diff options
Diffstat (limited to 'net/ipv4/tcp_minisocks.c')
| -rw-r--r-- | net/ipv4/tcp_minisocks.c | 880 |
1 files changed, 880 insertions, 0 deletions
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c new file mode 100644 index 000000000..42844d20d --- /dev/null +++ b/net/ipv4/tcp_minisocks.c @@ -0,0 +1,880 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * 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> + */ + +#include <net/tcp.h> +#include <net/xfrm.h> +#include <net/busy_poll.h> + +static bool tcp_in_window(u32 seq, u32 end_seq, u32 s_win, u32 e_win) +{ + if (seq == s_win) + return true; + if (after(end_seq, s_win) && before(seq, e_win)) + return true; + return seq == e_win && seq == end_seq; +} + +static enum tcp_tw_status +tcp_timewait_check_oow_rate_limit(struct inet_timewait_sock *tw, + const struct sk_buff *skb, int mib_idx) +{ + struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); + + if (!tcp_oow_rate_limited(twsk_net(tw), skb, mib_idx, + &tcptw->tw_last_oow_ack_time)) { + /* Send ACK. Note, we do not put the bucket, + * it will be released by caller. + */ + return TCP_TW_ACK; + } + + /* We are rate-limiting, so just release the tw sock and drop skb. */ + inet_twsk_put(tw); + return TCP_TW_SUCCESS; +} + +/* + * * Main purpose of TIME-WAIT state is to close connection gracefully, + * when one of ends sits in LAST-ACK or CLOSING retransmitting FIN + * (and, probably, tail of data) and one or more our ACKs are lost. + * * What is TIME-WAIT timeout? It is associated with maximal packet + * lifetime in the internet, which results in wrong conclusion, that + * it is set to catch "old duplicate segments" wandering out of their path. + * It is not quite correct. This timeout is calculated so that it exceeds + * maximal retransmission timeout enough to allow to lose one (or more) + * segments sent by peer and our ACKs. This time may be calculated from RTO. + * * When TIME-WAIT socket receives RST, it means that another end + * finally closed and we are allowed to kill TIME-WAIT too. + * * Second purpose of TIME-WAIT is catching old duplicate segments. + * Well, certainly it is pure paranoia, but if we load TIME-WAIT + * with this semantics, we MUST NOT kill TIME-WAIT state with RSTs. + * * If we invented some more clever way to catch duplicates + * (f.e. based on PAWS), we could truncate TIME-WAIT to several RTOs. + * + * The algorithm below is based on FORMAL INTERPRETATION of RFCs. + * When you compare it to RFCs, please, read section SEGMENT ARRIVES + * from the very beginning. + * + * NOTE. With recycling (and later with fin-wait-2) TW bucket + * is _not_ stateless. It means, that strictly speaking we must + * spinlock it. I do not want! Well, probability of misbehaviour + * is ridiculously low and, seems, we could use some mb() tricks + * to avoid misread sequence numbers, states etc. --ANK + * + * We don't need to initialize tmp_out.sack_ok as we don't use the results + */ +enum tcp_tw_status +tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb, + const struct tcphdr *th) +{ + struct tcp_options_received tmp_opt; + struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); + bool paws_reject = false; + + tmp_opt.saw_tstamp = 0; + if (th->doff > (sizeof(*th) >> 2) && tcptw->tw_ts_recent_stamp) { + tcp_parse_options(twsk_net(tw), skb, &tmp_opt, 0, NULL); + + if (tmp_opt.saw_tstamp) { + if (tmp_opt.rcv_tsecr) + tmp_opt.rcv_tsecr -= tcptw->tw_ts_offset; + tmp_opt.ts_recent = tcptw->tw_ts_recent; + tmp_opt.ts_recent_stamp = tcptw->tw_ts_recent_stamp; + paws_reject = tcp_paws_reject(&tmp_opt, th->rst); + } + } + + if (tw->tw_substate == TCP_FIN_WAIT2) { + /* Just repeat all the checks of tcp_rcv_state_process() */ + + /* Out of window, send ACK */ + if (paws_reject || + !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, + tcptw->tw_rcv_nxt, + tcptw->tw_rcv_nxt + tcptw->tw_rcv_wnd)) + return tcp_timewait_check_oow_rate_limit( + tw, skb, LINUX_MIB_TCPACKSKIPPEDFINWAIT2); + + if (th->rst) + goto kill; + + if (th->syn && !before(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt)) + return TCP_TW_RST; + + /* Dup ACK? */ + if (!th->ack || + !after(TCP_SKB_CB(skb)->end_seq, tcptw->tw_rcv_nxt) || + TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq) { + inet_twsk_put(tw); + return TCP_TW_SUCCESS; + } + + /* New data or FIN. If new data arrive after half-duplex close, + * reset. + */ + if (!th->fin || + TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) + return TCP_TW_RST; + + /* FIN arrived, enter true time-wait state. */ + tw->tw_substate = TCP_TIME_WAIT; + tcptw->tw_rcv_nxt = TCP_SKB_CB(skb)->end_seq; + if (tmp_opt.saw_tstamp) { + tcptw->tw_ts_recent_stamp = ktime_get_seconds(); + tcptw->tw_ts_recent = tmp_opt.rcv_tsval; + } + + inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); + return TCP_TW_ACK; + } + + /* + * Now real TIME-WAIT state. + * + * RFC 1122: + * "When a connection is [...] on TIME-WAIT state [...] + * [a TCP] MAY accept a new SYN from the remote TCP to + * reopen the connection directly, if it: + * + * (1) assigns its initial sequence number for the new + * connection to be larger than the largest sequence + * number it used on the previous connection incarnation, + * and + * + * (2) returns to TIME-WAIT state if the SYN turns out + * to be an old duplicate". + */ + + if (!paws_reject && + (TCP_SKB_CB(skb)->seq == tcptw->tw_rcv_nxt && + (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq || th->rst))) { + /* In window segment, it may be only reset or bare ack. */ + + if (th->rst) { + /* This is TIME_WAIT assassination, in two flavors. + * Oh well... nobody has a sufficient solution to this + * protocol bug yet. + */ + if (!READ_ONCE(twsk_net(tw)->ipv4.sysctl_tcp_rfc1337)) { +kill: + inet_twsk_deschedule_put(tw); + return TCP_TW_SUCCESS; + } + } else { + inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); + } + + if (tmp_opt.saw_tstamp) { + tcptw->tw_ts_recent = tmp_opt.rcv_tsval; + tcptw->tw_ts_recent_stamp = ktime_get_seconds(); + } + + inet_twsk_put(tw); + return TCP_TW_SUCCESS; + } + + /* Out of window segment. + + All the segments are ACKed immediately. + + The only exception is new SYN. We accept it, if it is + not old duplicate and we are not in danger to be killed + by delayed old duplicates. RFC check is that it has + newer sequence number works at rates <40Mbit/sec. + However, if paws works, it is reliable AND even more, + we even may relax silly seq space cutoff. + + RED-PEN: we violate main RFC requirement, if this SYN will appear + old duplicate (i.e. we receive RST in reply to SYN-ACK), + we must return socket to time-wait state. It is not good, + but not fatal yet. + */ + + if (th->syn && !th->rst && !th->ack && !paws_reject && + (after(TCP_SKB_CB(skb)->seq, tcptw->tw_rcv_nxt) || + (tmp_opt.saw_tstamp && + (s32)(tcptw->tw_ts_recent - tmp_opt.rcv_tsval) < 0))) { + u32 isn = tcptw->tw_snd_nxt + 65535 + 2; + if (isn == 0) + isn++; + TCP_SKB_CB(skb)->tcp_tw_isn = isn; + return TCP_TW_SYN; + } + + if (paws_reject) + __NET_INC_STATS(twsk_net(tw), LINUX_MIB_PAWSESTABREJECTED); + + if (!th->rst) { + /* In this case we must reset the TIMEWAIT timer. + * + * If it is ACKless SYN it may be both old duplicate + * and new good SYN with random sequence number <rcv_nxt. + * Do not reschedule in the last case. + */ + if (paws_reject || th->ack) + inet_twsk_reschedule(tw, TCP_TIMEWAIT_LEN); + + return tcp_timewait_check_oow_rate_limit( + tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT); + } + inet_twsk_put(tw); + return TCP_TW_SUCCESS; +} +EXPORT_SYMBOL(tcp_timewait_state_process); + +/* + * Move a socket to time-wait or dead fin-wait-2 state. + */ +void tcp_time_wait(struct sock *sk, int state, int timeo) +{ + const struct inet_connection_sock *icsk = inet_csk(sk); + const struct tcp_sock *tp = tcp_sk(sk); + struct net *net = sock_net(sk); + struct inet_timewait_sock *tw; + + tw = inet_twsk_alloc(sk, &net->ipv4.tcp_death_row, state); + + if (tw) { + struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw); + const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1); + struct inet_sock *inet = inet_sk(sk); + + tw->tw_transparent = inet->transparent; + tw->tw_mark = sk->sk_mark; + tw->tw_priority = sk->sk_priority; + tw->tw_rcv_wscale = tp->rx_opt.rcv_wscale; + tcptw->tw_rcv_nxt = tp->rcv_nxt; + tcptw->tw_snd_nxt = tp->snd_nxt; + tcptw->tw_rcv_wnd = tcp_receive_window(tp); + tcptw->tw_ts_recent = tp->rx_opt.ts_recent; + tcptw->tw_ts_recent_stamp = tp->rx_opt.ts_recent_stamp; + tcptw->tw_ts_offset = tp->tsoffset; + tcptw->tw_last_oow_ack_time = 0; + tcptw->tw_tx_delay = tp->tcp_tx_delay; +#if IS_ENABLED(CONFIG_IPV6) + if (tw->tw_family == PF_INET6) { + struct ipv6_pinfo *np = inet6_sk(sk); + + tw->tw_v6_daddr = sk->sk_v6_daddr; + tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr; + tw->tw_tclass = np->tclass; + tw->tw_flowlabel = be32_to_cpu(np->flow_label & IPV6_FLOWLABEL_MASK); + tw->tw_txhash = sk->sk_txhash; + tw->tw_ipv6only = sk->sk_ipv6only; + } +#endif + +#ifdef CONFIG_TCP_MD5SIG + /* + * The timewait bucket does not have the key DB from the + * sock structure. We just make a quick copy of the + * md5 key being used (if indeed we are using one) + * so the timewait ack generating code has the key. + */ + do { + tcptw->tw_md5_key = NULL; + if (static_branch_unlikely(&tcp_md5_needed)) { + struct tcp_md5sig_key *key; + + key = tp->af_specific->md5_lookup(sk, sk); + if (key) { + tcptw->tw_md5_key = kmemdup(key, sizeof(*key), GFP_ATOMIC); + BUG_ON(tcptw->tw_md5_key && !tcp_alloc_md5sig_pool()); + } + } + } while (0); +#endif + + /* Get the TIME_WAIT timeout firing. */ + if (timeo < rto) + timeo = rto; + + if (state == TCP_TIME_WAIT) + timeo = TCP_TIMEWAIT_LEN; + + /* tw_timer is pinned, so we need to make sure BH are disabled + * in following section, otherwise timer handler could run before + * we complete the initialization. + */ + local_bh_disable(); + inet_twsk_schedule(tw, timeo); + /* Linkage updates. + * Note that access to tw after this point is illegal. + */ + inet_twsk_hashdance(tw, sk, net->ipv4.tcp_death_row.hashinfo); + local_bh_enable(); + } else { + /* Sorry, if we're out of memory, just CLOSE this + * socket up. We've got bigger problems than + * non-graceful socket closings. + */ + NET_INC_STATS(net, LINUX_MIB_TCPTIMEWAITOVERFLOW); + } + + tcp_update_metrics(sk); + tcp_done(sk); +} +EXPORT_SYMBOL(tcp_time_wait); + +void tcp_twsk_destructor(struct sock *sk) +{ +#ifdef CONFIG_TCP_MD5SIG + if (static_branch_unlikely(&tcp_md5_needed)) { + struct tcp_timewait_sock *twsk = tcp_twsk(sk); + + if (twsk->tw_md5_key) + kfree_rcu(twsk->tw_md5_key, rcu); + } +#endif +} +EXPORT_SYMBOL_GPL(tcp_twsk_destructor); + +void tcp_twsk_purge(struct list_head *net_exit_list, int family) +{ + bool purged_once = false; + struct net *net; + + list_for_each_entry(net, net_exit_list, exit_list) { + if (net->ipv4.tcp_death_row.hashinfo->pernet) { + /* Even if tw_refcount == 1, we must clean up kernel reqsk */ + inet_twsk_purge(net->ipv4.tcp_death_row.hashinfo, family); + } else if (!purged_once) { + /* The last refcount is decremented in tcp_sk_exit_batch() */ + if (refcount_read(&net->ipv4.tcp_death_row.tw_refcount) == 1) + continue; + + inet_twsk_purge(&tcp_hashinfo, family); + purged_once = true; + } + } +} +EXPORT_SYMBOL_GPL(tcp_twsk_purge); + +/* Warning : This function is called without sk_listener being locked. + * Be sure to read socket fields once, as their value could change under us. + */ +void tcp_openreq_init_rwin(struct request_sock *req, + const struct sock *sk_listener, + const struct dst_entry *dst) +{ + struct inet_request_sock *ireq = inet_rsk(req); + const struct tcp_sock *tp = tcp_sk(sk_listener); + int full_space = tcp_full_space(sk_listener); + u32 window_clamp; + __u8 rcv_wscale; + u32 rcv_wnd; + int mss; + + mss = tcp_mss_clamp(tp, dst_metric_advmss(dst)); + window_clamp = READ_ONCE(tp->window_clamp); + /* Set this up on the first call only */ + req->rsk_window_clamp = window_clamp ? : dst_metric(dst, RTAX_WINDOW); + + /* limit the window selection if the user enforce a smaller rx buffer */ + if (sk_listener->sk_userlocks & SOCK_RCVBUF_LOCK && + (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) + req->rsk_window_clamp = full_space; + + rcv_wnd = tcp_rwnd_init_bpf((struct sock *)req); + if (rcv_wnd == 0) + rcv_wnd = dst_metric(dst, RTAX_INITRWND); + else if (full_space < rcv_wnd * mss) + full_space = rcv_wnd * mss; + + /* tcp_full_space because it is guaranteed to be the first packet */ + tcp_select_initial_window(sk_listener, full_space, + mss - (ireq->tstamp_ok ? TCPOLEN_TSTAMP_ALIGNED : 0), + &req->rsk_rcv_wnd, + &req->rsk_window_clamp, + ireq->wscale_ok, + &rcv_wscale, + rcv_wnd); + ireq->rcv_wscale = rcv_wscale; +} +EXPORT_SYMBOL(tcp_openreq_init_rwin); + +static void tcp_ecn_openreq_child(struct tcp_sock *tp, + const struct request_sock *req) +{ + tp->ecn_flags = inet_rsk(req)->ecn_ok ? TCP_ECN_OK : 0; +} + +void tcp_ca_openreq_child(struct sock *sk, const struct dst_entry *dst) +{ + struct inet_connection_sock *icsk = inet_csk(sk); + u32 ca_key = dst_metric(dst, RTAX_CC_ALGO); + bool ca_got_dst = false; + + if (ca_key != TCP_CA_UNSPEC) { + const struct tcp_congestion_ops *ca; + + rcu_read_lock(); + ca = tcp_ca_find_key(ca_key); + if (likely(ca && bpf_try_module_get(ca, ca->owner))) { + icsk->icsk_ca_dst_locked = tcp_ca_dst_locked(dst); + icsk->icsk_ca_ops = ca; + ca_got_dst = true; + } + rcu_read_unlock(); + } + + /* If no valid choice made yet, assign current system default ca. */ + if (!ca_got_dst && + (!icsk->icsk_ca_setsockopt || + !bpf_try_module_get(icsk->icsk_ca_ops, icsk->icsk_ca_ops->owner))) + tcp_assign_congestion_control(sk); + + tcp_set_ca_state(sk, TCP_CA_Open); +} +EXPORT_SYMBOL_GPL(tcp_ca_openreq_child); + +static void smc_check_reset_syn_req(struct tcp_sock *oldtp, + struct request_sock *req, + struct tcp_sock *newtp) +{ +#if IS_ENABLED(CONFIG_SMC) + struct inet_request_sock *ireq; + + if (static_branch_unlikely(&tcp_have_smc)) { + ireq = inet_rsk(req); + if (oldtp->syn_smc && !ireq->smc_ok) + newtp->syn_smc = 0; + } +#endif +} + +/* This is not only more efficient than what we used to do, it eliminates + * a lot of code duplication between IPv4/IPv6 SYN recv processing. -DaveM + * + * Actually, we could lots of memory writes here. tp of listening + * socket contains all necessary default parameters. + */ +struct sock *tcp_create_openreq_child(const struct sock *sk, + struct request_sock *req, + struct sk_buff *skb) +{ + struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC); + const struct inet_request_sock *ireq = inet_rsk(req); + struct tcp_request_sock *treq = tcp_rsk(req); + struct inet_connection_sock *newicsk; + struct tcp_sock *oldtp, *newtp; + u32 seq; + + if (!newsk) + return NULL; + + newicsk = inet_csk(newsk); + newtp = tcp_sk(newsk); + oldtp = tcp_sk(sk); + + smc_check_reset_syn_req(oldtp, req, newtp); + + /* Now setup tcp_sock */ + newtp->pred_flags = 0; + + seq = treq->rcv_isn + 1; + newtp->rcv_wup = seq; + WRITE_ONCE(newtp->copied_seq, seq); + WRITE_ONCE(newtp->rcv_nxt, seq); + newtp->segs_in = 1; + + seq = treq->snt_isn + 1; + newtp->snd_sml = newtp->snd_una = seq; + WRITE_ONCE(newtp->snd_nxt, seq); + newtp->snd_up = seq; + + INIT_LIST_HEAD(&newtp->tsq_node); + INIT_LIST_HEAD(&newtp->tsorted_sent_queue); + + tcp_init_wl(newtp, treq->rcv_isn); + + minmax_reset(&newtp->rtt_min, tcp_jiffies32, ~0U); + newicsk->icsk_ack.lrcvtime = tcp_jiffies32; + + newtp->lsndtime = tcp_jiffies32; + newsk->sk_txhash = READ_ONCE(treq->txhash); + newtp->total_retrans = req->num_retrans; + + tcp_init_xmit_timers(newsk); + WRITE_ONCE(newtp->write_seq, newtp->pushed_seq = treq->snt_isn + 1); + + if (sock_flag(newsk, SOCK_KEEPOPEN)) + inet_csk_reset_keepalive_timer(newsk, + keepalive_time_when(newtp)); + + newtp->rx_opt.tstamp_ok = ireq->tstamp_ok; + newtp->rx_opt.sack_ok = ireq->sack_ok; + newtp->window_clamp = req->rsk_window_clamp; + newtp->rcv_ssthresh = req->rsk_rcv_wnd; + newtp->rcv_wnd = req->rsk_rcv_wnd; + newtp->rx_opt.wscale_ok = ireq->wscale_ok; + if (newtp->rx_opt.wscale_ok) { + newtp->rx_opt.snd_wscale = ireq->snd_wscale; + newtp->rx_opt.rcv_wscale = ireq->rcv_wscale; + } else { + newtp->rx_opt.snd_wscale = newtp->rx_opt.rcv_wscale = 0; + newtp->window_clamp = min(newtp->window_clamp, 65535U); + } + newtp->snd_wnd = ntohs(tcp_hdr(skb)->window) << newtp->rx_opt.snd_wscale; + newtp->max_window = newtp->snd_wnd; + + if (newtp->rx_opt.tstamp_ok) { + newtp->rx_opt.ts_recent = READ_ONCE(req->ts_recent); + newtp->rx_opt.ts_recent_stamp = ktime_get_seconds(); + newtp->tcp_header_len = sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED; + } else { + newtp->rx_opt.ts_recent_stamp = 0; + newtp->tcp_header_len = sizeof(struct tcphdr); + } + if (req->num_timeout) { + newtp->undo_marker = treq->snt_isn; + newtp->retrans_stamp = div_u64(treq->snt_synack, + USEC_PER_SEC / TCP_TS_HZ); + } + newtp->tsoffset = treq->ts_off; +#ifdef CONFIG_TCP_MD5SIG + newtp->md5sig_info = NULL; /*XXX*/ + if (treq->af_specific->req_md5_lookup(sk, req_to_sk(req))) + newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; +#endif + if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) + newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; + newtp->rx_opt.mss_clamp = req->mss; + tcp_ecn_openreq_child(newtp, req); + newtp->fastopen_req = NULL; + RCU_INIT_POINTER(newtp->fastopen_rsk, NULL); + + newtp->bpf_chg_cc_inprogress = 0; + tcp_bpf_clone(sk, newsk); + + __TCP_INC_STATS(sock_net(sk), TCP_MIB_PASSIVEOPENS); + + return newsk; +} +EXPORT_SYMBOL(tcp_create_openreq_child); + +/* + * Process an incoming packet for SYN_RECV sockets represented as a + * request_sock. Normally sk is the listener socket but for TFO it + * points to the child socket. + * + * XXX (TFO) - The current impl contains a special check for ack + * validation and inside tcp_v4_reqsk_send_ack(). Can we do better? + * + * We don't need to initialize tmp_opt.sack_ok as we don't use the results + * + * Note: If @fastopen is true, this can be called from process context. + * Otherwise, this is from BH context. + */ + +struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb, + struct request_sock *req, + bool fastopen, bool *req_stolen) +{ + struct tcp_options_received tmp_opt; + struct sock *child; + const struct tcphdr *th = tcp_hdr(skb); + __be32 flg = tcp_flag_word(th) & (TCP_FLAG_RST|TCP_FLAG_SYN|TCP_FLAG_ACK); + bool paws_reject = false; + bool own_req; + + tmp_opt.saw_tstamp = 0; + if (th->doff > (sizeof(struct tcphdr)>>2)) { + tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0, NULL); + + if (tmp_opt.saw_tstamp) { + tmp_opt.ts_recent = READ_ONCE(req->ts_recent); + if (tmp_opt.rcv_tsecr) + tmp_opt.rcv_tsecr -= tcp_rsk(req)->ts_off; + /* We do not store true stamp, but it is not required, + * it can be estimated (approximately) + * from another data. + */ + tmp_opt.ts_recent_stamp = ktime_get_seconds() - reqsk_timeout(req, TCP_RTO_MAX) / HZ; + paws_reject = tcp_paws_reject(&tmp_opt, th->rst); + } + } + + /* Check for pure retransmitted SYN. */ + if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn && + flg == TCP_FLAG_SYN && + !paws_reject) { + /* + * RFC793 draws (Incorrectly! It was fixed in RFC1122) + * this case on figure 6 and figure 8, but formal + * protocol description says NOTHING. + * To be more exact, it says that we should send ACK, + * because this segment (at least, if it has no data) + * is out of window. + * + * CONCLUSION: RFC793 (even with RFC1122) DOES NOT + * describe SYN-RECV state. All the description + * is wrong, we cannot believe to it and should + * rely only on common sense and implementation + * experience. + * + * Enforce "SYN-ACK" according to figure 8, figure 6 + * of RFC793, fixed by RFC1122. + * + * Note that even if there is new data in the SYN packet + * they will be thrown away too. + * + * Reset timer after retransmitting SYNACK, similar to + * the idea of fast retransmit in recovery. + */ + if (!tcp_oow_rate_limited(sock_net(sk), skb, + LINUX_MIB_TCPACKSKIPPEDSYNRECV, + &tcp_rsk(req)->last_oow_ack_time) && + + !inet_rtx_syn_ack(sk, req)) { + unsigned long expires = jiffies; + + expires += reqsk_timeout(req, TCP_RTO_MAX); + if (!fastopen) + mod_timer_pending(&req->rsk_timer, expires); + else + req->rsk_timer.expires = expires; + } + return NULL; + } + + /* Further reproduces section "SEGMENT ARRIVES" + for state SYN-RECEIVED of RFC793. + It is broken, however, it does not work only + when SYNs are crossed. + + You would think that SYN crossing is impossible here, since + we should have a SYN_SENT socket (from connect()) on our end, + but this is not true if the crossed SYNs were sent to both + ends by a malicious third party. We must defend against this, + and to do that we first verify the ACK (as per RFC793, page + 36) and reset if it is invalid. Is this a true full defense? + To convince ourselves, let us consider a way in which the ACK + test can still pass in this 'malicious crossed SYNs' case. + Malicious sender sends identical SYNs (and thus identical sequence + numbers) to both A and B: + + A: gets SYN, seq=7 + B: gets SYN, seq=7 + + By our good fortune, both A and B select the same initial + send sequence number of seven :-) + + A: sends SYN|ACK, seq=7, ack_seq=8 + B: sends SYN|ACK, seq=7, ack_seq=8 + + So we are now A eating this SYN|ACK, ACK test passes. So + does sequence test, SYN is truncated, and thus we consider + it a bare ACK. + + If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this + bare ACK. Otherwise, we create an established connection. Both + ends (listening sockets) accept the new incoming connection and try + to talk to each other. 8-) + + Note: This case is both harmless, and rare. Possibility is about the + same as us discovering intelligent life on another plant tomorrow. + + But generally, we should (RFC lies!) to accept ACK + from SYNACK both here and in tcp_rcv_state_process(). + tcp_rcv_state_process() does not, hence, we do not too. + + Note that the case is absolutely generic: + we cannot optimize anything here without + violating protocol. All the checks must be made + before attempt to create socket. + */ + + /* RFC793 page 36: "If the connection is in any non-synchronized state ... + * and the incoming segment acknowledges something not yet + * sent (the segment carries an unacceptable ACK) ... + * a reset is sent." + * + * Invalid ACK: reset will be sent by listening socket. + * Note that the ACK validity check for a Fast Open socket is done + * elsewhere and is checked directly against the child socket rather + * than req because user data may have been sent out. + */ + if ((flg & TCP_FLAG_ACK) && !fastopen && + (TCP_SKB_CB(skb)->ack_seq != + tcp_rsk(req)->snt_isn + 1)) + return sk; + + /* Also, it would be not so bad idea to check rcv_tsecr, which + * is essentially ACK extension and too early or too late values + * should cause reset in unsynchronized states. + */ + + /* RFC793: "first check sequence number". */ + + if (paws_reject || !tcp_in_window(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq, + tcp_rsk(req)->rcv_nxt, tcp_rsk(req)->rcv_nxt + req->rsk_rcv_wnd)) { + /* Out of window: send ACK and drop. */ + if (!(flg & TCP_FLAG_RST) && + !tcp_oow_rate_limited(sock_net(sk), skb, + LINUX_MIB_TCPACKSKIPPEDSYNRECV, + &tcp_rsk(req)->last_oow_ack_time)) + req->rsk_ops->send_ack(sk, skb, req); + if (paws_reject) + NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED); + return NULL; + } + + /* In sequence, PAWS is OK. */ + + /* TODO: We probably should defer ts_recent change once + * we take ownership of @req. + */ + if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt)) + WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval); + + if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) { + /* Truncate SYN, it is out of window starting + at tcp_rsk(req)->rcv_isn + 1. */ + flg &= ~TCP_FLAG_SYN; + } + + /* RFC793: "second check the RST bit" and + * "fourth, check the SYN bit" + */ + if (flg & (TCP_FLAG_RST|TCP_FLAG_SYN)) { + TCP_INC_STATS(sock_net(sk), TCP_MIB_ATTEMPTFAILS); + goto embryonic_reset; + } + + /* ACK sequence verified above, just make sure ACK is + * set. If ACK not set, just silently drop the packet. + * + * XXX (TFO) - if we ever allow "data after SYN", the + * following check needs to be removed. + */ + if (!(flg & TCP_FLAG_ACK)) + return NULL; + + /* For Fast Open no more processing is needed (sk is the + * child socket). + */ + if (fastopen) + return sk; + + /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */ + if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept && + TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) { + inet_rsk(req)->acked = 1; + __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP); + return NULL; + } + + /* OK, ACK is valid, create big socket and + * feed this segment to it. It will repeat all + * the tests. THIS SEGMENT MUST MOVE SOCKET TO + * ESTABLISHED STATE. If it will be dropped after + * socket is created, wait for troubles. + */ + child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL, + req, &own_req); + if (!child) + goto listen_overflow; + + if (own_req && rsk_drop_req(req)) { + reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req); + inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req); + return child; + } + + sock_rps_save_rxhash(child, skb); + tcp_synack_rtt_meas(child, req); + *req_stolen = !own_req; + return inet_csk_complete_hashdance(sk, child, req, own_req); + +listen_overflow: + if (sk != req->rsk_listener) + __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMIGRATEREQFAILURE); + + if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_abort_on_overflow)) { + inet_rsk(req)->acked = 1; + return NULL; + } + +embryonic_reset: + if (!(flg & TCP_FLAG_RST)) { + /* Received a bad SYN pkt - for TFO We try not to reset + * the local connection unless it's really necessary to + * avoid becoming vulnerable to outside attack aiming at + * resetting legit local connections. + */ + req->rsk_ops->send_reset(sk, skb); + } else if (fastopen) { /* received a valid RST pkt */ + reqsk_fastopen_remove(sk, req, true); + tcp_reset(sk, skb); + } + if (!fastopen) { + bool unlinked = inet_csk_reqsk_queue_drop(sk, req); + + if (unlinked) + __NET_INC_STATS(sock_net(sk), LINUX_MIB_EMBRYONICRSTS); + *req_stolen = !unlinked; + } + return NULL; +} +EXPORT_SYMBOL(tcp_check_req); + +/* + * Queue segment on the new socket if the new socket is active, + * otherwise we just shortcircuit this and continue with + * the new socket. + * + * For the vast majority of cases child->sk_state will be TCP_SYN_RECV + * when entering. But other states are possible due to a race condition + * where after __inet_lookup_established() fails but before the listener + * locked is obtained, other packets cause the same connection to + * be created. + */ + +int tcp_child_process(struct sock *parent, struct sock *child, + struct sk_buff *skb) + __releases(&((child)->sk_lock.slock)) +{ + int ret = 0; + int state = child->sk_state; + + /* record sk_napi_id and sk_rx_queue_mapping of child. */ + sk_mark_napi_id_set(child, skb); + + tcp_segs_in(tcp_sk(child), skb); + if (!sock_owned_by_user(child)) { + ret = tcp_rcv_state_process(child, skb); + /* Wakeup parent, send SIGIO */ + if (state == TCP_SYN_RECV && child->sk_state != state) + parent->sk_data_ready(parent); + } else { + /* Alas, it is possible again, because we do lookup + * in main socket hash table and lock on listening + * socket does not protect us more. + */ + __sk_add_backlog(child, skb); + } + + bh_unlock_sock(child); + sock_put(child); + return ret; +} +EXPORT_SYMBOL(tcp_child_process); |