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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>
19#include <net/route.h>
20
21
22#define TSBITS 9
23#define TSMASK (((__u32)1 << TSBITS) - 1)
24
25extern int sysctl_tcp_syncookies;
26
27__u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];
28EXPORT_SYMBOL(syncookie_secret);
29
30static __init int init_syncookies(void)
31{
32 get_random_bytes(syncookie_secret, sizeof(syncookie_secret));
33 return 0;
34}
35__initcall(init_syncookies);
36
37#define COOKIEBITS 24
38#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
39
40static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
41 ipv4_cookie_scratch);
42
43static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
44 u32 count, int c)
45{
46 __u32 *tmp = __get_cpu_var(ipv4_cookie_scratch);
47
48 memcpy(tmp + 4, syncookie_secret[c], sizeof(syncookie_secret[c]));
49 tmp[0] = (__force u32)saddr;
50 tmp[1] = (__force u32)daddr;
51 tmp[2] = ((__force u32)sport << 16) + (__force u32)dport;
52 tmp[3] = count;
53 sha_transform(tmp + 16, (__u8 *)tmp, tmp + 16 + 5);
54
55 return tmp[17];
56}
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64
65
66__u32 cookie_init_timestamp(struct request_sock *req)
67{
68 struct inet_request_sock *ireq;
69 u32 ts, ts_now = tcp_time_stamp;
70 u32 options = 0;
71
72 ireq = inet_rsk(req);
73 if (ireq->wscale_ok) {
74 options = ireq->snd_wscale;
75 options |= ireq->rcv_wscale << 4;
76 }
77 options |= ireq->sack_ok << 8;
78
79 ts = ts_now & ~TSMASK;
80 ts |= options;
81 if (ts > ts_now) {
82 ts >>= TSBITS;
83 ts--;
84 ts <<= TSBITS;
85 ts |= options;
86 }
87 return ts;
88}
89
90
91static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
92 __be16 dport, __u32 sseq, __u32 count,
93 __u32 data)
94{
95
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105
106 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
107 sseq + (count << COOKIEBITS) +
108 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
109 & COOKIEMASK));
110}
111
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119
120
121static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
122 __be16 sport, __be16 dport, __u32 sseq,
123 __u32 count, __u32 maxdiff)
124{
125 __u32 diff;
126
127
128 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
129
130
131 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) - 1 >> COOKIEBITS);
132 if (diff >= maxdiff)
133 return (__u32)-1;
134
135 return (cookie -
136 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
137 & COOKIEMASK;
138}
139
140
141
142
143
144
145static __u16 const msstab[] = {
146 64 - 1,
147 256 - 1,
148 512 - 1,
149 536 - 1,
150 1024 - 1,
151 1440 - 1,
152 1460 - 1,
153 4312 - 1,
154 (__u16)-1
155};
156
157#define NUM_MSS (ARRAY_SIZE(msstab) - 1)
158
159
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161
162
163__u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
164{
165 const struct iphdr *iph = ip_hdr(skb);
166 const struct tcphdr *th = tcp_hdr(skb);
167 int mssind;
168 const __u16 mss = *mssp;
169
170 tcp_synq_overflow(sk);
171
172
173 for (mssind = 0; mss > msstab[mssind + 1]; mssind++)
174 ;
175 *mssp = msstab[mssind] + 1;
176
177 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
178
179 return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
180 th->source, th->dest, ntohl(th->seq),
181 jiffies / (HZ * 60), mssind);
182}
183
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188
189
190#define COUNTER_TRIES 4
191
192
193
194
195static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
196{
197 const struct iphdr *iph = ip_hdr(skb);
198 const struct tcphdr *th = tcp_hdr(skb);
199 __u32 seq = ntohl(th->seq) - 1;
200 __u32 mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr,
201 th->source, th->dest, seq,
202 jiffies / (HZ * 60),
203 COUNTER_TRIES);
204
205 return mssind < NUM_MSS ? msstab[mssind] + 1 : 0;
206}
207
208static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
209 struct request_sock *req,
210 struct dst_entry *dst)
211{
212 struct inet_connection_sock *icsk = inet_csk(sk);
213 struct sock *child;
214
215 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst);
216 if (child)
217 inet_csk_reqsk_queue_add(sk, req, child);
218 else
219 reqsk_free(req);
220
221 return child;
222}
223
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231
232
233
234void cookie_check_timestamp(struct tcp_options_received *tcp_opt)
235{
236
237 u32 options = tcp_opt->rcv_tsecr & TSMASK;
238
239 tcp_opt->snd_wscale = options & 0xf;
240 options >>= 4;
241 tcp_opt->rcv_wscale = options & 0xf;
242
243 tcp_opt->sack_ok = (options >> 4) & 0x1;
244
245 if (tcp_opt->sack_ok)
246 tcp_sack_reset(tcp_opt);
247
248 if (tcp_opt->snd_wscale || tcp_opt->rcv_wscale)
249 tcp_opt->wscale_ok = 1;
250}
251EXPORT_SYMBOL(cookie_check_timestamp);
252
253struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
254 struct ip_options *opt)
255{
256 struct inet_request_sock *ireq;
257 struct tcp_request_sock *treq;
258 struct tcp_sock *tp = tcp_sk(sk);
259 const struct tcphdr *th = tcp_hdr(skb);
260 __u32 cookie = ntohl(th->ack_seq) - 1;
261 struct sock *ret = sk;
262 struct request_sock *req;
263 int mss;
264 struct rtable *rt;
265 __u8 rcv_wscale;
266 struct tcp_options_received tcp_opt;
267
268 if (!sysctl_tcp_syncookies || !th->ack)
269 goto out;
270
271 if (tcp_synq_no_recent_overflow(sk) ||
272 (mss = cookie_check(skb, cookie)) == 0) {
273 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
274 goto out;
275 }
276
277 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
278
279
280 memset(&tcp_opt, 0, sizeof(tcp_opt));
281 tcp_parse_options(skb, &tcp_opt, 0);
282
283 if (tcp_opt.saw_tstamp)
284 cookie_check_timestamp(&tcp_opt);
285
286 ret = NULL;
287 req = inet_reqsk_alloc(&tcp_request_sock_ops);
288 if (!req)
289 goto out;
290
291 ireq = inet_rsk(req);
292 treq = tcp_rsk(req);
293 treq->rcv_isn = ntohl(th->seq) - 1;
294 treq->snt_isn = cookie;
295 req->mss = mss;
296 ireq->loc_port = th->dest;
297 ireq->rmt_port = th->source;
298 ireq->loc_addr = ip_hdr(skb)->daddr;
299 ireq->rmt_addr = ip_hdr(skb)->saddr;
300 ireq->ecn_ok = 0;
301 ireq->snd_wscale = tcp_opt.snd_wscale;
302 ireq->rcv_wscale = tcp_opt.rcv_wscale;
303 ireq->sack_ok = tcp_opt.sack_ok;
304 ireq->wscale_ok = tcp_opt.wscale_ok;
305 ireq->tstamp_ok = tcp_opt.saw_tstamp;
306 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
307
308
309
310
311 if (opt && opt->optlen) {
312 int opt_size = sizeof(struct ip_options) + opt->optlen;
313
314 ireq->opt = kmalloc(opt_size, GFP_ATOMIC);
315 if (ireq->opt != NULL && ip_options_echo(ireq->opt, skb)) {
316 kfree(ireq->opt);
317 ireq->opt = NULL;
318 }
319 }
320
321 if (security_inet_conn_request(sk, skb, req)) {
322 reqsk_free(req);
323 goto out;
324 }
325
326 req->expires = 0UL;
327 req->retrans = 0;
328
329
330
331
332
333
334
335 {
336 struct flowi fl = { .nl_u = { .ip4_u =
337 { .daddr = ((opt && opt->srr) ?
338 opt->faddr :
339 ireq->rmt_addr),
340 .saddr = ireq->loc_addr,
341 .tos = RT_CONN_FLAGS(sk) } },
342 .proto = IPPROTO_TCP,
343 .flags = inet_sk_flowi_flags(sk),
344 .uli_u = { .ports =
345 { .sport = th->dest,
346 .dport = th->source } } };
347 security_req_classify_flow(req, &fl);
348 if (ip_route_output_key(&init_net, &rt, &fl)) {
349 reqsk_free(req);
350 goto out;
351 }
352 }
353
354
355 req->window_clamp = tp->window_clamp ? :dst_metric(&rt->u.dst, RTAX_WINDOW);
356
357 tcp_select_initial_window(tcp_full_space(sk), req->mss,
358 &req->rcv_wnd, &req->window_clamp,
359 ireq->wscale_ok, &rcv_wscale);
360
361 ireq->rcv_wscale = rcv_wscale;
362
363 ret = get_cookie_sock(sk, skb, req, &rt->u.dst);
364out: return ret;
365}
366