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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 6
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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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
74 options = ireq->wscale_ok ? ireq->snd_wscale : 0xf;
75 options |= ireq->sack_ok << 4;
76 options |= ireq->ecn_ok << 5;
77
78 ts = ts_now & ~TSMASK;
79 ts |= options;
80 if (ts > ts_now) {
81 ts >>= TSBITS;
82 ts--;
83 ts <<= TSBITS;
84 ts |= options;
85 }
86 return ts;
87}
88
89
90static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
91 __be16 dport, __u32 sseq, __u32 count,
92 __u32 data)
93{
94
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103
104
105 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
106 sseq + (count << COOKIEBITS) +
107 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
108 & COOKIEMASK));
109}
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119
120static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
121 __be16 sport, __be16 dport, __u32 sseq,
122 __u32 count, __u32 maxdiff)
123{
124 __u32 diff;
125
126
127 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
128
129
130 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) - 1 >> COOKIEBITS);
131 if (diff >= maxdiff)
132 return (__u32)-1;
133
134 return (cookie -
135 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
136 & COOKIEMASK;
137}
138
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145
146
147static __u16 const msstab[] = {
148 64,
149 512,
150 536,
151 1024,
152 1440,
153 1460,
154 4312,
155 8960,
156};
157
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160
161
162__u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
163{
164 const struct iphdr *iph = ip_hdr(skb);
165 const struct tcphdr *th = tcp_hdr(skb);
166 int mssind;
167 const __u16 mss = *mssp;
168
169 tcp_synq_overflow(sk);
170
171 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
172 if (mss >= msstab[mssind])
173 break;
174 *mssp = msstab[mssind];
175
176 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESSENT);
177
178 return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
179 th->source, th->dest, ntohl(th->seq),
180 jiffies / (HZ * 60), mssind);
181}
182
183
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187
188
189#define COUNTER_TRIES 4
190
191
192
193
194static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
195{
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);
203
204 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
205}
206
207static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
208 struct request_sock *req,
209 struct dst_entry *dst)
210{
211 struct inet_connection_sock *icsk = inet_csk(sk);
212 struct sock *child;
213
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);
219
220 return child;
221}
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233
234bool cookie_check_timestamp(struct tcp_options_received *tcp_opt, bool *ecn_ok)
235{
236
237 u32 options = tcp_opt->rcv_tsecr & TSMASK;
238
239 if (!tcp_opt->saw_tstamp) {
240 tcp_clear_options(tcp_opt);
241 return true;
242 }
243
244 if (!sysctl_tcp_timestamps)
245 return false;
246
247 tcp_opt->sack_ok = (options >> 4) & 0x1;
248 *ecn_ok = (options >> 5) & 1;
249 if (*ecn_ok && !sysctl_tcp_ecn)
250 return false;
251
252 if (tcp_opt->sack_ok && !sysctl_tcp_sack)
253 return false;
254
255 if ((options & 0xf) == 0xf)
256 return true;
257
258 tcp_opt->wscale_ok = 1;
259 tcp_opt->snd_wscale = options & 0xf;
260 return sysctl_tcp_window_scaling != 0;
261}
262EXPORT_SYMBOL(cookie_check_timestamp);
263
264struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
265 struct ip_options *opt)
266{
267 struct tcp_options_received tcp_opt;
268 u8 *hash_location;
269 struct inet_request_sock *ireq;
270 struct tcp_request_sock *treq;
271 struct tcp_sock *tp = tcp_sk(sk);
272 const struct tcphdr *th = tcp_hdr(skb);
273 __u32 cookie = ntohl(th->ack_seq) - 1;
274 struct sock *ret = sk;
275 struct request_sock *req;
276 int mss;
277 struct rtable *rt;
278 __u8 rcv_wscale;
279 bool ecn_ok;
280
281 if (!sysctl_tcp_syncookies || !th->ack || th->rst)
282 goto out;
283
284 if (tcp_synq_no_recent_overflow(sk) ||
285 (mss = cookie_check(skb, cookie)) == 0) {
286 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
287 goto out;
288 }
289
290 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
291
292
293 memset(&tcp_opt, 0, sizeof(tcp_opt));
294 tcp_parse_options(skb, &tcp_opt, &hash_location, 0);
295
296 if (!cookie_check_timestamp(&tcp_opt, &ecn_ok))
297 goto out;
298
299 ret = NULL;
300 req = inet_reqsk_alloc(&tcp_request_sock_ops);
301 if (!req)
302 goto out;
303
304 ireq = inet_rsk(req);
305 treq = tcp_rsk(req);
306 treq->rcv_isn = ntohl(th->seq) - 1;
307 treq->snt_isn = cookie;
308 req->mss = mss;
309 ireq->loc_port = th->dest;
310 ireq->rmt_port = th->source;
311 ireq->loc_addr = ip_hdr(skb)->daddr;
312 ireq->rmt_addr = ip_hdr(skb)->saddr;
313 ireq->ecn_ok = ecn_ok;
314 ireq->snd_wscale = tcp_opt.snd_wscale;
315 ireq->sack_ok = tcp_opt.sack_ok;
316 ireq->wscale_ok = tcp_opt.wscale_ok;
317 ireq->tstamp_ok = tcp_opt.saw_tstamp;
318 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
319
320
321
322
323 if (opt && opt->optlen) {
324 int opt_size = sizeof(struct ip_options) + opt->optlen;
325
326 ireq->opt = kmalloc(opt_size, GFP_ATOMIC);
327 if (ireq->opt != NULL && ip_options_echo(ireq->opt, skb)) {
328 kfree(ireq->opt);
329 ireq->opt = NULL;
330 }
331 }
332
333 if (security_inet_conn_request(sk, skb, req)) {
334 reqsk_free(req);
335 goto out;
336 }
337
338 req->expires = 0UL;
339 req->retrans = 0;
340
341
342
343
344
345
346
347 {
348 struct flowi fl = { .mark = sk->sk_mark,
349 .fl4_dst = ((opt && opt->srr) ?
350 opt->faddr : ireq->rmt_addr),
351 .fl4_src = ireq->loc_addr,
352 .fl4_tos = RT_CONN_FLAGS(sk),
353 .proto = IPPROTO_TCP,
354 .flags = inet_sk_flowi_flags(sk),
355 .fl_ip_sport = th->dest,
356 .fl_ip_dport = th->source };
357 security_req_classify_flow(req, &fl);
358 if (ip_route_output_key(sock_net(sk), &rt, &fl)) {
359 reqsk_free(req);
360 goto out;
361 }
362 }
363
364
365 req->window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
366
367 tcp_select_initial_window(tcp_full_space(sk), req->mss,
368 &req->rcv_wnd, &req->window_clamp,
369 ireq->wscale_ok, &rcv_wscale,
370 dst_metric(&rt->dst, RTAX_INITRWND));
371
372 ireq->rcv_wscale = rcv_wscale;
373
374 ret = get_cookie_sock(sk, skb, req, &rt->dst);
375out: return ret;
376}
377