/* * IPv6 Syncookies implementation for the Linux kernel * * Authors: * Glenn Griffin <ggriffin.kernel@gmail.com> * * Based on IPv4 implementation by Andi Kleen * linux/net/ipv4/syncookies.c * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version * 2 of the License, or (at your option) any later version. * */ #include <linux/tcp.h> #include <linux/random.h> #include <linux/cryptohash.h> #include <linux/kernel.h> #include <net/ipv6.h> #include <net/tcp.h> extern int sysctl_tcp_syncookies; extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS]; #define COOKIEBITS 24 /* Upper bits store count */ #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) /* * This table has to be sorted and terminated with (__u16)-1. * XXX generate a better table. * Unresolved Issues: HIPPI with a 64k MSS is not well supported. * * Taken directly from ipv4 implementation. * Should this list be modified for ipv6 use or is it close enough? * rfc 2460 8.3 suggests mss values 20 bytes less than ipv4 counterpart */ static __u16 const msstab[] = { 64 - 1, 256 - 1, 512 - 1, 536 - 1, 1024 - 1, 1440 - 1, 1460 - 1, 4312 - 1, (__u16)-1 }; /* The number doesn't include the -1 terminator */ #define NUM_MSS (ARRAY_SIZE(msstab) - 1) /* * This (misnamed) value is the age of syncookie which is permitted. * Its ideal value should be dependent on TCP_TIMEOUT_INIT and * sysctl_tcp_retries1. It's a rather complicated formula (exponential * backoff) to compute at runtime so it's currently hardcoded here. */ #define COUNTER_TRIES 4 static inline struct sock *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; child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst); if (child) inet_csk_reqsk_queue_add(sk, req, child); else reqsk_free(req); return child; } static DEFINE_PER_CPU(__u32, cookie_scratch)[16 + 5 + SHA_WORKSPACE_WORDS]; static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr, __be16 sport, __be16 dport, u32 count, int c) { __u32 *tmp = __get_cpu_var(cookie_scratch); /* * we have 320 bits of information to hash, copy in the remaining * 192 bits required for sha_transform, from the syncookie_secret * and overwrite the digest with the secret */ memcpy(tmp + 10, syncookie_secret[c], 44); memcpy(tmp, saddr, 16); memcpy(tmp + 4, daddr, 16); tmp[8] = ((__force u32)sport << 16) + (__force u32)dport; tmp[9] = count; sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); return tmp[17]; } static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr, __be16 sport, __be16 dport, __u32 sseq, __u32 count, __u32 data) { return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq + (count << COOKIEBITS) + ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) & COOKIEMASK)); } static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr, struct in6_addr *daddr, __be16 sport, __be16 dport, __u32 sseq, __u32 count, __u32 maxdiff) { __u32 diff; cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS); if (diff >= maxdiff) return (__u32)-1; return (cookie - cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) & COOKIEMASK; } __u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp) { struct ipv6hdr *iph = ipv6_hdr(skb); const struct tcphdr *th = tcp_hdr(skb); int mssind; const __u16 mss = *mssp; tcp_sk(sk)->last_synq_overflow = jiffies; for (mssind = 0; mss > msstab[mssind + 1]; mssind++) ; *mssp = msstab[mssind] + 1; NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, th->dest, ntohl(th->seq), jiffies / (HZ * 60), mssind); } static inline int cookie_check(struct sk_buff *skb, __u32 cookie) { struct ipv6hdr *iph = ipv6_hdr(skb); const struct tcphdr *th = tcp_hdr(skb); __u32 seq = ntohl(th->seq) - 1; __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr, th->source, th->dest, seq, jiffies / (HZ * 60), COUNTER_TRIES); return mssind < NUM_MSS ? msstab[mssind] + 1 : 0; } struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) { struct inet_request_sock *ireq; struct inet6_request_sock *ireq6; struct tcp_request_sock *treq; struct ipv6_pinfo *np = inet6_sk(sk); struct tcp_sock *tp = tcp_sk(sk); const struct tcphdr *th = tcp_hdr(skb); __u32 cookie = ntohl(th->ack_seq) - 1; struct sock *ret = sk; struct request_sock *req; int mss; struct dst_entry *dst; __u8 rcv_wscale; struct tcp_options_received tcp_opt; if (!sysctl_tcp_syncookies || !th->ack) goto out; if (time_after(jiffies, tp->last_synq_overflow + TCP_TIMEOUT_INIT) || (mss = cookie_check(skb, cookie)) == 0) { NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); goto out; } NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); /* check for timestamp cookie support */ memset(&tcp_opt, 0, sizeof(tcp_opt)); tcp_parse_options(skb, &tcp_opt, 0); if (tcp_opt.saw_tstamp) cookie_check_timestamp(&tcp_opt); ret = NULL; req = inet6_reqsk_alloc(&tcp6_request_sock_ops); if (!req) goto out; ireq = inet_rsk(req); ireq6 = inet6_rsk(req); treq = tcp_rsk(req); if (security_inet_conn_request(sk, skb, req)) goto out_free; req->mss = mss; ireq->rmt_port = th->source; ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr); ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr); if (ipv6_opt_accepted(sk, skb) || np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { atomic_inc(&skb->users); ireq6->pktopts = skb; } ireq6->iif = sk->sk_bound_dev_if; /* So that link locals have meaning */ if (!sk->sk_bound_dev_if && ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL) ireq6->iif = inet6_iif(skb); req->expires = 0UL; req->retrans = 0; ireq->ecn_ok = 0; ireq->snd_wscale = tcp_opt.snd_wscale; ireq->rcv_wscale = tcp_opt.rcv_wscale; ireq->sack_ok = tcp_opt.sack_ok; ireq->wscale_ok = tcp_opt.wscale_ok; ireq->tstamp_ok = tcp_opt.saw_tstamp; req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0; treq->rcv_isn = ntohl(th->seq) - 1; treq->snt_isn = cookie; /* * We need to lookup the dst_entry to get the correct window size. * This is taken from tcp_v6_syn_recv_sock. Somebody please enlighten * me if there is a preferred way. */ { struct in6_addr *final_p = NULL, final; struct flowi fl; memset(&fl, 0, sizeof(fl)); fl.proto = IPPROTO_TCP; ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr); if (np->opt && np->opt->srcrt) { struct rt0_hdr *rt0 = (struct rt0_hdr *) np->opt->srcrt; ipv6_addr_copy(&final, &fl.fl6_dst); ipv6_addr_copy(&fl.fl6_dst, rt0->addr); final_p = &final; } ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr); fl.oif = sk->sk_bound_dev_if; fl.fl_ip_dport = inet_rsk(req)->rmt_port; fl.fl_ip_sport = inet_sk(sk)->sport; security_req_classify_flow(req, &fl); if (ip6_dst_lookup(sk, &dst, &fl)) goto out_free; if (final_p) ipv6_addr_copy(&fl.fl6_dst, final_p); if ((xfrm_lookup(&dst, &fl, sk, 0)) < 0) goto out_free; } req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); tcp_select_initial_window(tcp_full_space(sk), req->mss, &req->rcv_wnd, &req->window_clamp, ireq->wscale_ok, &rcv_wscale); ireq->rcv_wscale = rcv_wscale; ret = get_cookie_sock(sk, skb, req, dst); out: return ret; out_free: reqsk_free(req); return NULL; }