data packet received, initialize + * delayed ACK engine. + */ + tcp_incr_quickack(sk, TCP_MAX_QUICKACKS); + icsk->icsk_ack.ato = TCP_ATO_MIN; + } else { + int m = now - icsk->icsk_ack.lrcvtime; + + if (m <= TCP_ATO_MIN / 2) { + /* The fastest case is the first. */ + icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2; + } else if (m < icsk->icsk_ack.ato) { + icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m; + if (icsk->icsk_ack.ato > icsk->icsk_rto) + icsk->icsk_ack.ato = icsk->icsk_rto; + } else if (m > icsk->icsk_rto) { + /* Too long gap. Apparently sender failed to + * restart window, so that we send ACKs quickly. + */ + tcp_incr_quickack(sk, TCP_MAX_QUICKACKS); + sk_mem_reclaim(sk); + } + } + icsk->icsk_ack.lrcvtime = now; + + tcp_ecn_check_ce(sk, skb); + + if (skb->len >= 128) + tcp_grow_window(sk, skb, true); +} + +/* Called to compute a smoothed rtt estimate. The data fed to this + * routine either comes from timestamps, or from segments that were + * known _not_ to have been retransmitted [see Karn/Partridge + * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88 + * piece by Van Jacobson. + * NOTE: the next three routines used to be one big routine. + * To save cycles in the RFC 1323 implementation it was better to break + * it up into three procedures. -- erics + */ +static void tcp_rtt_estimator(struct sock *sk, long mrtt_us) +{ + struct tcp_sock *tp = tcp_sk(sk); + long m = mrtt_us; /* RTT */ + u32 srtt = tp->srtt_us; + + /* The following amusing code comes from Jacobson's + * article in SIGCOMM '88. Note that rtt and mdev + * are scaled versions of rtt and mean deviation. + * This is designed to be as fast as possible + * m stands for "measurement". + * + * On a 1990 paper the rto value is changed to: + * RTO = rtt + 4 * mdev + * + * Funny. This algorithm seems to be very broken. + * These formulae increase RTO, when it should be decreased, increase + * too slowly, when it should be increased quickly, decrease too quickly + * etc. I guess in BSD RTO takes ONE value, so that it is absolutely + * does not matter how to _calculate_ it. Seems, it was trap + * that VJ failed to avoid. 8) + */ + if (srtt != 0) { + m -= (srtt >> 3); /* m is now error in rtt est */ + srtt += m; /* rtt = 7/8 rtt + 1/8 new */ + if (m < 0) { + m = -m; /* m is now abs(error) */ + m -= (tp->mdev_us >> 2); /* similar update on mdev */ + /* This is similar to one of Eifel findings. + * Eifel blocks mdev updates when rtt decreases. + * This solution is a bit different: we use finer gain + * for mdev in this case (alpha*beta). + * Like Eifel it also prevents growth of rto, + * but also it limits too fast rto decreases, + * happening in pure Eifel. + */ + if (m > 0) + m >>= 3; + } else { + m -= (tp->mdev_us >> 2); /* similar update on mdev */ + } + tp->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */ + if (tp->mdev_us > tp->mdev_max_us) { + tp->mdev_max_us = tp->mdev_us; + if (tp->mdev_max_us > tp->rttvar_us) + tp->rttvar_us = tp->mdev_max_us; + } + if (after(tp->snd_una, tp->rtt_seq)) { + if (tp->mdev_max_us < tp->rttvar_us) + tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2; + tp->rtt_seq = tp->snd_nxt; + tp->mdev_max_us = tcp_rto_min_us(sk); + + tcp_bpf_rtt(sk); + } + } else { + /* no previous measure. */ + srtt = m << 3; /* take the measured time to be rtt */ + tp->mdev_us = m << 1; /* make sure rto = 3*rtt */ + tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk)); + tp->mdev_max_us = tp->rttvar_us; + tp->rtt_seq = tp->snd_nxt; + + tcp_bpf_rtt(sk); + } + tp->srtt_us = max(1U, srtt); +} + +static void tcp_update_pacing_rate(struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + u64 rate; + + /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */ + rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3); + + /* current rate is (cwnd * mss) / srtt + * In Slow Start [1], set sk_pacing_rate to 200 % the current rate. + * In Congestion Avoidance phase, set it to 120 % the current rate. + * + * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh) + * If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching + * end of slow start and should slow down. + */ + if (tp->snd_cwnd < tp->snd_ssthresh / 2) + rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio; + else + rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio; + + rate *= max(tp->snd_cwnd, tp->packets_out); + + if (likely(tp->srtt_us)) + do_div(rate, tp->srtt_us); + + /* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate + * without any lock. We want to make sure compiler wont store + * intermediate values in this location. + */ + WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate, + sk->sk_max_pacing_rate)); +} + +/* Calculate rto without backoff. This is the second half of Van Jacobson's + * routine referred to above. + */ +static void tcp_set_rto(struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + /* Old crap is replaced with new one. 8) + * + * More seriously: + * 1. If rtt variance happened to be less 50msec, it is hallucination. + * It cannot be less due to utterly erratic ACK generation made + * at least by solaris and freebsd. "Erratic ACKs" has _nothing_ + * to do with delayed acks, because at cwnd>2 true delack timeout + * is invisible. Actually, Linux-2.4 also generates erratic + * ACKs in some circumstances. + */ + inet_csk(sk)->icsk_rto = __tcp_set_rto(tp); + + /* 2. Fixups made earlier cannot be right. + * If we do not estimate RTO correctly without them, + * all the algo is pure shit and should be replaced + * with correct one. It is exactly, which we pretend to do. + */ + + /* NOTE: clamping at TCP_RTO_MIN is not required, current algo + * guarantees that rto is higher. + */ + tcp_bound_rto(sk); +} + +__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst) +{ + __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0); + + if (!cwnd) + cwnd = TCP_INIT_CWND; + return min_t(__u32, cwnd, tp->snd_cwnd_clamp); +} + +struct tcp_sacktag_state { + /* Timestamps for earliest and latest never-retransmitted segment + * that was SACKed. RTO needs the earliest RTT to stay conservative, + * but congestion control should still get an accurate delay signal. + */ + u64 first_sackt; + u64 last_sackt; + u32 reord; + u32 sack_delivered; + int flag; + unsigned int mss_now; + struct rate_sample *rate; +}; + +/* Take a notice that peer is sending D-SACKs. Skip update of data delivery + * and spurious retransmission information if this DSACK is unlikely caused by + * sender's action: + * - DSACKed sequence range is larger than maximum receiver's window. + * - Total no. of DSACKed segments exceed the total no. of retransmitted segs. + */ +static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq, + u32 end_seq, struct tcp_sacktag_state *state) +{ + u32 seq_len, dup_segs = 1; + + if (!before(start_seq, end_seq)) + return 0; + + seq_len = end_seq - start_seq; + /* Dubious DSACK: DSACKed range greater than maximum advertised rwnd */ + if (seq_len > tp->max_window) + return 0; + if (seq_len > tp->mss_cache) + dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache); + + tp->dsack_dups += dup_segs; + /* Skip the DSACK if dup segs weren't retransmitted by sender */ + if (tp->dsack_dups > tp->total_retrans) + return 0; + + tp->rx_opt.sack_ok |= TCP_DSACK_SEEN; + tp->rack.dsack_seen = 1; + + state->flag |= FLAG_DSACKING_ACK; + /* A spurious retransmission is delivered */ + state->sack_delivered += dup_segs; + + return dup_segs; +} + +/* It's reordering when higher sequence was delivered (i.e. sacked) before + * some lower never-retransmitted sequence ("low_seq"). The maximum reordering + * distance is approximated in full-mss packet distance ("reordering"). + */ +static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq, + const int ts) +{ + struct tcp_sock *tp = tcp_sk(sk); + const u32 mss = tp->mss_cache; + u32 fack, metric; + + fack = tcp_highest_sack_seq(tp); + if (!before(low_seq, fack)) + return; + + metric = fack - low_seq; + if ((metric > tp->reordering * mss) && mss) { +#if FASTRETRANS_DEBUG > 1 + pr_debug("Disorder%d %d %u f%u s%u rr%d\n", + tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state, + tp->reordering, + 0, + tp->sacked_out, + tp->undo_marker ? tp->undo_retrans : 0); +#endif + tp->reordering = min_t(u32, (metric + mss - 1) / mss, + READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering)); + } + + /* This exciting event is worth to be remembered. 8) */ + tp->reord_seen++; + NET_INC_STATS(sock_net(sk), + ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER); +} + + /* This must be called before lost_out or retrans_out are updated + * on a new loss, because we want to know if all skbs previously + * known to be lost have already been retransmitted, indicating + * that this newly lost skb is our next skb to retransmit. + */ +static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb) +{ + if ((!tp->retransmit_skb_hint && tp->retrans_out >= tp->lost_out) || + (tp->retransmit_skb_hint && + before(TCP_SKB_CB(skb)->seq, + TCP_SKB_CB(tp->retransmit_skb_hint)->seq))) + tp->retransmit_skb_hint = skb; +} + +/* Sum the number of packets on the wire we have marked as lost, and + * notify the congestion control module that the given skb was marked lost. + */ +static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff *skb) +{ + tp->lost += tcp_skb_pcount(skb); +} + +void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb) +{ + __u8 sacked = TCP_SKB_CB(skb)->sacked; + struct tcp_sock *tp = tcp_sk(sk); + + if (sacked & TCPCB_SACKED_ACKED) + return; + + tcp_verify_retransmit_hint(tp, skb); + if (sacked & TCPCB_LOST) { + if (sacked & TCPCB_SACKED_RETRANS) { + /* Account for retransmits that are lost again */ + TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; + tp->retrans_out -= tcp_skb_pcount(skb); + NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT, + tcp_skb_pcount(skb)); + tcp_notify_skb_loss_event(tp, skb); + } + } else { + tp->lost_out += tcp_skb_pcount(skb); + TCP_SKB_CB(skb)->sacked |= TCPCB_LOST; + tcp_notify_skb_loss_event(tp, skb); + } +} + +/* Updates the delivered and delivered_ce counts */ +static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered, + bool ece_ack) +{ + tp->delivered += delivered; + if (ece_ack) + tp->delivered_ce += delivered; +} + +/* This procedure tags the retransmission queue when SACKs arrive. + * + * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L). + * Packets in queue with these bits set are counted in variables + * sacked_out, retrans_out and lost_out, correspondingly. + * + * Valid combinations are: + * Tag InFlight Description + * 0 1 - orig segment is in flight. + * S 0 - nothing flies, orig reached receiver. + * L 0 - nothing flies, orig lost by net. + * R 2 - both orig and retransmit are in flight. + * L|R 1 - orig is lost, retransmit is in flight. + * S|R 1 - orig reached receiver, retrans is still in flight. + * (L|S|R is logically valid, it could occur when L|R is sacked, + * but it is equivalent to plain S and code short-curcuits it to S. + * L|S is logically invalid, it would mean -1 packet in flight 8)) + * + * These 6 states form finite state machine, controlled by the following events: + * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue()) + * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue()) + * 3. Loss detection event of two flavors: + * A. Scoreboard estimator decided the packet is lost. + * A'. Reno "three dupacks" marks head of queue lost. + * B. SACK arrives sacking SND.NXT at the moment, when the + * segment was retransmitted. + * 4. D-SACK added new rule: D-SACK changes any tag to S. + * + * It is pleasant to note, that state diagram turns out to be commutative, + * so that we are allowed not to be bothered by order of our actions, + * when multiple events arrive simultaneously. (see the function below). + * + * Reordering detection. + * -------------------- + * Reordering metric is maximal distance, which a packet can be displaced + * in packet stream. With SACKs we can estimate it: + * + * 1. SACK fills old hole and the corresponding segment was not + * ever retransmitted -> reordering. Alas, we cannot use it + * when segment was retransmitted. + * 2. The last flaw is solved with D-SACK. D-SACK arrives + * for retransmitted and already SACKed segment -> reordering.. + * Both of these heuristics are not used in Loss state, when we cannot + * account for retransmits accurately. + * + * SACK block validation. + * ---------------------- + * + * SACK block range validation checks that the received SACK block fits to + * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT. + * Note that SND.UNA is not included to the range though being valid because + * it means that the receiver is rather inconsistent with itself reporting + * SACK reneging when it should advance SND.UNA. Such SACK block this is + * perfectly valid, however, in light of RFC2018 which explicitly states + * that "SACK block MUST reflect the newest segment. Even if the newest + * segment is going to be discarded ...", not that it looks very clever + * in case of head skb. Due to potentional receiver driven attacks, we + * choose to avoid immediate execution of a walk in write queue due to + * reneging and defer head skb's loss recovery to standard loss recovery + * procedure that will eventually trigger (nothing forbids us doing this). + * + * Implements also blockage to start_seq wrap-around. Problem lies in the + * fact that though start_seq (s) is before end_seq (i.e., not reversed), + * there's no guarantee that it will be before snd_nxt (n). The problem + * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt + * wrap (s_w): + * + * <- outs wnd -> <- wrapzone -> + * u e n u_w e_w s n_w + * | | | | | | | + * |<------------+------+----- TCP seqno space --------------+---------->| + * ...-- <2^31 ->| |<--------... + * ...---- >2^31 ------>| |<--------... + * + * Current code wouldn't be vulnerable but it's better still to discard such + * crazy SACK blocks. Doing this check for start_seq alone closes somewhat + * similar case (end_seq after snd_nxt wrap) as earlier reversed check in + * snd_nxt wrap -> snd_una region will then become "well defined", i.e., + * equal to the ideal case (infinite seqno space without wrap caused issues). + * + * With D-SACK the lower bound is extended to cover sequence space below + * SND.UNA down to undo_marker, which is the last point of interest. Yet + * again, D-SACK block must not to go across snd_una (for the same reason as + * for the normal SACK blocks, explained above). But there all simplicity + * ends, TCP might receive valid D-SACKs below that. As long as they reside + * fully below undo_marker they do not affect behavior in anyway and can + * therefore be safely ignored. In rare cases (which are more or less + * theoretical ones), the D-SACK will nicely cross that boundary due to skb + * fragmentation and packet reordering past skb's retransmission. To consider + * them correctly, the acceptable range must be extended even more though + * the exact amount is rather hard to quantify. However, tp->max_window can + * be used as an exaggerated estimate. + */ +static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack, + u32 start_seq, u32 end_seq) +{ + /* Too far in future, or reversed (interpretation is ambiguous) */ + if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq)) + return false; + + /* Nasty start_seq wrap-around check (see comments above) */ + if (!before(start_seq, tp->snd_nxt)) + return false; + + /* In outstanding window? ...This is valid exit for D-SACKs too. + * start_seq == snd_una is non-sensical (see comments above) + */ + if (after(start_seq, tp->snd_una)) + return true; + + if (!is_dsack || !tp->undo_marker) + return false; + + /* ...Then it's D-SACK, and must reside below snd_una completely */ + if (after(end_seq, tp->snd_una)) + return false; + + if (!before(start_seq, tp->undo_marker)) + return true; + + /* Too old */ + if (!after(end_seq, tp->undo_marker)) + return false; + + /* Undo_marker boundary crossing (overestimates a lot). Known already: + * start_seq < undo_marker and end_seq >= undo_marker. + */ + return !before(start_seq, end_seq - tp->max_window); +} + +static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb, + struct tcp_sack_block_wire *sp, int num_sacks, + u32 prior_snd_una, struct tcp_sacktag_state *state) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq); + u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq); + u32 dup_segs; + + if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV); + } else if (num_sacks > 1) { + u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq); + u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq); + + if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1)) + return false; + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV); + } else { + return false; + } + + dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state); + if (!dup_segs) { /* Skip dubious DSACK */ + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKIGNOREDDUBIOUS); + return false; + } + + NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs); + + /* D-SACK for already forgotten data... Do dumb counting. */ + if (tp->undo_marker && tp->undo_retrans > 0 && + !after(end_seq_0, prior_snd_una) && + after(end_seq_0, tp->undo_marker)) + tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs); + + return true; +} + +/* Check if skb is fully within the SACK block. In presence of GSO skbs, + * the incoming SACK may not exactly match but we can find smaller MSS + * aligned portion of it that matches. Therefore we might need to fragment + * which may fail and creates some hassle (caller must handle error case + * returns). + * + * FIXME: this could be merged to shift decision code + */ +static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb, + u32 start_seq, u32 end_seq) +{ + int err; + bool in_sack; + unsigned int pkt_len; + unsigned int mss; + + in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && + !before(end_seq, TCP_SKB_CB(skb)->end_seq); + + if (tcp_skb_pcount(skb) > 1 && !in_sack && + after(TCP_SKB_CB(skb)->end_seq, start_seq)) { + mss = tcp_skb_mss(skb); + in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); + + if (!in_sack) { + pkt_len = start_seq - TCP_SKB_CB(skb)->seq; + if (pkt_len < mss) + pkt_len = mss; + } else { + pkt_len = end_seq - TCP_SKB_CB(skb)->seq; + if (pkt_len < mss) + return -EINVAL; + } + + /* Round if necessary so that SACKs cover only full MSSes + * and/or the remaining small portion (if present) + */ + if (pkt_len > mss) { + unsigned int new_len = (pkt_len / mss) * mss; + if (!in_sack && new_len < pkt_len) + new_len += mss; + pkt_len = new_len; + } + + if (pkt_len >= skb->len && !in_sack) + return 0; + + err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, + pkt_len, mss, GFP_ATOMIC); + if (err < 0) + return err; + } + + return in_sack; +} + +/* Mark the given newly-SACKed range as such, adjusting counters and hints. */ +static u8 tcp_sacktag_one(struct sock *sk, + struct tcp_sacktag_state *state, u8 sacked, + u32 start_seq, u32 end_seq, + int dup_sack, int pcount, + u64 xmit_time) +{ + struct tcp_sock *tp = tcp_sk(sk); + + /* Account D-SACK for retransmitted packet. */ + if (dup_sack && (sacked & TCPCB_RETRANS)) { + if (tp->undo_marker && tp->undo_retrans > 0 && + after(end_seq, tp->undo_marker)) + tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount); + if ((sacked & TCPCB_SACKED_ACKED) && + before(start_seq, state->reord)) + state->reord = start_seq; + } + + /* Nothing to do; acked frame is about to be dropped (was ACKed). */ + if (!after(end_seq, tp->snd_una)) + return sacked; + + if (!(sacked & TCPCB_SACKED_ACKED)) { + tcp_rack_advance(tp, sacked, end_seq, xmit_time); + + if (sacked & TCPCB_SACKED_RETRANS) { + /* If the segment is not tagged as lost, + * we do not clear RETRANS, believing + * that retransmission is still in flight. + */ + if (sacked & TCPCB_LOST) { + sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS); + tp->lost_out -= pcount; + tp->retrans_out -= pcount; + } + } else { + if (!(sacked & TCPCB_RETRANS)) { + /* New sack for not retransmitted frame, + * which was in hole. It is reordering. + */ + if (before(start_seq, + tcp_highest_sack_seq(tp)) && + before(start_seq, state->reord)) + state->reord = start_seq; + + if (!after(end_seq, tp->high_seq)) + state->flag |= FLAG_ORIG_SACK_ACKED; + if (state->first_sackt == 0) + state->first_sackt = xmit_time; + state->last_sackt = xmit_time; + } + + if (sacked & TCPCB_LOST) { + sacked &= ~TCPCB_LOST; + tp->lost_out -= pcount; + } + } + + sacked |= TCPCB_SACKED_ACKED; + state->flag |= FLAG_DATA_SACKED; + tp->sacked_out += pcount; + /* Out-of-order packets delivered */ + state->sack_delivered += pcount; + + /* Lost marker hint past SACKed? Tweak RFC3517 cnt */ + if (tp->lost_skb_hint && + before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq)) + tp->lost_cnt_hint += pcount; + } + + /* D-SACK. We can detect redundant retransmission in S|R and plain R + * frames and clear it. undo_retrans is decreased above, L|R frames + * are accounted above as well. + */ + if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) { + sacked &= ~TCPCB_SACKED_RETRANS; + tp->retrans_out -= pcount; + } + + return sacked; +} + +/* Shift newly-SACKed bytes from this skb to the immediately previous + * already-SACKed sk_buff. Mark the newly-SACKed bytes as such. + */ +static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev, + struct sk_buff *skb, + struct tcp_sacktag_state *state, + unsigned int pcount, int shifted, int mss, + bool dup_sack) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */ + u32 end_seq = start_seq + shifted; /* end of newly-SACKed */ + + BUG_ON(!pcount); + + /* Adjust counters and hints for the newly sacked sequence + * range but discard the return value since prev is already + * marked. We must tag the range first because the seq + * advancement below implicitly advances + * tcp_highest_sack_seq() when skb is highest_sack. + */ + tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked, + start_seq, end_seq, dup_sack, pcount, + tcp_skb_timestamp_us(skb)); + tcp_rate_skb_delivered(sk, skb, state->rate); + + if (skb == tp->lost_skb_hint) + tp->lost_cnt_hint += pcount; + + TCP_SKB_CB(prev)->end_seq += shifted; + TCP_SKB_CB(skb)->seq += shifted; + + tcp_skb_pcount_add(prev, pcount); + WARN_ON_ONCE(tcp_skb_pcount(skb) < pcount); + tcp_skb_pcount_add(skb, -pcount); + + /* When we're adding to gso_segs == 1, gso_size will be zero, + * in theory this shouldn't be necessary but as long as DSACK + * code can come after this skb later on it's better to keep + * setting gso_size to something. + */ + if (!TCP_SKB_CB(prev)->tcp_gso_size) + TCP_SKB_CB(prev)->tcp_gso_size = mss; + + /* CHECKME: To clear or not to clear? Mimics normal skb currently */ + if (tcp_skb_pcount(skb) <= 1) + TCP_SKB_CB(skb)->tcp_gso_size = 0; + + /* Difference in this won't matter, both ACKed by the same cumul. ACK */ + TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS); + + if (skb->len > 0) { + BUG_ON(!tcp_skb_pcount(skb)); + NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED); + return false; + } + + /* Whole SKB was eaten :-) */ + + if (skb == tp->retransmit_skb_hint) + tp->retransmit_skb_hint = prev; + if (skb == tp->lost_skb_hint) { + tp->lost_skb_hint = prev; + tp->lost_cnt_hint -= tcp_skb_pcount(prev); + } + + TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags; + TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor; + if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) + TCP_SKB_CB(prev)->end_seq++; + + if (skb == tcp_highest_sack(sk)) + tcp_advance_highest_sack(sk, skb); + + tcp_skb_collapse_tstamp(prev, skb); + if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp)) + TCP_SKB_CB(prev)->tx.delivered_mstamp = 0; + + tcp_rtx_queue_unlink_and_free(skb, sk); + + NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED); + + return true; +} + +/* I wish gso_size would have a bit more sane initialization than + * something-or-zero which complicates things + */ +static int tcp_skb_seglen(const struct sk_buff *skb) +{ + return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb); +} + +/* Shifting pages past head area doesn't work */ +static int skb_can_shift(const struct sk_buff *skb) +{ + return !skb_headlen(skb) && skb_is_nonlinear(skb); +} + +int tcp_skb_shift(struct sk_buff *to, struct sk_buff *from, + int pcount, int shiftlen) +{ + /* TCP min gso_size is 8 bytes (TCP_MIN_GSO_SIZE) + * Since TCP_SKB_CB(skb)->tcp_gso_segs is 16 bits, we need + * to make sure not storing more than 65535 * 8 bytes per skb, + * even if current MSS is bigger. + */ + if (unlikely(to->len + shiftlen >= 65535 * TCP_MIN_GSO_SIZE)) + return 0; + if (unlikely(tcp_skb_pcount(to) + pcount > 65535)) + return 0; + return skb_shift(to, from, shiftlen); +} + +/* Try collapsing SACK blocks spanning across multiple skbs to a single + * skb. + */ +static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb, + struct tcp_sacktag_state *state, + u32 start_seq, u32 end_seq, + bool dup_sack) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *prev; + int mss; + int pcount = 0; + int len; + int in_sack; + + /* Normally R but no L won't result in plain S */ + if (!dup_sack && + (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS) + goto fallback; + if (!skb_can_shift(skb)) + goto fallback; + /* This frame is about to be dropped (was ACKed). */ + if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)) + goto fallback; + + /* Can only happen with delayed DSACK + discard craziness */ + prev = skb_rb_prev(skb); + if (!prev) + goto fallback; + + if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) + goto fallback; + + if (!tcp_skb_can_collapse(prev, skb)) + goto fallback; + + in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) && + !before(end_seq, TCP_SKB_CB(skb)->end_seq); + + if (in_sack) { + len = skb->len; + pcount = tcp_skb_pcount(skb); + mss = tcp_skb_seglen(skb); + + /* TODO: Fix DSACKs to not fragment already SACKed and we can + * drop this restriction as unnecessary + */ + if (mss != tcp_skb_seglen(prev)) + goto fallback; + } else { + if (!after(TCP_SKB_CB(skb)->end_seq, start_seq)) + goto noop; + /* CHECKME: This is non-MSS split case only?, this will + * cause skipped skbs due to advancing loop btw, original + * has that feature too + */ + if (tcp_skb_pcount(skb) <= 1) + goto noop; + + in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq); + if (!in_sack) { + /* TODO: head merge to next could be attempted here + * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)), + * though it might not be worth of the additional hassle + * + * ...we can probably just fallback to what was done + * previously. We could try merging non-SACKed ones + * as well but it probably isn't going to buy off + * because later SACKs might again split them, and + * it would make skb timestamp tracking considerably + * harder problem. + */ + goto fallback; + } + + len = end_seq - TCP_SKB_CB(skb)->seq; + BUG_ON(len < 0); + BUG_ON(len > skb->len); + + /* MSS boundaries should be honoured or else pcount will + * severely break even though it makes things bit trickier. + * Optimize common case to avoid most of the divides + */ + mss = tcp_skb_mss(skb); + + /* TODO: Fix DSACKs to not fragment already SACKed and we can + * drop this restriction as unnecessary + */ + if (mss != tcp_skb_seglen(prev)) + goto fallback; + + if (len == mss) { + pcount = 1; + } else if (len < mss) { + goto noop; + } else { + pcount = len / mss; + len = pcount * mss; + } + } + + /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */ + if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una)) + goto fallback; + + if (!tcp_skb_shift(prev, skb, pcount, len)) + goto fallback; + if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack)) + goto out; + + /* Hole filled allows collapsing with the next as well, this is very + * useful when hole on every nth skb pattern happens + */ + skb = skb_rb_next(prev); + if (!skb) + goto out; + + if (!skb_can_shift(skb) || + ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) || + (mss != tcp_skb_seglen(skb))) + goto out; + + if (!tcp_skb_can_collapse(prev, skb)) + goto out; + len = skb->len; + pcount = tcp_skb_pcount(skb); + if (tcp_skb_shift(prev, skb, pcount, len)) + tcp_shifted_skb(sk, prev, skb, state, pcount, + len, mss, 0); + +out: + return prev; + +noop: + return skb; + +fallback: + NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK); + return NULL; +} + +static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk, + struct tcp_sack_block *next_dup, + struct tcp_sacktag_state *state, + u32 start_seq, u32 end_seq, + bool dup_sack_in) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *tmp; + + skb_rbtree_walk_from(skb) { + int in_sack = 0; + bool dup_sack = dup_sack_in; + + /* queue is in-order => we can short-circuit the walk early */ + if (!before(TCP_SKB_CB(skb)->seq, end_seq)) + break; + + if (next_dup && + before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) { + in_sack = tcp_match_skb_to_sack(sk, skb, + next_dup->start_seq, + next_dup->end_seq); + if (in_sack > 0) + dup_sack = true; + } + + /* skb reference here is a bit tricky to get right, since + * shifting can eat and free both this skb and the next, + * so not even _safe variant of the loop is enough. + */ + if (in_sack <= 0) { + tmp = tcp_shift_skb_data(sk, skb, state, + start_seq, end_seq, dup_sack); + if (tmp) { + if (tmp != skb) { + skb = tmp; + continue; + } + + in_sack = 0; + } else { + in_sack = tcp_match_skb_to_sack(sk, skb, + start_seq, + end_seq); + } + } + + if (unlikely(in_sack < 0)) + break; + + if (in_sack) { + TCP_SKB_CB(skb)->sacked = + tcp_sacktag_one(sk, + state, + TCP_SKB_CB(skb)->sacked, + TCP_SKB_CB(skb)->seq, + TCP_SKB_CB(skb)->end_seq, + dup_sack, + tcp_skb_pcount(skb), + tcp_skb_timestamp_us(skb)); + tcp_rate_skb_delivered(sk, skb, state->rate); + if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) + list_del_init(&skb->tcp_tsorted_anchor); + + if (!before(TCP_SKB_CB(skb)->seq, + tcp_highest_sack_seq(tp))) + tcp_advance_highest_sack(sk, skb); + } + } + return skb; +} + +static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk, u32 seq) +{ + struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node; + struct sk_buff *skb; + + while (*p) { + parent = *p; + skb = rb_to_skb(parent); + if (before(seq, TCP_SKB_CB(skb)->seq)) { + p = &parent->rb_left; + continue; + } + if (!before(seq, TCP_SKB_CB(skb)->end_seq)) { + p = &parent->rb_right; + continue; + } + return skb; + } + return NULL; +} + +static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk, + u32 skip_to_seq) +{ + if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq)) + return skb; + + return tcp_sacktag_bsearch(sk, skip_to_seq); +} + +static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb, + struct sock *sk, + struct tcp_sack_block *next_dup, + struct tcp_sacktag_state *state, + u32 skip_to_seq) +{ + if (!next_dup) + return skb; + + if (before(next_dup->start_seq, skip_to_seq)) { + skb = tcp_sacktag_skip(skb, sk, next_dup->start_seq); + skb = tcp_sacktag_walk(skb, sk, NULL, state, + next_dup->start_seq, next_dup->end_seq, + 1); + } + + return skb; +} + +static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache) +{ + return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); +} + +static int +tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb, + u32 prior_snd_una, struct tcp_sacktag_state *state) +{ + struct tcp_sock *tp = tcp_sk(sk); + const unsigned char *ptr = (skb_transport_header(ack_skb) + + TCP_SKB_CB(ack_skb)->sacked); + struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2); + struct tcp_sack_block sp[TCP_NUM_SACKS]; + struct tcp_sack_block *cache; + struct sk_buff *skb; + int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3); + int used_sacks; + bool found_dup_sack = false; + int i, j; + int first_sack_index; + + state->flag = 0; + state->reord = tp->snd_nxt; + + if (!tp->sacked_out) + tcp_highest_sack_reset(sk); + + found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire, + num_sacks, prior_snd_una, state); + + /* Eliminate too old ACKs, but take into + * account more or less fresh ones, they can + * contain valid SACK info. + */ + if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window)) + return 0; + + if (!tp->packets_out) + goto out; + + used_sacks = 0; + first_sack_index = 0; + for (i = 0; i < num_sacks; i++) { + bool dup_sack = !i && found_dup_sack; + + sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq); + sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq); + + if (!tcp_is_sackblock_valid(tp, dup_sack, + sp[used_sacks].start_seq, + sp[used_sacks].end_seq)) { + int mib_idx; + + if (dup_sack) { + if (!tp->undo_marker) + mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO; + else + mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD; + } else { + /* Don't count olds caused by ACK reordering */ + if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) && + !after(sp[used_sacks].end_seq, tp->snd_una)) + continue; + mib_idx = LINUX_MIB_TCPSACKDISCARD; + } + + NET_INC_STATS(sock_net(sk), mib_idx); + if (i == 0) + first_sack_index = -1; + continue; + } + + /* Ignore very old stuff early */ + if (!after(sp[used_sacks].end_seq, prior_snd_una)) { + if (i == 0) + first_sack_index = -1; + continue; + } + + used_sacks++; + } + + /* order SACK blocks to allow in order walk of the retrans queue */ + for (i = used_sacks - 1; i > 0; i--) { + for (j = 0; j < i; j++) { + if (after(sp[j].start_seq, sp[j + 1].start_seq)) { + swap(sp[j], sp[j + 1]); + + /* Track where the first SACK block goes to */ + if (j == first_sack_index) + first_sack_index = j + 1; + } + } + } + + state->mss_now = tcp_current_mss(sk); + skb = NULL; + i = 0; + + if (!tp->sacked_out) { + /* It's already past, so skip checking against it */ + cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache); + } else { + cache = tp->recv_sack_cache; + /* Skip empty blocks in at head of the cache */ + while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq && + !cache->end_seq) + cache++; + } + + while (i < used_sacks) { + u32 start_seq = sp[i].start_seq; + u32 end_seq = sp[i].end_seq; + bool dup_sack = (found_dup_sack && (i == first_sack_index)); + struct tcp_sack_block *next_dup = NULL; + + if (found_dup_sack && ((i + 1) == first_sack_index)) + next_dup = &sp[i + 1]; + + /* Skip too early cached blocks */ + while (tcp_sack_cache_ok(tp, cache) && + !before(start_seq, cache->end_seq)) + cache++; + + /* Can skip some work by looking recv_sack_cache? */ + if (tcp_sack_cache_ok(tp, cache) && !dup_sack && + after(end_seq, cache->start_seq)) { + + /* Head todo? */ + if (before(start_seq, cache->start_seq)) { + skb = tcp_sacktag_skip(skb, sk, start_seq); + skb = tcp_sacktag_walk(skb, sk, next_dup, + state, + start_seq, + cache->start_seq, + dup_sack); + } + + /* Rest of the block already fully processed? */ + if (!after(end_seq, cache->end_seq)) + goto advance_sp; + + skb = tcp_maybe_skipping_dsack(skb, sk, next_dup, + state, + cache->end_seq); + + /* ...tail remains todo... */ + if (tcp_highest_sack_seq(tp) == cache->end_seq) { + /* ...but better entrypoint exists! */ + skb = tcp_highest_sack(sk); + if (!skb) + break; + cache++; + goto walk; + } + + skb = tcp_sacktag_skip(skb, sk, cache->end_seq); + /* Check overlap against next cached too (past this one already) */ + cache++; + continue; + } + + if (!before(start_seq, tcp_highest_sack_seq(tp))) { + skb = tcp_highest_sack(sk); + if (!skb) + break; + } + skb = tcp_sacktag_skip(skb, sk, start_seq); + +walk: + skb = tcp_sacktag_walk(skb, sk, next_dup, state, + start_seq, end_seq, dup_sack); + +advance_sp: + i++; + } + + /* Clear the head of the cache sack blocks so we can skip it next time */ + for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) { + tp->recv_sack_cache[i].start_seq = 0; + tp->recv_sack_cache[i].end_seq = 0; + } + for (j = 0; j < used_sacks; j++) + tp->recv_sack_cache[i++] = sp[j]; + + if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker) + tcp_check_sack_reordering(sk, state->reord, 0); + + tcp_verify_left_out(tp); +out: + +#if FASTRETRANS_DEBUG > 0 + WARN_ON((int)tp->sacked_out < 0); + WARN_ON((int)tp->lost_out < 0); + WARN_ON((int)tp->retrans_out < 0); + WARN_ON((int)tcp_packets_in_flight(tp) < 0); +#endif + return state->flag; +} + +/* Limits sacked_out so that sum with lost_out isn't ever larger than + * packets_out. Returns false if sacked_out adjustement wasn't necessary. + */ +static bool tcp_limit_reno_sacked(struct tcp_sock *tp) +{ + u32 holes; + + holes = max(tp->lost_out, 1U); + holes = min(holes, tp->packets_out); + + if ((tp->sacked_out + holes) > tp->packets_out) { + tp->sacked_out = tp->packets_out - holes; + return true; + } + return false; +} + +/* If we receive more dupacks than we expected counting segments + * in assumption of absent reordering, interpret this as reordering. + * The only another reason could be bug in receiver TCP. + */ +static void tcp_check_reno_reordering(struct sock *sk, const int addend) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (!tcp_limit_reno_sacked(tp)) + return; + + tp->reordering = min_t(u32, tp->packets_out + addend, + READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_max_reordering)); + tp->reord_seen++; + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER); +} + +/* Emulate SACKs for SACKless connection: account for a new dupack. */ + +static void tcp_add_reno_sack(struct sock *sk, int num_dupack, bool ece_ack) +{ + if (num_dupack) { + struct tcp_sock *tp = tcp_sk(sk); + u32 prior_sacked = tp->sacked_out; + s32 delivered; + + tp->sacked_out += num_dupack; + tcp_check_reno_reordering(sk, 0); + delivered = tp->sacked_out - prior_sacked; + if (delivered > 0) + tcp_count_delivered(tp, delivered, ece_ack); + tcp_verify_left_out(tp); + } +} + +/* Account for ACK, ACKing some data in Reno Recovery phase. */ + +static void tcp_remove_reno_sacks(struct sock *sk, int acked, bool ece_ack) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (acked > 0) { + /* One ACK acked hole. The rest eat duplicate ACKs. */ + tcp_count_delivered(tp, max_t(int, acked - tp->sacked_out, 1), + ece_ack); + if (acked - 1 >= tp->sacked_out) + tp->sacked_out = 0; + else + tp->sacked_out -= acked - 1; + } + tcp_check_reno_reordering(sk, acked); + tcp_verify_left_out(tp); +} + +static inline void tcp_reset_reno_sack(struct tcp_sock *tp) +{ + tp->sacked_out = 0; +} + +void tcp_clear_retrans(struct tcp_sock *tp) +{ + tp->retrans_out = 0; + tp->lost_out = 0; + tp->undo_marker = 0; + tp->undo_retrans = -1; + tp->sacked_out = 0; +} + +static inline void tcp_init_undo(struct tcp_sock *tp) +{ + tp->undo_marker = tp->snd_una; + /* Retransmission still in flight may cause DSACKs later. */ + tp->undo_retrans = tp->retrans_out ? : -1; +} + +static bool tcp_is_rack(const struct sock *sk) +{ + return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) & + TCP_RACK_LOSS_DETECTION; +} + +/* If we detect SACK reneging, forget all SACK information + * and reset tags completely, otherwise preserve SACKs. If receiver + * dropped its ofo queue, we will know this due to reneging detection. + */ +static void tcp_timeout_mark_lost(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb, *head; + bool is_reneg; /* is receiver reneging on SACKs? */ + + head = tcp_rtx_queue_head(sk); + is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED); + if (is_reneg) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING); + tp->sacked_out = 0; + /* Mark SACK reneging until we recover from this loss event. */ + tp->is_sack_reneg = 1; + } else if (tcp_is_reno(tp)) { + tcp_reset_reno_sack(tp); + } + + skb = head; + skb_rbtree_walk_from(skb) { + if (is_reneg) + TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED; + else if (tcp_is_rack(sk) && skb != head && + tcp_rack_skb_timeout(tp, skb, 0) > 0) + continue; /* Don't mark recently sent ones lost yet */ + tcp_mark_skb_lost(sk, skb); + } + tcp_verify_left_out(tp); + tcp_clear_all_retrans_hints(tp); +} + +/* Enter Loss state. */ +void tcp_enter_loss(struct sock *sk) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + struct net *net = sock_net(sk); + bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery; + u8 reordering; + + tcp_timeout_mark_lost(sk); + + /* Reduce ssthresh if it has not yet been made inside this window. */ + if (icsk->icsk_ca_state <= TCP_CA_Disorder || + !after(tp->high_seq, tp->snd_una) || + (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) { + tp->prior_ssthresh = tcp_current_ssthresh(sk); + tp->prior_cwnd = tp->snd_cwnd; + tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk); + tcp_ca_event(sk, CA_EVENT_LOSS); + tcp_init_undo(tp); + } + tp->snd_cwnd = tcp_packets_in_flight(tp) + 1; + tp->snd_cwnd_cnt = 0; + tp->snd_cwnd_stamp = tcp_jiffies32; + + /* Timeout in disordered state after receiving substantial DUPACKs + * suggests that the degree of reordering is over-estimated. + */ + reordering = READ_ONCE(net->ipv4.sysctl_tcp_reordering); + if (icsk->icsk_ca_state <= TCP_CA_Disorder && + tp->sacked_out >= reordering) + tp->reordering = min_t(unsigned int, tp->reordering, + reordering); + + tcp_set_ca_state(sk, TCP_CA_Loss); + tp->high_seq = tp->snd_nxt; + tcp_ecn_queue_cwr(tp); + + /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous + * loss recovery is underway except recurring timeout(s) on + * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing + */ + tp->frto = READ_ONCE(net->ipv4.sysctl_tcp_frto) && + (new_recovery || icsk->icsk_retransmits) && + !inet_csk(sk)->icsk_mtup.probe_size; +} + +/* If ACK arrived pointing to a remembered SACK, it means that our + * remembered SACKs do not reflect real state of receiver i.e. + * receiver _host_ is heavily congested (or buggy). + * + * To avoid big spurious retransmission bursts due to transient SACK + * scoreboard oddities that look like reneging, we give the receiver a + * little time (max(RTT/2, 10ms)) to send us some more ACKs that will + * restore sanity to the SACK scoreboard. If the apparent reneging + * persists until this RTO then we'll clear the SACK scoreboard. + */ +static bool tcp_check_sack_reneging(struct sock *sk, int *ack_flag) +{ + if (*ack_flag & FLAG_SACK_RENEGING && + *ack_flag & FLAG_SND_UNA_ADVANCED) { + struct tcp_sock *tp = tcp_sk(sk); + unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4), + msecs_to_jiffies(10)); + + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, + delay, TCP_RTO_MAX); + *ack_flag &= ~FLAG_SET_XMIT_TIMER; + return true; + } + return false; +} + +/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs + * counter when SACK is enabled (without SACK, sacked_out is used for + * that purpose). + * + * With reordering, holes may still be in flight, so RFC3517 recovery + * uses pure sacked_out (total number of SACKed segments) even though + * it violates the RFC that uses duplicate ACKs, often these are equal + * but when e.g. out-of-window ACKs or packet duplication occurs, + * they differ. Since neither occurs due to loss, TCP should really + * ignore them. + */ +static inline int tcp_dupack_heuristics(const struct tcp_sock *tp) +{ + return tp->sacked_out + 1; +} + +/* Linux NewReno/SACK/ECN state machine. + * -------------------------------------- + * + * "Open" Normal state, no dubious events, fast path. + * "Disorder" In all the respects it is "Open", + * but requires a bit more attention. It is entered when + * we see some SACKs or dupacks. It is split of "Open" + * mainly to move some processing from fast path to slow one. + * "CWR" CWND was reduced due to some Congestion Notification event. + * It can be ECN, ICMP source quench, local device congestion. + * "Recovery" CWND was reduced, we are fast-retransmitting. + * "Loss" CWND was reduced due to RTO timeout or SACK reneging. + * + * tcp_fastretrans_alert() is entered: + * - each incoming ACK, if state is not "Open" + * - when arrived ACK is unusual, namely: + * * SACK + * * Duplicate ACK. + * * ECN ECE. + * + * Counting packets in flight is pretty simple. + * + * in_flight = packets_out - left_out + retrans_out + * + * packets_out is SND.NXT-SND.UNA counted in packets. + * + * retrans_out is number of retransmitted segments. + * + * left_out is number of segments left network, but not ACKed yet. + * + * left_out = sacked_out + lost_out + * + * sacked_out: Packets, which arrived to receiver out of order + * and hence not ACKed. With SACKs this number is simply + * amount of SACKed data. Even without SACKs + * it is easy to give pretty reliable estimate of this number, + * counting duplicate ACKs. + * + * lost_out: Packets lost by network. TCP has no explicit + * "loss notification" feedback from network (for now). + * It means that this number can be only _guessed_. + * Actually, it is the heuristics to predict lossage that + * distinguishes different algorithms. + * + * F.e. after RTO, when all the queue is considered as lost, + * lost_out = packets_out and in_flight = retrans_out. + * + * Essentially, we have now a few algorithms detecting + * lost packets. + * + * If the receiver supports SACK: + * + * RFC6675/3517: It is the conventional algorithm. A packet is + * considered lost if the number of higher sequence packets + * SACKed is greater than or equal the DUPACK thoreshold + * (reordering). This is implemented in tcp_mark_head_lost and + * tcp_update_scoreboard. + * + * RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm + * (2017-) that checks timing instead of counting DUPACKs. + * Essentially a packet is considered lost if it's not S/ACKed + * after RTT + reordering_window, where both metrics are + * dynamically measured and adjusted. This is implemented in + * tcp_rack_mark_lost. + * + * If the receiver does not support SACK: + * + * NewReno (RFC6582): in Recovery we assume that one segment + * is lost (classic Reno). While we are in Recovery and + * a partial ACK arrives, we assume that one more packet + * is lost (NewReno). This heuristics are the same in NewReno + * and SACK. + * + * Really tricky (and requiring careful tuning) part of algorithm + * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue(). + * The first determines the moment _when_ we should reduce CWND and, + * hence, slow down forward transmission. In fact, it determines the moment + * when we decide that hole is caused by loss, rather than by a reorder. + * + * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill + * holes, caused by lost packets. + * + * And the most logically complicated part of algorithm is undo + * heuristics. We detect false retransmits due to both too early + * fast retransmit (reordering) and underestimated RTO, analyzing + * timestamps and D-SACKs. When we detect that some segments were + * retransmitted by mistake and CWND reduction was wrong, we undo + * window reduction and abort recovery phase. This logic is hidden + * inside several functions named tcp_try_undo_<something>. + */ + +/* This function decides, when we should leave Disordered state + * and enter Recovery phase, reducing congestion window. + * + * Main question: may we further continue forward transmission + * with the same cwnd? + */ +static bool tcp_time_to_recover(struct sock *sk, int flag) +{ + struct tcp_sock *tp = tcp_sk(sk); + + /* Trick#1: The loss is proven. */ + if (tp->lost_out) + return true; + + /* Not-A-Trick#2 : Classic rule... */ + if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering) + return true; + + return false; +} + +/* Detect loss in event "A" above by marking head of queue up as lost. + * For RFC3517 SACK, a segment is considered lost if it + * has at least tp->reordering SACKed seqments above it; "packets" refers to + * the maximum SACKed segments to pass before reaching this limit. + */ +static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + int cnt; + /* Use SACK to deduce losses of new sequences sent during recovery */ + const u32 loss_high = tp->snd_nxt; + + WARN_ON(packets > tp->packets_out); + skb = tp->lost_skb_hint; + if (skb) { + /* Head already handled? */ + if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una)) + return; + cnt = tp->lost_cnt_hint; + } else { + skb = tcp_rtx_queue_head(sk); + cnt = 0; + } + + skb_rbtree_walk_from(skb) { + /* TODO: do this better */ + /* this is not the most efficient way to do this... */ + tp->lost_skb_hint = skb; + tp->lost_cnt_hint = cnt; + + if (after(TCP_SKB_CB(skb)->end_seq, loss_high)) + break; + + if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) + cnt += tcp_skb_pcount(skb); + + if (cnt > packets) + break; + + if (!(TCP_SKB_CB(skb)->sacked & TCPCB_LOST)) + tcp_mark_skb_lost(sk, skb); + + if (mark_head) + break; + } + tcp_verify_left_out(tp); +} + +/* Account newly detected lost packet(s) */ + +static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_is_sack(tp)) { + int sacked_upto = tp->sacked_out - tp->reordering; + if (sacked_upto >= 0) + tcp_mark_head_lost(sk, sacked_upto, 0); + else if (fast_rexmit) + tcp_mark_head_lost(sk, 1, 1); + } +} + +static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when) +{ + return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && + before(tp->rx_opt.rcv_tsecr, when); +} + +/* skb is spurious retransmitted if the returned timestamp echo + * reply is prior to the skb transmission time + */ +static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp, + const struct sk_buff *skb) +{ + return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) && + tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb)); +} + +/* Nothing was retransmitted or returned timestamp is less + * than timestamp of the first retransmission. + */ +static inline bool tcp_packet_delayed(const struct tcp_sock *tp) +{ + return tp->retrans_stamp && + tcp_tsopt_ecr_before(tp, tp->retrans_stamp); +} + +/* Undo procedures. */ + +/* We can clear retrans_stamp when there are no retransmissions in the + * window. It would seem that it is trivially available for us in + * tp->retrans_out, however, that kind of assumptions doesn't consider + * what will happen if errors occur when sending retransmission for the + * second time. ...It could the that such segment has only + * TCPCB_EVER_RETRANS set at the present time. It seems that checking + * the head skb is enough except for some reneging corner cases that + * are not worth the effort. + * + * Main reason for all this complexity is the fact that connection dying + * time now depends on the validity of the retrans_stamp, in particular, + * that successive retransmissions of a segment must not advance + * retrans_stamp under any conditions. + */ +static bool tcp_any_retrans_done(const struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + + if (tp->retrans_out) + return true; + + skb = tcp_rtx_queue_head(sk); + if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS)) + return true; + + return false; +} + +static void DBGUNDO(struct sock *sk, const char *msg) +{ +#if FASTRETRANS_DEBUG > 1 + struct tcp_sock *tp = tcp_sk(sk); + struct inet_sock *inet = inet_sk(sk); + + if (sk->sk_family == AF_INET) { + pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n", + msg, + &inet->inet_daddr, ntohs(inet->inet_dport), + tp->snd_cwnd, tcp_left_out(tp), + tp->snd_ssthresh, tp->prior_ssthresh, + tp->packets_out); + } +#if IS_ENABLED(CONFIG_IPV6) + else if (sk->sk_family == AF_INET6) { + pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n", + msg, + &sk->sk_v6_daddr, ntohs(inet->inet_dport), + tp->snd_cwnd, tcp_left_out(tp), + tp->snd_ssthresh, tp->prior_ssthresh, + tp->packets_out); + } +#endif +#endif +} + +static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (unmark_loss) { + struct sk_buff *skb; + + skb_rbtree_walk(skb, &sk->tcp_rtx_queue) { + TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST; + } + tp->lost_out = 0; + tcp_clear_all_retrans_hints(tp); + } + + if (tp->prior_ssthresh) { + const struct inet_connection_sock *icsk = inet_csk(sk); + + tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk); + + if (tp->prior_ssthresh > tp->snd_ssthresh) { + tp->snd_ssthresh = tp->prior_ssthresh; + tcp_ecn_withdraw_cwr(tp); + } + } + tp->snd_cwnd_stamp = tcp_jiffies32; + tp->undo_marker = 0; + tp->rack.advanced = 1; /* Force RACK to re-exam losses */ +} + +static inline bool tcp_may_undo(const struct tcp_sock *tp) +{ + return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp)); +} + +static bool tcp_is_non_sack_preventing_reopen(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) { + /* Hold old state until something *above* high_seq + * is ACKed. For Reno it is MUST to prevent false + * fast retransmits (RFC2582). SACK TCP is safe. */ + if (!tcp_any_retrans_done(sk)) + tp->retrans_stamp = 0; + return true; + } + return false; +} + +/* People celebrate: "We love our President!" */ +static bool tcp_try_undo_recovery(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_may_undo(tp)) { + int mib_idx; + + /* Happy end! We did not retransmit anything + * or our original transmission succeeded. + */ + DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans"); + tcp_undo_cwnd_reduction(sk, false); + if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss) + mib_idx = LINUX_MIB_TCPLOSSUNDO; + else + mib_idx = LINUX_MIB_TCPFULLUNDO; + + NET_INC_STATS(sock_net(sk), mib_idx); + } else if (tp->rack.reo_wnd_persist) { + tp->rack.reo_wnd_persist--; + } + if (tcp_is_non_sack_preventing_reopen(sk)) + return true; + tcp_set_ca_state(sk, TCP_CA_Open); + tp->is_sack_reneg = 0; + return false; +} + +/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */ +static bool tcp_try_undo_dsack(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tp->undo_marker && !tp->undo_retrans) { + tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH, + tp->rack.reo_wnd_persist + 1); + DBGUNDO(sk, "D-SACK"); + tcp_undo_cwnd_reduction(sk, false); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO); + return true; + } + return false; +} + +/* Undo during loss recovery after partial ACK or using F-RTO. */ +static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (frto_undo || tcp_may_undo(tp)) { + tcp_undo_cwnd_reduction(sk, true); + + DBGUNDO(sk, "partial loss"); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO); + if (frto_undo) + NET_INC_STATS(sock_net(sk), + LINUX_MIB_TCPSPURIOUSRTOS); + inet_csk(sk)->icsk_retransmits = 0; + if (tcp_is_non_sack_preventing_reopen(sk)) + return true; + if (frto_undo || tcp_is_sack(tp)) { + tcp_set_ca_state(sk, TCP_CA_Open); + tp->is_sack_reneg = 0; + } + return true; + } + return false; +} + +/* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937. + * It computes the number of packets to send (sndcnt) based on packets newly + * delivered: + * 1) If the packets in flight is larger than ssthresh, PRR spreads the + * cwnd reductions across a full RTT. + * 2) Otherwise PRR uses packet conservation to send as much as delivered. + * But when the retransmits are acked without further losses, PRR + * slow starts cwnd up to ssthresh to speed up the recovery. + */ +static void tcp_init_cwnd_reduction(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + tp->high_seq = tp->snd_nxt; + tp->tlp_high_seq = 0; + tp->snd_cwnd_cnt = 0; + tp->prior_cwnd = tp->snd_cwnd; + tp->prr_delivered = 0; + tp->prr_out = 0; + tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk); + tcp_ecn_queue_cwr(tp); +} + +void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int flag) +{ + struct tcp_sock *tp = tcp_sk(sk); + int sndcnt = 0; + int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp); + + if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd)) + return; + + tp->prr_delivered += newly_acked_sacked; + if (delta < 0) { + u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered + + tp->prior_cwnd - 1; + sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out; + } else if ((flag & (FLAG_RETRANS_DATA_ACKED | FLAG_LOST_RETRANS)) == + FLAG_RETRANS_DATA_ACKED) { + sndcnt = min_t(int, delta, + max_t(int, tp->prr_delivered - tp->prr_out, + newly_acked_sacked) + 1); + } else { + sndcnt = min(delta, newly_acked_sacked); + } + /* Force a fast retransmit upon entering fast recovery */ + sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1)); + tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt; +} + +static inline void tcp_end_cwnd_reduction(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (inet_csk(sk)->icsk_ca_ops->cong_control) + return; + + /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */ + if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH && + (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) { + tp->snd_cwnd = tp->snd_ssthresh; + tp->snd_cwnd_stamp = tcp_jiffies32; + } + tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR); +} + +/* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */ +void tcp_enter_cwr(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + tp->prior_ssthresh = 0; + if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) { + tp->undo_marker = 0; + tcp_init_cwnd_reduction(sk); + tcp_set_ca_state(sk, TCP_CA_CWR); + } +} +EXPORT_SYMBOL(tcp_enter_cwr); + +static void tcp_try_keep_open(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + int state = TCP_CA_Open; + + if (tcp_left_out(tp) || tcp_any_retrans_done(sk)) + state = TCP_CA_Disorder; + + if (inet_csk(sk)->icsk_ca_state != state) { + tcp_set_ca_state(sk, state); + tp->high_seq = tp->snd_nxt; + } +} + +static void tcp_try_to_open(struct sock *sk, int flag) +{ + struct tcp_sock *tp = tcp_sk(sk); + + tcp_verify_left_out(tp); + + if (!tcp_any_retrans_done(sk)) + tp->retrans_stamp = 0; + + if (flag & FLAG_ECE) + tcp_enter_cwr(sk); + + if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) { + tcp_try_keep_open(sk); + } +} + +static void tcp_mtup_probe_failed(struct sock *sk) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + + icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1; + icsk->icsk_mtup.probe_size = 0; + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL); +} + +static void tcp_mtup_probe_success(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + u64 val; + + tp->prior_ssthresh = tcp_current_ssthresh(sk); + + val = (u64)tp->snd_cwnd * tcp_mss_to_mtu(sk, tp->mss_cache); + do_div(val, icsk->icsk_mtup.probe_size); + WARN_ON_ONCE((u32)val != val); + tp->snd_cwnd = max_t(u32, 1U, val); + + tp->snd_cwnd_cnt = 0; + tp->snd_cwnd_stamp = tcp_jiffies32; + tp->snd_ssthresh = tcp_current_ssthresh(sk); + + icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size; + icsk->icsk_mtup.probe_size = 0; + tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS); +} + +/* Do a simple retransmit without using the backoff mechanisms in + * tcp_timer. This is used for path mtu discovery. + * The socket is already locked here. + */ +void tcp_simple_retransmit(struct sock *sk) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *skb; + unsigned int mss = tcp_current_mss(sk); + + skb_rbtree_walk(skb, &sk->tcp_rtx_queue) { + if (tcp_skb_seglen(skb) > mss) + tcp_mark_skb_lost(sk, skb); + } + + tcp_clear_retrans_hints_partial(tp); + + if (!tp->lost_out) + return; + + if (tcp_is_reno(tp)) + tcp_limit_reno_sacked(tp); + + tcp_verify_left_out(tp); + + /* Don't muck with the congestion window here. + * Reason is that we do not increase amount of _data_ + * in network, but units changed and effective + * cwnd/ssthresh really reduced now. + */ + if (icsk->icsk_ca_state != TCP_CA_Loss) { + tp->high_seq = tp->snd_nxt; + tp->snd_ssthresh = tcp_current_ssthresh(sk); + tp->prior_ssthresh = 0; + tp->undo_marker = 0; + tcp_set_ca_state(sk, TCP_CA_Loss); + } + tcp_xmit_retransmit_queue(sk); +} +EXPORT_SYMBOL(tcp_simple_retransmit); + +void tcp_enter_recovery(struct sock *sk, bool ece_ack) +{ + struct tcp_sock *tp = tcp_sk(sk); + int mib_idx; + + if (tcp_is_reno(tp)) + mib_idx = LINUX_MIB_TCPRENORECOVERY; + else + mib_idx = LINUX_MIB_TCPSACKRECOVERY; + + NET_INC_STATS(sock_net(sk), mib_idx); + + tp->prior_ssthresh = 0; + tcp_init_undo(tp); + + if (!tcp_in_cwnd_reduction(sk)) { + if (!ece_ack) + tp->prior_ssthresh = tcp_current_ssthresh(sk); + tcp_init_cwnd_reduction(sk); + } + tcp_set_ca_state(sk, TCP_CA_Recovery); +} + +/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are + * recovered or spurious. Otherwise retransmits more on partial ACKs. + */ +static void tcp_process_loss(struct sock *sk, int flag, int num_dupack, + int *rexmit) +{ + struct tcp_sock *tp = tcp_sk(sk); + bool recovered = !before(tp->snd_una, tp->high_seq); + + if ((flag & FLAG_SND_UNA_ADVANCED || rcu_access_pointer(tp->fastopen_rsk)) && + tcp_try_undo_loss(sk, false)) + return; + + if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */ + /* Step 3.b. A timeout is spurious if not all data are + * lost, i.e., never-retransmitted data are (s)acked. + */ + if ((flag & FLAG_ORIG_SACK_ACKED) && + tcp_try_undo_loss(sk, true)) + return; + + if (after(tp->snd_nxt, tp->high_seq)) { + if (flag & FLAG_DATA_SACKED || num_dupack) + tp->frto = 0; /* Step 3.a. loss was real */ + } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) { + tp->high_seq = tp->snd_nxt; + /* Step 2.b. Try send new data (but deferred until cwnd + * is updated in tcp_ack()). Otherwise fall back to + * the conventional recovery. + */ + if (!tcp_write_queue_empty(sk) && + after(tcp_wnd_end(tp), tp->snd_nxt)) { + *rexmit = REXMIT_NEW; + return; + } + tp->frto = 0; + } + } + + if (recovered) { + /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */ + tcp_try_undo_recovery(sk); + return; + } + if (tcp_is_reno(tp)) { + /* A Reno DUPACK means new data in F-RTO step 2.b above are + * delivered. Lower inflight to clock out (re)tranmissions. + */ + if (after(tp->snd_nxt, tp->high_seq) && num_dupack) + tcp_add_reno_sack(sk, num_dupack, flag & FLAG_ECE); + else if (flag & FLAG_SND_UNA_ADVANCED) + tcp_reset_reno_sack(tp); + } + *rexmit = REXMIT_LOST; +} + +static bool tcp_force_fast_retransmit(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + return after(tcp_highest_sack_seq(tp), + tp->snd_una + tp->reordering * tp->mss_cache); +} + +/* Undo during fast recovery after partial ACK. */ +static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una, + bool *do_lost) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tp->undo_marker && tcp_packet_delayed(tp)) { + /* Plain luck! Hole if filled with delayed + * packet, rather than with a retransmit. Check reordering. + */ + tcp_check_sack_reordering(sk, prior_snd_una, 1); + + /* We are getting evidence that the reordering degree is higher + * than we realized. If there are no retransmits out then we + * can undo. Otherwise we clock out new packets but do not + * mark more packets lost or retransmit more. + */ + if (tp->retrans_out) + return true; + + if (!tcp_any_retrans_done(sk)) + tp->retrans_stamp = 0; + + DBGUNDO(sk, "partial recovery"); + tcp_undo_cwnd_reduction(sk, true); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO); + tcp_try_keep_open(sk); + } else { + /* Partial ACK arrived. Force fast retransmit. */ + *do_lost = tcp_force_fast_retransmit(sk); + } + return false; +} + +static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_rtx_queue_empty(sk)) + return; + + if (unlikely(tcp_is_reno(tp))) { + tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED); + } else if (tcp_is_rack(sk)) { + u32 prior_retrans = tp->retrans_out; + + if (tcp_rack_mark_lost(sk)) + *ack_flag &= ~FLAG_SET_XMIT_TIMER; + if (prior_retrans > tp->retrans_out) + *ack_flag |= FLAG_LOST_RETRANS; + } +} + +/* Process an event, which can update packets-in-flight not trivially. + * Main goal of this function is to calculate new estimate for left_out, + * taking into account both packets sitting in receiver's buffer and + * packets lost by network. + * + * Besides that it updates the congestion state when packet loss or ECN + * is detected. But it does not reduce the cwnd, it is done by the + * congestion control later. + * + * It does _not_ decide what to send, it is made in function + * tcp_xmit_retransmit_queue(). + */ +static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una, + int num_dupack, int *ack_flag, int *rexmit) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + int fast_rexmit = 0, flag = *ack_flag; + bool ece_ack = flag & FLAG_ECE; + bool do_lost = num_dupack || ((flag & FLAG_DATA_SACKED) && + tcp_force_fast_retransmit(sk)); + + if (!tp->packets_out && tp->sacked_out) + tp->sacked_out = 0; + + /* Now state machine starts. + * A. ECE, hence prohibit cwnd undoing, the reduction is required. */ + if (ece_ack) + tp->prior_ssthresh = 0; + + /* B. In all the states check for reneging SACKs. */ + if (tcp_check_sack_reneging(sk, ack_flag)) + return; + + /* C. Check consistency of the current state. */ + tcp_verify_left_out(tp); + + /* D. Check state exit conditions. State can be terminated + * when high_seq is ACKed. */ + if (icsk->icsk_ca_state == TCP_CA_Open) { + WARN_ON(tp->retrans_out != 0); + tp->retrans_stamp = 0; + } else if (!before(tp->snd_una, tp->high_seq)) { + switch (icsk->icsk_ca_state) { + case TCP_CA_CWR: + /* CWR is to be held something *above* high_seq + * is ACKed for CWR bit to reach receiver. */ + if (tp->snd_una != tp->high_seq) { + tcp_end_cwnd_reduction(sk); + tcp_set_ca_state(sk, TCP_CA_Open); + } + break; + + case TCP_CA_Recovery: + if (tcp_is_reno(tp)) + tcp_reset_reno_sack(tp); + if (tcp_try_undo_recovery(sk)) + return; + tcp_end_cwnd_reduction(sk); + break; + } + } + + /* E. Process state. */ + switch (icsk->icsk_ca_state) { + case TCP_CA_Recovery: + if (!(flag & FLAG_SND_UNA_ADVANCED)) { + if (tcp_is_reno(tp)) + tcp_add_reno_sack(sk, num_dupack, ece_ack); + } else if (tcp_try_undo_partial(sk, prior_snd_una, &do_lost)) + return; + + if (tcp_try_undo_dsack(sk)) + tcp_try_keep_open(sk); + + tcp_identify_packet_loss(sk, ack_flag); + if (icsk->icsk_ca_state != TCP_CA_Recovery) { + if (!tcp_time_to_recover(sk, flag)) + return; + /* Undo reverts the recovery state. If loss is evident, + * starts a new recovery (e.g. reordering then loss); + */ + tcp_enter_recovery(sk, ece_ack); + } + break; + case TCP_CA_Loss: + tcp_process_loss(sk, flag, num_dupack, rexmit); + tcp_identify_packet_loss(sk, ack_flag); + if (!(icsk->icsk_ca_state == TCP_CA_Open || + (*ack_flag & FLAG_LOST_RETRANS))) + return; + /* Change state if cwnd is undone or retransmits are lost */ + fallthrough; + default: + if (tcp_is_reno(tp)) { + if (flag & FLAG_SND_UNA_ADVANCED) + tcp_reset_reno_sack(tp); + tcp_add_reno_sack(sk, num_dupack, ece_ack); + } + + if (icsk->icsk_ca_state <= TCP_CA_Disorder) + tcp_try_undo_dsack(sk); + + tcp_identify_packet_loss(sk, ack_flag); + if (!tcp_time_to_recover(sk, flag)) { + tcp_try_to_open(sk, flag); + return; + } + + /* MTU probe failure: don't reduce cwnd */ + if (icsk->icsk_ca_state < TCP_CA_CWR && + icsk->icsk_mtup.probe_size && + tp->snd_una == tp->mtu_probe.probe_seq_start) { + tcp_mtup_probe_failed(sk); + /* Restores the reduction we did in tcp_mtup_probe() */ + tp->snd_cwnd++; + tcp_simple_retransmit(sk); + return; + } + + /* Otherwise enter Recovery state */ + tcp_enter_recovery(sk, ece_ack); + fast_rexmit = 1; + } + + if (!tcp_is_rack(sk) && do_lost) + tcp_update_scoreboard(sk, fast_rexmit); + *rexmit = REXMIT_LOST; +} + +static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag) +{ + u32 wlen = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen) * HZ; + struct tcp_sock *tp = tcp_sk(sk); + + if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) { + /* If the remote keeps returning delayed ACKs, eventually + * the min filter would pick it up and overestimate the + * prop. delay when it expires. Skip suspected delayed ACKs. + */ + return; + } + minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32, + rtt_us ? : jiffies_to_usecs(1)); +} + +static bool tcp_ack_update_rtt(struct sock *sk, const int flag, + long seq_rtt_us, long sack_rtt_us, + long ca_rtt_us, struct rate_sample *rs) +{ + const struct tcp_sock *tp = tcp_sk(sk); + + /* Prefer RTT measured from ACK's timing to TS-ECR. This is because + * broken middle-boxes or peers may corrupt TS-ECR fields. But + * Karn's algorithm forbids taking RTT if some retransmitted data + * is acked (RFC6298). + */ + if (seq_rtt_us < 0) + seq_rtt_us = sack_rtt_us; + + /* RTTM Rule: A TSecr value received in a segment is used to + * update the averaged RTT measurement only if the segment + * acknowledges some new data, i.e., only if it advances the + * left edge of the send window. + * See draft-ietf-tcplw-high-performance-00, section 3.3. + */ + if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && + flag & FLAG_ACKED) { + u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr; + + if (likely(delta < INT_MAX / (USEC_PER_SEC / TCP_TS_HZ))) { + if (!delta) + delta = 1; + seq_rtt_us = delta * (USEC_PER_SEC / TCP_TS_HZ); + ca_rtt_us = seq_rtt_us; + } + } + rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */ + if (seq_rtt_us < 0) + return false; + + /* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is + * always taken together with ACK, SACK, or TS-opts. Any negative + * values will be skipped with the seq_rtt_us < 0 check above. + */ + tcp_update_rtt_min(sk, ca_rtt_us, flag); + tcp_rtt_estimator(sk, seq_rtt_us); + tcp_set_rto(sk); + + /* RFC6298: only reset backoff on valid RTT measurement. */ + inet_csk(sk)->icsk_backoff = 0; + return true; +} + +/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */ +void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req) +{ + struct rate_sample rs; + long rtt_us = -1L; + + if (req && !req->num_retrans && tcp_rsk(req)->snt_synack) + rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack); + + tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs); +} + + +static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + + icsk->icsk_ca_ops->cong_avoid(sk, ack, acked); + tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32; +} + +/* Restart timer after forward progress on connection. + * RFC2988 recommends to restart timer to now+rto. + */ +void tcp_rearm_rto(struct sock *sk) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + + /* If the retrans timer is currently being used by Fast Open + * for SYN-ACK retrans purpose, stay put. + */ + if (rcu_access_pointer(tp->fastopen_rsk)) + return; + + if (!tp->packets_out) { + inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS); + } else { + u32 rto = inet_csk(sk)->icsk_rto; + /* Offset the time elapsed after installing regular RTO */ + if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT || + icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) { + s64 delta_us = tcp_rto_delta_us(sk); + /* delta_us may not be positive if the socket is locked + * when the retrans timer fires and is rescheduled. + */ + rto = usecs_to_jiffies(max_t(int, delta_us, 1)); + } + tcp_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto, + TCP_RTO_MAX); + } +} + +/* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */ +static void tcp_set_xmit_timer(struct sock *sk) +{ + if (!tcp_schedule_loss_probe(sk, true)) + tcp_rearm_rto(sk); +} + +/* If we get here, the whole TSO packet has not been acked. */ +static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 packets_acked; + + BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una)); + + packets_acked = tcp_skb_pcount(skb); + if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq)) + return 0; + packets_acked -= tcp_skb_pcount(skb); + + if (packets_acked) { + BUG_ON(tcp_skb_pcount(skb) == 0); + BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)); + } + + return packets_acked; +} + +static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb, + u32 prior_snd_una) +{ + const struct skb_shared_info *shinfo; + + /* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */ + if (likely(!TCP_SKB_CB(skb)->txstamp_ack)) + return; + + shinfo = skb_shinfo(skb); + if (!before(shinfo->tskey, prior_snd_una) && + before(shinfo->tskey, tcp_sk(sk)->snd_una)) { + tcp_skb_tsorted_save(skb) { + __skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK); + } tcp_skb_tsorted_restore(skb); + } +} + +/* Remove acknowledged frames from the retransmission queue. If our packet + * is before the ack sequence we can discard it as it's confirmed to have + * arrived at the other end. + */ +static int tcp_clean_rtx_queue(struct sock *sk, u32 prior_fack, + u32 prior_snd_una, + struct tcp_sacktag_state *sack, bool ece_ack) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + u64 first_ackt, last_ackt; + struct tcp_sock *tp = tcp_sk(sk); + u32 prior_sacked = tp->sacked_out; + u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */ + struct sk_buff *skb, *next; + bool fully_acked = true; + long sack_rtt_us = -1L; + long seq_rtt_us = -1L; + long ca_rtt_us = -1L; + u32 pkts_acked = 0; + u32 last_in_flight = 0; + bool rtt_update; + int flag = 0; + + first_ackt = 0; + + for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) { + struct tcp_skb_cb *scb = TCP_SKB_CB(skb); + const u32 start_seq = scb->seq; + u8 sacked = scb->sacked; + u32 acked_pcount; + + /* Determine how many packets and what bytes were acked, tso and else */ + if (after(scb->end_seq, tp->snd_una)) { + if (tcp_skb_pcount(skb) == 1 || + !after(tp->snd_una, scb->seq)) + break; + + acked_pcount = tcp_tso_acked(sk, skb); + if (!acked_pcount) + break; + fully_acked = false; + } else { + acked_pcount = tcp_skb_pcount(skb); + } + + if (unlikely(sacked & TCPCB_RETRANS)) { + if (sacked & TCPCB_SACKED_RETRANS) + tp->retrans_out -= acked_pcount; + flag |= FLAG_RETRANS_DATA_ACKED; + } else if (!(sacked & TCPCB_SACKED_ACKED)) { + last_ackt = tcp_skb_timestamp_us(skb); + WARN_ON_ONCE(last_ackt == 0); + if (!first_ackt) + first_ackt = last_ackt; + + last_in_flight = TCP_SKB_CB(skb)->tx.in_flight; + if (before(start_seq, reord)) + reord = start_seq; + if (!after(scb->end_seq, tp->high_seq)) + flag |= FLAG_ORIG_SACK_ACKED; + } + + if (sacked & TCPCB_SACKED_ACKED) { + tp->sacked_out -= acked_pcount; + } else if (tcp_is_sack(tp)) { + tcp_count_delivered(tp, acked_pcount, ece_ack); + if (!tcp_skb_spurious_retrans(tp, skb)) + tcp_rack_advance(tp, sacked, scb->end_seq, + tcp_skb_timestamp_us(skb)); + } + if (sacked & TCPCB_LOST) + tp->lost_out -= acked_pcount; + + tp->packets_out -= acked_pcount; + pkts_acked += acked_pcount; + tcp_rate_skb_delivered(sk, skb, sack->rate); + + /* Initial outgoing SYN's get put onto the write_queue + * just like anything else we transmit. It is not + * true data, and if we misinform our callers that + * this ACK acks real data, we will erroneously exit + * connection startup slow start one packet too + * quickly. This is severely frowned upon behavior. + */ + if (likely(!(scb->tcp_flags & TCPHDR_SYN))) { + flag |= FLAG_DATA_ACKED; + } else { + flag |= FLAG_SYN_ACKED; + tp->retrans_stamp = 0; + } + + if (!fully_acked) + break; + + tcp_ack_tstamp(sk, skb, prior_snd_una); + + next = skb_rb_next(skb); + if (unlikely(skb == tp->retransmit_skb_hint)) + tp->retransmit_skb_hint = NULL; + if (unlikely(skb == tp->lost_skb_hint)) + tp->lost_skb_hint = NULL; + tcp_highest_sack_replace(sk, skb, next); + tcp_rtx_queue_unlink_and_free(skb, sk); + } + + if (!skb) + tcp_chrono_stop(sk, TCP_CHRONO_BUSY); + + if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una))) + tp->snd_up = tp->snd_una; + + if (skb) { + tcp_ack_tstamp(sk, skb, prior_snd_una); + if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) + flag |= FLAG_SACK_RENEGING; + } + + if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) { + seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt); + ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt); + + if (pkts_acked == 1 && last_in_flight < tp->mss_cache && + last_in_flight && !prior_sacked && fully_acked && + sack->rate->prior_delivered + 1 == tp->delivered && + !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) { + /* Conservatively mark a delayed ACK. It's typically + * from a lone runt packet over the round trip to + * a receiver w/o out-of-order or CE events. + */ + flag |= FLAG_ACK_MAYBE_DELAYED; + } + } + if (sack->first_sackt) { + sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt); + ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt); + } + rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us, + ca_rtt_us, sack->rate); + + if (flag & FLAG_ACKED) { + flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */ + if (unlikely(icsk->icsk_mtup.probe_size && + !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) { + tcp_mtup_probe_success(sk); + } + + if (tcp_is_reno(tp)) { + tcp_remove_reno_sacks(sk, pkts_acked, ece_ack); + + /* If any of the cumulatively ACKed segments was + * retransmitted, non-SACK case cannot confirm that + * progress was due to original transmission due to + * lack of TCPCB_SACKED_ACKED bits even if some of + * the packets may have been never retransmitted. + */ + if (flag & FLAG_RETRANS_DATA_ACKED) + flag &= ~FLAG_ORIG_SACK_ACKED; + } else { + int delta; + + /* Non-retransmitted hole got filled? That's reordering */ + if (before(reord, prior_fack)) + tcp_check_sack_reordering(sk, reord, 0); + + delta = prior_sacked - tp->sacked_out; + tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta); + } + } else if (skb && rtt_update && sack_rtt_us >= 0 && + sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp, + tcp_skb_timestamp_us(skb))) { + /* Do not re-arm RTO if the sack RTT is measured from data sent + * after when the head was last (re)transmitted. Otherwise the + * timeout may continue to extend in loss recovery. + */ + flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */ + } + + if (icsk->icsk_ca_ops->pkts_acked) { + struct ack_sample sample = { .pkts_acked = pkts_acked, + .rtt_us = sack->rate->rtt_us, + .in_flight = last_in_flight }; + + icsk->icsk_ca_ops->pkts_acked(sk, &sample); + } + +#if FASTRETRANS_DEBUG > 0 + WARN_ON((int)tp->sacked_out < 0); + WARN_ON((int)tp->lost_out < 0); + WARN_ON((int)tp->retrans_out < 0); + if (!tp->packets_out && tcp_is_sack(tp)) { + icsk = inet_csk(sk); + if (tp->lost_out) { + pr_debug("Leak l=%u %d\n", + tp->lost_out, icsk->icsk_ca_state); + tp->lost_out = 0; + } + if (tp->sacked_out) { + pr_debug("Leak s=%u %d\n", + tp->sacked_out, icsk->icsk_ca_state); + tp->sacked_out = 0; + } + if (tp->retrans_out) { + pr_debug("Leak r=%u %d\n", + tp->retrans_out, icsk->icsk_ca_state); + tp->retrans_out = 0; + } + } +#endif + return flag; +} + +static void tcp_ack_probe(struct sock *sk) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + struct sk_buff *head = tcp_send_head(sk); + const struct tcp_sock *tp = tcp_sk(sk); + + /* Was it a usable window open? */ + if (!head) + return; + if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) { + icsk->icsk_backoff = 0; + icsk->icsk_probes_tstamp = 0; + inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0); + /* Socket must be waked up by subsequent tcp_data_snd_check(). + * This function is not for random using! + */ + } else { + unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX); + + when = tcp_clamp_probe0_to_user_timeout(sk, when); + tcp_reset_xmit_timer(sk, ICSK_TIME_PROBE0, when, TCP_RTO_MAX); + } +} + +static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag) +{ + return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) || + inet_csk(sk)->icsk_ca_state != TCP_CA_Open; +} + +/* Decide wheather to run the increase function of congestion control. */ +static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag) +{ + /* If reordering is high then always grow cwnd whenever data is + * delivered regardless of its ordering. Otherwise stay conservative + * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/ + * new SACK or ECE mark may first advance cwnd here and later reduce + * cwnd in tcp_fastretrans_alert() based on more states. + */ + if (tcp_sk(sk)->reordering > + READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_reordering)) + return flag & FLAG_FORWARD_PROGRESS; + + return flag & FLAG_DATA_ACKED; +} + +/* The "ultimate" congestion control function that aims to replace the rigid + * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction). + * It's called toward the end of processing an ACK with precise rate + * information. All transmission or retransmission are delayed afterwards. + */ +static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked, + int flag, const struct rate_sample *rs) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + + if (icsk->icsk_ca_ops->cong_control) { + icsk->icsk_ca_ops->cong_control(sk, rs); + return; + } + + if (tcp_in_cwnd_reduction(sk)) { + /* Reduce cwnd if state mandates */ + tcp_cwnd_reduction(sk, acked_sacked, flag); + } else if (tcp_may_raise_cwnd(sk, flag)) { + /* Advance cwnd if state allows */ + tcp_cong_avoid(sk, ack, acked_sacked); + } + tcp_update_pacing_rate(sk); +} + +/* Check that window update is acceptable. + * The function assumes that snd_una<=ack<=snd_next. + */ +static inline bool tcp_may_update_window(const struct tcp_sock *tp, + const u32 ack, const u32 ack_seq, + const u32 nwin) +{ + return after(ack, tp->snd_una) || + after(ack_seq, tp->snd_wl1) || + (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd); +} + +/* If we update tp->snd_una, also update tp->bytes_acked */ +static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack) +{ + u32 delta = ack - tp->snd_una; + + sock_owned_by_me((struct sock *)tp); + tp->bytes_acked += delta; + tp->snd_una = ack; +} + +/* If we update tp->rcv_nxt, also update tp->bytes_received */ +static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq) +{ + u32 delta = seq - tp->rcv_nxt; + + sock_owned_by_me((struct sock *)tp); + tp->bytes_received += delta; + WRITE_ONCE(tp->rcv_nxt, seq); +} + +/* Update our send window. + * + * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2 + * and in FreeBSD. NetBSD's one is even worse.) is wrong. + */ +static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack, + u32 ack_seq) +{ + struct tcp_sock *tp = tcp_sk(sk); + int flag = 0; + u32 nwin = ntohs(tcp_hdr(skb)->window); + + if (likely(!tcp_hdr(skb)->syn)) + nwin <<= tp->rx_opt.snd_wscale; + + if (tcp_may_update_window(tp, ack, ack_seq, nwin)) { + flag |= FLAG_WIN_UPDATE; + tcp_update_wl(tp, ack_seq); + + if (tp->snd_wnd != nwin) { + tp->snd_wnd = nwin; + + /* Note, it is the only place, where + * fast path is recovered for sending TCP. + */ + tp->pred_flags = 0; + tcp_fast_path_check(sk); + + if (!tcp_write_queue_empty(sk)) + tcp_slow_start_after_idle_check(sk); + + if (nwin > tp->max_window) { + tp->max_window = nwin; + tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie); + } + } + } + + tcp_snd_una_update(tp, ack); + + return flag; +} + +static bool __tcp_oow_rate_limited(struct net *net, int mib_idx, + u32 *last_oow_ack_time) +{ + /* Paired with the WRITE_ONCE() in this function. */ + u32 val = READ_ONCE(*last_oow_ack_time); + + if (val) { + s32 elapsed = (s32)(tcp_jiffies32 - val); + + if (0 <= elapsed && + elapsed < READ_ONCE(net->ipv4.sysctl_tcp_invalid_ratelimit)) { + NET_INC_STATS(net, mib_idx); + return true; /* rate-limited: don't send yet! */ + } + } + + /* Paired with the prior READ_ONCE() and with itself, + * as we might be lockless. + */ + WRITE_ONCE(*last_oow_ack_time, tcp_jiffies32); + + return false; /* not rate-limited: go ahead, send dupack now! */ +} + +/* Return true if we're currently rate-limiting out-of-window ACKs and + * thus shouldn't send a dupack right now. We rate-limit dupacks in + * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS + * attacks that send repeated SYNs or ACKs for the same connection. To + * do this, we do not send a duplicate SYNACK or ACK if the remote + * endpoint is sending out-of-window SYNs or pure ACKs at a high rate. + */ +bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb, + int mib_idx, u32 *last_oow_ack_time) +{ + /* Data packets without SYNs are not likely part of an ACK loop. */ + if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) && + !tcp_hdr(skb)->syn) + return false; + + return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time); +} + +/* RFC 5961 7 [ACK Throttling] */ +static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb) +{ + /* unprotected vars, we dont care of overwrites */ + static u32 challenge_timestamp; + static unsigned int challenge_count; + struct tcp_sock *tp = tcp_sk(sk); + struct net *net = sock_net(sk); + u32 count, now; + + /* First check our per-socket dupack rate limit. */ + if (__tcp_oow_rate_limited(net, + LINUX_MIB_TCPACKSKIPPEDCHALLENGE, + &tp->last_oow_ack_time)) + return; + + /* Then check host-wide RFC 5961 rate limit. */ + now = jiffies / HZ; + if (now != READ_ONCE(challenge_timestamp)) { + u32 ack_limit = READ_ONCE(net->ipv4.sysctl_tcp_challenge_ack_limit); + u32 half = (ack_limit + 1) >> 1; + + WRITE_ONCE(challenge_timestamp, now); + WRITE_ONCE(challenge_count, half + prandom_u32_max(ack_limit)); + } + count = READ_ONCE(challenge_count); + if (count > 0) { + WRITE_ONCE(challenge_count, count - 1); + NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK); + tcp_send_ack(sk); + } +} + +static void tcp_store_ts_recent(struct tcp_sock *tp) +{ + tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval; + tp->rx_opt.ts_recent_stamp = ktime_get_seconds(); +} + +static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq) +{ + if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) { + /* PAWS bug workaround wrt. ACK frames, the PAWS discard + * extra check below makes sure this can only happen + * for pure ACK frames. -DaveM + * + * Not only, also it occurs for expired timestamps. + */ + + if (tcp_paws_check(&tp->rx_opt, 0)) + tcp_store_ts_recent(tp); + } +} + +/* This routine deals with acks during a TLP episode and ends an episode by + * resetting tlp_high_seq. Ref: TLP algorithm in draft-ietf-tcpm-rack + */ +static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (before(ack, tp->tlp_high_seq)) + return; + + if (!tp->tlp_retrans) { + /* TLP of new data has been acknowledged */ + tp->tlp_high_seq = 0; + } else if (flag & FLAG_DSACKING_ACK) { + /* This DSACK means original and TLP probe arrived; no loss */ + tp->tlp_high_seq = 0; + } else if (after(ack, tp->tlp_high_seq)) { + /* ACK advances: there was a loss, so reduce cwnd. Reset + * tlp_high_seq in tcp_init_cwnd_reduction() + */ + tcp_init_cwnd_reduction(sk); + tcp_set_ca_state(sk, TCP_CA_CWR); + tcp_end_cwnd_reduction(sk); + tcp_try_keep_open(sk); + NET_INC_STATS(sock_net(sk), + LINUX_MIB_TCPLOSSPROBERECOVERY); + } else if (!(flag & (FLAG_SND_UNA_ADVANCED | + FLAG_NOT_DUP | FLAG_DATA_SACKED))) { + /* Pure dupack: original and TLP probe arrived; no loss */ + tp->tlp_high_seq = 0; + } +} + +static inline void tcp_in_ack_event(struct sock *sk, u32 flags) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + + if (icsk->icsk_ca_ops->in_ack_event) + icsk->icsk_ca_ops->in_ack_event(sk, flags); +} + +/* Congestion control has updated the cwnd already. So if we're in + * loss recovery then now we do any new sends (for FRTO) or + * retransmits (for CA_Loss or CA_recovery) that make sense. + */ +static void tcp_xmit_recovery(struct sock *sk, int rexmit) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (rexmit == REXMIT_NONE || sk->sk_state == TCP_SYN_SENT) + return; + + if (unlikely(rexmit == REXMIT_NEW)) { + __tcp_push_pending_frames(sk, tcp_current_mss(sk), + TCP_NAGLE_OFF); + if (after(tp->snd_nxt, tp->high_seq)) + return; + tp->frto = 0; + } + tcp_xmit_retransmit_queue(sk); +} + +/* Returns the number of packets newly acked or sacked by the current ACK */ +static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag) +{ + const struct net *net = sock_net(sk); + struct tcp_sock *tp = tcp_sk(sk); + u32 delivered; + + delivered = tp->delivered - prior_delivered; + NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered); + if (flag & FLAG_ECE) + NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered); + + return delivered; +} + +/* This routine deals with incoming acks, but not outgoing ones. */ +static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + struct tcp_sacktag_state sack_state; + struct rate_sample rs = { .prior_delivered = 0 }; + u32 prior_snd_una = tp->snd_una; + bool is_sack_reneg = tp->is_sack_reneg; + u32 ack_seq = TCP_SKB_CB(skb)->seq; + u32 ack = TCP_SKB_CB(skb)->ack_seq; + int num_dupack = 0; + int prior_packets = tp->packets_out; + u32 delivered = tp->delivered; + u32 lost = tp->lost; + int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */ + u32 prior_fack; + + sack_state.first_sackt = 0; + sack_state.rate = &rs; + sack_state.sack_delivered = 0; + + /* We very likely will need to access rtx queue. */ + prefetch(sk->tcp_rtx_queue.rb_node); + + /* If the ack is older than previous acks + * then we can probably ignore it. + */ + if (before(ack, prior_snd_una)) { + u32 max_window; + + /* do not accept ACK for bytes we never sent. */ + max_window = min_t(u64, tp->max_window, tp->bytes_acked); + /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */ + if (before(ack, prior_snd_una - max_window)) { + if (!(flag & FLAG_NO_CHALLENGE_ACK)) + tcp_send_challenge_ack(sk, skb); + return -1; + } + goto old_ack; + } + + /* If the ack includes data we haven't sent yet, discard + * this segment (RFC793 Section 3.9). + */ + if (after(ack, tp->snd_nxt)) + return -1; + + if (after(ack, prior_snd_una)) { + flag |= FLAG_SND_UNA_ADVANCED; + icsk->icsk_retransmits = 0; + +#if IS_ENABLED(CONFIG_TLS_DEVICE) + if (static_branch_unlikely(&clean_acked_data_enabled.key)) + if (icsk->icsk_clean_acked) + icsk->icsk_clean_acked(sk, ack); +#endif + } + + prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una; + rs.prior_in_flight = tcp_packets_in_flight(tp); + + /* ts_recent update must be made after we are sure that the packet + * is in window. + */ + if (flag & FLAG_UPDATE_TS_RECENT) + tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq); + + if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) == + FLAG_SND_UNA_ADVANCED) { + /* Window is constant, pure forward advance. + * No more checks are required. + * Note, we use the fact that SND.UNA>=SND.WL2. + */ + tcp_update_wl(tp, ack_seq); + tcp_snd_una_update(tp, ack); + flag |= FLAG_WIN_UPDATE; + + tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE); + + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS); + } else { + u32 ack_ev_flags = CA_ACK_SLOWPATH; + + if (ack_seq != TCP_SKB_CB(skb)->end_seq) + flag |= FLAG_DATA; + else + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS); + + flag |= tcp_ack_update_window(sk, skb, ack, ack_seq); + + if (TCP_SKB_CB(skb)->sacked) + flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una, + &sack_state); + + if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) { + flag |= FLAG_ECE; + ack_ev_flags |= CA_ACK_ECE; + } + + if (sack_state.sack_delivered) + tcp_count_delivered(tp, sack_state.sack_delivered, + flag & FLAG_ECE); + + if (flag & FLAG_WIN_UPDATE) + ack_ev_flags |= CA_ACK_WIN_UPDATE; + + tcp_in_ack_event(sk, ack_ev_flags); + } + + /* This is a deviation from RFC3168 since it states that: + * "When the TCP data sender is ready to set the CWR bit after reducing + * the congestion window, it SHOULD set the CWR bit only on the first + * new data packet that it transmits." + * We accept CWR on pure ACKs to be more robust + * with widely-deployed TCP implementations that do this. + */ + tcp_ecn_accept_cwr(sk, skb); + + /* We passed data and got it acked, remove any soft error + * log. Something worked... + */ + sk->sk_err_soft = 0; + icsk->icsk_probes_out = 0; + tp->rcv_tstamp = tcp_jiffies32; + if (!prior_packets) + goto no_queue; + + /* See if we can take anything off of the retransmit queue. */ + flag |= tcp_clean_rtx_queue(sk, prior_fack, prior_snd_una, &sack_state, + flag & FLAG_ECE); + + tcp_rack_update_reo_wnd(sk, &rs); + + if (tp->tlp_high_seq) + tcp_process_tlp_ack(sk, ack, flag); + + if (tcp_ack_is_dubious(sk, flag)) { + if (!(flag & (FLAG_SND_UNA_ADVANCED | + FLAG_NOT_DUP | FLAG_DSACKING_ACK))) { + num_dupack = 1; + /* Consider if pure acks were aggregated in tcp_add_backlog() */ + if (!(flag & FLAG_DATA)) + num_dupack = max_t(u16, 1, skb_shinfo(skb)->gso_segs); + } + tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag, + &rexmit); + } + + /* If needed, reset TLP/RTO timer when RACK doesn't set. */ + if (flag & FLAG_SET_XMIT_TIMER) + tcp_set_xmit_timer(sk); + + if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) + sk_dst_confirm(sk); + + delivered = tcp_newly_delivered(sk, delivered, flag); + lost = tp->lost - lost; /* freshly marked lost */ + rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED); + tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate); + tcp_cong_control(sk, ack, delivered, flag, sack_state.rate); + tcp_xmit_recovery(sk, rexmit); + return 1; + +no_queue: + /* If data was DSACKed, see if we can undo a cwnd reduction. */ + if (flag & FLAG_DSACKING_ACK) { + tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag, + &rexmit); + tcp_newly_delivered(sk, delivered, flag); + } + /* If this ack opens up a zero window, clear backoff. It was + * being used to time the probes, and is probably far higher than + * it needs to be for normal retransmission. + */ + tcp_ack_probe(sk); + + if (tp->tlp_high_seq) + tcp_process_tlp_ack(sk, ack, flag); + return 1; + +old_ack: + /* If data was SACKed, tag it and see if we should send more data. + * If data was DSACKed, see if we can undo a cwnd reduction. + */ + if (TCP_SKB_CB(skb)->sacked) { + flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una, + &sack_state); + tcp_fastretrans_alert(sk, prior_snd_una, num_dupack, &flag, + &rexmit); + tcp_newly_delivered(sk, delivered, flag); + tcp_xmit_recovery(sk, rexmit); + } + + return 0; +} + +static void tcp_parse_fastopen_option(int len, const unsigned char *cookie, + bool syn, struct tcp_fastopen_cookie *foc, + bool exp_opt) +{ + /* Valid only in SYN or SYN-ACK with an even length. */ + if (!foc || !syn || len < 0 || (len & 1)) + return; + + if (len >= TCP_FASTOPEN_COOKIE_MIN && + len <= TCP_FASTOPEN_COOKIE_MAX) + memcpy(foc->val, cookie, len); + else if (len != 0) + len = -1; + foc->len = len; + foc->exp = exp_opt; +} + +static bool smc_parse_options(const struct tcphdr *th, + struct tcp_options_received *opt_rx, + const unsigned char *ptr, + int opsize) +{ +#if IS_ENABLED(CONFIG_SMC) + if (static_branch_unlikely(&tcp_have_smc)) { + if (th->syn && !(opsize & 1) && + opsize >= TCPOLEN_EXP_SMC_BASE && + get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC) { + opt_rx->smc_ok = 1; + return true; + } + } +#endif + return false; +} + +/* Try to parse the MSS option from the TCP header. Return 0 on failure, clamped + * value on success. + */ +static u16 tcp_parse_mss_option(const struct tcphdr *th, u16 user_mss) +{ + const unsigned char *ptr = (const unsigned char *)(th + 1); + int length = (th->doff * 4) - sizeof(struct tcphdr); + u16 mss = 0; + + while (length > 0) { + int opcode = *ptr++; + int opsize; + + switch (opcode) { + case TCPOPT_EOL: + return mss; + case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */ + length--; + continue; + default: + if (length < 2) + return mss; + opsize = *ptr++; + if (opsize < 2) /* "silly options" */ + return mss; + if (opsize > length) + return mss; /* fail on partial options */ + if (opcode == TCPOPT_MSS && opsize == TCPOLEN_MSS) { + u16 in_mss = get_unaligned_be16(ptr); + + if (in_mss) { + if (user_mss && user_mss < in_mss) + in_mss = user_mss; + mss = in_mss; + } + } + ptr += opsize - 2; + length -= opsize; + } + } + return mss; +} + +/* Look for tcp options. Normally only called on SYN and SYNACK packets. + * But, this can also be called on packets in the established flow when + * the fast version below fails. + */ +void tcp_parse_options(const struct net *net, + const struct sk_buff *skb, + struct tcp_options_received *opt_rx, int estab, + struct tcp_fastopen_cookie *foc) +{ + const unsigned char *ptr; + const struct tcphdr *th = tcp_hdr(skb); + int length = (th->doff * 4) - sizeof(struct tcphdr); + + ptr = (const unsigned char *)(th + 1); + opt_rx->saw_tstamp = 0; + opt_rx->saw_unknown = 0; + + while (length > 0) { + int opcode = *ptr++; + int opsize; + + switch (opcode) { + case TCPOPT_EOL: + return; + case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */ + length--; + continue; + default: + if (length < 2) + return; + opsize = *ptr++; + if (opsize < 2) /* "silly options" */ + return; + if (opsize > length) + return; /* don't parse partial options */ + switch (opcode) { + case TCPOPT_MSS: + if (opsize == TCPOLEN_MSS && th->syn && !estab) { + u16 in_mss = get_unaligned_be16(ptr); + if (in_mss) { + if (opt_rx->user_mss && + opt_rx->user_mss < in_mss) + in_mss = opt_rx->user_mss; + opt_rx->mss_clamp = in_mss; + } + } + break; + case TCPOPT_WINDOW: + if (opsize == TCPOLEN_WINDOW && th->syn && + !estab && READ_ONCE(net->ipv4.sysctl_tcp_window_scaling)) { + __u8 snd_wscale = *(__u8 *)ptr; + opt_rx->wscale_ok = 1; + if (snd_wscale > TCP_MAX_WSCALE) { + net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n", + __func__, + snd_wscale, + TCP_MAX_WSCALE); + snd_wscale = TCP_MAX_WSCALE; + } + opt_rx->snd_wscale = snd_wscale; + } + break; + case TCPOPT_TIMESTAMP: + if ((opsize == TCPOLEN_TIMESTAMP) && + ((estab && opt_rx->tstamp_ok) || + (!estab && READ_ONCE(net->ipv4.sysctl_tcp_timestamps)))) { + opt_rx->saw_tstamp = 1; + opt_rx->rcv_tsval = get_unaligned_be32(ptr); + opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4); + } + break; + case TCPOPT_SACK_PERM: + if (opsize == TCPOLEN_SACK_PERM && th->syn && + !estab && READ_ONCE(net->ipv4.sysctl_tcp_sack)) { + opt_rx->sack_ok = TCP_SACK_SEEN; + tcp_sack_reset(opt_rx); + } + break; + + case TCPOPT_SACK: + if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) && + !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) && + opt_rx->sack_ok) { + TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th; + } + break; +#ifdef CONFIG_TCP_MD5SIG + case TCPOPT_MD5SIG: + /* + * The MD5 Hash has already been + * checked (see tcp_v{4,6}_do_rcv()). + */ + break; +#endif + case TCPOPT_FASTOPEN: + tcp_parse_fastopen_option( + opsize - TCPOLEN_FASTOPEN_BASE, + ptr, th->syn, foc, false); + break; + + case TCPOPT_EXP: + /* Fast Open option shares code 254 using a + * 16 bits magic number. + */ + if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE && + get_unaligned_be16(ptr) == + TCPOPT_FASTOPEN_MAGIC) { + tcp_parse_fastopen_option(opsize - + TCPOLEN_EXP_FASTOPEN_BASE, + ptr + 2, th->syn, foc, true); + break; + } + + if (smc_parse_options(th, opt_rx, ptr, opsize)) + break; + + opt_rx->saw_unknown = 1; + break; + + default: + opt_rx->saw_unknown = 1; + } + ptr += opsize-2; + length -= opsize; + } + } +} +EXPORT_SYMBOL(tcp_parse_options); + +static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th) +{ + const __be32 *ptr = (const __be32 *)(th + 1); + + if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16) + | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) { + tp->rx_opt.saw_tstamp = 1; + ++ptr; + tp->rx_opt.rcv_tsval = ntohl(*ptr); + ++ptr; + if (*ptr) + tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset; + else + tp->rx_opt.rcv_tsecr = 0; + return true; + } + return false; +} + +/* Fast parse options. This hopes to only see timestamps. + * If it is wrong it falls back on tcp_parse_options(). + */ +static bool tcp_fast_parse_options(const struct net *net, + const struct sk_buff *skb, + const struct tcphdr *th, struct tcp_sock *tp) +{ + /* In the spirit of fast parsing, compare doff directly to constant + * values. Because equality is used, short doff can be ignored here. + */ + if (th->doff == (sizeof(*th) / 4)) { + tp->rx_opt.saw_tstamp = 0; + return false; + } else if (tp->rx_opt.tstamp_ok && + th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) { + if (tcp_parse_aligned_timestamp(tp, th)) + return true; + } + + tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL); + if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) + tp->rx_opt.rcv_tsecr -= tp->tsoffset; + + return true; +} + +#ifdef CONFIG_TCP_MD5SIG +/* + * Parse MD5 Signature option + */ +const u8 *tcp_parse_md5sig_option(const struct tcphdr *th) +{ + int length = (th->doff << 2) - sizeof(*th); + const u8 *ptr = (const u8 *)(th + 1); + + /* If not enough data remaining, we can short cut */ + while (length >= TCPOLEN_MD5SIG) { + int opcode = *ptr++; + int opsize; + + switch (opcode) { + case TCPOPT_EOL: + return NULL; + case TCPOPT_NOP: + length--; + continue; + default: + opsize = *ptr++; + if (opsize < 2 || opsize > length) + return NULL; + if (opcode == TCPOPT_MD5SIG) + return opsize == TCPOLEN_MD5SIG ? ptr : NULL; + } + ptr += opsize - 2; + length -= opsize; + } + return NULL; +} +EXPORT_SYMBOL(tcp_parse_md5sig_option); +#endif + +/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM + * + * It is not fatal. If this ACK does _not_ change critical state (seqs, window) + * it can pass through stack. So, the following predicate verifies that + * this segment is not used for anything but congestion avoidance or + * fast retransmit. Moreover, we even are able to eliminate most of such + * second order effects, if we apply some small "replay" window (~RTO) + * to timestamp space. + * + * All these measures still do not guarantee that we reject wrapped ACKs + * on networks with high bandwidth, when sequence space is recycled fastly, + * but it guarantees that such events will be very rare and do not affect + * connection seriously. This doesn't look nice, but alas, PAWS is really + * buggy extension. + * + * [ Later note. Even worse! It is buggy for segments _with_ data. RFC + * states that events when retransmit arrives after original data are rare. + * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is + * the biggest problem on large power networks even with minor reordering. + * OK, let's give it small replay window. If peer clock is even 1hz, it is safe + * up to bandwidth of 18Gigabit/sec. 8) ] + */ + +static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb) +{ + const struct tcp_sock *tp = tcp_sk(sk); + const struct tcphdr *th = tcp_hdr(skb); + u32 seq = TCP_SKB_CB(skb)->seq; + u32 ack = TCP_SKB_CB(skb)->ack_seq; + + return (/* 1. Pure ACK with correct sequence number. */ + (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) && + + /* 2. ... and duplicate ACK. */ + ack == tp->snd_una && + + /* 3. ... and does not update window. */ + !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) && + + /* 4. ... and sits in replay window. */ + (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ); +} + +static inline bool tcp_paws_discard(const struct sock *sk, + const struct sk_buff *skb) +{ + const struct tcp_sock *tp = tcp_sk(sk); + + return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) && + !tcp_disordered_ack(sk, skb); +} + +/* Check segment sequence number for validity. + * + * Segment controls are considered valid, if the segment + * fits to the window after truncation to the window. Acceptability + * of data (and SYN, FIN, of course) is checked separately. + * See tcp_data_queue(), for example. + * + * Also, controls (RST is main one) are accepted using RCV.WUP instead + * of RCV.NXT. Peer still did not advance his SND.UNA when we + * delayed ACK, so that hisSND.UNA<=ourRCV.WUP. + * (borrowed from freebsd) + */ + +static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq) +{ + return !before(end_seq, tp->rcv_wup) && + !after(seq, tp->rcv_nxt + tcp_receive_window(tp)); +} + +/* When we get a reset we do this. */ +void tcp_reset(struct sock *sk) +{ + trace_tcp_receive_reset(sk); + + /* We want the right error as BSD sees it (and indeed as we do). */ + switch (sk->sk_state) { + case TCP_SYN_SENT: + sk->sk_err = ECONNREFUSED; + break; + case TCP_CLOSE_WAIT: + sk->sk_err = EPIPE; + break; + case TCP_CLOSE: + return; + default: + sk->sk_err = ECONNRESET; + } + /* This barrier is coupled with smp_rmb() in tcp_poll() */ + smp_wmb(); + + tcp_write_queue_purge(sk); + tcp_done(sk); + + if (!sock_flag(sk, SOCK_DEAD)) + sk->sk_error_report(sk); +} + +/* + * Process the FIN bit. This now behaves as it is supposed to work + * and the FIN takes effect when it is validly part of sequence + * space. Not before when we get holes. + * + * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT + * (and thence onto LAST-ACK and finally, CLOSE, we never enter + * TIME-WAIT) + * + * If we are in FINWAIT-1, a received FIN indicates simultaneous + * close and we go into CLOSING (and later onto TIME-WAIT) + * + * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT. + */ +void tcp_fin(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + inet_csk_schedule_ack(sk); + + WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | RCV_SHUTDOWN); + sock_set_flag(sk, SOCK_DONE); + + switch (sk->sk_state) { + case TCP_SYN_RECV: + case TCP_ESTABLISHED: + /* Move to CLOSE_WAIT */ + tcp_set_state(sk, TCP_CLOSE_WAIT); + inet_csk_enter_pingpong_mode(sk); + break; + + case TCP_CLOSE_WAIT: + case TCP_CLOSING: + /* Received a retransmission of the FIN, do + * nothing. + */ + break; + case TCP_LAST_ACK: + /* RFC793: Remain in the LAST-ACK state. */ + break; + + case TCP_FIN_WAIT1: + /* This case occurs when a simultaneous close + * happens, we must ack the received FIN and + * enter the CLOSING state. + */ + tcp_send_ack(sk); + tcp_set_state(sk, TCP_CLOSING); + break; + case TCP_FIN_WAIT2: + /* Received a FIN -- send ACK and enter TIME_WAIT. */ + tcp_send_ack(sk); + tcp_time_wait(sk, TCP_TIME_WAIT, 0); + break; + default: + /* Only TCP_LISTEN and TCP_CLOSE are left, in these + * cases we should never reach this piece of code. + */ + pr_err("%s: Impossible, sk->sk_state=%d\n", + __func__, sk->sk_state); + break; + } + + /* It _is_ possible, that we have something out-of-order _after_ FIN. + * Probably, we should reset in this case. For now drop them. + */ + skb_rbtree_purge(&tp->out_of_order_queue); + if (tcp_is_sack(tp)) + tcp_sack_reset(&tp->rx_opt); + sk_mem_reclaim(sk); + + if (!sock_flag(sk, SOCK_DEAD)) { + sk->sk_state_change(sk); + + /* Do not send POLL_HUP for half duplex close. */ + if (sk->sk_shutdown == SHUTDOWN_MASK || + sk->sk_state == TCP_CLOSE) + sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP); + else + sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN); + } +} + +static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq, + u32 end_seq) +{ + if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) { + if (before(seq, sp->start_seq)) + sp->start_seq = seq; + if (after(end_seq, sp->end_seq)) + sp->end_seq = end_seq; + return true; + } + return false; +} + +static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) { + int mib_idx; + + if (before(seq, tp->rcv_nxt)) + mib_idx = LINUX_MIB_TCPDSACKOLDSENT; + else + mib_idx = LINUX_MIB_TCPDSACKOFOSENT; + + NET_INC_STATS(sock_net(sk), mib_idx); + + tp->rx_opt.dsack = 1; + tp->duplicate_sack[0].start_seq = seq; + tp->duplicate_sack[0].end_seq = end_seq; + } +} + +static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (!tp->rx_opt.dsack) + tcp_dsack_set(sk, seq, end_seq); + else + tcp_sack_extend(tp->duplicate_sack, seq, end_seq); +} + +static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb) +{ + /* When the ACK path fails or drops most ACKs, the sender would + * timeout and spuriously retransmit the same segment repeatedly. + * The receiver remembers and reflects via DSACKs. Leverage the + * DSACK state and change the txhash to re-route speculatively. + */ + if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq && + sk_rethink_txhash(sk)) + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH); +} + +static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && + before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST); + tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS); + + if (tcp_is_sack(tp) && READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_dsack)) { + u32 end_seq = TCP_SKB_CB(skb)->end_seq; + + tcp_rcv_spurious_retrans(sk, skb); + if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) + end_seq = tp->rcv_nxt; + tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq); + } + } + + tcp_send_ack(sk); +} + +/* These routines update the SACK block as out-of-order packets arrive or + * in-order packets close up the sequence space. + */ +static void tcp_sack_maybe_coalesce(struct tcp_sock *tp) +{ + int this_sack; + struct tcp_sack_block *sp = &tp->selective_acks[0]; + struct tcp_sack_block *swalk = sp + 1; + + /* See if the recent change to the first SACK eats into + * or hits the sequence space of other SACK blocks, if so coalesce. + */ + for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) { + if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) { + int i; + + /* Zap SWALK, by moving every further SACK up by one slot. + * Decrease num_sacks. + */ + tp->rx_opt.num_sacks--; + for (i = this_sack; i < tp->rx_opt.num_sacks; i++) + sp[i] = sp[i + 1]; + continue; + } + this_sack++; + swalk++; + } +} + +static void tcp_sack_compress_send_ack(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (!tp->compressed_ack) + return; + + if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1) + __sock_put(sk); + + /* Since we have to send one ack finally, + * substract one from tp->compressed_ack to keep + * LINUX_MIB_TCPACKCOMPRESSED accurate. + */ + NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED, + tp->compressed_ack - 1); + + tp->compressed_ack = 0; + tcp_send_ack(sk); +} + +/* Reasonable amount of sack blocks included in TCP SACK option + * The max is 4, but this becomes 3 if TCP timestamps are there. + * Given that SACK packets might be lost, be conservative and use 2. + */ +#define TCP_SACK_BLOCKS_EXPECTED 2 + +static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct tcp_sack_block *sp = &tp->selective_acks[0]; + int cur_sacks = tp->rx_opt.num_sacks; + int this_sack; + + if (!cur_sacks) + goto new_sack; + + for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) { + if (tcp_sack_extend(sp, seq, end_seq)) { + if (this_sack >= TCP_SACK_BLOCKS_EXPECTED) + tcp_sack_compress_send_ack(sk); + /* Rotate this_sack to the first one. */ + for (; this_sack > 0; this_sack--, sp--) + swap(*sp, *(sp - 1)); + if (cur_sacks > 1) + tcp_sack_maybe_coalesce(tp); + return; + } + } + + if (this_sack >= TCP_SACK_BLOCKS_EXPECTED) + tcp_sack_compress_send_ack(sk); + + /* Could not find an adjacent existing SACK, build a new one, + * put it at the front, and shift everyone else down. We + * always know there is at least one SACK present already here. + * + * If the sack array is full, forget about the last one. + */ + if (this_sack >= TCP_NUM_SACKS) { + this_sack--; + tp->rx_opt.num_sacks--; + sp--; + } + for (; this_sack > 0; this_sack--, sp--) + *sp = *(sp - 1); + +new_sack: + /* Build the new head SACK, and we're done. */ + sp->start_seq = seq; + sp->end_seq = end_seq; + tp->rx_opt.num_sacks++; +} + +/* RCV.NXT advances, some SACKs should be eaten. */ + +static void tcp_sack_remove(struct tcp_sock *tp) +{ + struct tcp_sack_block *sp = &tp->selective_acks[0]; + int num_sacks = tp->rx_opt.num_sacks; + int this_sack; + + /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */ + if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) { + tp->rx_opt.num_sacks = 0; + return; + } + + for (this_sack = 0; this_sack < num_sacks;) { + /* Check if the start of the sack is covered by RCV.NXT. */ + if (!before(tp->rcv_nxt, sp->start_seq)) { + int i; + + /* RCV.NXT must cover all the block! */ + WARN_ON(before(tp->rcv_nxt, sp->end_seq)); + + /* Zap this SACK, by moving forward any other SACKS. */ + for (i = this_sack+1; i < num_sacks; i++) + tp->selective_acks[i-1] = tp->selective_acks[i]; + num_sacks--; + continue; + } + this_sack++; + sp++; + } + tp->rx_opt.num_sacks = num_sacks; +} + +/** + * tcp_try_coalesce - try to merge skb to prior one + * @sk: socket + * @to: prior buffer + * @from: buffer to add in queue + * @fragstolen: pointer to boolean + * + * Before queueing skb @from after @to, try to merge them + * to reduce overall memory use and queue lengths, if cost is small. + * Packets in ofo or receive queues can stay a long time. + * Better try to coalesce them right now to avoid future collapses. + * Returns true if caller should free @from instead of queueing it + */ +static bool tcp_try_coalesce(struct sock *sk, + struct sk_buff *to, + struct sk_buff *from, + bool *fragstolen) +{ + int delta; + + *fragstolen = false; + + /* Its possible this segment overlaps with prior segment in queue */ + if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq) + return false; + + if (!mptcp_skb_can_collapse(to, from)) + return false; + +#ifdef CONFIG_TLS_DEVICE + if (from->decrypted != to->decrypted) + return false; +#endif + + if (!skb_try_coalesce(to, from, fragstolen, &delta)) + return false; + + atomic_add(delta, &sk->sk_rmem_alloc); + sk_mem_charge(sk, delta); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE); + TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq; + TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq; + TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags; + + if (TCP_SKB_CB(from)->has_rxtstamp) { + TCP_SKB_CB(to)->has_rxtstamp = true; + to->tstamp = from->tstamp; + skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp; + } + + return true; +} + +static bool tcp_ooo_try_coalesce(struct sock *sk, + struct sk_buff *to, + struct sk_buff *from, + bool *fragstolen) +{ + bool res = tcp_try_coalesce(sk, to, from, fragstolen); + + /* In case tcp_drop() is called later, update to->gso_segs */ + if (res) { + u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) + + max_t(u16, 1, skb_shinfo(from)->gso_segs); + + skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF); + } + return res; +} + +static void tcp_drop(struct sock *sk, struct sk_buff *skb) +{ + sk_drops_add(sk, skb); + __kfree_skb(skb); +} + +/* This one checks to see if we can put data from the + * out_of_order queue into the receive_queue. + */ +static void tcp_ofo_queue(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + __u32 dsack_high = tp->rcv_nxt; + bool fin, fragstolen, eaten; + struct sk_buff *skb, *tail; + struct rb_node *p; + + p = rb_first(&tp->out_of_order_queue); + while (p) { + skb = rb_to_skb(p); + if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) + break; + + if (before(TCP_SKB_CB(skb)->seq, dsack_high)) { + __u32 dsack = dsack_high; + if (before(TCP_SKB_CB(skb)->end_seq, dsack_high)) + dsack_high = TCP_SKB_CB(skb)->end_seq; + tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack); + } + p = rb_next(p); + rb_erase(&skb->rbnode, &tp->out_of_order_queue); + + if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) { + tcp_drop(sk, skb); + continue; + } + + tail = skb_peek_tail(&sk->sk_receive_queue); + eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen); + tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq); + fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN; + if (!eaten) + __skb_queue_tail(&sk->sk_receive_queue, skb); + else + kfree_skb_partial(skb, fragstolen); + + if (unlikely(fin)) { + tcp_fin(sk); + /* tcp_fin() purges tp->out_of_order_queue, + * so we must end this loop right now. + */ + break; + } + } +} + +static bool tcp_prune_ofo_queue(struct sock *sk); +static int tcp_prune_queue(struct sock *sk); + +static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb, + unsigned int size) +{ + if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf || + !sk_rmem_schedule(sk, skb, size)) { + + if (tcp_prune_queue(sk) < 0) + return -1; + + while (!sk_rmem_schedule(sk, skb, size)) { + if (!tcp_prune_ofo_queue(sk)) + return -1; + } + } + return 0; +} + +static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct rb_node **p, *parent; + struct sk_buff *skb1; + u32 seq, end_seq; + bool fragstolen; + + tcp_ecn_check_ce(sk, skb); + + if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP); + sk->sk_data_ready(sk); + tcp_drop(sk, skb); + return; + } + + /* Disable header prediction. */ + tp->pred_flags = 0; + inet_csk_schedule_ack(sk); + + tp->rcv_ooopack += max_t(u16, 1, skb_shinfo(skb)->gso_segs); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE); + seq = TCP_SKB_CB(skb)->seq; + end_seq = TCP_SKB_CB(skb)->end_seq; + + p = &tp->out_of_order_queue.rb_node; + if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) { + /* Initial out of order segment, build 1 SACK. */ + if (tcp_is_sack(tp)) { + tp->rx_opt.num_sacks = 1; + tp->selective_acks[0].start_seq = seq; + tp->selective_acks[0].end_seq = end_seq; + } + rb_link_node(&skb->rbnode, NULL, p); + rb_insert_color(&skb->rbnode, &tp->out_of_order_queue); + tp->ooo_last_skb = skb; + goto end; + } + + /* In the typical case, we are adding an skb to the end of the list. + * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup. + */ + if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb, + skb, &fragstolen)) { +coalesce_done: + /* For non sack flows, do not grow window to force DUPACK + * and trigger fast retransmit. + */ + if (tcp_is_sack(tp)) + tcp_grow_window(sk, skb, true); + kfree_skb_partial(skb, fragstolen); + skb = NULL; + goto add_sack; + } + /* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */ + if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) { + parent = &tp->ooo_last_skb->rbnode; + p = &parent->rb_right; + goto insert; + } + + /* Find place to insert this segment. Handle overlaps on the way. */ + parent = NULL; + while (*p) { + parent = *p; + skb1 = rb_to_skb(parent); + if (before(seq, TCP_SKB_CB(skb1)->seq)) { + p = &parent->rb_left; + continue; + } + if (before(seq, TCP_SKB_CB(skb1)->end_seq)) { + if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) { + /* All the bits are present. Drop. */ + NET_INC_STATS(sock_net(sk), + LINUX_MIB_TCPOFOMERGE); + tcp_drop(sk, skb); + skb = NULL; + tcp_dsack_set(sk, seq, end_seq); + goto add_sack; + } + if (after(seq, TCP_SKB_CB(skb1)->seq)) { + /* Partial overlap. */ + tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq); + } else { + /* skb's seq == skb1's seq and skb covers skb1. + * Replace skb1 with skb. + */ + rb_replace_node(&skb1->rbnode, &skb->rbnode, + &tp->out_of_order_queue); + tcp_dsack_extend(sk, + TCP_SKB_CB(skb1)->seq, + TCP_SKB_CB(skb1)->end_seq); + NET_INC_STATS(sock_net(sk), + LINUX_MIB_TCPOFOMERGE); + tcp_drop(sk, skb1); + goto merge_right; + } + } else if (tcp_ooo_try_coalesce(sk, skb1, + skb, &fragstolen)) { + goto coalesce_done; + } + p = &parent->rb_right; + } +insert: + /* Insert segment into RB tree. */ + rb_link_node(&skb->rbnode, parent, p); + rb_insert_color(&skb->rbnode, &tp->out_of_order_queue); + +merge_right: + /* Remove other segments covered by skb. */ + while ((skb1 = skb_rb_next(skb)) != NULL) { + if (!after(end_seq, TCP_SKB_CB(skb1)->seq)) + break; + if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) { + tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq, + end_seq); + break; + } + rb_erase(&skb1->rbnode, &tp->out_of_order_queue); + tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq, + TCP_SKB_CB(skb1)->end_seq); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE); + tcp_drop(sk, skb1); + } + /* If there is no skb after us, we are the last_skb ! */ + if (!skb1) + tp->ooo_last_skb = skb; + +add_sack: + if (tcp_is_sack(tp)) + tcp_sack_new_ofo_skb(sk, seq, end_seq); +end: + if (skb) { + /* For non sack flows, do not grow window to force DUPACK + * and trigger fast retransmit. + */ + if (tcp_is_sack(tp)) + tcp_grow_window(sk, skb, false); + skb_condense(skb); + skb_set_owner_r(skb, sk); + } +} + +static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, + bool *fragstolen) +{ + int eaten; + struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue); + + eaten = (tail && + tcp_try_coalesce(sk, tail, + skb, fragstolen)) ? 1 : 0; + tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq); + if (!eaten) { + __skb_queue_tail(&sk->sk_receive_queue, skb); + skb_set_owner_r(skb, sk); + } + return eaten; +} + +int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size) +{ + struct sk_buff *skb; + int err = -ENOMEM; + int data_len = 0; + bool fragstolen; + + if (size == 0) + return 0; + + if (size > PAGE_SIZE) { + int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS); + + data_len = npages << PAGE_SHIFT; + size = data_len + (size & ~PAGE_MASK); + } + skb = alloc_skb_with_frags(size - data_len, data_len, + PAGE_ALLOC_COSTLY_ORDER, + &err, sk->sk_allocation); + if (!skb) + goto err; + + skb_put(skb, size - data_len); + skb->data_len = data_len; + skb->len = size; + + if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP); + goto err_free; + } + + err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size); + if (err) + goto err_free; + + TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt; + TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size; + TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1; + + if (tcp_queue_rcv(sk, skb, &fragstolen)) { + WARN_ON_ONCE(fragstolen); /* should not happen */ + __kfree_skb(skb); + } + return size; + +err_free: + kfree_skb(skb); +err: + return err; + +} + +void tcp_data_ready(struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + int avail = tp->rcv_nxt - tp->copied_seq; + + if (avail < sk->sk_rcvlowat && !tcp_rmem_pressure(sk) && + !sock_flag(sk, SOCK_DONE) && + tcp_receive_window(tp) > inet_csk(sk)->icsk_ack.rcv_mss) + return; + + sk->sk_data_ready(sk); +} + +static void tcp_data_queue(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + bool fragstolen; + int eaten; + + if (sk_is_mptcp(sk)) + mptcp_incoming_options(sk, skb); + + if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) { + __kfree_skb(skb); + return; + } + skb_dst_drop(skb); + __skb_pull(skb, tcp_hdr(skb)->doff * 4); + + tp->rx_opt.dsack = 0; + + /* Queue data for delivery to the user. + * Packets in sequence go to the receive queue. + * Out of sequence packets to the out_of_order_queue. + */ + if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) { + if (tcp_receive_window(tp) == 0) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP); + goto out_of_window; + } + + /* Ok. In sequence. In window. */ +queue_and_out: + if (skb_queue_len(&sk->sk_receive_queue) == 0) + sk_forced_mem_schedule(sk, skb->truesize); + else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP); + sk->sk_data_ready(sk); + goto drop; + } + + eaten = tcp_queue_rcv(sk, skb, &fragstolen); + if (skb->len) + tcp_event_data_recv(sk, skb); + if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN) + tcp_fin(sk); + + if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) { + tcp_ofo_queue(sk); + + /* RFC5681. 4.2. SHOULD send immediate ACK, when + * gap in queue is filled. + */ + if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) + inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW; + } + + if (tp->rx_opt.num_sacks) + tcp_sack_remove(tp); + + tcp_fast_path_check(sk); + + if (eaten > 0) + kfree_skb_partial(skb, fragstolen); + if (!sock_flag(sk, SOCK_DEAD)) + tcp_data_ready(sk); + return; + } + + if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) { + tcp_rcv_spurious_retrans(sk, skb); + /* A retransmit, 2nd most common case. Force an immediate ack. */ + NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST); + tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq); + +out_of_window: + tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS); + inet_csk_schedule_ack(sk); +drop: + tcp_drop(sk, skb); + return; + } + + /* Out of window. F.e. zero window probe. */ + if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp))) + goto out_of_window; + + if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { + /* Partial packet, seq < rcv_next < end_seq */ + tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt); + + /* If window is closed, drop tail of packet. But after + * remembering D-SACK for its head made in previous line. + */ + if (!tcp_receive_window(tp)) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP); + goto out_of_window; + } + goto queue_and_out; + } + + tcp_data_queue_ofo(sk, skb); +} + +static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list) +{ + if (list) + return !skb_queue_is_last(list, skb) ? skb->next : NULL; + + return skb_rb_next(skb); +} + +static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb, + struct sk_buff_head *list, + struct rb_root *root) +{ + struct sk_buff *next = tcp_skb_next(skb, list); + + if (list) + __skb_unlink(skb, list); + else + rb_erase(&skb->rbnode, root); + + __kfree_skb(skb); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED); + + return next; +} + +/* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */ +void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb) +{ + struct rb_node **p = &root->rb_node; + struct rb_node *parent = NULL; + struct sk_buff *skb1; + + while (*p) { + parent = *p; + skb1 = rb_to_skb(parent); + if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq)) + p = &parent->rb_left; + else + p = &parent->rb_right; + } + rb_link_node(&skb->rbnode, parent, p); + rb_insert_color(&skb->rbnode, root); +} + +/* Collapse contiguous sequence of skbs head..tail with + * sequence numbers start..end. + * + * If tail is NULL, this means until the end of the queue. + * + * Segments with FIN/SYN are not collapsed (only because this + * simplifies code) + */ +static void +tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root, + struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end) +{ + struct sk_buff *skb = head, *n; + struct sk_buff_head tmp; + bool end_of_skbs; + + /* First, check that queue is collapsible and find + * the point where collapsing can be useful. + */ +restart: + for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) { + n = tcp_skb_next(skb, list); + + /* No new bits? It is possible on ofo queue. */ + if (!before(start, TCP_SKB_CB(skb)->end_seq)) { + skb = tcp_collapse_one(sk, skb, list, root); + if (!skb) + break; + goto restart; + } + + /* The first skb to collapse is: + * - not SYN/FIN and + * - bloated or contains data before "start" or + * overlaps to the next one and mptcp allow collapsing. + */ + if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) && + (tcp_win_from_space(sk, skb->truesize) > skb->len || + before(TCP_SKB_CB(skb)->seq, start))) { + end_of_skbs = false; + break; + } + + if (n && n != tail && mptcp_skb_can_collapse(skb, n) && + TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) { + end_of_skbs = false; + break; + } + + /* Decided to skip this, advance start seq. */ + start = TCP_SKB_CB(skb)->end_seq; + } + if (end_of_skbs || + (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN))) + return; + + __skb_queue_head_init(&tmp); + + while (before(start, end)) { + int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start); + struct sk_buff *nskb; + + nskb = alloc_skb(copy, GFP_ATOMIC); + if (!nskb) + break; + + memcpy(nskb->cb, skb->cb, sizeof(skb->cb)); +#ifdef CONFIG_TLS_DEVICE + nskb->decrypted = skb->decrypted; +#endif + TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start; + if (list) + __skb_queue_before(list, skb, nskb); + else + __skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */ + skb_set_owner_r(nskb, sk); + mptcp_skb_ext_move(nskb, skb); + + /* Copy data, releasing collapsed skbs. */ + while (copy > 0) { + int offset = start - TCP_SKB_CB(skb)->seq; + int size = TCP_SKB_CB(skb)->end_seq - start; + + BUG_ON(offset < 0); + if (size > 0) { + size = min(copy, size); + if (skb_copy_bits(skb, offset, skb_put(nskb, size), size)) + BUG(); + TCP_SKB_CB(nskb)->end_seq += size; + copy -= size; + start += size; + } + if (!before(start, TCP_SKB_CB(skb)->end_seq)) { + skb = tcp_collapse_one(sk, skb, list, root); + if (!skb || + skb == tail || + !mptcp_skb_can_collapse(nskb, skb) || + (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN))) + goto end; +#ifdef CONFIG_TLS_DEVICE + if (skb->decrypted != nskb->decrypted) + goto end; +#endif + } + } + } +end: + skb_queue_walk_safe(&tmp, skb, n) + tcp_rbtree_insert(root, skb); +} + +/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs + * and tcp_collapse() them until all the queue is collapsed. + */ +static void tcp_collapse_ofo_queue(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 range_truesize, sum_tiny = 0; + struct sk_buff *skb, *head; + u32 start, end; + + skb = skb_rb_first(&tp->out_of_order_queue); +new_range: + if (!skb) { + tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue); + return; + } + start = TCP_SKB_CB(skb)->seq; + end = TCP_SKB_CB(skb)->end_seq; + range_truesize = skb->truesize; + + for (head = skb;;) { + skb = skb_rb_next(skb); + + /* Range is terminated when we see a gap or when + * we are at the queue end. + */ + if (!skb || + after(TCP_SKB_CB(skb)->seq, end) || + before(TCP_SKB_CB(skb)->end_seq, start)) { + /* Do not attempt collapsing tiny skbs */ + if (range_truesize != head->truesize || + end - start >= SKB_WITH_OVERHEAD(SK_MEM_QUANTUM)) { + tcp_collapse(sk, NULL, &tp->out_of_order_queue, + head, skb, start, end); + } else { + sum_tiny += range_truesize; + if (sum_tiny > sk->sk_rcvbuf >> 3) + return; + } + goto new_range; + } + + range_truesize += skb->truesize; + if (unlikely(before(TCP_SKB_CB(skb)->seq, start))) + start = TCP_SKB_CB(skb)->seq; + if (after(TCP_SKB_CB(skb)->end_seq, end)) + end = TCP_SKB_CB(skb)->end_seq; + } +} + +/* + * Clean the out-of-order queue to make room. + * We drop high sequences packets to : + * 1) Let a chance for holes to be filled. + * 2) not add too big latencies if thousands of packets sit there. + * (But if application shrinks SO_RCVBUF, we could still end up + * freeing whole queue here) + * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks. + * + * Return true if queue has shrunk. + */ +static bool tcp_prune_ofo_queue(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct rb_node *node, *prev; + int goal; + + if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) + return false; + + NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED); + goal = sk->sk_rcvbuf >> 3; + node = &tp->ooo_last_skb->rbnode; + do { + prev = rb_prev(node); + rb_erase(node, &tp->out_of_order_queue); + goal -= rb_to_skb(node)->truesize; + tcp_drop(sk, rb_to_skb(node)); + if (!prev || goal <= 0) { + sk_mem_reclaim(sk); + if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf && + !tcp_under_memory_pressure(sk)) + break; + goal = sk->sk_rcvbuf >> 3; + } + node = prev; + } while (node); + tp->ooo_last_skb = rb_to_skb(prev); + + /* Reset SACK state. A conforming SACK implementation will + * do the same at a timeout based retransmit. When a connection + * is in a sad state like this, we care only about integrity + * of the connection not performance. + */ + if (tp->rx_opt.sack_ok) + tcp_sack_reset(&tp->rx_opt); + return true; +} + +/* Reduce allocated memory if we can, trying to get + * the socket within its memory limits again. + * + * Return less than zero if we should start dropping frames + * until the socket owning process reads some of the data + * to stabilize the situation. + */ +static int tcp_prune_queue(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED); + + if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) + tcp_clamp_window(sk); + else if (tcp_under_memory_pressure(sk)) + tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss); + + if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) + return 0; + + tcp_collapse_ofo_queue(sk); + if (!skb_queue_empty(&sk->sk_receive_queue)) + tcp_collapse(sk, &sk->sk_receive_queue, NULL, + skb_peek(&sk->sk_receive_queue), + NULL, + tp->copied_seq, tp->rcv_nxt); + sk_mem_reclaim(sk); + + if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) + return 0; + + /* Collapsing did not help, destructive actions follow. + * This must not ever occur. */ + + tcp_prune_ofo_queue(sk); + + if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf) + return 0; + + /* If we are really being abused, tell the caller to silently + * drop receive data on the floor. It will get retransmitted + * and hopefully then we'll have sufficient space. + */ + NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED); + + /* Massive buffer overcommit. */ + tp->pred_flags = 0; + return -1; +} + +static bool tcp_should_expand_sndbuf(const struct sock *sk) +{ + const struct tcp_sock *tp = tcp_sk(sk); + + /* If the user specified a specific send buffer setting, do + * not modify it. + */ + if (sk->sk_userlocks & SOCK_SNDBUF_LOCK) + return false; + + /* If we are under global TCP memory pressure, do not expand. */ + if (tcp_under_memory_pressure(sk)) + return false; + + /* If we are under soft global TCP memory pressure, do not expand. */ + if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0)) + return false; + + /* If we filled the congestion window, do not expand. */ + if (tcp_packets_in_flight(tp) >= tp->snd_cwnd) + return false; + + return true; +} + +static void tcp_new_space(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + + if (tcp_should_expand_sndbuf(sk)) { + tcp_sndbuf_expand(sk); + tp->snd_cwnd_stamp = tcp_jiffies32; + } + + sk->sk_write_space(sk); +} + +/* Caller made space either from: + * 1) Freeing skbs in rtx queues (after tp->snd_una has advanced) + * 2) Sent skbs from output queue (and thus advancing tp->snd_nxt) + * + * We might be able to generate EPOLLOUT to the application if: + * 1) Space consumed in output/rtx queues is below sk->sk_sndbuf/2 + * 2) notsent amount (tp->write_seq - tp->snd_nxt) became + * small enough that tcp_stream_memory_free() decides it + * is time to generate EPOLLOUT. + */ +void tcp_check_space(struct sock *sk) +{ + /* pairs with tcp_poll() */ + smp_mb(); + if (sk->sk_socket && + test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) { + tcp_new_space(sk); + if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) + tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED); + } +} + +static inline void tcp_data_snd_check(struct sock *sk) +{ + tcp_push_pending_frames(sk); + tcp_check_space(sk); +} + +/* + * Check if sending an ack is needed. + */ +static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible) +{ + struct tcp_sock *tp = tcp_sk(sk); + unsigned long rtt, delay; + + /* More than one full frame received... */ + if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss && + /* ... and right edge of window advances far enough. + * (tcp_recvmsg() will send ACK otherwise). + * If application uses SO_RCVLOWAT, we want send ack now if + * we have not received enough bytes to satisfy the condition. + */ + (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat || + __tcp_select_window(sk) >= tp->rcv_wnd)) || + /* We ACK each frame or... */ + tcp_in_quickack_mode(sk) || + /* Protocol state mandates a one-time immediate ACK */ + inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) { +send_now: + tcp_send_ack(sk); + return; + } + + if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) { + tcp_send_delayed_ack(sk); + return; + } + + if (!tcp_is_sack(tp) || + tp->compressed_ack >= READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr)) + goto send_now; + + if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) { + tp->compressed_ack_rcv_nxt = tp->rcv_nxt; + tp->dup_ack_counter = 0; + } + if (tp->dup_ack_counter < TCP_FASTRETRANS_THRESH) { + tp->dup_ack_counter++; + goto send_now; + } + tp->compressed_ack++; + if (hrtimer_is_queued(&tp->compressed_ack_timer)) + return; + + /* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */ + + rtt = tp->rcv_rtt_est.rtt_us; + if (tp->srtt_us && tp->srtt_us < rtt) + rtt = tp->srtt_us; + + delay = min_t(unsigned long, + READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns), + rtt * (NSEC_PER_USEC >> 3)/20); + sock_hold(sk); + hrtimer_start_range_ns(&tp->compressed_ack_timer, ns_to_ktime(delay), + READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_comp_sack_slack_ns), + HRTIMER_MODE_REL_PINNED_SOFT); +} + +static inline void tcp_ack_snd_check(struct sock *sk) +{ + if (!inet_csk_ack_scheduled(sk)) { + /* We sent a data segment already. */ + return; + } + __tcp_ack_snd_check(sk, 1); +} + +/* + * This routine is only called when we have urgent data + * signaled. Its the 'slow' part of tcp_urg. It could be + * moved inline now as tcp_urg is only called from one + * place. We handle URGent data wrong. We have to - as + * BSD still doesn't use the correction from RFC961. + * For 1003.1g we should support a new option TCP_STDURG to permit + * either form (or just set the sysctl tcp_stdurg). + */ + +static void tcp_check_urg(struct sock *sk, const struct tcphdr *th) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 ptr = ntohs(th->urg_ptr); + + if (ptr && !READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_stdurg)) + ptr--; + ptr += ntohl(th->seq); + + /* Ignore urgent data that we've already seen and read. */ + if (after(tp->copied_seq, ptr)) + return; + + /* Do not replay urg ptr. + * + * NOTE: interesting situation not covered by specs. + * Misbehaving sender may send urg ptr, pointing to segment, + * which we already have in ofo queue. We are not able to fetch + * such data and will stay in TCP_URG_NOTYET until will be eaten + * by recvmsg(). Seems, we are not obliged to handle such wicked + * situations. But it is worth to think about possibility of some + * DoSes using some hypothetical application level deadlock. + */ + if (before(ptr, tp->rcv_nxt)) + return; + + /* Do we already have a newer (or duplicate) urgent pointer? */ + if (tp->urg_data && !after(ptr, tp->urg_seq)) + return; + + /* Tell the world about our new urgent pointer. */ + sk_send_sigurg(sk); + + /* We may be adding urgent data when the last byte read was + * urgent. To do this requires some care. We cannot just ignore + * tp->copied_seq since we would read the last urgent byte again + * as data, nor can we alter copied_seq until this data arrives + * or we break the semantics of SIOCATMARK (and thus sockatmark()) + * + * NOTE. Double Dutch. Rendering to plain English: author of comment + * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB); + * and expect that both A and B disappear from stream. This is _wrong_. + * Though this happens in BSD with high probability, this is occasional. + * Any application relying on this is buggy. Note also, that fix "works" + * only in this artificial test. Insert some normal data between A and B and we will + * decline of BSD again. Verdict: it is better to remove to trap + * buggy users. + */ + if (tp->urg_seq == tp->copied_seq && tp->urg_data && + !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) { + struct sk_buff *skb = skb_peek(&sk->sk_receive_queue); + tp->copied_seq++; + if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) { + __skb_unlink(skb, &sk->sk_receive_queue); + __kfree_skb(skb); + } + } + + tp->urg_data = TCP_URG_NOTYET; + WRITE_ONCE(tp->urg_seq, ptr); + + /* Disable header prediction. */ + tp->pred_flags = 0; +} + +/* This is the 'fast' part of urgent handling. */ +static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th) +{ + struct tcp_sock *tp = tcp_sk(sk); + + /* Check if we get a new urgent pointer - normally not. */ + if (th->urg) + tcp_check_urg(sk, th); + + /* Do we wait for any urgent data? - normally not... */ + if (tp->urg_data == TCP_URG_NOTYET) { + u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) - + th->syn; + + /* Is the urgent pointer pointing into this packet? */ + if (ptr < skb->len) { + u8 tmp; + if (skb_copy_bits(skb, ptr, &tmp, 1)) + BUG(); + tp->urg_data = TCP_URG_VALID | tmp; + if (!sock_flag(sk, SOCK_DEAD)) + sk->sk_data_ready(sk); + } + } +} + +/* Accept RST for rcv_nxt - 1 after a FIN. + * When tcp connections are abruptly terminated from Mac OSX (via ^C), a + * FIN is sent followed by a RST packet. The RST is sent with the same + * sequence number as the FIN, and thus according to RFC 5961 a challenge + * ACK should be sent. However, Mac OSX rate limits replies to challenge + * ACKs on the closed socket. In addition middleboxes can drop either the + * challenge ACK or a subsequent RST. + */ +static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + + return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) && + (1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK | + TCPF_CLOSING)); +} + +/* Does PAWS and seqno based validation of an incoming segment, flags will + * play significant role here. + */ +static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb, + const struct tcphdr *th, int syn_inerr) +{ + struct tcp_sock *tp = tcp_sk(sk); + bool rst_seq_match = false; + + /* RFC1323: H1. Apply PAWS check first. */ + if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) && + tp->rx_opt.saw_tstamp && + tcp_paws_discard(sk, skb)) { + if (!th->rst) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); + if (!tcp_oow_rate_limited(sock_net(sk), skb, + LINUX_MIB_TCPACKSKIPPEDPAWS, + &tp->last_oow_ack_time)) + tcp_send_dupack(sk, skb); + goto discard; + } + /* Reset is accepted even if it did not pass PAWS. */ + } + + /* Step 1: check sequence number */ + if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) { + /* RFC793, page 37: "In all states except SYN-SENT, all reset + * (RST) segments are validated by checking their SEQ-fields." + * And page 69: "If an incoming segment is not acceptable, + * an acknowledgment should be sent in reply (unless the RST + * bit is set, if so drop the segment and return)". + */ + if (!th->rst) { + if (th->syn) + goto syn_challenge; + if (!tcp_oow_rate_limited(sock_net(sk), skb, + LINUX_MIB_TCPACKSKIPPEDSEQ, + &tp->last_oow_ack_time)) + tcp_send_dupack(sk, skb); + } else if (tcp_reset_check(sk, skb)) { + tcp_reset(sk); + } + goto discard; + } + + /* Step 2: check RST bit */ + if (th->rst) { + /* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a + * FIN and SACK too if available): + * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or + * the right-most SACK block, + * then + * RESET the connection + * else + * Send a challenge ACK + */ + if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt || + tcp_reset_check(sk, skb)) { + rst_seq_match = true; + } else if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) { + struct tcp_sack_block *sp = &tp->selective_acks[0]; + int max_sack = sp[0].end_seq; + int this_sack; + + for (this_sack = 1; this_sack < tp->rx_opt.num_sacks; + ++this_sack) { + max_sack = after(sp[this_sack].end_seq, + max_sack) ? + sp[this_sack].end_seq : max_sack; + } + + if (TCP_SKB_CB(skb)->seq == max_sack) + rst_seq_match = true; + } + + if (rst_seq_match) + tcp_reset(sk); + else { + /* Disable TFO if RST is out-of-order + * and no data has been received + * for current active TFO socket + */ + if (tp->syn_fastopen && !tp->data_segs_in && + sk->sk_state == TCP_ESTABLISHED) + tcp_fastopen_active_disable(sk); + tcp_send_challenge_ack(sk, skb); + } + goto discard; + } + + /* step 3: check security and precedence [ignored] */ + + /* step 4: Check for a SYN + * RFC 5961 4.2 : Send a challenge ack + */ + if (th->syn) { +syn_challenge: + if (syn_inerr) + TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE); + tcp_send_challenge_ack(sk, skb); + goto discard; + } + + bpf_skops_parse_hdr(sk, skb); + + return true; + +discard: + tcp_drop(sk, skb); + return false; +} + +/* + * TCP receive function for the ESTABLISHED state. + * + * It is split into a fast path and a slow path. The fast path is + * disabled when: + * - A zero window was announced from us - zero window probing + * is only handled properly in the slow path. + * - Out of order segments arrived. + * - Urgent data is expected. + * - There is no buffer space left + * - Unexpected TCP flags/window values/header lengths are received + * (detected by checking the TCP header against pred_flags) + * - Data is sent in both directions. Fast path only supports pure senders + * or pure receivers (this means either the sequence number or the ack + * value must stay constant) + * - Unexpected TCP option. + * + * When these conditions are not satisfied it drops into a standard + * receive procedure patterned after RFC793 to handle all cases. + * The first three cases are guaranteed by proper pred_flags setting, + * the rest is checked inline. Fast processing is turned on in + * tcp_data_queue when everything is OK. + */ +void tcp_rcv_established(struct sock *sk, struct sk_buff *skb) +{ + const struct tcphdr *th = (const struct tcphdr *)skb->data; + struct tcp_sock *tp = tcp_sk(sk); + unsigned int len = skb->len; + + /* TCP congestion window tracking */ + trace_tcp_probe(sk, skb); + + tcp_mstamp_refresh(tp); + if (unlikely(!rcu_access_pointer(sk->sk_rx_dst))) + inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb); + /* + * Header prediction. + * The code loosely follows the one in the famous + * "30 instruction TCP receive" Van Jacobson mail. + * + * Van's trick is to deposit buffers into socket queue + * on a device interrupt, to call tcp_recv function + * on the receive process context and checksum and copy + * the buffer to user space. smart... + * + * Our current scheme is not silly either but we take the + * extra cost of the net_bh soft interrupt processing... + * We do checksum and copy also but from device to kernel. + */ + + tp->rx_opt.saw_tstamp = 0; + + /* pred_flags is 0xS?10 << 16 + snd_wnd + * if header_prediction is to be made + * 'S' will always be tp->tcp_header_len >> 2 + * '?' will be 0 for the fast path, otherwise pred_flags is 0 to + * turn it off (when there are holes in the receive + * space for instance) + * PSH flag is ignored. + */ + + if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags && + TCP_SKB_CB(skb)->seq == tp->rcv_nxt && + !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) { + int tcp_header_len = tp->tcp_header_len; + + /* Timestamp header prediction: tcp_header_len + * is automatically equal to th->doff*4 due to pred_flags + * match. + */ + + /* Check timestamp */ + if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) { + /* No? Slow path! */ + if (!tcp_parse_aligned_timestamp(tp, th)) + goto slow_path; + + /* If PAWS failed, check it more carefully in slow path */ + if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0) + goto slow_path; + + /* DO NOT update ts_recent here, if checksum fails + * and timestamp was corrupted part, it will result + * in a hung connection since we will drop all + * future packets due to the PAWS test. + */ + } + + if (len <= tcp_header_len) { + /* Bulk data transfer: sender */ + if (len == tcp_header_len) { + /* Predicted packet is in window by definition. + * seq == rcv_nxt and rcv_wup <= rcv_nxt. + * Hence, check seq<=rcv_wup reduces to: + */ + if (tcp_header_len == + (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && + tp->rcv_nxt == tp->rcv_wup) + tcp_store_ts_recent(tp); + + /* We know that such packets are checksummed + * on entry. + */ + tcp_ack(sk, skb, 0); + __kfree_skb(skb); + tcp_data_snd_check(sk); + /* When receiving pure ack in fast path, update + * last ts ecr directly instead of calling + * tcp_rcv_rtt_measure_ts() + */ + tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr; + return; + } else { /* Header too small */ + TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS); + goto discard; + } + } else { + int eaten = 0; + bool fragstolen = false; + + if (tcp_checksum_complete(skb)) + goto csum_error; + + if ((int)skb->truesize > sk->sk_forward_alloc) + goto step5; + + /* Predicted packet is in window by definition. + * seq == rcv_nxt and rcv_wup <= rcv_nxt. + * Hence, check seq<=rcv_wup reduces to: + */ + if (tcp_header_len == + (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) && + tp->rcv_nxt == tp->rcv_wup) + tcp_store_ts_recent(tp); + + tcp_rcv_rtt_measure_ts(sk, skb); + + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS); + + /* Bulk data transfer: receiver */ + __skb_pull(skb, tcp_header_len); + eaten = tcp_queue_rcv(sk, skb, &fragstolen); + + tcp_event_data_recv(sk, skb); + + if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) { + /* Well, only one small jumplet in fast path... */ + tcp_ack(sk, skb, FLAG_DATA); + tcp_data_snd_check(sk); + if (!inet_csk_ack_scheduled(sk)) + goto no_ack; + } else { + tcp_update_wl(tp, TCP_SKB_CB(skb)->seq); + } + + __tcp_ack_snd_check(sk, 0); +no_ack: + if (eaten) + kfree_skb_partial(skb, fragstolen); + tcp_data_ready(sk); + return; + } + } + +slow_path: + if (len < (th->doff << 2) || tcp_checksum_complete(skb)) + goto csum_error; + + if (!th->ack && !th->rst && !th->syn) + goto discard; + + /* + * Standard slow path. + */ + + if (!tcp_validate_incoming(sk, skb, th, 1)) + return; + +step5: + if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0) + goto discard; + + tcp_rcv_rtt_measure_ts(sk, skb); + + /* Process urgent data. */ + tcp_urg(sk, skb, th); + + /* step 7: process the segment text */ + tcp_data_queue(sk, skb); + + tcp_data_snd_check(sk); + tcp_ack_snd_check(sk); + return; + +csum_error: + TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS); + TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS); + +discard: + tcp_drop(sk, skb); +} +EXPORT_SYMBOL(tcp_rcv_established); + +void tcp_init_transfer(struct sock *sk, int bpf_op, struct sk_buff *skb) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + + tcp_mtup_init(sk); + icsk->icsk_af_ops->rebuild_header(sk); + tcp_init_metrics(sk); + + /* Initialize the congestion window to start the transfer. + * Cut cwnd down to 1 per RFC5681 if SYN or SYN-ACK has been + * retransmitted. In light of RFC6298 more aggressive 1sec + * initRTO, we only reset cwnd when more than 1 SYN/SYN-ACK + * retransmission has occurred. + */ + if (tp->total_retrans > 1 && tp->undo_marker) + tp->snd_cwnd = 1; + else + tp->snd_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk)); + tp->snd_cwnd_stamp = tcp_jiffies32; + + bpf_skops_established(sk, bpf_op, skb); + /* Initialize congestion control unless BPF initialized it already: */ + if (!icsk->icsk_ca_initialized) + tcp_init_congestion_control(sk); + tcp_init_buffer_space(sk); +} + +void tcp_finish_connect(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + + tcp_set_state(sk, TCP_ESTABLISHED); + icsk->icsk_ack.lrcvtime = tcp_jiffies32; + + if (skb) { + icsk->icsk_af_ops->sk_rx_dst_set(sk, skb); + security_inet_conn_established(sk, skb); + sk_mark_napi_id(sk, skb); + } + + tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, skb); + + /* Prevent spurious tcp_cwnd_restart() on first data + * packet. + */ + tp->lsndtime = tcp_jiffies32; + + if (sock_flag(sk, SOCK_KEEPOPEN)) + inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp)); + + if (!tp->rx_opt.snd_wscale) + __tcp_fast_path_on(tp, tp->snd_wnd); + else + tp->pred_flags = 0; +} + +static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack, + struct tcp_fastopen_cookie *cookie) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL; + u16 mss = tp->rx_opt.mss_clamp, try_exp = 0; + bool syn_drop = false; + + if (mss == tp->rx_opt.user_mss) { + struct tcp_options_received opt; + + /* Get original SYNACK MSS value if user MSS sets mss_clamp */ + tcp_clear_options(&opt); + opt.user_mss = opt.mss_clamp = 0; + tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL); + mss = opt.mss_clamp; + } + + if (!tp->syn_fastopen) { + /* Ignore an unsolicited cookie */ + cookie->len = -1; + } else if (tp->total_retrans) { + /* SYN timed out and the SYN-ACK neither has a cookie nor + * acknowledges data. Presumably the remote received only + * the retransmitted (regular) SYNs: either the original + * SYN-data or the corresponding SYN-ACK was dropped. + */ + syn_drop = (cookie->len < 0 && data); + } else if (cookie->len < 0 && !tp->syn_data) { + /* We requested a cookie but didn't get it. If we did not use + * the (old) exp opt format then try so next time (try_exp=1). + * Otherwise we go back to use the RFC7413 opt (try_exp=2). + */ + try_exp = tp->syn_fastopen_exp ? 2 : 1; + } + + tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp); + + if (data) { /* Retransmit unacked data in SYN */ + if (tp->total_retrans) + tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED; + else + tp->fastopen_client_fail = TFO_DATA_NOT_ACKED; + skb_rbtree_walk_from(data) { + if (__tcp_retransmit_skb(sk, data, 1)) + break; + } + tcp_rearm_rto(sk); + NET_INC_STATS(sock_net(sk), + LINUX_MIB_TCPFASTOPENACTIVEFAIL); + return true; + } + tp->syn_data_acked = tp->syn_data; + if (tp->syn_data_acked) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE); + /* SYN-data is counted as two separate packets in tcp_ack() */ + if (tp->delivered > 1) + --tp->delivered; + } + + tcp_fastopen_add_skb(sk, synack); + + return false; +} + +static void smc_check_reset_syn(struct tcp_sock *tp) +{ +#if IS_ENABLED(CONFIG_SMC) + if (static_branch_unlikely(&tcp_have_smc)) { + if (tp->syn_smc && !tp->rx_opt.smc_ok) + tp->syn_smc = 0; + } +#endif +} + +static void tcp_try_undo_spurious_syn(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 syn_stamp; + + /* undo_marker is set when SYN or SYNACK times out. The timeout is + * spurious if the ACK's timestamp option echo value matches the + * original SYN timestamp. + */ + syn_stamp = tp->retrans_stamp; + if (tp->undo_marker && syn_stamp && tp->rx_opt.saw_tstamp && + syn_stamp == tp->rx_opt.rcv_tsecr) + tp->undo_marker = 0; +} + +static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb, + const struct tcphdr *th) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + struct tcp_sock *tp = tcp_sk(sk); + struct tcp_fastopen_cookie foc = { .len = -1 }; + int saved_clamp = tp->rx_opt.mss_clamp; + bool fastopen_fail; + + tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc); + if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) + tp->rx_opt.rcv_tsecr -= tp->tsoffset; + + if (th->ack) { + /* rfc793: + * "If the state is SYN-SENT then + * first check the ACK bit + * If the ACK bit is set + * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send + * a reset (unless the RST bit is set, if so drop + * the segment and return)" + */ + if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) || + after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) { + /* Previous FIN/ACK or RST/ACK might be ignored. */ + if (icsk->icsk_retransmits == 0) + inet_csk_reset_xmit_timer(sk, + ICSK_TIME_RETRANS, + TCP_TIMEOUT_MIN, TCP_RTO_MAX); + goto reset_and_undo; + } + + if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr && + !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp, + tcp_time_stamp(tp))) { + NET_INC_STATS(sock_net(sk), + LINUX_MIB_PAWSACTIVEREJECTED); + goto reset_and_undo; + } + + /* Now ACK is acceptable. + * + * "If the RST bit is set + * If the ACK was acceptable then signal the user "error: + * connection reset", drop the segment, enter CLOSED state, + * delete TCB, and return." + */ + + if (th->rst) { + tcp_reset(sk); + goto discard; + } + + /* rfc793: + * "fifth, if neither of the SYN or RST bits is set then + * drop the segment and return." + * + * See note below! + * --ANK(990513) + */ + if (!th->syn) + goto discard_and_undo; + + /* rfc793: + * "If the SYN bit is on ... + * are acceptable then ... + * (our SYN has been ACKed), change the connection + * state to ESTABLISHED..." + */ + + tcp_ecn_rcv_synack(tp, th); + + tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); + tcp_try_undo_spurious_syn(sk); + tcp_ack(sk, skb, FLAG_SLOWPATH); + + /* Ok.. it's good. Set up sequence numbers and + * move to established. + */ + WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1); + tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; + + /* RFC1323: The window in SYN & SYN/ACK segments is + * never scaled. + */ + tp->snd_wnd = ntohs(th->window); + + if (!tp->rx_opt.wscale_ok) { + tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0; + tp->window_clamp = min(tp->window_clamp, 65535U); + } + + if (tp->rx_opt.saw_tstamp) { + tp->rx_opt.tstamp_ok = 1; + tp->tcp_header_len = + sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; + tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; + tcp_store_ts_recent(tp); + } else { + tp->tcp_header_len = sizeof(struct tcphdr); + } + + tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); + tcp_initialize_rcv_mss(sk); + + /* Remember, tcp_poll() does not lock socket! + * Change state from SYN-SENT only after copied_seq + * is initialized. */ + WRITE_ONCE(tp->copied_seq, tp->rcv_nxt); + + smc_check_reset_syn(tp); + + smp_mb(); + + tcp_finish_connect(sk, skb); + + fastopen_fail = (tp->syn_fastopen || tp->syn_data) && + tcp_rcv_fastopen_synack(sk, skb, &foc); + + if (!sock_flag(sk, SOCK_DEAD)) { + sk->sk_state_change(sk); + sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); + } + if (fastopen_fail) + return -1; + if (sk->sk_write_pending || + icsk->icsk_accept_queue.rskq_defer_accept || + inet_csk_in_pingpong_mode(sk)) { + /* Save one ACK. Data will be ready after + * several ticks, if write_pending is set. + * + * It may be deleted, but with this feature tcpdumps + * look so _wonderfully_ clever, that I was not able + * to stand against the temptation 8) --ANK + */ + inet_csk_schedule_ack(sk); + tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS); + inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, + TCP_DELACK_MAX, TCP_RTO_MAX); + +discard: + tcp_drop(sk, skb); + return 0; + } else { + tcp_send_ack(sk); + } + return -1; + } + + /* No ACK in the segment */ + + if (th->rst) { + /* rfc793: + * "If the RST bit is set + * + * Otherwise (no ACK) drop the segment and return." + */ + + goto discard_and_undo; + } + + /* PAWS check. */ + if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp && + tcp_paws_reject(&tp->rx_opt, 0)) + goto discard_and_undo; + + if (th->syn) { + /* We see SYN without ACK. It is attempt of + * simultaneous connect with crossed SYNs. + * Particularly, it can be connect to self. + */ + tcp_set_state(sk, TCP_SYN_RECV); + + if (tp->rx_opt.saw_tstamp) { + tp->rx_opt.tstamp_ok = 1; + tcp_store_ts_recent(tp); + tp->tcp_header_len = + sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; + } else { + tp->tcp_header_len = sizeof(struct tcphdr); + } + + WRITE_ONCE(tp->rcv_nxt, TCP_SKB_CB(skb)->seq + 1); + WRITE_ONCE(tp->copied_seq, tp->rcv_nxt); + tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1; + + /* RFC1323: The window in SYN & SYN/ACK segments is + * never scaled. + */ + tp->snd_wnd = ntohs(th->window); + tp->snd_wl1 = TCP_SKB_CB(skb)->seq; + tp->max_window = tp->snd_wnd; + + tcp_ecn_rcv_syn(tp, th); + + tcp_mtup_init(sk); + tcp_sync_mss(sk, icsk->icsk_pmtu_cookie); + tcp_initialize_rcv_mss(sk); + + tcp_send_synack(sk); +#if 0 + /* Note, we could accept data and URG from this segment. + * There are no obstacles to make this (except that we must + * either change tcp_recvmsg() to prevent it from returning data + * before 3WHS completes per RFC793, or employ TCP Fast Open). + * + * However, if we ignore data in ACKless segments sometimes, + * we have no reasons to accept it sometimes. + * Also, seems the code doing it in step6 of tcp_rcv_state_process + * is not flawless. So, discard packet for sanity. + * Uncomment this return to process the data. + */ + return -1; +#else + goto discard; +#endif + } + /* "fifth, if neither of the SYN or RST bits is set then + * drop the segment and return." + */ + +discard_and_undo: + tcp_clear_options(&tp->rx_opt); + tp->rx_opt.mss_clamp = saved_clamp; + goto discard; + +reset_and_undo: + tcp_clear_options(&tp->rx_opt); + tp->rx_opt.mss_clamp = saved_clamp; + return 1; +} + +static void tcp_rcv_synrecv_state_fastopen(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct request_sock *req; + + /* If we are still handling the SYNACK RTO, see if timestamp ECR allows + * undo. If peer SACKs triggered fast recovery, we can't undo here. + */ + if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss && !tp->packets_out) + tcp_try_undo_recovery(sk); + + /* Reset rtx states to prevent spurious retransmits_timed_out() */ + tp->retrans_stamp = 0; + inet_csk(sk)->icsk_retransmits = 0; + + /* Once we leave TCP_SYN_RECV or TCP_FIN_WAIT_1, + * we no longer need req so release it. + */ + req = rcu_dereference_protected(tp->fastopen_rsk, + lockdep_sock_is_held(sk)); + reqsk_fastopen_remove(sk, req, false); + + /* Re-arm the timer because data may have been sent out. + * This is similar to the regular data transmission case + * when new data has just been ack'ed. + * + * (TFO) - we could try to be more aggressive and + * retransmitting any data sooner based on when they + * are sent out. + */ + tcp_rearm_rto(sk); +} + +/* + * This function implements the receiving procedure of RFC 793 for + * all states except ESTABLISHED and TIME_WAIT. + * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be + * address independent. + */ + +int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + struct inet_connection_sock *icsk = inet_csk(sk); + const struct tcphdr *th = tcp_hdr(skb); + struct request_sock *req; + int queued = 0; + bool acceptable; + + switch (sk->sk_state) { + case TCP_CLOSE: + goto discard; + + case TCP_LISTEN: + if (th->ack) + return 1; + + if (th->rst) + goto discard; + + if (th->syn) { + if (th->fin) + goto discard; + /* It is possible that we process SYN packets from backlog, + * so we need to make sure to disable BH and RCU right there. + */ + rcu_read_lock(); + local_bh_disable(); + acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0; + local_bh_enable(); + rcu_read_unlock(); + + if (!acceptable) + return 1; + consume_skb(skb); + return 0; + } + goto discard; + + case TCP_SYN_SENT: + tp->rx_opt.saw_tstamp = 0; + tcp_mstamp_refresh(tp); + queued = tcp_rcv_synsent_state_process(sk, skb, th); + if (queued >= 0) + return queued; + + /* Do step6 onward by hand. */ + tcp_urg(sk, skb, th); + __kfree_skb(skb); + tcp_data_snd_check(sk); + return 0; + } + + tcp_mstamp_refresh(tp); + tp->rx_opt.saw_tstamp = 0; + req = rcu_dereference_protected(tp->fastopen_rsk, + lockdep_sock_is_held(sk)); + if (req) { + bool req_stolen; + + WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV && + sk->sk_state != TCP_FIN_WAIT1); + + if (!tcp_check_req(sk, skb, req, true, &req_stolen)) + goto discard; + } + + if (!th->ack && !th->rst && !th->syn) + goto discard; + + if (!tcp_validate_incoming(sk, skb, th, 0)) + return 0; + + /* step 5: check the ACK field */ + acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH | + FLAG_UPDATE_TS_RECENT | + FLAG_NO_CHALLENGE_ACK) > 0; + + if (!acceptable) { + if (sk->sk_state == TCP_SYN_RECV) + return 1; /* send one RST */ + tcp_send_challenge_ack(sk, skb); + goto discard; + } + switch (sk->sk_state) { + case TCP_SYN_RECV: + tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */ + if (!tp->srtt_us) + tcp_synack_rtt_meas(sk, req); + + if (req) { + tcp_rcv_synrecv_state_fastopen(sk); + } else { + tcp_try_undo_spurious_syn(sk); + tp->retrans_stamp = 0; + tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB, + skb); + WRITE_ONCE(tp->copied_seq, tp->rcv_nxt); + } + smp_mb(); + tcp_set_state(sk, TCP_ESTABLISHED); + sk->sk_state_change(sk); + + /* Note, that this wakeup is only for marginal crossed SYN case. + * Passively open sockets are not waked up, because + * sk->sk_sleep == NULL and sk->sk_socket == NULL. + */ + if (sk->sk_socket) + sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT); + + tp->snd_una = TCP_SKB_CB(skb)->ack_seq; + tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale; + tcp_init_wl(tp, TCP_SKB_CB(skb)->seq); + + if (tp->rx_opt.tstamp_ok) + tp->advmss -= TCPOLEN_TSTAMP_ALIGNED; + + if (!inet_csk(sk)->icsk_ca_ops->cong_control) + tcp_update_pacing_rate(sk); + + /* Prevent spurious tcp_cwnd_restart() on first data packet */ + tp->lsndtime = tcp_jiffies32; + + tcp_initialize_rcv_mss(sk); + tcp_fast_path_on(tp); + break; + + case TCP_FIN_WAIT1: { + int tmo; + + if (req) + tcp_rcv_synrecv_state_fastopen(sk); + + if (tp->snd_una != tp->write_seq) + break; + + tcp_set_state(sk, TCP_FIN_WAIT2); + WRITE_ONCE(sk->sk_shutdown, sk->sk_shutdown | SEND_SHUTDOWN); + + sk_dst_confirm(sk); + + if (!sock_flag(sk, SOCK_DEAD)) { + /* Wake up lingering close() */ + sk->sk_state_change(sk); + break; + } + + if (tp->linger2 < 0) { + tcp_done(sk); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA); + return 1; + } + if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && + after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) { + /* Receive out of order FIN after close() */ + if (tp->syn_fastopen && th->fin) + tcp_fastopen_active_disable(sk); + tcp_done(sk); + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA); + return 1; + } + + tmo = tcp_fin_time(sk); + if (tmo > TCP_TIMEWAIT_LEN) { + inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN); + } else if (th->fin || sock_owned_by_user(sk)) { + /* Bad case. We could lose such FIN otherwise. + * It is not a big problem, but it looks confusing + * and not so rare event. We still can lose it now, + * if it spins in bh_lock_sock(), but it is really + * marginal case. + */ + inet_csk_reset_keepalive_timer(sk, tmo); + } else { + tcp_time_wait(sk, TCP_FIN_WAIT2, tmo); + goto discard; + } + break; + } + + case TCP_CLOSING: + if (tp->snd_una == tp->write_seq) { + tcp_time_wait(sk, TCP_TIME_WAIT, 0); + goto discard; + } + break; + + case TCP_LAST_ACK: + if (tp->snd_una == tp->write_seq) { + tcp_update_metrics(sk); + tcp_done(sk); + goto discard; + } + break; + } + + /* step 6: check the URG bit */ + tcp_urg(sk, skb, th); + + /* step 7: process the segment text */ + switch (sk->sk_state) { + case TCP_CLOSE_WAIT: + case TCP_CLOSING: + case TCP_LAST_ACK: + if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) { + if (sk_is_mptcp(sk)) + mptcp_incoming_options(sk, skb); + break; + } + fallthrough; + case TCP_FIN_WAIT1: + case TCP_FIN_WAIT2: + /* RFC 793 says to queue data in these states, + * RFC 1122 says we MUST send a reset. + * BSD 4.4 also does reset. + */ + if (sk->sk_shutdown & RCV_SHUTDOWN) { + if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq && + after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA); + tcp_reset(sk); + return 1; + } + } + fallthrough; + case TCP_ESTABLISHED: + tcp_data_queue(sk, skb); + queued = 1; + break; + } + + /* tcp_data could move socket to TIME-WAIT */ + if (sk->sk_state != TCP_CLOSE) { + tcp_data_snd_check(sk); + tcp_ack_snd_check(sk); + } + + if (!queued) { +discard: + tcp_drop(sk, skb); + } + return 0; +} +EXPORT_SYMBOL(tcp_rcv_state_process); + +static inline void pr_drop_req(struct request_sock *req, __u16 port, int family) +{ + struct inet_request_sock *ireq = inet_rsk(req); + + if (family == AF_INET) + net_dbg_ratelimited("drop open request from %pI4/%u\n", + &ireq->ir_rmt_addr, port); +#if IS_ENABLED(CONFIG_IPV6) + else if (family == AF_INET6) + net_dbg_ratelimited("drop open request from %pI6/%u\n", + &ireq->ir_v6_rmt_addr, port); +#endif +} + +/* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set + * + * If we receive a SYN packet with these bits set, it means a + * network is playing bad games with TOS bits. In order to + * avoid possible false congestion notifications, we disable + * TCP ECN negotiation. + * + * Exception: tcp_ca wants ECN. This is required for DCTCP + * congestion control: Linux DCTCP asserts ECT on all packets, + * including SYN, which is most optimal solution; however, + * others, such as FreeBSD do not. + * + * Exception: At least one of the reserved bits of the TCP header (th->res1) is + * set, indicating the use of a future TCP extension (such as AccECN). See + * RFC8311 ยง4.3 which updates RFC3168 to allow the development of such + * extensions. + */ +static void tcp_ecn_create_request(struct request_sock *req, + const struct sk_buff *skb, + const struct sock *listen_sk, + const struct dst_entry *dst) +{ + const struct tcphdr *th = tcp_hdr(skb); + const struct net *net = sock_net(listen_sk); + bool th_ecn = th->ece && th->cwr; + bool ect, ecn_ok; + u32 ecn_ok_dst; + + if (!th_ecn) + return; + + ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield); + ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK); + ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst; + + if (((!ect || th->res1) && ecn_ok) || tcp_ca_needs_ecn(listen_sk) || + (ecn_ok_dst & DST_FEATURE_ECN_CA) || + tcp_bpf_ca_needs_ecn((struct sock *)req)) + inet_rsk(req)->ecn_ok = 1; +} + +static void tcp_openreq_init(struct request_sock *req, + const struct tcp_options_received *rx_opt, + struct sk_buff *skb, const struct sock *sk) +{ + struct inet_request_sock *ireq = inet_rsk(req); + + req->rsk_rcv_wnd = 0; /* So that tcp_send_synack() knows! */ + tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq; + tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1; + tcp_rsk(req)->snt_synack = 0; + tcp_rsk(req)->last_oow_ack_time = 0; + req->mss = rx_opt->mss_clamp; + req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0; + ireq->tstamp_ok = rx_opt->tstamp_ok; + ireq->sack_ok = rx_opt->sack_ok; + ireq->snd_wscale = rx_opt->snd_wscale; + ireq->wscale_ok = rx_opt->wscale_ok; + ireq->acked = 0; + ireq->ecn_ok = 0; + ireq->ir_rmt_port = tcp_hdr(skb)->source; + ireq->ir_num = ntohs(tcp_hdr(skb)->dest); + ireq->ir_mark = inet_request_mark(sk, skb); +#if IS_ENABLED(CONFIG_SMC) + ireq->smc_ok = rx_opt->smc_ok; +#endif +} + +struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops, + struct sock *sk_listener, + bool attach_listener) +{ + struct request_sock *req = reqsk_alloc(ops, sk_listener, + attach_listener); + + if (req) { + struct inet_request_sock *ireq = inet_rsk(req); + + ireq->ireq_opt = NULL; +#if IS_ENABLED(CONFIG_IPV6) + ireq->pktopts = NULL; +#endif + atomic64_set(&ireq->ir_cookie, 0); + ireq->ireq_state = TCP_NEW_SYN_RECV; + write_pnet(&ireq->ireq_net, sock_net(sk_listener)); + ireq->ireq_family = sk_listener->sk_family; + } + + return req; +} +EXPORT_SYMBOL(inet_reqsk_alloc); + +/* + * Return true if a syncookie should be sent + */ +static bool tcp_syn_flood_action(const struct sock *sk, const char *proto) +{ + struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue; + const char *msg = "Dropping request"; + struct net *net = sock_net(sk); + bool want_cookie = false; + u8 syncookies; + + syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies); + +#ifdef CONFIG_SYN_COOKIES + if (syncookies) { + msg = "Sending cookies"; + want_cookie = true; + __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES); + } else +#endif + __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP); + + if (!queue->synflood_warned && syncookies != 2 && + xchg(&queue->synflood_warned, 1) == 0) + net_info_ratelimited("%s: Possible SYN flooding on port %d. %s. Check SNMP counters.\n", + proto, sk->sk_num, msg); + + return want_cookie; +} + +static void tcp_reqsk_record_syn(const struct sock *sk, + struct request_sock *req, + const struct sk_buff *skb) +{ + if (tcp_sk(sk)->save_syn) { + u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb); + struct saved_syn *saved_syn; + u32 mac_hdrlen; + void *base; + + if (tcp_sk(sk)->save_syn == 2) { /* Save full header. */ + base = skb_mac_header(skb); + mac_hdrlen = skb_mac_header_len(skb); + len += mac_hdrlen; + } else { + base = skb_network_header(skb); + mac_hdrlen = 0; + } + + saved_syn = kmalloc(struct_size(saved_syn, data, len), + GFP_ATOMIC); + if (saved_syn) { + saved_syn->mac_hdrlen = mac_hdrlen; + saved_syn->network_hdrlen = skb_network_header_len(skb); + saved_syn->tcp_hdrlen = tcp_hdrlen(skb); + memcpy(saved_syn->data, base, len); + req->saved_syn = saved_syn; + } + } +} + +/* If a SYN cookie is required and supported, returns a clamped MSS value to be + * used for SYN cookie generation. + */ +u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops, + const struct tcp_request_sock_ops *af_ops, + struct sock *sk, struct tcphdr *th) +{ + struct tcp_sock *tp = tcp_sk(sk); + u16 mss; + + if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 && + !inet_csk_reqsk_queue_is_full(sk)) + return 0; + + if (!tcp_syn_flood_action(sk, rsk_ops->slab_name)) + return 0; + + if (sk_acceptq_is_full(sk)) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS); + return 0; + } + + mss = tcp_parse_mss_option(th, tp->rx_opt.user_mss); + if (!mss) + mss = af_ops->mss_clamp; + + return mss; +} +EXPORT_SYMBOL_GPL(tcp_get_syncookie_mss); + +int tcp_conn_request(struct request_sock_ops *rsk_ops, + const struct tcp_request_sock_ops *af_ops, + struct sock *sk, struct sk_buff *skb) +{ + struct tcp_fastopen_cookie foc = { .len = -1 }; + __u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn; + struct tcp_options_received tmp_opt; + struct tcp_sock *tp = tcp_sk(sk); + struct net *net = sock_net(sk); + struct sock *fastopen_sk = NULL; + struct request_sock *req; + bool want_cookie = false; + struct dst_entry *dst; + struct flowi fl; + u8 syncookies; + + syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies); + + /* TW buckets are converted to open requests without + * limitations, they conserve resources and peer is + * evidently real one. + */ + if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) { + want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name); + if (!want_cookie) + goto drop; + } + + if (sk_acceptq_is_full(sk)) { + NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS); + goto drop; + } + + req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie); + if (!req) + goto drop; + + req->syncookie = want_cookie; + tcp_rsk(req)->af_specific = af_ops; + tcp_rsk(req)->ts_off = 0; +#if IS_ENABLED(CONFIG_MPTCP) + tcp_rsk(req)->is_mptcp = 0; +#endif + + tcp_clear_options(&tmp_opt); + tmp_opt.mss_clamp = af_ops->mss_clamp; + tmp_opt.user_mss = tp->rx_opt.user_mss; + tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, + want_cookie ? NULL : &foc); + + if (want_cookie && !tmp_opt.saw_tstamp) + tcp_clear_options(&tmp_opt); + + if (IS_ENABLED(CONFIG_SMC) && want_cookie) + tmp_opt.smc_ok = 0; + + tmp_opt.tstamp_ok = tmp_opt.saw_tstamp; + tcp_openreq_init(req, &tmp_opt, skb, sk); + inet_rsk(req)->no_srccheck = inet_sk(sk)->transparent; + + /* Note: tcp_v6_init_req() might override ir_iif for link locals */ + inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb); + + af_ops->init_req(req, sk, skb); + + if (security_inet_conn_request(sk, skb, req)) + goto drop_and_free; + + if (tmp_opt.tstamp_ok) + tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb); + + dst = af_ops->route_req(sk, &fl, req); + if (!dst) + goto drop_and_free; + + if (!want_cookie && !isn) { + int max_syn_backlog = READ_ONCE(net->ipv4.sysctl_max_syn_backlog); + + /* Kill the following clause, if you dislike this way. */ + if (!syncookies && + (max_syn_backlog - inet_csk_reqsk_queue_len(sk) < + (max_syn_backlog >> 2)) && + !tcp_peer_is_proven(req, dst)) { + /* Without syncookies last quarter of + * backlog is filled with destinations, + * proven to be alive. + * It means that we continue to communicate + * to destinations, already remembered + * to the moment of synflood. + */ + pr_drop_req(req, ntohs(tcp_hdr(skb)->source), + rsk_ops->family); + goto drop_and_release; + } + + isn = af_ops->init_seq(skb); + } + + tcp_ecn_create_request(req, skb, sk, dst); + + if (want_cookie) { + isn = cookie_init_sequence(af_ops, sk, skb, &req->mss); + if (!tmp_opt.tstamp_ok) + inet_rsk(req)->ecn_ok = 0; + } + + tcp_rsk(req)->snt_isn = isn; + tcp_rsk(req)->txhash = net_tx_rndhash(); + tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield; + tcp_openreq_init_rwin(req, sk, dst); + sk_rx_queue_set(req_to_sk(req), skb); + if (!want_cookie) { + tcp_reqsk_record_syn(sk, req, skb); + fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst); + } + if (fastopen_sk) { + af_ops->send_synack(fastopen_sk, dst, &fl, req, + &foc, TCP_SYNACK_FASTOPEN, skb); + /* Add the child socket directly into the accept queue */ + if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) { + reqsk_fastopen_remove(fastopen_sk, req, false); + bh_unlock_sock(fastopen_sk); + sock_put(fastopen_sk); + goto drop_and_free; + } + sk->sk_data_ready(sk); + bh_unlock_sock(fastopen_sk); + sock_put(fastopen_sk); + } else { + tcp_rsk(req)->tfo_listener = false; + if (!want_cookie) + inet_csk_reqsk_queue_hash_add(sk, req, + tcp_timeout_init((struct sock *)req)); + af_ops->send_synack(sk, dst, &fl, req, &foc, + !want_cookie ? TCP_SYNACK_NORMAL : + TCP_SYNACK_COOKIE, + skb); + if (want_cookie) { + reqsk_free(req); + return 0; + } + } + reqsk_put(req); + return 0; + +drop_and_release: + dst_release(dst); +drop_and_free: + __reqsk_free(req); +drop: + tcp_listendrop(sk); + return 0; +} +EXPORT_SYMBOL(tcp_conn_request); |