| /* |
| * 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> |
| |
| #define COOKIEBITS 24 /* Upper bits store count */ |
| #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) |
| |
| static u32 syncookie6_secret[2][16-4+SHA_DIGEST_WORDS] __read_mostly; |
| |
| /* RFC 2460, Section 8.3: |
| * [ipv6 tcp] MSS must be computed as the maximum packet size minus 60 [..] |
| * |
| * Due to IPV6_MIN_MTU=1280 the lowest possible MSS is 1220, which allows |
| * using higher values than ipv4 tcp syncookies. |
| * The other values are chosen based on ethernet (1500 and 9k MTU), plus |
| * one that accounts for common encap (PPPoe) overhead. Table must be sorted. |
| */ |
| static __u16 const msstab[] = { |
| 1280 - 60, /* IPV6_MIN_MTU - 60 */ |
| 1480 - 60, |
| 1500 - 60, |
| 9000 - 60, |
| }; |
| |
| static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], ipv6_cookie_scratch); |
| |
| static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, |
| __be16 sport, __be16 dport, u32 count, int c) |
| { |
| __u32 *tmp; |
| |
| net_get_random_once(syncookie6_secret, sizeof(syncookie6_secret)); |
| |
| tmp = this_cpu_ptr(ipv6_cookie_scratch); |
| |
| /* |
| * we have 320 bits of information to hash, copy in the remaining |
| * 192 bits required for sha_transform, from the syncookie6_secret |
| * and overwrite the digest with the secret |
| */ |
| memcpy(tmp + 10, syncookie6_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(const struct in6_addr *saddr, |
| const struct in6_addr *daddr, |
| __be16 sport, __be16 dport, __u32 sseq, |
| __u32 data) |
| { |
| 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)); |
| } |
| |
| static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, |
| const struct in6_addr *daddr, __be16 sport, |
| __be16 dport, __u32 sseq) |
| { |
| __u32 diff, count = tcp_cookie_time(); |
| |
| cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; |
| |
| 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; |
| } |
| |
| u32 __cookie_v6_init_sequence(const struct ipv6hdr *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_v6_init_sequence); |
| |
| __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mssp) |
| { |
| const struct ipv6hdr *iph = ipv6_hdr(skb); |
| const struct tcphdr *th = tcp_hdr(skb); |
| |
| return __cookie_v6_init_sequence(iph, th, mssp); |
| } |
| |
| int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th, |
| __u32 cookie) |
| { |
| __u32 seq = ntohl(th->seq) - 1; |
| __u32 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_v6_check); |
| |
| struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) |
| { |
| struct tcp_options_received tcp_opt; |
| struct inet_request_sock *ireq; |
| 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; |
| |
| if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst) |
| goto out; |
| |
| if (tcp_synq_no_recent_overflow(sk)) |
| goto out; |
| |
| mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie); |
| if (mss == 0) { |
| __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); |
| goto out; |
| } |
| |
| __NET_INC_STATS(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, NULL); |
| |
| if (!cookie_timestamp_decode(&tcp_opt)) |
| goto out; |
| |
| ret = NULL; |
| req = inet_reqsk_alloc(&tcp6_request_sock_ops, sk, false); |
| if (!req) |
| goto out; |
| |
| ireq = inet_rsk(req); |
| treq = tcp_rsk(req); |
| treq->tfo_listener = false; |
| |
| if (security_inet_conn_request(sk, skb, req)) |
| goto out_free; |
| |
| req->mss = mss; |
| ireq->ir_rmt_port = th->source; |
| ireq->ir_num = ntohs(th->dest); |
| ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr; |
| ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr; |
| if (ipv6_opt_accepted(sk, skb, &TCP_SKB_CB(skb)->header.h6) || |
| np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo || |
| np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) { |
| atomic_inc(&skb->users); |
| ireq->pktopts = skb; |
| } |
| |
| ireq->ir_iif = inet_request_bound_dev_if(sk, skb); |
| /* So that link locals have meaning */ |
| if (!sk->sk_bound_dev_if && |
| ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL) |
| ireq->ir_iif = tcp_v6_iif(skb); |
| |
| ireq->ir_mark = inet_request_mark(sk, skb); |
| |
| req->num_retrans = 0; |
| ireq->snd_wscale = tcp_opt.snd_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->snt_synack.v64 = 0; |
| treq->rcv_isn = ntohl(th->seq) - 1; |
| treq->snt_isn = cookie; |
| treq->txhash = net_tx_rndhash(); |
| |
| /* |
| * 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, final; |
| struct flowi6 fl6; |
| memset(&fl6, 0, sizeof(fl6)); |
| fl6.flowi6_proto = IPPROTO_TCP; |
| fl6.daddr = ireq->ir_v6_rmt_addr; |
| final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final); |
| fl6.saddr = ireq->ir_v6_loc_addr; |
| fl6.flowi6_oif = ireq->ir_iif; |
| fl6.flowi6_mark = ireq->ir_mark; |
| fl6.fl6_dport = ireq->ir_rmt_port; |
| fl6.fl6_sport = inet_sk(sk)->inet_sport; |
| fl6.flowi6_uid = sk->sk_uid; |
| security_req_classify_flow(req, flowi6_to_flowi(&fl6)); |
| |
| dst = ip6_dst_lookup_flow(sk, &fl6, final_p); |
| if (IS_ERR(dst)) |
| goto out_free; |
| } |
| |
| req->rsk_window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); |
| tcp_select_initial_window(tcp_full_space(sk), req->mss, |
| &req->rsk_rcv_wnd, &req->rsk_window_clamp, |
| ireq->wscale_ok, &rcv_wscale, |
| dst_metric(dst, RTAX_INITRWND)); |
| |
| ireq->rcv_wscale = rcv_wscale; |
| ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), dst); |
| |
| ret = tcp_get_cookie_sock(sk, skb, req, dst); |
| out: |
| return ret; |
| out_free: |
| reqsk_free(req); |
| return NULL; |
| } |