// SPDX-License-Identifier: GPL-2.0-or-later/* * Syncookies implementation for the Linux kernel * * Copyright (C) 1997 Andi Kleen * Based on ideas by D.J.Bernstein and Eric Schenk. */ #include <linux/tcp.h>#include <linux/siphash.h>#include <linux/kernel.h>#include <linux/export.h>#include <net/secure_seq.h>#include <net/tcp.h>#include <net/tcp_ecn.h>#include <net/route.h> static siphash_aligned_key_t syncookie_secret[2]; #define COOKIEBITS 24 /* Upper bits store count */#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) /* TCP Timestamp: 6 lowest bits of timestamp sent in the cookie SYN-ACK * stores TCP options: * * MSB LSB * | 31 ... 6 | 5 | 4 | 3 2 1 0 | * | Timestamp | ECN | SACK | WScale | * * When we receive a valid cookie-ACK, we look at the echoed tsval (if * any) to figure out which TCP options we should use for the rebuilt * connection. * * A WScale setting of '0xf' (which is an invalid scaling value) * means that original syn did not include the TCP window scaling option. */#define TS_OPT_WSCALE_MASK 0xf#define TS_OPT_SACK BIT(4)#define TS_OPT_ECN BIT(5)/* There is no TS_OPT_TIMESTAMP: * if ACK contains timestamp option, we already know it was * requested/supported by the syn/synack exchange. */#define TSBITS 6 static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, u32 count, int c){ net_get_random_once(syncookie_secret, sizeof(syncookie_secret)); return siphash_4u32((__force u32)saddr, (__force u32)daddr, (__force u32)sport << 16 | (__force u32)dport, count, &syncookie_secret[c]);} /* * when syncookies are in effect and tcp timestamps are enabled we encode * tcp options in the lower bits of the timestamp value that will be * sent in the syn-ack. * Since subsequent timestamps use the normal tcp_time_stamp value, we * must make sure that the resulting initial timestamp is <= tcp_time_stamp. */u64 cookie_init_timestamp(struct request_sock *req, u64 now){ const struct inet_request_sock *ireq = inet_rsk(req); u64 ts, ts_now = tcp_ns_to_ts(false, now); u32 options = 0; options = ireq->wscale_ok ? ireq->snd_wscale : TS_OPT_WSCALE_MASK; if (ireq->sack_ok) options |= TS_OPT_SACK; if (ireq->ecn_ok) options |= TS_OPT_ECN; ts = (ts_now >> TSBITS) << TSBITS; ts |= options; if (ts > ts_now) ts -= (1UL << TSBITS); if (tcp_rsk(req)->req_usec_ts) return ts * NSEC_PER_USEC; return ts * NSEC_PER_MSEC;} static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, __u32 sseq, __u32 data){ /* * Compute the secure sequence number. * The output should be: * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24) * + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24). * Where sseq is their sequence number and count increases every * minute by 1. * As an extra hack, we add a small "data" value that encodes the * MSS into the second hash value. */ u32 count = tcp_cookie_time(); return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq + (count << COOKIEBITS) + ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) & COOKIEMASK));} /* * This retrieves the small "data" value from the syncookie. * If the syncookie is bad, the data returned will be out of * range. This must be checked by the caller. * * The count value used to generate the cookie must be less than * MAX_SYNCOOKIE_AGE minutes in the past. * The return value (__u32)-1 if this test fails. */static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr, __be16 sport, __be16 dport, __u32 sseq){ u32 diff, count = tcp_cookie_time(); /* Strip away the layers from the cookie */ cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */ diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); if (diff >= MAX_SYNCOOKIE_AGE) return (__u32)-1; return (cookie - cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) & COOKIEMASK; /* Leaving the data behind */} /* * MSS Values are chosen based on the 2011 paper * 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson. * Values .. * .. lower than 536 are rare (< 0.2%) * .. between 537 and 1299 account for less than < 1.5% of observed values * .. in the 1300-1349 range account for about 15 to 20% of observed mss values * .. exceeding 1460 are very rare (< 0.04%) * * 1460 is the single most frequently announced mss value (30 to 46% depending * on monitor location). Table must be sorted. */static __u16 const msstab[] = { 536, 1300, 1440, /* 1440, 1452: PPPoE */ 1460,}; /* * Generate a syncookie. mssp points to the mss, which is returned * rounded down to the value encoded in the cookie. */u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th, u16 *mssp){ int mssind; const __u16 mss = *mssp; for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) if (mss >= msstab[mssind]) break; *mssp = msstab[mssind]; return secure_tcp_syn_cookie(iph->saddr, iph->daddr, th->source, th->dest, ntohl(th->seq), mssind);}EXPORT_SYMBOL_GPL(__cookie_v4_init_sequence); __u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mssp){ const struct iphdr *iph = ip_hdr(skb); const struct tcphdr *th = tcp_hdr(skb); return __cookie_v4_init_sequence(iph, th, mssp);} /* * Check if a ack sequence number is a valid syncookie. * Return the decoded mss if it is, or 0 if not. */int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th){ __u32 cookie = ntohl(th->ack_seq) - 1; __u32 seq = ntohl(th->seq) - 1; __u32 mssind; mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr, th->source, th->dest, seq); return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;}EXPORT_SYMBOL_GPL(__cookie_v4_check); struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb, struct request_sock *req, struct dst_entry *dst){ struct inet_connection_sock *icsk = inet_csk(sk); struct sock *child; bool own_req; child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst, NULL, &own_req, NULL); if (child) { refcount_set(&req->rsk_refcnt, 1); sock_rps_save_rxhash(child, skb); if (rsk_drop_req(req)) { reqsk_put(req); return child; } if (inet_csk_reqsk_queue_add(sk, req, child)) return child; bh_unlock_sock(child); sock_put(child); } __reqsk_free(req); return NULL;} /* * when syncookies are in effect and tcp timestamps are enabled we stored * additional tcp options in the timestamp. * This extracts these options from the timestamp echo. * * return false if we decode a tcp option that is disabled * on the host. */bool cookie_timestamp_decode(const struct net *net, struct tcp_options_received *tcp_opt){ /* echoed timestamp, lowest bits contain options */ u32 options = tcp_opt->rcv_tsecr; if (!tcp_opt->saw_tstamp) { tcp_clear_options(tcp_opt); return true; } if (!READ_ONCE(net->ipv4.sysctl_tcp_timestamps)) return false; tcp_opt->sack_ok = (options & TS_OPT_SACK) ? TCP_SACK_SEEN : 0; if (tcp_opt->sack_ok && !READ_ONCE(net->ipv4.sysctl_tcp_sack)) return false; if ((options & TS_OPT_WSCALE_MASK) == TS_OPT_WSCALE_MASK) return true; /* no window scaling */ tcp_opt->wscale_ok = 1; tcp_opt->snd_wscale = options & TS_OPT_WSCALE_MASK; return READ_ONCE(net->ipv4.sysctl_tcp_window_scaling) != 0;} static int cookie_tcp_reqsk_init(struct sock *sk, struct sk_buff *skb, struct request_sock *req){ struct inet_request_sock *ireq = inet_rsk(req); struct tcp_request_sock *treq = tcp_rsk(req); const struct tcphdr *th = tcp_hdr(skb); req->num_retrans = 0; ireq->ir_num = ntohs(th->dest); ireq->ir_rmt_port = th->source; ireq->ir_iif = inet_request_bound_dev_if(sk, skb); ireq->ir_mark = inet_request_mark(sk, skb); if (IS_ENABLED(CONFIG_SMC)) ireq->smc_ok = 0; treq->snt_synack = 0; treq->snt_tsval_first = 0; treq->tfo_listener = false; treq->rcv_isn = ntohl(th->seq) - 1; treq->snt_isn = ntohl(th->ack_seq) - 1; /* The request socket was freed after the SYN-ACK; use the cookie * (snt_isn) as txhash so the full socket and the SYN-ACK make the * same egress choice (IPv6 ECMP path; IPv4 TX queue). */ treq->txhash = treq->snt_isn; treq->syn_tos = TCP_SKB_CB(skb)->ip_dsfield; #if IS_ENABLED(CONFIG_MPTCP) treq->is_mptcp = sk_is_mptcp(sk); if (treq->is_mptcp) return mptcp_subflow_init_cookie_req(req, sk, skb);#endif return 0;} #if IS_ENABLED(CONFIG_BPF)struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb){ struct request_sock *req = inet_reqsk(skb->sk); skb->sk = NULL; skb->destructor = NULL; if (cookie_tcp_reqsk_init(sk, skb, req)) { reqsk_free(req); req = NULL; } return req;}#endif struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk, struct sk_buff *skb, struct tcp_options_received *tcp_opt, int mss, u32 tsoff){ struct inet_request_sock *ireq; struct tcp_request_sock *treq; struct request_sock *req; if (sk_is_mptcp(sk)) req = mptcp_subflow_reqsk_alloc(ops, sk, false); else req = inet_reqsk_alloc(ops, sk, false); if (!req) return NULL; if (cookie_tcp_reqsk_init(sk, skb, req)) { reqsk_free(req); return NULL; } ireq = inet_rsk(req); treq = tcp_rsk(req); req->mss = mss; req->ts_recent = tcp_opt->saw_tstamp ? tcp_opt->rcv_tsval : 0; ireq->snd_wscale = tcp_opt->snd_wscale; ireq->tstamp_ok = tcp_opt->saw_tstamp; ireq->sack_ok = tcp_opt->sack_ok; ireq->wscale_ok = tcp_opt->wscale_ok; ireq->ecn_ok = !!(tcp_opt->rcv_tsecr & TS_OPT_ECN); treq->req_usec_ts = false; treq->ts_off = tsoff; return req;} static struct request_sock *cookie_tcp_check(struct net *net, struct sock *sk, struct sk_buff *skb){ struct tcp_options_received tcp_opt; u32 tsoff = 0; int mss; if (tcp_synq_no_recent_overflow(sk)) goto out; mss = __cookie_v4_check(ip_hdr(skb), tcp_hdr(skb)); if (!mss) { __NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESFAILED); goto out; } __NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESRECV); /* check for timestamp cookie support */ memset(&tcp_opt, 0, sizeof(tcp_opt)); tcp_parse_options(net, skb, &tcp_opt, 0, NULL); if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) { union tcp_seq_and_ts_off st; st = secure_tcp_seq_and_ts_off(net, ip_hdr(skb)->daddr, ip_hdr(skb)->saddr, tcp_hdr(skb)->dest, tcp_hdr(skb)->source); tsoff = st.ts_off; tcp_opt.rcv_tsecr -= tsoff; } if (!cookie_timestamp_decode(net, &tcp_opt)) goto out; return cookie_tcp_reqsk_alloc(&tcp_request_sock_ops, sk, skb, &tcp_opt, mss, tsoff);out: return ERR_PTR(-EINVAL);} /* On input, sk is a listener. * Output is listener if incoming packet would not create a child * NULL if memory could not be allocated. */struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb){ struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt; const struct tcphdr *th = tcp_hdr(skb); struct tcp_sock *tp = tcp_sk(sk); struct inet_request_sock *ireq; struct net *net = sock_net(sk); struct tcp_request_sock *treq; struct request_sock *req; struct sock *ret = sk; struct flowi4 fl4; struct rtable *rt; __u8 rcv_wscale; int full_space; SKB_DR(reason); if (!READ_ONCE(net->ipv4.sysctl_tcp_syncookies) || !th->ack || th->rst) goto out; if (cookie_bpf_ok(skb)) { req = cookie_bpf_check(sk, skb); } else { req = cookie_tcp_check(net, sk, skb); if (IS_ERR(req)) goto out; } if (!req) { SKB_DR_SET(reason, NO_SOCKET); goto out_drop; } ireq = inet_rsk(req); treq = tcp_rsk(req); sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr); sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr); /* We throwed the options of the initial SYN away, so we hope * the ACK carries the same options again (see RFC1122 4.2.3.8) */ RCU_INIT_POINTER(ireq->ireq_opt, tcp_v4_save_options(net, skb)); if (security_inet_conn_request(sk, skb, req)) { SKB_DR_SET(reason, SECURITY_HOOK); goto out_free; } tcp_ao_syncookie(sk, skb, req, AF_INET); /* * We need to lookup the route here to get at the correct * window size. We should better make sure that the window size * hasn't changed since we received the original syn, but I see * no easy way to do this. */ flowi4_init_output(&fl4, ireq->ir_iif, ireq->ir_mark, ip_sock_rt_tos(sk), ip_sock_rt_scope(sk), IPPROTO_TCP, inet_sk_flowi_flags(sk), opt->srr ? opt->faddr : ireq->ir_rmt_addr, ireq->ir_loc_addr, th->source, th->dest, sk_uid(sk)); security_req_classify_flow(req, flowi4_to_flowi_common(&fl4)); rt = ip_route_output_key(net, &fl4); if (IS_ERR(rt)) { SKB_DR_SET(reason, IP_OUTNOROUTES); goto out_free; } /* Try to redo what tcp_v4_send_synack did. */ req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? : dst_metric(&rt->dst, RTAX_WINDOW); /* limit the window selection if the user enforce a smaller rx buffer */ full_space = tcp_full_space(sk); if (sk->sk_userlocks & SOCK_RCVBUF_LOCK && (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) req->rsk_window_clamp = full_space; tcp_select_initial_window(sk, full_space, req->mss, &req->rsk_rcv_wnd, &req->rsk_window_clamp, ireq->wscale_ok, &rcv_wscale, dst_metric(&rt->dst, RTAX_INITRWND)); /* req->syncookie is set true only if ACK is validated * by BPF kfunc, then, rcv_wscale is already configured. */ if (!req->syncookie) ireq->rcv_wscale = rcv_wscale; ireq->ecn_ok &= cookie_ecn_ok(net, &rt->dst); treq->accecn_ok = ireq->ecn_ok && cookie_accecn_ok(th); ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst); /* ip_queue_xmit() depends on our flow being setup * Normal sockets get it right from inet_csk_route_child_sock() */ if (!ret) {Lines 1–500 of 512. 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// SPDX-License-Identifier: GPL-2.0-or-later /* * Syncookies implementation for the Linux kernel * * Copyright (C) 1997 Andi Kleen * Based on ideas by D.J.Bernstein and Eric Schenk. */ #include <linux/tcp.h> #include <linux/siphash.h> #include <linux/kernel.h> #include <linux/export.h> #include <net/secure_seq.h> #include <net/tcp.h> #include <net/tcp_ecn.h> #include <net/route.h> static siphash_aligned_key_t syncookie_secret[2]; #define COOKIEBITS 24 /* Upper bits store count */ #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) /* TCP Timestamp: 6 lowest bits of timestamp sent in the cookie SYN-ACK * stores TCP options: * * MSB LSB * | 31 ... 6 | 5 | 4 | 3 2 1 0 | * | Timestamp | ECN | SACK | WScale | * * When we receive a valid cookie-ACK, we look at the echoed tsval (if * any) to figure out which TCP options we should use for the rebuilt * connection. * * A WScale setting of '0xf' (which is an invalid scaling value) * means that original syn did not include the TCP window scaling option. */ #define TS_OPT_WSCALE_MASK 0xf #define TS_OPT_SACK BIT(4) #define TS_OPT_ECN BIT(5) /* There is no TS_OPT_TIMESTAMP: * if ACK contains timestamp option, we already know it was * requested/supported by the syn/synack exchange. */ #define TSBITS 6 static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, u32 count, int c) { net_get_random_once(syncookie_secret, sizeof(syncookie_secret)); return siphash_4u32((__force u32)saddr, (__force u32)daddr, (__force u32)sport << 16 | (__force u32)dport, count, &syncookie_secret[c]); } /* * when syncookies are in effect and tcp timestamps are enabled we encode * tcp options in the lower bits of the timestamp value that will be * sent in the syn-ack. * Since subsequent timestamps use the normal tcp_time_stamp value, we * must make sure that the resulting initial timestamp is <= tcp_time_stamp. */ u64 cookie_init_timestamp(struct request_sock *req, u64 now) { const struct inet_request_sock *ireq = inet_rsk(req); u64 ts, ts_now = tcp_ns_to_ts(false, now); u32 options = 0; options = ireq->wscale_ok ? ireq->snd_wscale : TS_OPT_WSCALE_MASK; if (ireq->sack_ok) options |= TS_OPT_SACK; if (ireq->ecn_ok) options |= TS_OPT_ECN; ts = (ts_now >> TSBITS) << TSBITS; ts |= options; if (ts > ts_now) ts -= (1UL << TSBITS); if (tcp_rsk(req)->req_usec_ts) return ts * NSEC_PER_USEC; return ts * NSEC_PER_MSEC; } static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, __u32 sseq, __u32 data) { /* * Compute the secure sequence number. * The output should be: * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24) * + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24). * Where sseq is their sequence number and count increases every * minute by 1. * As an extra hack, we add a small "data" value that encodes the * MSS into the second hash value. */ u32 count = tcp_cookie_time(); return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq + (count << COOKIEBITS) + ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) & COOKIEMASK)); } /* * This retrieves the small "data" value from the syncookie. * If the syncookie is bad, the data returned will be out of * range. This must be checked by the caller. * * The count value used to generate the cookie must be less than * MAX_SYNCOOKIE_AGE minutes in the past. * The return value (__u32)-1 if this test fails. */ static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr, __be16 sport, __be16 dport, __u32 sseq) { u32 diff, count = tcp_cookie_time(); /* Strip away the layers from the cookie */ cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */ diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); if (diff >= MAX_SYNCOOKIE_AGE) return (__u32)-1; return (cookie - cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) & COOKIEMASK; /* Leaving the data behind */ } /* * MSS Values are chosen based on the 2011 paper * 'An Analysis of TCP Maximum Segement Sizes' by S. Alcock and R. Nelson. * Values .. * .. lower than 536 are rare (< 0.2%) * .. between 537 and 1299 account for less than < 1.5% of observed values * .. in the 1300-1349 range account for about 15 to 20% of observed mss values * .. exceeding 1460 are very rare (< 0.04%) * * 1460 is the single most frequently announced mss value (30 to 46% depending * on monitor location). Table must be sorted. */ static __u16 const msstab[] = { 536, 1300, 1440, /* 1440, 1452: PPPoE */ 1460, }; /* * Generate a syncookie. mssp points to the mss, which is returned * rounded down to the value encoded in the cookie. */ u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th, u16 *mssp) { int mssind; const __u16 mss = *mssp; for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) if (mss >= msstab[mssind]) break; *mssp = msstab[mssind]; return secure_tcp_syn_cookie(iph->saddr, iph->daddr, th->source, th->dest, ntohl(th->seq), mssind); } EXPORT_SYMBOL_GPL(__cookie_v4_init_sequence); __u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mssp) { const struct iphdr *iph = ip_hdr(skb); const struct tcphdr *th = tcp_hdr(skb); return __cookie_v4_init_sequence(iph, th, mssp); } /* * Check if a ack sequence number is a valid syncookie. * Return the decoded mss if it is, or 0 if not. */ int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th) { __u32 cookie = ntohl(th->ack_seq) - 1; __u32 seq = ntohl(th->seq) - 1; __u32 mssind; mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr, th->source, th->dest, seq); return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; } EXPORT_SYMBOL_GPL(__cookie_v4_check); struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb, struct request_sock *req, struct dst_entry *dst) { struct inet_connection_sock *icsk = inet_csk(sk); struct sock *child; bool own_req; child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst, NULL, &own_req, NULL); if (child) { refcount_set(&req->rsk_refcnt, 1); sock_rps_save_rxhash(child, skb); if (rsk_drop_req(req)) { reqsk_put(req); return child; } if (inet_csk_reqsk_queue_add(sk, req, child)) return child; bh_unlock_sock(child); sock_put(child); } __reqsk_free(req); return NULL; } /* * when syncookies are in effect and tcp timestamps are enabled we stored * additional tcp options in the timestamp. * This extracts these options from the timestamp echo. * * return false if we decode a tcp option that is disabled * on the host. */ bool cookie_timestamp_decode(const struct net *net, struct tcp_options_received *tcp_opt) { /* echoed timestamp, lowest bits contain options */ u32 options = tcp_opt->rcv_tsecr; if (!tcp_opt->saw_tstamp) { tcp_clear_options(tcp_opt); return true; } if (!READ_ONCE(net->ipv4.sysctl_tcp_timestamps)) return false; tcp_opt->sack_ok = (options & TS_OPT_SACK) ? TCP_SACK_SEEN : 0; if (tcp_opt->sack_ok && !READ_ONCE(net->ipv4.sysctl_tcp_sack)) return false; if ((options & TS_OPT_WSCALE_MASK) == TS_OPT_WSCALE_MASK) return true; /* no window scaling */ tcp_opt->wscale_ok = 1; tcp_opt->snd_wscale = options & TS_OPT_WSCALE_MASK; return READ_ONCE(net->ipv4.sysctl_tcp_window_scaling) != 0; } static int cookie_tcp_reqsk_init(struct sock *sk, struct sk_buff *skb, struct request_sock *req) { struct inet_request_sock *ireq = inet_rsk(req); struct tcp_request_sock *treq = tcp_rsk(req); const struct tcphdr *th = tcp_hdr(skb); req->num_retrans = 0; ireq->ir_num = ntohs(th->dest); ireq->ir_rmt_port = th->source; ireq->ir_iif = inet_request_bound_dev_if(sk, skb); ireq->ir_mark = inet_request_mark(sk, skb); if (IS_ENABLED(CONFIG_SMC)) ireq->smc_ok = 0; treq->snt_synack = 0; treq->snt_tsval_first = 0; treq->tfo_listener = false; treq->rcv_isn = ntohl(th->seq) - 1; treq->snt_isn = ntohl(th->ack_seq) - 1; /* The request socket was freed after the SYN-ACK; use the cookie * (snt_isn) as txhash so the full socket and the SYN-ACK make the * same egress choice (IPv6 ECMP path; IPv4 TX queue). */ treq->txhash = treq->snt_isn; treq->syn_tos = TCP_SKB_CB(skb)->ip_dsfield; #if IS_ENABLED(CONFIG_MPTCP) treq->is_mptcp = sk_is_mptcp(sk); if (treq->is_mptcp) return mptcp_subflow_init_cookie_req(req, sk, skb); #endif return 0; } #if IS_ENABLED(CONFIG_BPF) struct request_sock *cookie_bpf_check(struct sock *sk, struct sk_buff *skb) { struct request_sock *req = inet_reqsk(skb->sk); skb->sk = NULL; skb->destructor = NULL; if (cookie_tcp_reqsk_init(sk, skb, req)) { reqsk_free(req); req = NULL; } return req; } #endif struct request_sock *cookie_tcp_reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk, struct sk_buff *skb, struct tcp_options_received *tcp_opt, int mss, u32 tsoff) { struct inet_request_sock *ireq; struct tcp_request_sock *treq; struct request_sock *req; if (sk_is_mptcp(sk)) req = mptcp_subflow_reqsk_alloc(ops, sk, false); else req = inet_reqsk_alloc(ops, sk, false); if (!req) return NULL; if (cookie_tcp_reqsk_init(sk, skb, req)) { reqsk_free(req); return NULL; } ireq = inet_rsk(req); treq = tcp_rsk(req); req->mss = mss; req->ts_recent = tcp_opt->saw_tstamp ? tcp_opt->rcv_tsval : 0; ireq->snd_wscale = tcp_opt->snd_wscale; ireq->tstamp_ok = tcp_opt->saw_tstamp; ireq->sack_ok = tcp_opt->sack_ok; ireq->wscale_ok = tcp_opt->wscale_ok; ireq->ecn_ok = !!(tcp_opt->rcv_tsecr & TS_OPT_ECN); treq->req_usec_ts = false; treq->ts_off = tsoff; return req; } static struct request_sock *cookie_tcp_check(struct net *net, struct sock *sk, struct sk_buff *skb) { struct tcp_options_received tcp_opt; u32 tsoff = 0; int mss; if (tcp_synq_no_recent_overflow(sk)) goto out; mss = __cookie_v4_check(ip_hdr(skb), tcp_hdr(skb)); if (!mss) { __NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESFAILED); goto out; } __NET_INC_STATS(net, LINUX_MIB_SYNCOOKIESRECV); /* check for timestamp cookie support */ memset(&tcp_opt, 0, sizeof(tcp_opt)); tcp_parse_options(net, skb, &tcp_opt, 0, NULL); if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) { union tcp_seq_and_ts_off st; st = secure_tcp_seq_and_ts_off(net, ip_hdr(skb)->daddr, ip_hdr(skb)->saddr, tcp_hdr(skb)->dest, tcp_hdr(skb)->source); tsoff = st.ts_off; tcp_opt.rcv_tsecr -= tsoff; } if (!cookie_timestamp_decode(net, &tcp_opt)) goto out; return cookie_tcp_reqsk_alloc(&tcp_request_sock_ops, sk, skb, &tcp_opt, mss, tsoff); out: return ERR_PTR(-EINVAL); } /* On input, sk is a listener. * Output is listener if incoming packet would not create a child * NULL if memory could not be allocated. */ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb) { struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt; const struct tcphdr *th = tcp_hdr(skb); struct tcp_sock *tp = tcp_sk(sk); struct inet_request_sock *ireq; struct net *net = sock_net(sk); struct tcp_request_sock *treq; struct request_sock *req; struct sock *ret = sk; struct flowi4 fl4; struct rtable *rt; __u8 rcv_wscale; int full_space; SKB_DR(reason); if (!READ_ONCE(net->ipv4.sysctl_tcp_syncookies) || !th->ack || th->rst) goto out; if (cookie_bpf_ok(skb)) { req = cookie_bpf_check(sk, skb); } else { req = cookie_tcp_check(net, sk, skb); if (IS_ERR(req)) goto out; } if (!req) { SKB_DR_SET(reason, NO_SOCKET); goto out_drop; } ireq = inet_rsk(req); treq = tcp_rsk(req); sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr); sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr); /* We throwed the options of the initial SYN away, so we hope * the ACK carries the same options again (see RFC1122 4.2.3.8) */ RCU_INIT_POINTER(ireq->ireq_opt, tcp_v4_save_options(net, skb)); if (security_inet_conn_request(sk, skb, req)) { SKB_DR_SET(reason, SECURITY_HOOK); goto out_free; } tcp_ao_syncookie(sk, skb, req, AF_INET); /* * We need to lookup the route here to get at the correct * window size. We should better make sure that the window size * hasn't changed since we received the original syn, but I see * no easy way to do this. */ flowi4_init_output(&fl4, ireq->ir_iif, ireq->ir_mark, ip_sock_rt_tos(sk), ip_sock_rt_scope(sk), IPPROTO_TCP, inet_sk_flowi_flags(sk), opt->srr ? opt->faddr : ireq->ir_rmt_addr, ireq->ir_loc_addr, th->source, th->dest, sk_uid(sk)); security_req_classify_flow(req, flowi4_to_flowi_common(&fl4)); rt = ip_route_output_key(net, &fl4); if (IS_ERR(rt)) { SKB_DR_SET(reason, IP_OUTNOROUTES); goto out_free; } /* Try to redo what tcp_v4_send_synack did. */ req->rsk_window_clamp = READ_ONCE(tp->window_clamp) ? : dst_metric(&rt->dst, RTAX_WINDOW); /* limit the window selection if the user enforce a smaller rx buffer */ full_space = tcp_full_space(sk); if (sk->sk_userlocks & SOCK_RCVBUF_LOCK && (req->rsk_window_clamp > full_space || req->rsk_window_clamp == 0)) req->rsk_window_clamp = full_space; tcp_select_initial_window(sk, full_space, req->mss, &req->rsk_rcv_wnd, &req->rsk_window_clamp, ireq->wscale_ok, &rcv_wscale, dst_metric(&rt->dst, RTAX_INITRWND)); /* req->syncookie is set true only if ACK is validated * by BPF kfunc, then, rcv_wscale is already configured. */ if (!req->syncookie) ireq->rcv_wscale = rcv_wscale; ireq->ecn_ok &= cookie_ecn_ok(net, &rt->dst); treq->accecn_ok = ireq->ecn_ok && cookie_accecn_ok(th); ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst); /* ip_queue_xmit() depends on our flow being setup * Normal sockets get it right from inet_csk_route_child_sock() */ if (!ret) {