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13#include <linux/tcp.h>
14#include <linux/slab.h>
15#include <linux/random.h>
16#include <linux/siphash.h>
17#include <linux/kernel.h>
18#include <linux/export.h>
19#include <net/secure_seq.h>
20#include <net/tcp.h>
21#include <net/route.h>
22
23static siphash_key_t syncookie_secret[2] __read_mostly;
24
25#define COOKIEBITS 24
26#define COOKIEMASK (((__u32)1 << COOKIEBITS) - 1)
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40
41
42#define TS_OPT_WSCALE_MASK 0xf
43#define TS_OPT_SACK BIT(4)
44#define TS_OPT_ECN BIT(5)
45
46
47
48
49#define TSBITS 6
50#define TSMASK (((__u32)1 << TSBITS) - 1)
51
52static u32 cookie_hash(__be32 saddr, __be32 daddr, __be16 sport, __be16 dport,
53 u32 count, int c)
54{
55 net_get_random_once(syncookie_secret, sizeof(syncookie_secret));
56 return siphash_4u32((__force u32)saddr, (__force u32)daddr,
57 (__force u32)sport << 16 | (__force u32)dport,
58 count, &syncookie_secret[c]);
59}
60
61
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66
67
68
69__u32 cookie_init_timestamp(struct request_sock *req)
70{
71 struct inet_request_sock *ireq;
72 u32 ts, ts_now = tcp_time_stamp;
73 u32 options = 0;
74
75 ireq = inet_rsk(req);
76
77 options = ireq->wscale_ok ? ireq->snd_wscale : TS_OPT_WSCALE_MASK;
78 if (ireq->sack_ok)
79 options |= TS_OPT_SACK;
80 if (ireq->ecn_ok)
81 options |= TS_OPT_ECN;
82
83 ts = ts_now & ~TSMASK;
84 ts |= options;
85 if (ts > ts_now) {
86 ts >>= TSBITS;
87 ts--;
88 ts <<= TSBITS;
89 ts |= options;
90 }
91 return ts;
92}
93
94
95static __u32 secure_tcp_syn_cookie(__be32 saddr, __be32 daddr, __be16 sport,
96 __be16 dport, __u32 sseq, __u32 data)
97{
98
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108 u32 count = tcp_cookie_time();
109 return (cookie_hash(saddr, daddr, sport, dport, 0, 0) +
110 sseq + (count << COOKIEBITS) +
111 ((cookie_hash(saddr, daddr, sport, dport, count, 1) + data)
112 & COOKIEMASK));
113}
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122
123
124static __u32 check_tcp_syn_cookie(__u32 cookie, __be32 saddr, __be32 daddr,
125 __be16 sport, __be16 dport, __u32 sseq)
126{
127 u32 diff, count = tcp_cookie_time();
128
129
130 cookie -= cookie_hash(saddr, daddr, sport, dport, 0, 0) + sseq;
131
132
133 diff = (count - (cookie >> COOKIEBITS)) & ((__u32) -1 >> COOKIEBITS);
134 if (diff >= MAX_SYNCOOKIE_AGE)
135 return (__u32)-1;
136
137 return (cookie -
138 cookie_hash(saddr, daddr, sport, dport, count - diff, 1))
139 & COOKIEMASK;
140}
141
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153
154static __u16 const msstab[] = {
155 536,
156 1300,
157 1440,
158 1460,
159};
160
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164
165u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,
166 u16 *mssp)
167{
168 int mssind;
169 const __u16 mss = *mssp;
170
171 for (mssind = ARRAY_SIZE(msstab) - 1; mssind ; mssind--)
172 if (mss >= msstab[mssind])
173 break;
174 *mssp = msstab[mssind];
175
176 return secure_tcp_syn_cookie(iph->saddr, iph->daddr,
177 th->source, th->dest, ntohl(th->seq),
178 mssind);
179}
180EXPORT_SYMBOL_GPL(__cookie_v4_init_sequence);
181
182__u32 cookie_v4_init_sequence(const struct sk_buff *skb, __u16 *mssp)
183{
184 const struct iphdr *iph = ip_hdr(skb);
185 const struct tcphdr *th = tcp_hdr(skb);
186
187 return __cookie_v4_init_sequence(iph, th, mssp);
188}
189
190
191
192
193
194int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
195 u32 cookie)
196{
197 __u32 seq = ntohl(th->seq) - 1;
198 __u32 mssind = check_tcp_syn_cookie(cookie, iph->saddr, iph->daddr,
199 th->source, th->dest, seq);
200
201 return mssind < ARRAY_SIZE(msstab) ? msstab[mssind] : 0;
202}
203EXPORT_SYMBOL_GPL(__cookie_v4_check);
204
205struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
206 struct request_sock *req,
207 struct dst_entry *dst, u32 tsoff)
208{
209 struct inet_connection_sock *icsk = inet_csk(sk);
210 struct sock *child;
211 bool own_req;
212
213 child = icsk->icsk_af_ops->syn_recv_sock(sk, skb, req, dst,
214 NULL, &own_req);
215 if (child) {
216 atomic_set(&req->rsk_refcnt, 1);
217 tcp_sk(child)->tsoffset = tsoff;
218 sock_rps_save_rxhash(child, skb);
219 inet_csk_reqsk_queue_add(sk, req, child);
220 } else {
221 reqsk_free(req);
222 }
223 return child;
224}
225EXPORT_SYMBOL(tcp_get_cookie_sock);
226
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230
231
232
233
234
235bool cookie_timestamp_decode(struct tcp_options_received *tcp_opt)
236{
237
238 u32 options = tcp_opt->rcv_tsecr;
239
240 if (!tcp_opt->saw_tstamp) {
241 tcp_clear_options(tcp_opt);
242 return true;
243 }
244
245 if (!sysctl_tcp_timestamps)
246 return false;
247
248 tcp_opt->sack_ok = (options & TS_OPT_SACK) ? TCP_SACK_SEEN : 0;
249
250 if (tcp_opt->sack_ok && !sysctl_tcp_sack)
251 return false;
252
253 if ((options & TS_OPT_WSCALE_MASK) == TS_OPT_WSCALE_MASK)
254 return true;
255
256 tcp_opt->wscale_ok = 1;
257 tcp_opt->snd_wscale = options & TS_OPT_WSCALE_MASK;
258
259 return sysctl_tcp_window_scaling != 0;
260}
261EXPORT_SYMBOL(cookie_timestamp_decode);
262
263bool cookie_ecn_ok(const struct tcp_options_received *tcp_opt,
264 const struct net *net, const struct dst_entry *dst)
265{
266 bool ecn_ok = tcp_opt->rcv_tsecr & TS_OPT_ECN;
267
268 if (!ecn_ok)
269 return false;
270
271 if (net->ipv4.sysctl_tcp_ecn)
272 return true;
273
274 return dst_feature(dst, RTAX_FEATURE_ECN);
275}
276EXPORT_SYMBOL(cookie_ecn_ok);
277
278
279
280
281
282struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
283{
284 struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
285 struct tcp_options_received tcp_opt;
286 struct inet_request_sock *ireq;
287 struct tcp_request_sock *treq;
288 struct tcp_sock *tp = tcp_sk(sk);
289 const struct tcphdr *th = tcp_hdr(skb);
290 __u32 cookie = ntohl(th->ack_seq) - 1;
291 struct sock *ret = sk;
292 struct request_sock *req;
293 int mss;
294 struct rtable *rt;
295 __u8 rcv_wscale;
296 struct flowi4 fl4;
297 u32 tsoff = 0;
298
299 if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
300 goto out;
301
302 if (tcp_synq_no_recent_overflow(sk))
303 goto out;
304
305 mss = __cookie_v4_check(ip_hdr(skb), th, cookie);
306 if (mss == 0) {
307 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESFAILED);
308 goto out;
309 }
310
311 __NET_INC_STATS(sock_net(sk), LINUX_MIB_SYNCOOKIESRECV);
312
313
314 memset(&tcp_opt, 0, sizeof(tcp_opt));
315 tcp_parse_options(skb, &tcp_opt, 0, NULL);
316
317 if (tcp_opt.saw_tstamp && tcp_opt.rcv_tsecr) {
318 tsoff = secure_tcp_ts_off(ip_hdr(skb)->daddr, ip_hdr(skb)->saddr);
319 tcp_opt.rcv_tsecr -= tsoff;
320 }
321
322 if (!cookie_timestamp_decode(&tcp_opt))
323 goto out;
324
325 ret = NULL;
326 req = inet_reqsk_alloc(&tcp_request_sock_ops, sk, false);
327 if (!req)
328 goto out;
329
330 ireq = inet_rsk(req);
331 treq = tcp_rsk(req);
332 treq->rcv_isn = ntohl(th->seq) - 1;
333 treq->snt_isn = cookie;
334 treq->ts_off = 0;
335 req->mss = mss;
336 ireq->ir_num = ntohs(th->dest);
337 ireq->ir_rmt_port = th->source;
338 sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr);
339 sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr);
340 ireq->ir_mark = inet_request_mark(sk, skb);
341 ireq->snd_wscale = tcp_opt.snd_wscale;
342 ireq->sack_ok = tcp_opt.sack_ok;
343 ireq->wscale_ok = tcp_opt.wscale_ok;
344 ireq->tstamp_ok = tcp_opt.saw_tstamp;
345 req->ts_recent = tcp_opt.saw_tstamp ? tcp_opt.rcv_tsval : 0;
346 treq->snt_synack.v64 = 0;
347 treq->tfo_listener = false;
348
349 ireq->ir_iif = inet_request_bound_dev_if(sk, skb);
350
351
352
353
354 ireq->opt = tcp_v4_save_options(skb);
355
356 if (security_inet_conn_request(sk, skb, req)) {
357 reqsk_free(req);
358 goto out;
359 }
360
361 req->num_retrans = 0;
362
363
364
365
366
367
368
369 flowi4_init_output(&fl4, ireq->ir_iif, ireq->ir_mark,
370 RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE, IPPROTO_TCP,
371 inet_sk_flowi_flags(sk),
372 opt->srr ? opt->faddr : ireq->ir_rmt_addr,
373 ireq->ir_loc_addr, th->source, th->dest, sk->sk_uid);
374 security_req_classify_flow(req, flowi4_to_flowi(&fl4));
375 rt = ip_route_output_key(sock_net(sk), &fl4);
376 if (IS_ERR(rt)) {
377 reqsk_free(req);
378 goto out;
379 }
380
381
382 req->rsk_window_clamp = tp->window_clamp ? :dst_metric(&rt->dst, RTAX_WINDOW);
383
384 tcp_select_initial_window(tcp_full_space(sk), req->mss,
385 &req->rsk_rcv_wnd, &req->rsk_window_clamp,
386 ireq->wscale_ok, &rcv_wscale,
387 dst_metric(&rt->dst, RTAX_INITRWND));
388
389 ireq->rcv_wscale = rcv_wscale;
390 ireq->ecn_ok = cookie_ecn_ok(&tcp_opt, sock_net(sk), &rt->dst);
391
392 ret = tcp_get_cookie_sock(sk, skb, req, &rt->dst, tsoff);
393
394
395
396 if (ret)
397 inet_sk(ret)->cork.fl.u.ip4 = fl4;
398out: return ret;
399}
400