Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Syncookies implementation for the Linux kernel |
| 3 | * |
| 4 | * Copyright (C) 1997 Andi Kleen |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 5 | * Based on ideas by D.J.Bernstein and Eric Schenk. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 6 | * |
| 7 | * This program is free software; you can redistribute it and/or |
| 8 | * modify it under the terms of the GNU General Public License |
| 9 | * as published by the Free Software Foundation; either version |
| 10 | * 2 of the License, or (at your option) any later version. |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 11 | * |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 12 | * $Id: syncookies.c,v 1.18 2002/02/01 22:01:04 davem Exp $ |
| 13 | * |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 14 | * Missing: IPv6 support. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 15 | */ |
| 16 | |
| 17 | #include <linux/tcp.h> |
| 18 | #include <linux/slab.h> |
| 19 | #include <linux/random.h> |
| 20 | #include <linux/cryptohash.h> |
| 21 | #include <linux/kernel.h> |
| 22 | #include <net/tcp.h> |
| 23 | |
| 24 | extern int sysctl_tcp_syncookies; |
| 25 | |
| 26 | static __u32 syncookie_secret[2][16-3+SHA_DIGEST_WORDS]; |
| 27 | |
| 28 | static __init int init_syncookies(void) |
| 29 | { |
| 30 | get_random_bytes(syncookie_secret, sizeof(syncookie_secret)); |
| 31 | return 0; |
| 32 | } |
| 33 | module_init(init_syncookies); |
| 34 | |
| 35 | #define COOKIEBITS 24 /* Upper bits store count */ |
| 36 | #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1) |
| 37 | |
Eric Dumazet | 11baab7 | 2008-02-07 10:40:19 +0100 | [diff] [blame^] | 38 | static DEFINE_PER_CPU(__u32, cookie_scratch)[16 + 5 + SHA_WORKSPACE_WORDS]; |
| 39 | |
Al Viro | 714e85b | 2006-11-14 20:51:49 -0800 | [diff] [blame] | 40 | static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 41 | u32 count, int c) |
| 42 | { |
Eric Dumazet | 11baab7 | 2008-02-07 10:40:19 +0100 | [diff] [blame^] | 43 | __u32 *tmp = __get_cpu_var(cookie_scratch); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 44 | |
| 45 | memcpy(tmp + 3, syncookie_secret[c], sizeof(syncookie_secret[c])); |
Al Viro | 714e85b | 2006-11-14 20:51:49 -0800 | [diff] [blame] | 46 | tmp[0] = (__force u32)saddr; |
| 47 | tmp[1] = (__force u32)daddr; |
| 48 | tmp[2] = ((__force u32)sport << 16) + (__force u32)dport; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 49 | tmp[3] = count; |
| 50 | sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5); |
| 51 | |
| 52 | return tmp[17]; |
| 53 | } |
| 54 | |
Al Viro | 714e85b | 2006-11-14 20:51:49 -0800 | [diff] [blame] | 55 | static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport, |
| 56 | __be16 dport, __u32 sseq, __u32 count, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 57 | __u32 data) |
| 58 | { |
| 59 | /* |
| 60 | * Compute the secure sequence number. |
| 61 | * The output should be: |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 62 | * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 63 | * + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24). |
| 64 | * Where sseq is their sequence number and count increases every |
| 65 | * minute by 1. |
| 66 | * As an extra hack, we add a small "data" value that encodes the |
| 67 | * MSS into the second hash value. |
| 68 | */ |
| 69 | |
| 70 | return (cookie_hash(saddr, daddr, sport, dport, 0, 0) + |
| 71 | sseq + (count << COOKIEBITS) + |
| 72 | ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data) |
| 73 | & COOKIEMASK)); |
| 74 | } |
| 75 | |
| 76 | /* |
| 77 | * This retrieves the small "data" value from the syncookie. |
| 78 | * If the syncookie is bad, the data returned will be out of |
| 79 | * range. This must be checked by the caller. |
| 80 | * |
| 81 | * The count value used to generate the cookie must be within |
| 82 | * "maxdiff" if the current (passed-in) "count". The return value |
| 83 | * is (__u32)-1 if this test fails. |
| 84 | */ |
Al Viro | 714e85b | 2006-11-14 20:51:49 -0800 | [diff] [blame] | 85 | static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr, |
| 86 | __be16 sport, __be16 dport, __u32 sseq, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 87 | __u32 count, __u32 maxdiff) |
| 88 | { |
| 89 | __u32 diff; |
| 90 | |
| 91 | /* Strip away the layers from the cookie */ |
| 92 | cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq; |
| 93 | |
| 94 | /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */ |
| 95 | diff = (count - (cookie >> COOKIEBITS)) & ((__u32) - 1 >> COOKIEBITS); |
| 96 | if (diff >= maxdiff) |
| 97 | return (__u32)-1; |
| 98 | |
| 99 | return (cookie - |
| 100 | cookie_hash(saddr, daddr, sport, dport, count - diff, 1)) |
| 101 | & COOKIEMASK; /* Leaving the data behind */ |
| 102 | } |
| 103 | |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 104 | /* |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 105 | * This table has to be sorted and terminated with (__u16)-1. |
| 106 | * XXX generate a better table. |
| 107 | * Unresolved Issues: HIPPI with a 64k MSS is not well supported. |
| 108 | */ |
| 109 | static __u16 const msstab[] = { |
| 110 | 64 - 1, |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 111 | 256 - 1, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 112 | 512 - 1, |
| 113 | 536 - 1, |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 114 | 1024 - 1, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 115 | 1440 - 1, |
| 116 | 1460 - 1, |
| 117 | 4312 - 1, |
| 118 | (__u16)-1 |
| 119 | }; |
| 120 | /* The number doesn't include the -1 terminator */ |
| 121 | #define NUM_MSS (ARRAY_SIZE(msstab) - 1) |
| 122 | |
| 123 | /* |
| 124 | * Generate a syncookie. mssp points to the mss, which is returned |
| 125 | * rounded down to the value encoded in the cookie. |
| 126 | */ |
| 127 | __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp) |
| 128 | { |
| 129 | struct tcp_sock *tp = tcp_sk(sk); |
Arnaldo Carvalho de Melo | aa8223c | 2007-04-10 21:04:22 -0700 | [diff] [blame] | 130 | const struct iphdr *iph = ip_hdr(skb); |
| 131 | const struct tcphdr *th = tcp_hdr(skb); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 132 | int mssind; |
| 133 | const __u16 mss = *mssp; |
| 134 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 135 | tp->last_synq_overflow = jiffies; |
| 136 | |
| 137 | /* XXX sort msstab[] by probability? Binary search? */ |
| 138 | for (mssind = 0; mss > msstab[mssind + 1]; mssind++) |
| 139 | ; |
| 140 | *mssp = msstab[mssind] + 1; |
| 141 | |
| 142 | NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESSENT); |
| 143 | |
Arnaldo Carvalho de Melo | aa8223c | 2007-04-10 21:04:22 -0700 | [diff] [blame] | 144 | return secure_tcp_syn_cookie(iph->saddr, iph->daddr, |
| 145 | th->source, th->dest, ntohl(th->seq), |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 146 | jiffies / (HZ * 60), mssind); |
| 147 | } |
| 148 | |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 149 | /* |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 150 | * This (misnamed) value is the age of syncookie which is permitted. |
| 151 | * Its ideal value should be dependent on TCP_TIMEOUT_INIT and |
| 152 | * sysctl_tcp_retries1. It's a rather complicated formula (exponential |
| 153 | * backoff) to compute at runtime so it's currently hardcoded here. |
| 154 | */ |
| 155 | #define COUNTER_TRIES 4 |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 156 | /* |
| 157 | * Check if a ack sequence number is a valid syncookie. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 158 | * Return the decoded mss if it is, or 0 if not. |
| 159 | */ |
| 160 | static inline int cookie_check(struct sk_buff *skb, __u32 cookie) |
| 161 | { |
Arnaldo Carvalho de Melo | aa8223c | 2007-04-10 21:04:22 -0700 | [diff] [blame] | 162 | const struct iphdr *iph = ip_hdr(skb); |
| 163 | const struct tcphdr *th = tcp_hdr(skb); |
| 164 | __u32 seq = ntohl(th->seq) - 1; |
| 165 | __u32 mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr, |
| 166 | th->source, th->dest, seq, |
| 167 | jiffies / (HZ * 60), |
| 168 | COUNTER_TRIES); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 169 | |
| 170 | return mssind < NUM_MSS ? msstab[mssind] + 1 : 0; |
| 171 | } |
| 172 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 173 | static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb, |
Arnaldo Carvalho de Melo | 60236fd | 2005-06-18 22:47:21 -0700 | [diff] [blame] | 174 | struct request_sock *req, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 175 | struct dst_entry *dst) |
| 176 | { |
Arnaldo Carvalho de Melo | 8292a17 | 2005-12-13 23:15:52 -0800 | [diff] [blame] | 177 | struct inet_connection_sock *icsk = inet_csk(sk); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 178 | struct sock *child; |
| 179 | |
Arnaldo Carvalho de Melo | 8292a17 | 2005-12-13 23:15:52 -0800 | [diff] [blame] | 180 | child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 181 | if (child) |
Arnaldo Carvalho de Melo | 463c84b | 2005-08-09 20:10:42 -0700 | [diff] [blame] | 182 | inet_csk_reqsk_queue_add(sk, req, child); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 183 | else |
Arnaldo Carvalho de Melo | 60236fd | 2005-06-18 22:47:21 -0700 | [diff] [blame] | 184 | reqsk_free(req); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 185 | |
| 186 | return child; |
| 187 | } |
| 188 | |
| 189 | struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb, |
| 190 | struct ip_options *opt) |
| 191 | { |
Arnaldo Carvalho de Melo | 2e6599c | 2005-06-18 22:46:52 -0700 | [diff] [blame] | 192 | struct inet_request_sock *ireq; |
| 193 | struct tcp_request_sock *treq; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 194 | struct tcp_sock *tp = tcp_sk(sk); |
Arnaldo Carvalho de Melo | aa8223c | 2007-04-10 21:04:22 -0700 | [diff] [blame] | 195 | const struct tcphdr *th = tcp_hdr(skb); |
| 196 | __u32 cookie = ntohl(th->ack_seq) - 1; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 197 | struct sock *ret = sk; |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 198 | struct request_sock *req; |
| 199 | int mss; |
| 200 | struct rtable *rt; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 201 | __u8 rcv_wscale; |
| 202 | |
Arnaldo Carvalho de Melo | aa8223c | 2007-04-10 21:04:22 -0700 | [diff] [blame] | 203 | if (!sysctl_tcp_syncookies || !th->ack) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 204 | goto out; |
| 205 | |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 206 | if (time_after(jiffies, tp->last_synq_overflow + TCP_TIMEOUT_INIT) || |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 207 | (mss = cookie_check(skb, cookie)) == 0) { |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 208 | NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESFAILED); |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 209 | goto out; |
| 210 | } |
| 211 | |
| 212 | NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESRECV); |
| 213 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 214 | ret = NULL; |
Arnaldo Carvalho de Melo | 60236fd | 2005-06-18 22:47:21 -0700 | [diff] [blame] | 215 | req = reqsk_alloc(&tcp_request_sock_ops); /* for safety */ |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 216 | if (!req) |
| 217 | goto out; |
| 218 | |
Venkat Yekkirala | 4237c75 | 2006-07-24 23:32:50 -0700 | [diff] [blame] | 219 | if (security_inet_conn_request(sk, skb, req)) { |
| 220 | reqsk_free(req); |
| 221 | goto out; |
| 222 | } |
Arnaldo Carvalho de Melo | 2e6599c | 2005-06-18 22:46:52 -0700 | [diff] [blame] | 223 | ireq = inet_rsk(req); |
| 224 | treq = tcp_rsk(req); |
Arnaldo Carvalho de Melo | aa8223c | 2007-04-10 21:04:22 -0700 | [diff] [blame] | 225 | treq->rcv_isn = ntohl(th->seq) - 1; |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 226 | treq->snt_isn = cookie; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 227 | req->mss = mss; |
Arnaldo Carvalho de Melo | aa8223c | 2007-04-10 21:04:22 -0700 | [diff] [blame] | 228 | ireq->rmt_port = th->source; |
Arnaldo Carvalho de Melo | eddc9ec | 2007-04-20 22:47:35 -0700 | [diff] [blame] | 229 | ireq->loc_addr = ip_hdr(skb)->daddr; |
| 230 | ireq->rmt_addr = ip_hdr(skb)->saddr; |
Arnaldo Carvalho de Melo | 2e6599c | 2005-06-18 22:46:52 -0700 | [diff] [blame] | 231 | ireq->opt = NULL; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 232 | |
| 233 | /* We throwed the options of the initial SYN away, so we hope |
| 234 | * the ACK carries the same options again (see RFC1122 4.2.3.8) |
| 235 | */ |
| 236 | if (opt && opt->optlen) { |
| 237 | int opt_size = sizeof(struct ip_options) + opt->optlen; |
| 238 | |
Arnaldo Carvalho de Melo | 2e6599c | 2005-06-18 22:46:52 -0700 | [diff] [blame] | 239 | ireq->opt = kmalloc(opt_size, GFP_ATOMIC); |
| 240 | if (ireq->opt != NULL && ip_options_echo(ireq->opt, skb)) { |
| 241 | kfree(ireq->opt); |
| 242 | ireq->opt = NULL; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 243 | } |
| 244 | } |
| 245 | |
Arnaldo Carvalho de Melo | 2e6599c | 2005-06-18 22:46:52 -0700 | [diff] [blame] | 246 | ireq->snd_wscale = ireq->rcv_wscale = ireq->tstamp_ok = 0; |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 247 | ireq->wscale_ok = ireq->sack_ok = 0; |
| 248 | req->expires = 0UL; |
| 249 | req->retrans = 0; |
| 250 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 251 | /* |
| 252 | * We need to lookup the route here to get at the correct |
| 253 | * window size. We should better make sure that the window size |
| 254 | * hasn't changed since we received the original syn, but I see |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 255 | * no easy way to do this. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 256 | */ |
| 257 | { |
| 258 | struct flowi fl = { .nl_u = { .ip4_u = |
| 259 | { .daddr = ((opt && opt->srr) ? |
| 260 | opt->faddr : |
Arnaldo Carvalho de Melo | 2e6599c | 2005-06-18 22:46:52 -0700 | [diff] [blame] | 261 | ireq->rmt_addr), |
| 262 | .saddr = ireq->loc_addr, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 263 | .tos = RT_CONN_FLAGS(sk) } }, |
| 264 | .proto = IPPROTO_TCP, |
| 265 | .uli_u = { .ports = |
Arnaldo Carvalho de Melo | aa8223c | 2007-04-10 21:04:22 -0700 | [diff] [blame] | 266 | { .sport = th->dest, |
| 267 | .dport = th->source } } }; |
Venkat Yekkirala | 4237c75 | 2006-07-24 23:32:50 -0700 | [diff] [blame] | 268 | security_req_classify_flow(req, &fl); |
Denis V. Lunev | f206351 | 2008-01-22 22:07:34 -0800 | [diff] [blame] | 269 | if (ip_route_output_key(&init_net, &rt, &fl)) { |
Arnaldo Carvalho de Melo | 60236fd | 2005-06-18 22:47:21 -0700 | [diff] [blame] | 270 | reqsk_free(req); |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 271 | goto out; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 272 | } |
| 273 | } |
| 274 | |
| 275 | /* Try to redo what tcp_v4_send_synack did. */ |
| 276 | req->window_clamp = dst_metric(&rt->u.dst, RTAX_WINDOW); |
| 277 | tcp_select_initial_window(tcp_full_space(sk), req->mss, |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 278 | &req->rcv_wnd, &req->window_clamp, |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 279 | 0, &rcv_wscale); |
| 280 | /* BTW win scale with syncookies is 0 by definition */ |
YOSHIFUJI Hideaki | e905a9e | 2007-02-09 23:24:47 +0900 | [diff] [blame] | 281 | ireq->rcv_wscale = rcv_wscale; |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 282 | |
| 283 | ret = get_cookie_sock(sk, skb, req, &rt->u.dst); |
| 284 | out: return ret; |
| 285 | } |