r6040: prefix all functions with r6040
[linux-2.6/linux-2.6-openrd.git] / net / ipv4 / syncookies.c
blob51bc24d3b8a71580a097ff13df9a4781f10b0575
1 /*
2 * Syncookies implementation for the Linux kernel
4 * Copyright (C) 1997 Andi Kleen
5 * Based on ideas by D.J.Bernstein and Eric Schenk.
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.
13 #include <linux/tcp.h>
14 #include <linux/slab.h>
15 #include <linux/random.h>
16 #include <linux/cryptohash.h>
17 #include <linux/kernel.h>
18 #include <net/tcp.h>
20 /* Timestamps: lowest 9 bits store TCP options */
21 #define TSBITS 9
22 #define TSMASK (((__u32)1 << TSBITS) - 1)
24 extern int sysctl_tcp_syncookies;
26 __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
27 EXPORT_SYMBOL(syncookie_secret);
29 static __init int init_syncookies(void)
31 get_random_bytes(syncookie_secret, sizeof(syncookie_secret));
32 return 0;
34 __initcall(init_syncookies);
36 #define COOKIEBITS 24 /* Upper bits store count */
37 #define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
39 static DEFINE_PER_CPU(__u32, cookie_scratch)[16 + 5 + SHA_WORKSPACE_WORDS];
41 static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
42 u32 count, int c)
44 __u32 *tmp = __get_cpu_var(cookie_scratch);
46 memcpy(tmp + 4, syncookie_secret[c], sizeof(syncookie_secret[c]));
47 tmp[0] = (__force u32)saddr;
48 tmp[1] = (__force u32)daddr;
49 tmp[2] = ((__force u32)sport << 16) + (__force u32)dport;
50 tmp[3] = count;
51 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
53 return tmp[17];
58 * when syncookies are in effect and tcp timestamps are enabled we encode
59 * tcp options in the lowest 9 bits of the timestamp value that will be
60 * sent in the syn-ack.
61 * Since subsequent timestamps use the normal tcp_time_stamp value, we
62 * must make sure that the resulting initial timestamp is <= tcp_time_stamp.
64 __u32 cookie_init_timestamp(struct request_sock *req)
66 struct inet_request_sock *ireq;
67 u32 ts, ts_now = tcp_time_stamp;
68 u32 options = 0;
70 ireq = inet_rsk(req);
71 if (ireq->wscale_ok) {
72 options = ireq->snd_wscale;
73 options |= ireq->rcv_wscale << 4;
75 options |= ireq->sack_ok << 8;
77 ts = ts_now & ~TSMASK;
78 ts |= options;
79 if (ts > ts_now) {
80 ts >>= TSBITS;
81 ts--;
82 ts <<= TSBITS;
83 ts |= options;
85 return ts;
89 static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
90 __be16 dport, __u32 sseq, __u32 count,
91 __u32 data)
94 * Compute the secure sequence number.
95 * The output should be:
96 * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24)
97 * + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24).
98 * Where sseq is their sequence number and count increases every
99 * minute by 1.
100 * As an extra hack, we add a small "data" value that encodes the
101 * MSS into the second hash value.
104 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
105 sseq + (count << COOKIEBITS) +
106 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
107 & COOKIEMASK));
111 * This retrieves the small "data" value from the syncookie.
112 * If the syncookie is bad, the data returned will be out of
113 * range. This must be checked by the caller.
115 * The count value used to generate the cookie must be within
116 * "maxdiff" if the current (passed-in) "count". The return value
117 * is (__u32)-1 if this test fails.
119 static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
120 __be16 sport, __be16 dport, __u32 sseq,
121 __u32 count, __u32 maxdiff)
123 __u32 diff;
125 /* Strip away the layers from the cookie */
126 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
128 /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */
129 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) - 1 >> COOKIEBITS);
130 if (diff >= maxdiff)
131 return (__u32)-1;
133 return (cookie -
134 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
135 & COOKIEMASK; /* Leaving the data behind */
139 * This table has to be sorted and terminated with (__u16)-1.
140 * XXX generate a better table.
141 * Unresolved Issues: HIPPI with a 64k MSS is not well supported.
143 static __u16 const msstab[] = {
144 64 - 1,
145 256 - 1,
146 512 - 1,
147 536 - 1,
148 1024 - 1,
149 1440 - 1,
150 1460 - 1,
151 4312 - 1,
152 (__u16)-1
154 /* The number doesn't include the -1 terminator */
155 #define NUM_MSS (ARRAY_SIZE(msstab) - 1)
158 * Generate a syncookie. mssp points to the mss, which is returned
159 * rounded down to the value encoded in the cookie.
161 __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
163 struct tcp_sock *tp = tcp_sk(sk);
164 const struct iphdr *iph = ip_hdr(skb);
165 const struct tcphdr *th = tcp_hdr(skb);
166 int mssind;
167 const __u16 mss = *mssp;
169 tp->last_synq_overflow = jiffies;
171 /* XXX sort msstab[] by probability? Binary search? */
172 for (mssind = 0; mss > msstab[mssind + 1]; mssind++)
174 *mssp = msstab[mssind] + 1;
176 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
178 return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
179 th->source, th->dest, ntohl(th->seq),
180 jiffies / (HZ * 60), mssind);
184 * This (misnamed) value is the age of syncookie which is permitted.
185 * Its ideal value should be dependent on TCP_TIMEOUT_INIT and
186 * sysctl_tcp_retries1. It's a rather complicated formula (exponential
187 * backoff) to compute at runtime so it's currently hardcoded here.
189 #define COUNTER_TRIES 4
191 * Check if a ack sequence number is a valid syncookie.
192 * Return the decoded mss if it is, or 0 if not.
194 static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
196 const struct iphdr *iph = ip_hdr(skb);
197 const struct tcphdr *th = tcp_hdr(skb);
198 __u32 seq = ntohl(th->seq) - 1;
199 __u32 mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr,
200 th->source, th->dest, seq,
201 jiffies / (HZ * 60),
202 COUNTER_TRIES);
204 return mssind < NUM_MSS ? msstab[mssind] + 1 : 0;
207 static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
208 struct request_sock *req,
209 struct dst_entry *dst)
211 struct inet_connection_sock *icsk = inet_csk(sk);
212 struct sock *child;
214 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
215 if (child)
216 inet_csk_reqsk_queue_add(sk, req, child);
217 else
218 reqsk_free(req);
220 return child;
225 * when syncookies are in effect and tcp timestamps are enabled we stored
226 * additional tcp options in the timestamp.
227 * This extracts these options from the timestamp echo.
229 * The lowest 4 bits are for snd_wscale
230 * The next 4 lsb are for rcv_wscale
231 * The next lsb is for sack_ok
233 void cookie_check_timestamp(struct tcp_options_received *tcp_opt)
235 /* echoed timestamp, 9 lowest bits contain options */
236 u32 options = tcp_opt->rcv_tsecr & TSMASK;
238 tcp_opt->snd_wscale = options & 0xf;
239 options >>= 4;
240 tcp_opt->rcv_wscale = options & 0xf;
242 tcp_opt->sack_ok = (options >> 4) & 0x1;
244 if (tcp_opt->sack_ok)
245 tcp_sack_reset(tcp_opt);
247 if (tcp_opt->snd_wscale || tcp_opt->rcv_wscale)
248 tcp_opt->wscale_ok = 1;
250 EXPORT_SYMBOL(cookie_check_timestamp);
252 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
253 struct ip_options *opt)
255 struct inet_request_sock *ireq;
256 struct tcp_request_sock *treq;
257 struct tcp_sock *tp = tcp_sk(sk);
258 const struct tcphdr *th = tcp_hdr(skb);
259 __u32 cookie = ntohl(th->ack_seq) - 1;
260 struct sock *ret = sk;
261 struct request_sock *req;
262 int mss;
263 struct rtable *rt;
264 __u8 rcv_wscale;
265 struct tcp_options_received tcp_opt;
267 if (!sysctl_tcp_syncookies || !th->ack)
268 goto out;
270 if (time_after(jiffies, tp->last_synq_overflow + TCP_TIMEOUT_INIT) ||
271 (mss = cookie_check(skb, cookie)) == 0) {
272 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
273 goto out;
276 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
278 /* check for timestamp cookie support */
279 memset(&tcp_opt, 0, sizeof(tcp_opt));
280 tcp_parse_options(skb, &tcp_opt, 0);
282 if (tcp_opt.saw_tstamp)
283 cookie_check_timestamp(&tcp_opt);
285 ret = NULL;
286 req = inet_reqsk_alloc(&tcp_request_sock_ops); /* for safety */
287 if (!req)
288 goto out;
290 if (security_inet_conn_request(sk, skb, req)) {
291 reqsk_free(req);
292 goto out;
294 ireq = inet_rsk(req);
295 treq = tcp_rsk(req);
296 treq->rcv_isn = ntohl(th->seq) - 1;
297 treq->snt_isn = cookie;
298 req->mss = mss;
299 ireq->rmt_port = th->source;
300 ireq->loc_addr = ip_hdr(skb)->daddr;
301 ireq->rmt_addr = ip_hdr(skb)->saddr;
302 ireq->snd_wscale = tcp_opt.snd_wscale;
303 ireq->rcv_wscale = tcp_opt.rcv_wscale;
304 ireq->sack_ok = tcp_opt.sack_ok;
305 ireq->wscale_ok = tcp_opt.wscale_ok;
306 ireq->tstamp_ok = tcp_opt.saw_tstamp;
307 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
309 /* We throwed the options of the initial SYN away, so we hope
310 * the ACK carries the same options again (see RFC1122 4.2.3.8)
312 if (opt && opt->optlen) {
313 int opt_size = sizeof(struct ip_options) + opt->optlen;
315 ireq->opt = kmalloc(opt_size, GFP_ATOMIC);
316 if (ireq->opt != NULL && ip_options_echo(ireq->opt, skb)) {
317 kfree(ireq->opt);
318 ireq->opt = NULL;
322 req->expires = 0UL;
323 req->retrans = 0;
326 * We need to lookup the route here to get at the correct
327 * window size. We should better make sure that the window size
328 * hasn't changed since we received the original syn, but I see
329 * no easy way to do this.
332 struct flowi fl = { .nl_u = { .ip4_u =
333 { .daddr = ((opt && opt->srr) ?
334 opt->faddr :
335 ireq->rmt_addr),
336 .saddr = ireq->loc_addr,
337 .tos = RT_CONN_FLAGS(sk) } },
338 .proto = IPPROTO_TCP,
339 .uli_u = { .ports =
340 { .sport = th->dest,
341 .dport = th->source } } };
342 security_req_classify_flow(req, &fl);
343 if (ip_route_output_key(&init_net, &rt, &fl)) {
344 reqsk_free(req);
345 goto out;
349 /* Try to redo what tcp_v4_send_synack did. */
350 req->window_clamp = tp->window_clamp ? :dst_metric(&rt->u.dst, RTAX_WINDOW);
352 tcp_select_initial_window(tcp_full_space(sk), req->mss,
353 &req->rcv_wnd, &req->window_clamp,
354 ireq->wscale_ok, &rcv_wscale);
356 ireq->rcv_wscale = rcv_wscale;
358 ret = get_cookie_sock(sk, skb, req, &rt->u.dst);
359 out: return ret;