aboutsummaryrefslogtreecommitdiffstats
path: root/net/ipv4/syncookies.c
diff options
context:
space:
mode:
Diffstat (limited to 'net/ipv4/syncookies.c')
-rw-r--r--net/ipv4/syncookies.c279
1 files changed, 279 insertions, 0 deletions
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
new file mode 100644
index 000000000000..e923d2f021aa
--- /dev/null
+++ b/net/ipv4/syncookies.c
@@ -0,0 +1,279 @@
1/*
2 * Syncookies implementation for the Linux kernel
3 *
4 * Copyright (C) 1997 Andi Kleen
5 * Based on ideas by D.J.Bernstein and Eric Schenk.
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.
11 *
12 * $Id: syncookies.c,v 1.18 2002/02/01 22:01:04 davem Exp $
13 *
14 * Missing: IPv6 support.
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
24extern int sysctl_tcp_syncookies;
25
26static __u32 syncookie_secret[2][16-3+SHA_DIGEST_WORDS];
27
28static __init int init_syncookies(void)
29{
30 get_random_bytes(syncookie_secret, sizeof(syncookie_secret));
31 return 0;
32}
33module_init(init_syncookies);
34
35#define COOKIEBITS 24 /* Upper bits store count */
36#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
37
38static u32 cookie_hash(u32 saddr, u32 daddr, u32 sport, u32 dport,
39 u32 count, int c)
40{
41 __u32 tmp[16 + 5 + SHA_WORKSPACE_WORDS];
42
43 memcpy(tmp + 3, syncookie_secret[c], sizeof(syncookie_secret[c]));
44 tmp[0] = saddr;
45 tmp[1] = daddr;
46 tmp[2] = (sport << 16) + dport;
47 tmp[3] = count;
48 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
49
50 return tmp[17];
51}
52
53static __u32 secure_tcp_syn_cookie(__u32 saddr, __u32 daddr, __u16 sport,
54 __u16 dport, __u32 sseq, __u32 count,
55 __u32 data)
56{
57 /*
58 * Compute the secure sequence number.
59 * The output should be:
60 * HASH(sec1,saddr,sport,daddr,dport,sec1) + sseq + (count * 2^24)
61 * + (HASH(sec2,saddr,sport,daddr,dport,count,sec2) % 2^24).
62 * Where sseq is their sequence number and count increases every
63 * minute by 1.
64 * As an extra hack, we add a small "data" value that encodes the
65 * MSS into the second hash value.
66 */
67
68 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
69 sseq + (count << COOKIEBITS) +
70 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
71 & COOKIEMASK));
72}
73
74/*
75 * This retrieves the small "data" value from the syncookie.
76 * If the syncookie is bad, the data returned will be out of
77 * range. This must be checked by the caller.
78 *
79 * The count value used to generate the cookie must be within
80 * "maxdiff" if the current (passed-in) "count". The return value
81 * is (__u32)-1 if this test fails.
82 */
83static __u32 check_tcp_syn_cookie(__u32 cookie, __u32 saddr, __u32 daddr,
84 __u16 sport, __u16 dport, __u32 sseq,
85 __u32 count, __u32 maxdiff)
86{
87 __u32 diff;
88
89 /* Strip away the layers from the cookie */
90 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
91
92 /* Cookie is now reduced to (count * 2^24) ^ (hash % 2^24) */
93 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) - 1 >> COOKIEBITS);
94 if (diff >= maxdiff)
95 return (__u32)-1;
96
97 return (cookie -
98 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
99 & COOKIEMASK; /* Leaving the data behind */
100}
101
102/*
103 * This table has to be sorted and terminated with (__u16)-1.
104 * XXX generate a better table.
105 * Unresolved Issues: HIPPI with a 64k MSS is not well supported.
106 */
107static __u16 const msstab[] = {
108 64 - 1,
109 256 - 1,
110 512 - 1,
111 536 - 1,
112 1024 - 1,
113 1440 - 1,
114 1460 - 1,
115 4312 - 1,
116 (__u16)-1
117};
118/* The number doesn't include the -1 terminator */
119#define NUM_MSS (ARRAY_SIZE(msstab) - 1)
120
121/*
122 * Generate a syncookie. mssp points to the mss, which is returned
123 * rounded down to the value encoded in the cookie.
124 */
125__u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
126{
127 struct tcp_sock *tp = tcp_sk(sk);
128 int mssind;
129 const __u16 mss = *mssp;
130
131
132 tp->last_synq_overflow = jiffies;
133
134 /* XXX sort msstab[] by probability? Binary search? */
135 for (mssind = 0; mss > msstab[mssind + 1]; mssind++)
136 ;
137 *mssp = msstab[mssind] + 1;
138
139 NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESSENT);
140
141 return secure_tcp_syn_cookie(skb->nh.iph->saddr, skb->nh.iph->daddr,
142 skb->h.th->source, skb->h.th->dest,
143 ntohl(skb->h.th->seq),
144 jiffies / (HZ * 60), mssind);
145}
146
147/*
148 * This (misnamed) value is the age of syncookie which is permitted.
149 * Its ideal value should be dependent on TCP_TIMEOUT_INIT and
150 * sysctl_tcp_retries1. It's a rather complicated formula (exponential
151 * backoff) to compute at runtime so it's currently hardcoded here.
152 */
153#define COUNTER_TRIES 4
154/*
155 * Check if a ack sequence number is a valid syncookie.
156 * Return the decoded mss if it is, or 0 if not.
157 */
158static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
159{
160 __u32 seq;
161 __u32 mssind;
162
163 seq = ntohl(skb->h.th->seq)-1;
164 mssind = check_tcp_syn_cookie(cookie,
165 skb->nh.iph->saddr, skb->nh.iph->daddr,
166 skb->h.th->source, skb->h.th->dest,
167 seq, jiffies / (HZ * 60), COUNTER_TRIES);
168
169 return mssind < NUM_MSS ? msstab[mssind] + 1 : 0;
170}
171
172extern struct or_calltable or_ipv4;
173
174static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
175 struct open_request *req,
176 struct dst_entry *dst)
177{
178 struct tcp_sock *tp = tcp_sk(sk);
179 struct sock *child;
180
181 child = tp->af_specific->syn_recv_sock(sk, skb, req, dst);
182 if (child)
183 tcp_acceptq_queue(sk, req, child);
184 else
185 tcp_openreq_free(req);
186
187 return child;
188}
189
190struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
191 struct ip_options *opt)
192{
193 struct tcp_sock *tp = tcp_sk(sk);
194 __u32 cookie = ntohl(skb->h.th->ack_seq) - 1;
195 struct sock *ret = sk;
196 struct open_request *req;
197 int mss;
198 struct rtable *rt;
199 __u8 rcv_wscale;
200
201 if (!sysctl_tcp_syncookies || !skb->h.th->ack)
202 goto out;
203
204 if (time_after(jiffies, tp->last_synq_overflow + TCP_TIMEOUT_INIT) ||
205 (mss = cookie_check(skb, cookie)) == 0) {
206 NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESFAILED);
207 goto out;
208 }
209
210 NET_INC_STATS_BH(LINUX_MIB_SYNCOOKIESRECV);
211
212 req = tcp_openreq_alloc();
213 ret = NULL;
214 if (!req)
215 goto out;
216
217 req->rcv_isn = htonl(skb->h.th->seq) - 1;
218 req->snt_isn = cookie;
219 req->mss = mss;
220 req->rmt_port = skb->h.th->source;
221 req->af.v4_req.loc_addr = skb->nh.iph->daddr;
222 req->af.v4_req.rmt_addr = skb->nh.iph->saddr;
223 req->class = &or_ipv4; /* for savety */
224 req->af.v4_req.opt = NULL;
225
226 /* We throwed the options of the initial SYN away, so we hope
227 * the ACK carries the same options again (see RFC1122 4.2.3.8)
228 */
229 if (opt && opt->optlen) {
230 int opt_size = sizeof(struct ip_options) + opt->optlen;
231
232 req->af.v4_req.opt = kmalloc(opt_size, GFP_ATOMIC);
233 if (req->af.v4_req.opt) {
234 if (ip_options_echo(req->af.v4_req.opt, skb)) {
235 kfree(req->af.v4_req.opt);
236 req->af.v4_req.opt = NULL;
237 }
238 }
239 }
240
241 req->snd_wscale = req->rcv_wscale = req->tstamp_ok = 0;
242 req->wscale_ok = req->sack_ok = 0;
243 req->expires = 0UL;
244 req->retrans = 0;
245
246 /*
247 * We need to lookup the route here to get at the correct
248 * window size. We should better make sure that the window size
249 * hasn't changed since we received the original syn, but I see
250 * no easy way to do this.
251 */
252 {
253 struct flowi fl = { .nl_u = { .ip4_u =
254 { .daddr = ((opt && opt->srr) ?
255 opt->faddr :
256 req->af.v4_req.rmt_addr),
257 .saddr = req->af.v4_req.loc_addr,
258 .tos = RT_CONN_FLAGS(sk) } },
259 .proto = IPPROTO_TCP,
260 .uli_u = { .ports =
261 { .sport = skb->h.th->dest,
262 .dport = skb->h.th->source } } };
263 if (ip_route_output_key(&rt, &fl)) {
264 tcp_openreq_free(req);
265 goto out;
266 }
267 }
268
269 /* Try to redo what tcp_v4_send_synack did. */
270 req->window_clamp = dst_metric(&rt->u.dst, RTAX_WINDOW);
271 tcp_select_initial_window(tcp_full_space(sk), req->mss,
272 &req->rcv_wnd, &req->window_clamp,
273 0, &rcv_wscale);
274 /* BTW win scale with syncookies is 0 by definition */
275 req->rcv_wscale = rcv_wscale;
276
277 ret = get_cookie_sock(sk, skb, req, &rt->u.dst);
278out: return ret;
279}
generated by cgit v1.2.2 (git 2.25.0) at 2024-11-28 09:42:06 -0500