diff options
Diffstat (limited to 'net/netfilter/nf_synproxy_core.c')
| -rw-r--r-- | net/netfilter/nf_synproxy_core.c | 1220 |
1 files changed, 1220 insertions, 0 deletions
diff --git a/net/netfilter/nf_synproxy_core.c b/net/netfilter/nf_synproxy_core.c new file mode 100644 index 000000000..16915f8ee --- /dev/null +++ b/net/netfilter/nf_synproxy_core.c @@ -0,0 +1,1220 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (c) 2013 Patrick McHardy <kaber@trash.net> + */ + +#include <linux/module.h> +#include <linux/skbuff.h> +#include <asm/unaligned.h> +#include <net/tcp.h> +#include <net/netns/generic.h> +#include <linux/proc_fs.h> + +#include <linux/netfilter_ipv6.h> +#include <linux/netfilter/nf_synproxy.h> + +#include <net/netfilter/nf_conntrack.h> +#include <net/netfilter/nf_conntrack_ecache.h> +#include <net/netfilter/nf_conntrack_extend.h> +#include <net/netfilter/nf_conntrack_seqadj.h> +#include <net/netfilter/nf_conntrack_synproxy.h> +#include <net/netfilter/nf_conntrack_zones.h> +#include <net/netfilter/nf_synproxy.h> + +unsigned int synproxy_net_id; +EXPORT_SYMBOL_GPL(synproxy_net_id); + +bool +synproxy_parse_options(const struct sk_buff *skb, unsigned int doff, + const struct tcphdr *th, struct synproxy_options *opts) +{ + int length = (th->doff * 4) - sizeof(*th); + u8 buf[40], *ptr; + + if (unlikely(length < 0)) + return false; + + ptr = skb_header_pointer(skb, doff + sizeof(*th), length, buf); + if (ptr == NULL) + return false; + + opts->options = 0; + while (length > 0) { + int opcode = *ptr++; + int opsize; + + switch (opcode) { + case TCPOPT_EOL: + return true; + case TCPOPT_NOP: + length--; + continue; + default: + if (length < 2) + return true; + opsize = *ptr++; + if (opsize < 2) + return true; + if (opsize > length) + return true; + + switch (opcode) { + case TCPOPT_MSS: + if (opsize == TCPOLEN_MSS) { + opts->mss_option = get_unaligned_be16(ptr); + opts->options |= NF_SYNPROXY_OPT_MSS; + } + break; + case TCPOPT_WINDOW: + if (opsize == TCPOLEN_WINDOW) { + opts->wscale = *ptr; + if (opts->wscale > TCP_MAX_WSCALE) + opts->wscale = TCP_MAX_WSCALE; + opts->options |= NF_SYNPROXY_OPT_WSCALE; + } + break; + case TCPOPT_TIMESTAMP: + if (opsize == TCPOLEN_TIMESTAMP) { + opts->tsval = get_unaligned_be32(ptr); + opts->tsecr = get_unaligned_be32(ptr + 4); + opts->options |= NF_SYNPROXY_OPT_TIMESTAMP; + } + break; + case TCPOPT_SACK_PERM: + if (opsize == TCPOLEN_SACK_PERM) + opts->options |= NF_SYNPROXY_OPT_SACK_PERM; + break; + } + + ptr += opsize - 2; + length -= opsize; + } + } + return true; +} +EXPORT_SYMBOL_GPL(synproxy_parse_options); + +static unsigned int +synproxy_options_size(const struct synproxy_options *opts) +{ + unsigned int size = 0; + + if (opts->options & NF_SYNPROXY_OPT_MSS) + size += TCPOLEN_MSS_ALIGNED; + if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP) + size += TCPOLEN_TSTAMP_ALIGNED; + else if (opts->options & NF_SYNPROXY_OPT_SACK_PERM) + size += TCPOLEN_SACKPERM_ALIGNED; + if (opts->options & NF_SYNPROXY_OPT_WSCALE) + size += TCPOLEN_WSCALE_ALIGNED; + + return size; +} + +static void +synproxy_build_options(struct tcphdr *th, const struct synproxy_options *opts) +{ + __be32 *ptr = (__be32 *)(th + 1); + u8 options = opts->options; + + if (options & NF_SYNPROXY_OPT_MSS) + *ptr++ = htonl((TCPOPT_MSS << 24) | + (TCPOLEN_MSS << 16) | + opts->mss_option); + + if (options & NF_SYNPROXY_OPT_TIMESTAMP) { + if (options & NF_SYNPROXY_OPT_SACK_PERM) + *ptr++ = htonl((TCPOPT_SACK_PERM << 24) | + (TCPOLEN_SACK_PERM << 16) | + (TCPOPT_TIMESTAMP << 8) | + TCPOLEN_TIMESTAMP); + else + *ptr++ = htonl((TCPOPT_NOP << 24) | + (TCPOPT_NOP << 16) | + (TCPOPT_TIMESTAMP << 8) | + TCPOLEN_TIMESTAMP); + + *ptr++ = htonl(opts->tsval); + *ptr++ = htonl(opts->tsecr); + } else if (options & NF_SYNPROXY_OPT_SACK_PERM) + *ptr++ = htonl((TCPOPT_NOP << 24) | + (TCPOPT_NOP << 16) | + (TCPOPT_SACK_PERM << 8) | + TCPOLEN_SACK_PERM); + + if (options & NF_SYNPROXY_OPT_WSCALE) + *ptr++ = htonl((TCPOPT_NOP << 24) | + (TCPOPT_WINDOW << 16) | + (TCPOLEN_WINDOW << 8) | + opts->wscale); +} + +void synproxy_init_timestamp_cookie(const struct nf_synproxy_info *info, + struct synproxy_options *opts) +{ + opts->tsecr = opts->tsval; + opts->tsval = tcp_time_stamp_raw() & ~0x3f; + + if (opts->options & NF_SYNPROXY_OPT_WSCALE) { + opts->tsval |= opts->wscale; + opts->wscale = info->wscale; + } else + opts->tsval |= 0xf; + + if (opts->options & NF_SYNPROXY_OPT_SACK_PERM) + opts->tsval |= 1 << 4; + + if (opts->options & NF_SYNPROXY_OPT_ECN) + opts->tsval |= 1 << 5; +} +EXPORT_SYMBOL_GPL(synproxy_init_timestamp_cookie); + +static void +synproxy_check_timestamp_cookie(struct synproxy_options *opts) +{ + opts->wscale = opts->tsecr & 0xf; + if (opts->wscale != 0xf) + opts->options |= NF_SYNPROXY_OPT_WSCALE; + + opts->options |= opts->tsecr & (1 << 4) ? NF_SYNPROXY_OPT_SACK_PERM : 0; + + opts->options |= opts->tsecr & (1 << 5) ? NF_SYNPROXY_OPT_ECN : 0; +} + +static unsigned int +synproxy_tstamp_adjust(struct sk_buff *skb, unsigned int protoff, + struct tcphdr *th, struct nf_conn *ct, + enum ip_conntrack_info ctinfo, + const struct nf_conn_synproxy *synproxy) +{ + unsigned int optoff, optend; + __be32 *ptr, old; + + if (synproxy->tsoff == 0) + return 1; + + optoff = protoff + sizeof(struct tcphdr); + optend = protoff + th->doff * 4; + + if (skb_ensure_writable(skb, optend)) + return 0; + + while (optoff < optend) { + unsigned char *op = skb->data + optoff; + + switch (op[0]) { + case TCPOPT_EOL: + return 1; + case TCPOPT_NOP: + optoff++; + continue; + default: + if (optoff + 1 == optend || + optoff + op[1] > optend || + op[1] < 2) + return 0; + if (op[0] == TCPOPT_TIMESTAMP && + op[1] == TCPOLEN_TIMESTAMP) { + if (CTINFO2DIR(ctinfo) == IP_CT_DIR_REPLY) { + ptr = (__be32 *)&op[2]; + old = *ptr; + *ptr = htonl(ntohl(*ptr) - + synproxy->tsoff); + } else { + ptr = (__be32 *)&op[6]; + old = *ptr; + *ptr = htonl(ntohl(*ptr) + + synproxy->tsoff); + } + inet_proto_csum_replace4(&th->check, skb, + old, *ptr, false); + return 1; + } + optoff += op[1]; + } + } + return 1; +} + +#ifdef CONFIG_PROC_FS +static void *synproxy_cpu_seq_start(struct seq_file *seq, loff_t *pos) +{ + struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq)); + int cpu; + + if (*pos == 0) + return SEQ_START_TOKEN; + + for (cpu = *pos - 1; cpu < nr_cpu_ids; cpu++) { + if (!cpu_possible(cpu)) + continue; + *pos = cpu + 1; + return per_cpu_ptr(snet->stats, cpu); + } + + return NULL; +} + +static void *synproxy_cpu_seq_next(struct seq_file *seq, void *v, loff_t *pos) +{ + struct synproxy_net *snet = synproxy_pernet(seq_file_net(seq)); + int cpu; + + for (cpu = *pos; cpu < nr_cpu_ids; cpu++) { + if (!cpu_possible(cpu)) + continue; + *pos = cpu + 1; + return per_cpu_ptr(snet->stats, cpu); + } + (*pos)++; + return NULL; +} + +static void synproxy_cpu_seq_stop(struct seq_file *seq, void *v) +{ + return; +} + +static int synproxy_cpu_seq_show(struct seq_file *seq, void *v) +{ + struct synproxy_stats *stats = v; + + if (v == SEQ_START_TOKEN) { + seq_puts(seq, "entries\t\tsyn_received\t" + "cookie_invalid\tcookie_valid\t" + "cookie_retrans\tconn_reopened\n"); + return 0; + } + + seq_printf(seq, "%08x\t%08x\t%08x\t%08x\t%08x\t%08x\n", 0, + stats->syn_received, + stats->cookie_invalid, + stats->cookie_valid, + stats->cookie_retrans, + stats->conn_reopened); + + return 0; +} + +static const struct seq_operations synproxy_cpu_seq_ops = { + .start = synproxy_cpu_seq_start, + .next = synproxy_cpu_seq_next, + .stop = synproxy_cpu_seq_stop, + .show = synproxy_cpu_seq_show, +}; + +static int __net_init synproxy_proc_init(struct net *net) +{ + if (!proc_create_net("synproxy", 0444, net->proc_net_stat, + &synproxy_cpu_seq_ops, sizeof(struct seq_net_private))) + return -ENOMEM; + return 0; +} + +static void __net_exit synproxy_proc_exit(struct net *net) +{ + remove_proc_entry("synproxy", net->proc_net_stat); +} +#else +static int __net_init synproxy_proc_init(struct net *net) +{ + return 0; +} + +static void __net_exit synproxy_proc_exit(struct net *net) +{ + return; +} +#endif /* CONFIG_PROC_FS */ + +static int __net_init synproxy_net_init(struct net *net) +{ + struct synproxy_net *snet = synproxy_pernet(net); + struct nf_conn *ct; + int err = -ENOMEM; + + ct = nf_ct_tmpl_alloc(net, &nf_ct_zone_dflt, GFP_KERNEL); + if (!ct) + goto err1; + + if (!nfct_seqadj_ext_add(ct)) + goto err2; + if (!nfct_synproxy_ext_add(ct)) + goto err2; + + __set_bit(IPS_CONFIRMED_BIT, &ct->status); + snet->tmpl = ct; + + snet->stats = alloc_percpu(struct synproxy_stats); + if (snet->stats == NULL) + goto err2; + + err = synproxy_proc_init(net); + if (err < 0) + goto err3; + + return 0; + +err3: + free_percpu(snet->stats); +err2: + nf_ct_tmpl_free(ct); +err1: + return err; +} + +static void __net_exit synproxy_net_exit(struct net *net) +{ + struct synproxy_net *snet = synproxy_pernet(net); + + nf_ct_put(snet->tmpl); + synproxy_proc_exit(net); + free_percpu(snet->stats); +} + +static struct pernet_operations synproxy_net_ops = { + .init = synproxy_net_init, + .exit = synproxy_net_exit, + .id = &synproxy_net_id, + .size = sizeof(struct synproxy_net), +}; + +static int __init synproxy_core_init(void) +{ + return register_pernet_subsys(&synproxy_net_ops); +} + +static void __exit synproxy_core_exit(void) +{ + unregister_pernet_subsys(&synproxy_net_ops); +} + +module_init(synproxy_core_init); +module_exit(synproxy_core_exit); + +static struct iphdr * +synproxy_build_ip(struct net *net, struct sk_buff *skb, __be32 saddr, + __be32 daddr) +{ + struct iphdr *iph; + + skb_reset_network_header(skb); + iph = skb_put(skb, sizeof(*iph)); + iph->version = 4; + iph->ihl = sizeof(*iph) / 4; + iph->tos = 0; + iph->id = 0; + iph->frag_off = htons(IP_DF); + iph->ttl = READ_ONCE(net->ipv4.sysctl_ip_default_ttl); + iph->protocol = IPPROTO_TCP; + iph->check = 0; + iph->saddr = saddr; + iph->daddr = daddr; + + return iph; +} + +static void +synproxy_send_tcp(struct net *net, + const struct sk_buff *skb, struct sk_buff *nskb, + struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo, + struct iphdr *niph, struct tcphdr *nth, + unsigned int tcp_hdr_size) +{ + nth->check = ~tcp_v4_check(tcp_hdr_size, niph->saddr, niph->daddr, 0); + nskb->ip_summed = CHECKSUM_PARTIAL; + nskb->csum_start = (unsigned char *)nth - nskb->head; + nskb->csum_offset = offsetof(struct tcphdr, check); + + skb_dst_set_noref(nskb, skb_dst(skb)); + nskb->protocol = htons(ETH_P_IP); + if (ip_route_me_harder(net, nskb->sk, nskb, RTN_UNSPEC)) + goto free_nskb; + + if (nfct) { + nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo); + nf_conntrack_get(nfct); + } + + ip_local_out(net, nskb->sk, nskb); + return; + +free_nskb: + kfree_skb(nskb); +} + +void +synproxy_send_client_synack(struct net *net, + const struct sk_buff *skb, const struct tcphdr *th, + const struct synproxy_options *opts) +{ + struct sk_buff *nskb; + struct iphdr *iph, *niph; + struct tcphdr *nth; + unsigned int tcp_hdr_size; + u16 mss = opts->mss_encode; + + iph = ip_hdr(skb); + + tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); + nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, + GFP_ATOMIC); + if (!nskb) + return; + skb_reserve(nskb, MAX_TCP_HEADER); + + niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr); + + skb_reset_transport_header(nskb); + nth = skb_put(nskb, tcp_hdr_size); + nth->source = th->dest; + nth->dest = th->source; + nth->seq = htonl(__cookie_v4_init_sequence(iph, th, &mss)); + nth->ack_seq = htonl(ntohl(th->seq) + 1); + tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK; + if (opts->options & NF_SYNPROXY_OPT_ECN) + tcp_flag_word(nth) |= TCP_FLAG_ECE; + nth->doff = tcp_hdr_size / 4; + nth->window = 0; + nth->check = 0; + nth->urg_ptr = 0; + + synproxy_build_options(nth, opts); + + synproxy_send_tcp(net, skb, nskb, skb_nfct(skb), + IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size); +} +EXPORT_SYMBOL_GPL(synproxy_send_client_synack); + +static void +synproxy_send_server_syn(struct net *net, + const struct sk_buff *skb, const struct tcphdr *th, + const struct synproxy_options *opts, u32 recv_seq) +{ + struct synproxy_net *snet = synproxy_pernet(net); + struct sk_buff *nskb; + struct iphdr *iph, *niph; + struct tcphdr *nth; + unsigned int tcp_hdr_size; + + iph = ip_hdr(skb); + + tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); + nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, + GFP_ATOMIC); + if (!nskb) + return; + skb_reserve(nskb, MAX_TCP_HEADER); + + niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr); + + skb_reset_transport_header(nskb); + nth = skb_put(nskb, tcp_hdr_size); + nth->source = th->source; + nth->dest = th->dest; + nth->seq = htonl(recv_seq - 1); + /* ack_seq is used to relay our ISN to the synproxy hook to initialize + * sequence number translation once a connection tracking entry exists. + */ + nth->ack_seq = htonl(ntohl(th->ack_seq) - 1); + tcp_flag_word(nth) = TCP_FLAG_SYN; + if (opts->options & NF_SYNPROXY_OPT_ECN) + tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR; + nth->doff = tcp_hdr_size / 4; + nth->window = th->window; + nth->check = 0; + nth->urg_ptr = 0; + + synproxy_build_options(nth, opts); + + synproxy_send_tcp(net, skb, nskb, &snet->tmpl->ct_general, IP_CT_NEW, + niph, nth, tcp_hdr_size); +} + +static void +synproxy_send_server_ack(struct net *net, + const struct ip_ct_tcp *state, + const struct sk_buff *skb, const struct tcphdr *th, + const struct synproxy_options *opts) +{ + struct sk_buff *nskb; + struct iphdr *iph, *niph; + struct tcphdr *nth; + unsigned int tcp_hdr_size; + + iph = ip_hdr(skb); + + tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); + nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, + GFP_ATOMIC); + if (!nskb) + return; + skb_reserve(nskb, MAX_TCP_HEADER); + + niph = synproxy_build_ip(net, nskb, iph->daddr, iph->saddr); + + skb_reset_transport_header(nskb); + nth = skb_put(nskb, tcp_hdr_size); + nth->source = th->dest; + nth->dest = th->source; + nth->seq = htonl(ntohl(th->ack_seq)); + nth->ack_seq = htonl(ntohl(th->seq) + 1); + tcp_flag_word(nth) = TCP_FLAG_ACK; + nth->doff = tcp_hdr_size / 4; + nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin); + nth->check = 0; + nth->urg_ptr = 0; + + synproxy_build_options(nth, opts); + + synproxy_send_tcp(net, skb, nskb, NULL, 0, niph, nth, tcp_hdr_size); +} + +static void +synproxy_send_client_ack(struct net *net, + const struct sk_buff *skb, const struct tcphdr *th, + const struct synproxy_options *opts) +{ + struct sk_buff *nskb; + struct iphdr *iph, *niph; + struct tcphdr *nth; + unsigned int tcp_hdr_size; + + iph = ip_hdr(skb); + + tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); + nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, + GFP_ATOMIC); + if (!nskb) + return; + skb_reserve(nskb, MAX_TCP_HEADER); + + niph = synproxy_build_ip(net, nskb, iph->saddr, iph->daddr); + + skb_reset_transport_header(nskb); + nth = skb_put(nskb, tcp_hdr_size); + nth->source = th->source; + nth->dest = th->dest; + nth->seq = htonl(ntohl(th->seq) + 1); + nth->ack_seq = th->ack_seq; + tcp_flag_word(nth) = TCP_FLAG_ACK; + nth->doff = tcp_hdr_size / 4; + nth->window = htons(ntohs(th->window) >> opts->wscale); + nth->check = 0; + nth->urg_ptr = 0; + + synproxy_build_options(nth, opts); + + synproxy_send_tcp(net, skb, nskb, skb_nfct(skb), + IP_CT_ESTABLISHED_REPLY, niph, nth, tcp_hdr_size); +} + +bool +synproxy_recv_client_ack(struct net *net, + const struct sk_buff *skb, const struct tcphdr *th, + struct synproxy_options *opts, u32 recv_seq) +{ + struct synproxy_net *snet = synproxy_pernet(net); + int mss; + + mss = __cookie_v4_check(ip_hdr(skb), th, ntohl(th->ack_seq) - 1); + if (mss == 0) { + this_cpu_inc(snet->stats->cookie_invalid); + return false; + } + + this_cpu_inc(snet->stats->cookie_valid); + opts->mss_option = mss; + opts->options |= NF_SYNPROXY_OPT_MSS; + + if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP) + synproxy_check_timestamp_cookie(opts); + + synproxy_send_server_syn(net, skb, th, opts, recv_seq); + return true; +} +EXPORT_SYMBOL_GPL(synproxy_recv_client_ack); + +unsigned int +ipv4_synproxy_hook(void *priv, struct sk_buff *skb, + const struct nf_hook_state *nhs) +{ + struct net *net = nhs->net; + struct synproxy_net *snet = synproxy_pernet(net); + enum ip_conntrack_info ctinfo; + struct nf_conn *ct; + struct nf_conn_synproxy *synproxy; + struct synproxy_options opts = {}; + const struct ip_ct_tcp *state; + struct tcphdr *th, _th; + unsigned int thoff; + + ct = nf_ct_get(skb, &ctinfo); + if (!ct) + return NF_ACCEPT; + + synproxy = nfct_synproxy(ct); + if (!synproxy) + return NF_ACCEPT; + + if (nf_is_loopback_packet(skb) || + ip_hdr(skb)->protocol != IPPROTO_TCP) + return NF_ACCEPT; + + thoff = ip_hdrlen(skb); + th = skb_header_pointer(skb, thoff, sizeof(_th), &_th); + if (!th) + return NF_DROP; + + state = &ct->proto.tcp; + switch (state->state) { + case TCP_CONNTRACK_CLOSE: + if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) { + nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - + ntohl(th->seq) + 1); + break; + } + + if (!th->syn || th->ack || + CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) + break; + + /* Reopened connection - reset the sequence number and timestamp + * adjustments, they will get initialized once the connection is + * reestablished. + */ + nf_ct_seqadj_init(ct, ctinfo, 0); + synproxy->tsoff = 0; + this_cpu_inc(snet->stats->conn_reopened); + fallthrough; + case TCP_CONNTRACK_SYN_SENT: + if (!synproxy_parse_options(skb, thoff, th, &opts)) + return NF_DROP; + + if (!th->syn && th->ack && + CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) { + /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1, + * therefore we need to add 1 to make the SYN sequence + * number match the one of first SYN. + */ + if (synproxy_recv_client_ack(net, skb, th, &opts, + ntohl(th->seq) + 1)) { + this_cpu_inc(snet->stats->cookie_retrans); + consume_skb(skb); + return NF_STOLEN; + } else { + return NF_DROP; + } + } + + synproxy->isn = ntohl(th->ack_seq); + if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP) + synproxy->its = opts.tsecr; + + nf_conntrack_event_cache(IPCT_SYNPROXY, ct); + break; + case TCP_CONNTRACK_SYN_RECV: + if (!th->syn || !th->ack) + break; + + if (!synproxy_parse_options(skb, thoff, th, &opts)) + return NF_DROP; + + if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP) { + synproxy->tsoff = opts.tsval - synproxy->its; + nf_conntrack_event_cache(IPCT_SYNPROXY, ct); + } + + opts.options &= ~(NF_SYNPROXY_OPT_MSS | + NF_SYNPROXY_OPT_WSCALE | + NF_SYNPROXY_OPT_SACK_PERM); + + swap(opts.tsval, opts.tsecr); + synproxy_send_server_ack(net, state, skb, th, &opts); + + nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq)); + nf_conntrack_event_cache(IPCT_SEQADJ, ct); + + swap(opts.tsval, opts.tsecr); + synproxy_send_client_ack(net, skb, th, &opts); + + consume_skb(skb); + return NF_STOLEN; + default: + break; + } + + synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy); + return NF_ACCEPT; +} +EXPORT_SYMBOL_GPL(ipv4_synproxy_hook); + +static const struct nf_hook_ops ipv4_synproxy_ops[] = { + { + .hook = ipv4_synproxy_hook, + .pf = NFPROTO_IPV4, + .hooknum = NF_INET_LOCAL_IN, + .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, + }, + { + .hook = ipv4_synproxy_hook, + .pf = NFPROTO_IPV4, + .hooknum = NF_INET_POST_ROUTING, + .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, + }, +}; + +int nf_synproxy_ipv4_init(struct synproxy_net *snet, struct net *net) +{ + int err; + + if (snet->hook_ref4 == 0) { + err = nf_register_net_hooks(net, ipv4_synproxy_ops, + ARRAY_SIZE(ipv4_synproxy_ops)); + if (err) + return err; + } + + snet->hook_ref4++; + return 0; +} +EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_init); + +void nf_synproxy_ipv4_fini(struct synproxy_net *snet, struct net *net) +{ + snet->hook_ref4--; + if (snet->hook_ref4 == 0) + nf_unregister_net_hooks(net, ipv4_synproxy_ops, + ARRAY_SIZE(ipv4_synproxy_ops)); +} +EXPORT_SYMBOL_GPL(nf_synproxy_ipv4_fini); + +#if IS_ENABLED(CONFIG_IPV6) +static struct ipv6hdr * +synproxy_build_ip_ipv6(struct net *net, struct sk_buff *skb, + const struct in6_addr *saddr, + const struct in6_addr *daddr) +{ + struct ipv6hdr *iph; + + skb_reset_network_header(skb); + iph = skb_put(skb, sizeof(*iph)); + ip6_flow_hdr(iph, 0, 0); + iph->hop_limit = net->ipv6.devconf_all->hop_limit; + iph->nexthdr = IPPROTO_TCP; + iph->saddr = *saddr; + iph->daddr = *daddr; + + return iph; +} + +static void +synproxy_send_tcp_ipv6(struct net *net, + const struct sk_buff *skb, struct sk_buff *nskb, + struct nf_conntrack *nfct, enum ip_conntrack_info ctinfo, + struct ipv6hdr *niph, struct tcphdr *nth, + unsigned int tcp_hdr_size) +{ + struct dst_entry *dst; + struct flowi6 fl6; + int err; + + nth->check = ~tcp_v6_check(tcp_hdr_size, &niph->saddr, &niph->daddr, 0); + nskb->ip_summed = CHECKSUM_PARTIAL; + nskb->csum_start = (unsigned char *)nth - nskb->head; + nskb->csum_offset = offsetof(struct tcphdr, check); + + memset(&fl6, 0, sizeof(fl6)); + fl6.flowi6_proto = IPPROTO_TCP; + fl6.saddr = niph->saddr; + fl6.daddr = niph->daddr; + fl6.fl6_sport = nth->source; + fl6.fl6_dport = nth->dest; + security_skb_classify_flow((struct sk_buff *)skb, + flowi6_to_flowi_common(&fl6)); + err = nf_ip6_route(net, &dst, flowi6_to_flowi(&fl6), false); + if (err) { + goto free_nskb; + } + + dst = xfrm_lookup(net, dst, flowi6_to_flowi(&fl6), NULL, 0); + if (IS_ERR(dst)) + goto free_nskb; + + skb_dst_set(nskb, dst); + + if (nfct) { + nf_ct_set(nskb, (struct nf_conn *)nfct, ctinfo); + nf_conntrack_get(nfct); + } + + ip6_local_out(net, nskb->sk, nskb); + return; + +free_nskb: + kfree_skb(nskb); +} + +void +synproxy_send_client_synack_ipv6(struct net *net, + const struct sk_buff *skb, + const struct tcphdr *th, + const struct synproxy_options *opts) +{ + struct sk_buff *nskb; + struct ipv6hdr *iph, *niph; + struct tcphdr *nth; + unsigned int tcp_hdr_size; + u16 mss = opts->mss_encode; + + iph = ipv6_hdr(skb); + + tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); + nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, + GFP_ATOMIC); + if (!nskb) + return; + skb_reserve(nskb, MAX_TCP_HEADER); + + niph = synproxy_build_ip_ipv6(net, nskb, &iph->daddr, &iph->saddr); + + skb_reset_transport_header(nskb); + nth = skb_put(nskb, tcp_hdr_size); + nth->source = th->dest; + nth->dest = th->source; + nth->seq = htonl(nf_ipv6_cookie_init_sequence(iph, th, &mss)); + nth->ack_seq = htonl(ntohl(th->seq) + 1); + tcp_flag_word(nth) = TCP_FLAG_SYN | TCP_FLAG_ACK; + if (opts->options & NF_SYNPROXY_OPT_ECN) + tcp_flag_word(nth) |= TCP_FLAG_ECE; + nth->doff = tcp_hdr_size / 4; + nth->window = 0; + nth->check = 0; + nth->urg_ptr = 0; + + synproxy_build_options(nth, opts); + + synproxy_send_tcp_ipv6(net, skb, nskb, skb_nfct(skb), + IP_CT_ESTABLISHED_REPLY, niph, nth, + tcp_hdr_size); +} +EXPORT_SYMBOL_GPL(synproxy_send_client_synack_ipv6); + +static void +synproxy_send_server_syn_ipv6(struct net *net, const struct sk_buff *skb, + const struct tcphdr *th, + const struct synproxy_options *opts, u32 recv_seq) +{ + struct synproxy_net *snet = synproxy_pernet(net); + struct sk_buff *nskb; + struct ipv6hdr *iph, *niph; + struct tcphdr *nth; + unsigned int tcp_hdr_size; + + iph = ipv6_hdr(skb); + + tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); + nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, + GFP_ATOMIC); + if (!nskb) + return; + skb_reserve(nskb, MAX_TCP_HEADER); + + niph = synproxy_build_ip_ipv6(net, nskb, &iph->saddr, &iph->daddr); + + skb_reset_transport_header(nskb); + nth = skb_put(nskb, tcp_hdr_size); + nth->source = th->source; + nth->dest = th->dest; + nth->seq = htonl(recv_seq - 1); + /* ack_seq is used to relay our ISN to the synproxy hook to initialize + * sequence number translation once a connection tracking entry exists. + */ + nth->ack_seq = htonl(ntohl(th->ack_seq) - 1); + tcp_flag_word(nth) = TCP_FLAG_SYN; + if (opts->options & NF_SYNPROXY_OPT_ECN) + tcp_flag_word(nth) |= TCP_FLAG_ECE | TCP_FLAG_CWR; + nth->doff = tcp_hdr_size / 4; + nth->window = th->window; + nth->check = 0; + nth->urg_ptr = 0; + + synproxy_build_options(nth, opts); + + synproxy_send_tcp_ipv6(net, skb, nskb, &snet->tmpl->ct_general, + IP_CT_NEW, niph, nth, tcp_hdr_size); +} + +static void +synproxy_send_server_ack_ipv6(struct net *net, const struct ip_ct_tcp *state, + const struct sk_buff *skb, + const struct tcphdr *th, + const struct synproxy_options *opts) +{ + struct sk_buff *nskb; + struct ipv6hdr *iph, *niph; + struct tcphdr *nth; + unsigned int tcp_hdr_size; + + iph = ipv6_hdr(skb); + + tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); + nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, + GFP_ATOMIC); + if (!nskb) + return; + skb_reserve(nskb, MAX_TCP_HEADER); + + niph = synproxy_build_ip_ipv6(net, nskb, &iph->daddr, &iph->saddr); + + skb_reset_transport_header(nskb); + nth = skb_put(nskb, tcp_hdr_size); + nth->source = th->dest; + nth->dest = th->source; + nth->seq = htonl(ntohl(th->ack_seq)); + nth->ack_seq = htonl(ntohl(th->seq) + 1); + tcp_flag_word(nth) = TCP_FLAG_ACK; + nth->doff = tcp_hdr_size / 4; + nth->window = htons(state->seen[IP_CT_DIR_ORIGINAL].td_maxwin); + nth->check = 0; + nth->urg_ptr = 0; + + synproxy_build_options(nth, opts); + + synproxy_send_tcp_ipv6(net, skb, nskb, NULL, 0, niph, nth, + tcp_hdr_size); +} + +static void +synproxy_send_client_ack_ipv6(struct net *net, const struct sk_buff *skb, + const struct tcphdr *th, + const struct synproxy_options *opts) +{ + struct sk_buff *nskb; + struct ipv6hdr *iph, *niph; + struct tcphdr *nth; + unsigned int tcp_hdr_size; + + iph = ipv6_hdr(skb); + + tcp_hdr_size = sizeof(*nth) + synproxy_options_size(opts); + nskb = alloc_skb(sizeof(*niph) + tcp_hdr_size + MAX_TCP_HEADER, + GFP_ATOMIC); + if (!nskb) + return; + skb_reserve(nskb, MAX_TCP_HEADER); + + niph = synproxy_build_ip_ipv6(net, nskb, &iph->saddr, &iph->daddr); + + skb_reset_transport_header(nskb); + nth = skb_put(nskb, tcp_hdr_size); + nth->source = th->source; + nth->dest = th->dest; + nth->seq = htonl(ntohl(th->seq) + 1); + nth->ack_seq = th->ack_seq; + tcp_flag_word(nth) = TCP_FLAG_ACK; + nth->doff = tcp_hdr_size / 4; + nth->window = htons(ntohs(th->window) >> opts->wscale); + nth->check = 0; + nth->urg_ptr = 0; + + synproxy_build_options(nth, opts); + + synproxy_send_tcp_ipv6(net, skb, nskb, skb_nfct(skb), + IP_CT_ESTABLISHED_REPLY, niph, nth, + tcp_hdr_size); +} + +bool +synproxy_recv_client_ack_ipv6(struct net *net, + const struct sk_buff *skb, + const struct tcphdr *th, + struct synproxy_options *opts, u32 recv_seq) +{ + struct synproxy_net *snet = synproxy_pernet(net); + int mss; + + mss = nf_cookie_v6_check(ipv6_hdr(skb), th, ntohl(th->ack_seq) - 1); + if (mss == 0) { + this_cpu_inc(snet->stats->cookie_invalid); + return false; + } + + this_cpu_inc(snet->stats->cookie_valid); + opts->mss_option = mss; + opts->options |= NF_SYNPROXY_OPT_MSS; + + if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP) + synproxy_check_timestamp_cookie(opts); + + synproxy_send_server_syn_ipv6(net, skb, th, opts, recv_seq); + return true; +} +EXPORT_SYMBOL_GPL(synproxy_recv_client_ack_ipv6); + +unsigned int +ipv6_synproxy_hook(void *priv, struct sk_buff *skb, + const struct nf_hook_state *nhs) +{ + struct net *net = nhs->net; + struct synproxy_net *snet = synproxy_pernet(net); + enum ip_conntrack_info ctinfo; + struct nf_conn *ct; + struct nf_conn_synproxy *synproxy; + struct synproxy_options opts = {}; + const struct ip_ct_tcp *state; + struct tcphdr *th, _th; + __be16 frag_off; + u8 nexthdr; + int thoff; + + ct = nf_ct_get(skb, &ctinfo); + if (!ct) + return NF_ACCEPT; + + synproxy = nfct_synproxy(ct); + if (!synproxy) + return NF_ACCEPT; + + if (nf_is_loopback_packet(skb)) + return NF_ACCEPT; + + nexthdr = ipv6_hdr(skb)->nexthdr; + thoff = ipv6_skip_exthdr(skb, sizeof(struct ipv6hdr), &nexthdr, + &frag_off); + if (thoff < 0 || nexthdr != IPPROTO_TCP) + return NF_ACCEPT; + + th = skb_header_pointer(skb, thoff, sizeof(_th), &_th); + if (!th) + return NF_DROP; + + state = &ct->proto.tcp; + switch (state->state) { + case TCP_CONNTRACK_CLOSE: + if (th->rst && CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) { + nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - + ntohl(th->seq) + 1); + break; + } + + if (!th->syn || th->ack || + CTINFO2DIR(ctinfo) != IP_CT_DIR_ORIGINAL) + break; + + /* Reopened connection - reset the sequence number and timestamp + * adjustments, they will get initialized once the connection is + * reestablished. + */ + nf_ct_seqadj_init(ct, ctinfo, 0); + synproxy->tsoff = 0; + this_cpu_inc(snet->stats->conn_reopened); + fallthrough; + case TCP_CONNTRACK_SYN_SENT: + if (!synproxy_parse_options(skb, thoff, th, &opts)) + return NF_DROP; + + if (!th->syn && th->ack && + CTINFO2DIR(ctinfo) == IP_CT_DIR_ORIGINAL) { + /* Keep-Alives are sent with SEG.SEQ = SND.NXT-1, + * therefore we need to add 1 to make the SYN sequence + * number match the one of first SYN. + */ + if (synproxy_recv_client_ack_ipv6(net, skb, th, &opts, + ntohl(th->seq) + 1)) { + this_cpu_inc(snet->stats->cookie_retrans); + consume_skb(skb); + return NF_STOLEN; + } else { + return NF_DROP; + } + } + + synproxy->isn = ntohl(th->ack_seq); + if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP) + synproxy->its = opts.tsecr; + + nf_conntrack_event_cache(IPCT_SYNPROXY, ct); + break; + case TCP_CONNTRACK_SYN_RECV: + if (!th->syn || !th->ack) + break; + + if (!synproxy_parse_options(skb, thoff, th, &opts)) + return NF_DROP; + + if (opts.options & NF_SYNPROXY_OPT_TIMESTAMP) { + synproxy->tsoff = opts.tsval - synproxy->its; + nf_conntrack_event_cache(IPCT_SYNPROXY, ct); + } + + opts.options &= ~(NF_SYNPROXY_OPT_MSS | + NF_SYNPROXY_OPT_WSCALE | + NF_SYNPROXY_OPT_SACK_PERM); + + swap(opts.tsval, opts.tsecr); + synproxy_send_server_ack_ipv6(net, state, skb, th, &opts); + + nf_ct_seqadj_init(ct, ctinfo, synproxy->isn - ntohl(th->seq)); + nf_conntrack_event_cache(IPCT_SEQADJ, ct); + + swap(opts.tsval, opts.tsecr); + synproxy_send_client_ack_ipv6(net, skb, th, &opts); + + consume_skb(skb); + return NF_STOLEN; + default: + break; + } + + synproxy_tstamp_adjust(skb, thoff, th, ct, ctinfo, synproxy); + return NF_ACCEPT; +} +EXPORT_SYMBOL_GPL(ipv6_synproxy_hook); + +static const struct nf_hook_ops ipv6_synproxy_ops[] = { + { + .hook = ipv6_synproxy_hook, + .pf = NFPROTO_IPV6, + .hooknum = NF_INET_LOCAL_IN, + .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, + }, + { + .hook = ipv6_synproxy_hook, + .pf = NFPROTO_IPV6, + .hooknum = NF_INET_POST_ROUTING, + .priority = NF_IP_PRI_CONNTRACK_CONFIRM - 1, + }, +}; + +int +nf_synproxy_ipv6_init(struct synproxy_net *snet, struct net *net) +{ + int err; + + if (snet->hook_ref6 == 0) { + err = nf_register_net_hooks(net, ipv6_synproxy_ops, + ARRAY_SIZE(ipv6_synproxy_ops)); + if (err) + return err; + } + + snet->hook_ref6++; + return 0; +} +EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_init); + +void +nf_synproxy_ipv6_fini(struct synproxy_net *snet, struct net *net) +{ + snet->hook_ref6--; + if (snet->hook_ref6 == 0) + nf_unregister_net_hooks(net, ipv6_synproxy_ops, + ARRAY_SIZE(ipv6_synproxy_ops)); +} +EXPORT_SYMBOL_GPL(nf_synproxy_ipv6_fini); +#endif /* CONFIG_IPV6 */ + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>"); +MODULE_DESCRIPTION("nftables SYNPROXY expression support"); |