LXR linux/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
  24extern int sysctl_tcp_syncookies;
  25extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
  26
  27#define COOKIEBITS 24   /* Upper bits store count */
  28#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
  29
  30/* Table must be sorted. */
  31static __u16 const msstab[] = {
  32        64,
  33        512,
  34        536,
  35        1280 - 60,
  36        1480 - 60,
  37        1500 - 60,
  38        4460 - 60,
  39        9000 - 60,
  40};
  41
  42/*
  43 * This (misnamed) value is the age of syncookie which is permitted.
  44 * Its ideal value should be dependent on TCP_TIMEOUT_INIT and
  45 * sysctl_tcp_retries1. It's a rather complicated formula (exponential
  46 * backoff) to compute at runtime so it's currently hardcoded here.
  47 */
  48#define COUNTER_TRIES 4
  49
  50static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
  51                                           struct request_sock *req,
  52                                           struct dst_entry *dst)
  53{
  54        struct inet_connection_sock *icsk = inet_csk(sk);
  55        struct sock *child;
  56
  57        child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
  58        if (child)
  59                inet_csk_reqsk_queue_add(sk, req, child);
  60        else
  61                reqsk_free(req);
  62
  63        return child;
  64}
  65
  66static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
  67                      ipv6_cookie_scratch);
  68
  69static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr,
  70                       __be16 sport, __be16 dport, u32 count, int c)
  71{
  72        __u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
  73
  74        /*
  75         * we have 320 bits of information to hash, copy in the remaining
  76         * 192 bits required for sha_transform, from the syncookie_secret
  77         * and overwrite the digest with the secret
  78         */
  79        memcpy(tmp + 10, syncookie_secret[c], 44);
  80        memcpy(tmp, saddr, 16);
  81        memcpy(tmp + 4, daddr, 16);
  82        tmp[8] = ((__force u32)sport << 16) + (__force u32)dport;
  83        tmp[9] = count;
  84        sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
  85
  86        return tmp[17];
  87}
  88
  89static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr,
  90                                   __be16 sport, __be16 dport, __u32 sseq,
  91                                   __u32 count, __u32 data)
  92{
  93        return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
  94                sseq + (count << COOKIEBITS) +
  95                ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
  96                & COOKIEMASK));
  97}
  98
  99static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr,
 100                                  struct in6_addr *daddr, __be16 sport,
 101                                  __be16 dport, __u32 sseq, __u32 count,
 102                                  __u32 maxdiff)
 103{
 104        __u32 diff;
 105
 106        cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
 107
 108        diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
 109        if (diff >= maxdiff)
 110                return (__u32)-1;
 111
 112        return (cookie -
 113                cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
 114                & COOKIEMASK;
 115}
 116
 117__u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
 118{
 119        struct ipv6hdr *iph = ipv6_hdr(skb);
 120        const struct tcphdr *th = tcp_hdr(skb);
 121        int mssind;
 122        const __u16 mss = *mssp;
 123
 124        tcp_synq_overflow(sk);
 125
 126        for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
 127                if (mss >= msstab[mssind])
 128                        break;
 129
 130        *mssp = msstab[mssind];
 131
 132        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
 133
 134        return secure_tcp_syn_cookie(&iph->saddr, &iph->daddr, th->source,
 135                                     th->dest, ntohl(th->seq),
 136                                     jiffies / (HZ * 60), mssind);
 137}
 138
 139static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
 140{
 141        struct ipv6hdr *iph = ipv6_hdr(skb);
 142        const struct tcphdr *th = tcp_hdr(skb);
 143        __u32 seq = ntohl(th->seq) - 1;
 144        __u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,
 145                                            th->source, th->dest, seq,
 146                                            jiffies / (HZ * 60), COUNTER_TRIES);
 147
 148        return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
 149}
 150
 151struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
 152{
 153        struct tcp_options_received tcp_opt;
 154        u8 *hash_location;
 155        struct inet_request_sock *ireq;
 156        struct inet6_request_sock *ireq6;
 157        struct tcp_request_sock *treq;
 158        struct ipv6_pinfo *np = inet6_sk(sk);
 159        struct tcp_sock *tp = tcp_sk(sk);
 160        const struct tcphdr *th = tcp_hdr(skb);
 161        __u32 cookie = ntohl(th->ack_seq) - 1;
 162        struct sock *ret = sk;
 163        struct request_sock *req;
 164        int mss;
 165        struct dst_entry *dst;
 166        __u8 rcv_wscale;
 167        bool ecn_ok;
 168
 169        if (!sysctl_tcp_syncookies || !th->ack || th->rst)
 170                goto out;
 171
 172        if (tcp_synq_no_recent_overflow(sk) ||
 173                (mss = cookie_check(skb, cookie)) == 0) {
 174                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
 175                goto out;
 176        }
 177
 178        NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
 179
 180        /* check for timestamp cookie support */
 181        memset(&tcp_opt, 0, sizeof(tcp_opt));
 182        tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
 183
 184        if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
 185                goto out;
 186
 187        ret = NULL;
 188        req = inet6_reqsk_alloc(&tcp6_request_sock_ops);
 189        if (!req)
 190                goto out;
 191
 192        ireq = inet_rsk(req);
 193        ireq6 = inet6_rsk(req);
 194        treq = tcp_rsk(req);
 195
 196        if (security_inet_conn_request(sk, skb, req))
 197                goto out_free;
 198
 199        req->mss = mss;
 200        ireq->rmt_port = th->source;
 201        ireq->loc_port = th->dest;
 202        ipv6_addr_copy(&ireq6->rmt_addr, &ipv6_hdr(skb)->saddr);
 203        ipv6_addr_copy(&ireq6->loc_addr, &ipv6_hdr(skb)->daddr);
 204        if (ipv6_opt_accepted(sk, skb) ||
 205            np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
 206            np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
 207                atomic_inc(&skb->users);
 208                ireq6->pktopts = skb;
 209        }
 210
 211        ireq6->iif = sk->sk_bound_dev_if;
 212        /* So that link locals have meaning */
 213        if (!sk->sk_bound_dev_if &&
 214            ipv6_addr_type(&ireq6->rmt_addr) & IPV6_ADDR_LINKLOCAL)
 215                ireq6->iif = inet6_iif(skb);
 216
 217        req->expires = 0UL;
 218        req->retrans = 0;
 219        ireq->ecn_ok            = ecn_ok;
 220        ireq->snd_wscale        = tcp_opt.snd_wscale;
 221        ireq->sack_ok           = tcp_opt.sack_ok;
 222        ireq->wscale_ok         = tcp_opt.wscale_ok;
 223        ireq->tstamp_ok         = tcp_opt.saw_tstamp;
 224        req->ts_recent          = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
 225        treq->rcv_isn = ntohl(th->seq) - 1;
 226        treq->snt_isn = cookie;
 227
 228        /*
 229         * We need to lookup the dst_entry to get the correct window size.
 230         * This is taken from tcp_v6_syn_recv_sock.  Somebody please enlighten
 231         * me if there is a preferred way.
 232         */
 233        {
 234                struct in6_addr *final_p, final;
 235                struct flowi fl;
 236                memset(&fl, 0, sizeof(fl));
 237                fl.proto = IPPROTO_TCP;
 238                ipv6_addr_copy(&fl.fl6_dst, &ireq6->rmt_addr);
 239                final_p = fl6_update_dst(&fl, np->opt, &final);
 240                ipv6_addr_copy(&fl.fl6_src, &ireq6->loc_addr);
 241                fl.oif = sk->sk_bound_dev_if;
 242                fl.mark = sk->sk_mark;
 243                fl.fl_ip_dport = inet_rsk(req)->rmt_port;
 244                fl.fl_ip_sport = inet_sk(sk)->inet_sport;
 245                security_req_classify_flow(req, &fl);
 246                if (ip6_dst_lookup(sk, &dst, &fl))
 247                        goto out_free;
 248
 249                if (final_p)
 250                        ipv6_addr_copy(&fl.fl6_dst, final_p);
 251                if ((xfrm_lookup(sock_net(sk), &dst, &fl, sk, 0)) < 0)
 252                        goto out_free;
 253        }
 254
 255        req->window_clamp = tp->window_clamp ? :dst_metric(dst, RTAX_WINDOW);
 256        tcp_select_initial_window(tcp_full_space(sk), req->mss,
 257                                  &req->rcv_wnd, &req->window_clamp,
 258                                  ireq->wscale_ok, &rcv_wscale,
 259                                  dst_metric(dst, RTAX_INITRWND));
 260
 261        ireq->rcv_wscale = rcv_wscale;
 262
 263        ret = get_cookie_sock(sk, skb, req, dst);
 264out:
 265        return ret;
 266out_free:
 267        reqsk_free(req);
 268        return NULL;
 269}
 270
 271