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net/ipv6/syncookies.c
7.32 KB
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/* * 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; |
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extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS]; |
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#define COOKIEBITS 24 /* Upper bits store count */ #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) |
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/* Table must be sorted. */ |
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static __u16 const msstab[] = { |
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64, 512, 536, 1280 - 60, 1480 - 60, 1500 - 60, 4460 - 60, 9000 - 60, |
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}; |
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/* * 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; } |
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static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS], ipv6_cookie_scratch); |
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static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr, |
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__be16 sport, __be16 dport, u32 count, int c) { |
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__u32 *tmp = __get_cpu_var(ipv6_cookie_scratch); |
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/* * 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]; } |
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static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr, const struct in6_addr *daddr, |
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__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)); } |
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static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr, const struct in6_addr *daddr, __be16 sport, |
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__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; } |
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__u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp) |
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{ |
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const struct ipv6hdr *iph = ipv6_hdr(skb); |
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const struct tcphdr *th = tcp_hdr(skb); int mssind; const __u16 mss = *mssp; |
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tcp_synq_overflow(sk); |
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for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--) if (mss >= msstab[mssind]) break; *mssp = msstab[mssind]; |
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NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT); |
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return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source, th->dest, ntohl(th->seq), jiffies / (HZ * 60), mssind); } |
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static inline int cookie_check(const struct sk_buff *skb, __u32 cookie) |
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{ |
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const struct ipv6hdr *iph = ipv6_hdr(skb); |
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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); |
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return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0; |
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} struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) { |
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struct tcp_options_received tcp_opt; |
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const u8 *hash_location; |
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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; |
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bool ecn_ok = false; |
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if (!sysctl_tcp_syncookies || !th->ack || th->rst) |
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goto out; |
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if (tcp_synq_no_recent_overflow(sk) || |
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(mss = cookie_check(skb, cookie)) == 0) { |
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NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED); |
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goto out; } |
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NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV); |
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/* check for timestamp cookie support */ memset(&tcp_opt, 0, sizeof(tcp_opt)); tcp_parse_options(skb, &tcp_opt, &hash_location, 0); |
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if (!cookie_check_timestamp(&tcp_opt, &ecn_ok)) |
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goto out; |
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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); |
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if (security_inet_conn_request(sk, skb, req)) goto out_free; |
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req->mss = mss; ireq->rmt_port = th->source; |
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ireq->loc_port = th->dest; |
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ireq6->rmt_addr = ipv6_hdr(skb)->saddr; ireq6->loc_addr = ipv6_hdr(skb)->daddr; |
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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; |
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ireq->ecn_ok = ecn_ok; |
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ireq->snd_wscale = tcp_opt.snd_wscale; |
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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; |
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treq->snt_synack = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0; |
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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. */ { |
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struct in6_addr *final_p, final; |
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struct flowi6 fl6; memset(&fl6, 0, sizeof(fl6)); fl6.flowi6_proto = IPPROTO_TCP; |
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fl6.daddr = ireq6->rmt_addr; |
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final_p = fl6_update_dst(&fl6, np->opt, &final); |
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fl6.saddr = ireq6->loc_addr; |
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fl6.flowi6_oif = sk->sk_bound_dev_if; fl6.flowi6_mark = sk->sk_mark; |
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fl6.fl6_dport = inet_rsk(req)->rmt_port; fl6.fl6_sport = inet_sk(sk)->inet_sport; |
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security_req_classify_flow(req, flowi6_to_flowi(&fl6)); dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false); |
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if (IS_ERR(dst)) |
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goto out_free; |
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} |
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req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW); |
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tcp_select_initial_window(tcp_full_space(sk), req->mss, &req->rcv_wnd, &req->window_clamp, |
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ireq->wscale_ok, &rcv_wscale, dst_metric(dst, RTAX_INITRWND)); |
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ireq->rcv_wscale = rcv_wscale; ret = get_cookie_sock(sk, skb, req, dst); |
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out: return ret; out_free: reqsk_free(req); return NULL; |
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} |