net/ipv6/syncookies.c

   1 /*
   2  *  IPv6 Syncookies implementation for the Linux kernel
   3  *
   4  *  Authors:
   5  *  Glenn Griffin       <ggriffin.kernel@gmail.com>
   6  *
   7  *  Based on IPv4 implementation by Andi Kleen
   8  *  linux/net/ipv4/syncookies.c
   9  *
  10  *      This program is free software; you can redistribute it and/or
  11  *      modify it under the terms of the GNU General Public License
  12  *      as published by the Free Software Foundation; either version
  13  *      2 of the License, or (at your option) any later version.
  14  *
  15  */
  16
  17 #include <linux/tcp.h>
  18 #include <linux/random.h>
  19 #include <linux/cryptohash.h>
  20 #include <linux/kernel.h>
  21 #include <net/ipv6.h>
  22 #include <net/tcp.h>
  23
  24 #define COOKIEBITS 24   /* Upper bits store count */
  25 #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
  26
  27 /* Table must be sorted. */
  28 static __u16 const msstab[] = {
  29         64,
  30         512,
  31         536,
  32         1280 - 60,
  33         1480 - 60,
  34         1500 - 60,
  35         4460 - 60,
  36         9000 - 60,
  37 };
  38
  39 static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
  40                                            struct request_sock *req,
  41                                            struct dst_entry *dst)
  42 {
  43         struct inet_connection_sock *icsk = inet_csk(sk);
  44         struct sock *child;
  45
  46         child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
  47         if (child)
  48                 inet_csk_reqsk_queue_add(sk, req, child);
  49         else
  50                 reqsk_free(req);
  51
  52         return child;
  53 }
  54
  55 static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
  56                       ipv6_cookie_scratch);
  57
  58 static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
  59                        __be16 sport, __be16 dport, u32 count, int c)
  60 {
  61         __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
  62
  63         /*
  64          * we have 320 bits of information to hash, copy in the remaining
  65          * 192 bits required for sha_transform, from the syncookie_secret
  66          * and overwrite the digest with the secret
  67          */
  68         memcpy(tmp + 10, syncookie_secret[c], 44);
  69         memcpy(tmp, saddr, 16);
  70         memcpy(tmp + 4, daddr, 16);
  71         tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
  72         tmp[9] = count;
  73         sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
  74
  75         return tmp[17];
  76 }
  77
  78 static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
  79                                    const struct in6_addr *daddr,
  80                                    __be16 sport, __be16 dport, __u32 sseq,
  81                                    __u32 data)
  82 {
  83         u32 count = tcp_cookie_time();
  84         return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
  85                 sseq + (count << COOKIEBITS) +
  86                 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
  87                 & COOKIEMASK));
  88 }
  89
  90 static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
  91                                   const struct in6_addr *daddr, __be16 sport,
  92                                   __be16 dport, __u32 sseq)
  93 {
  94         __u32 diff, count = tcp_cookie_time();
  95
  96         cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
  97
  98         diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
  99         if (diff >= MAX_SYNCOOKIE_AGE)
 100                 return (__u32)-1;
 101
 102         return (cookie -
 103                 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
 104                 & COOKIEMASK;
 105 }
 106
 107 u32 __cookie_v6_init_sequence(const struct ipv6hdr *iph,
 108                               const struct tcphdr *th, __u16 *mssp)
 109 {
 110         int mssind;
 111         const __u16 mss = *mssp;
 112
 113         for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
 114                 if (mss >= msstab[mssind])
 115                         break;
 116
 117         *mssp = msstab[mssind];
 118
 119         return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
 120                                      th->dest, ntohl(th->seq), mssind);
 121 }
 122 EXPORT_SYMBOL_GPL(__cookie_v6_init_sequence);
 123
 124 __u32 cookie_v6_init_sequence(struct sock *sk, const struct sk_buff *skb, __u16 *mssp)
 125 {
 126         const struct ipv6hdr *iph = ipv6_hdr(skb);
 127         const struct tcphdr *th = tcp_hdr(skb);
 128
 129         tcp_synq_overflow(sk);
 130         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
 131
 132         return __cookie_v6_init_sequence(iph, th, mssp);
 133 }
 134
 135 int __cookie_v6_check(const struct ipv6hdr *iph, const struct tcphdr *th,
 136                       __u32 cookie)
 137 {
 138         __u32 seq = ntohl(th->seq) - 1;
 139         __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
 140                                             th->source, th->dest, seq);
 141
 142         return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
 143 }
 144 EXPORT_SYMBOL_GPL(__cookie_v6_check);
 145
 146 struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 147 {
 148         struct tcp_options_received tcp_opt;
 149         struct inet_request_sock *ireq;
 150         struct inet6_request_sock *ireq6;
 151         struct tcp_request_sock *treq;
 152         struct ipv6_pinfo *np = inet6_sk(sk);
 153         struct tcp_sock *tp = tcp_sk(sk);
 154         const struct tcphdr *th = tcp_hdr(skb);
 155         __u32 cookie = ntohl(th->ack_seq) - 1;
 156         struct sock *ret = sk;
 157         struct request_sock *req;
 158         int mss;
 159         struct dst_entry *dst;
 160         __u8 rcv_wscale;
 161         bool ecn_ok = false;
 162
 163         if (!sysctl_tcp_syncookies || !th->ack || th->rst)
 164                 goto out;
 165
 166         if (tcp_synq_no_recent_overflow(sk) ||
 167                 (mss = __cookie_v6_check(ipv6_hdr(skb), th, cookie)) == 0) {
 168                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
 169                 goto out;
 170         }
 171
 172         NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
 173
 174         /* check for timestamp cookie support */
 175         memset(&tcp_opt, 0, sizeof(tcp_opt));
 176         tcp_parse_options(skb, &tcp_opt, 0, NULL);
 177
 178         if (!cookie_check_timestamp(&tcp_opt, sock_net(sk), &ecn_ok))
 179                 goto out;
 180
 181         ret = NULL;
 182         req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
 183         if (!req)
 184                 goto out;
 185
 186         ireq = inet_rsk(req);
 187         ireq6 = inet6_rsk(req);
 188         treq = tcp_rsk(req);
 189         treq->listener = NULL;
 190
 191         if (security_inet_conn_request(sk, skb, req))
 192                 goto out_free;
 193
 194         req->mss = mss;
 195         ireq->rmt_port = th->source;
 196         ireq->loc_port = th->dest;
 197         ireq6->rmt_addr = ipv6_hdr(skb)->saddr;
 198         ireq6->loc_addr = ipv6_hdr(skb)->daddr;
 199         if (ipv6_opt_accepted(sk, skb) ||
 200             np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
 201             np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
 202                 atomic_inc(&skb->users);
 203                 ireq6->pktopts = skb;
 204         }
 205
 206         ireq6->iif = sk->sk_bound_dev_if;
 207         /* So that link locals have meaning */
 208         if (!sk->sk_bound_dev_if &&
 209             ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
 210                 ireq6->iif = inet6_iif(skb);
 211
 212         req->expires = 0UL;
 213         req->num_retrans = 0;
 214         ireq->ecn_ok            = ecn_ok;
 215         ireq->snd_wscale        = tcp_opt.snd_wscale;
 216         ireq->sack_ok           = tcp_opt.sack_ok;
 217         ireq->wscale_ok         = tcp_opt.wscale_ok;
 218         ireq->tstamp_ok         = tcp_opt.saw_tstamp;
 219         req->ts_recent          = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
 220         treq->snt_synack        = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsecr : 0;
 221         treq->rcv_isn = ntohl(th->seq) - 1;
 222         treq->snt_isn = cookie;
 223
 224         /*
 225          * We need to lookup the dst_entry to get the correct window size.
 226          * This is taken from tcp_v6_syn_recv_sock.  Somebody please enlighten
 227          * me if there is a preferred way.
 228          */
 229         {
 230                 struct in6_addr *final_p, final;
 231                 struct flowi6 fl6;
 232                 memset(&fl6, 0, sizeof(fl6));
 233                 fl6.flowi6_proto = IPPROTO_TCP;
 234                 fl6.daddr = ireq6->rmt_addr;
 235                 final_p = fl6_update_dst(&fl6, np->opt, &final);
 236                 fl6.saddr = ireq6->loc_addr;
 237                 fl6.flowi6_oif = sk->sk_bound_dev_if;
 238                 fl6.flowi6_mark = sk->sk_mark;
 239                 fl6.fl6_dport = inet_rsk(req)->rmt_port;
 240                 fl6.fl6_sport = inet_sk(sk)->inet_sport;
 241                 security_req_classify_flow(req, flowi6_to_flowi(&fl6));
 242
 243                 dst = ip6_dst_lookup_flow(sk, &fl6, final_p, false);
 244                 if (IS_ERR(dst))
 245                         goto out_free;
 246         }
 247
 248         req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
 249         tcp_select_initial_window(tcp_full_space(sk), req->mss,
 250                                   &req->rcv_wnd, &req->window_clamp,
 251                                   ireq->wscale_ok, &rcv_wscale,
 252                                   dst_metric(dst, RTAX_INITRWND));
 253
 254         ireq->rcv_wscale = rcv_wscale;
 255
 256         ret = get_cookie_sock(sk, skb, req, dst);
 257 out:
 258         return ret;
 259 out_free:
 260         reqsk_free(req);
 261         return NULL;
 262 }
 263