1 /* SPDX-License-Identifier: ISC
2 *
3 * Copyright (C) 2015-2021 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
4 * Copyright (C) 2019-2021 Matt Dunwoodie <ncon@noconroy.net>
5 */
6
7 #include "opt_inet.h"
8 #include "opt_inet6.h"
9
10 #include <sys/param.h>
11 #include <sys/systm.h>
12 #include <sys/kernel.h>
13 #include <sys/lock.h>
14 #include <sys/mutex.h>
15 #include <sys/rwlock.h>
16 #include <sys/socket.h>
17 #include <crypto/siphash/siphash.h>
18 #include <netinet/in.h>
19 #include <vm/uma.h>
20
21 #include "wg_cookie.h"
22
23 #define COOKIE_MAC1_KEY_LABEL "mac1----"
24 #define COOKIE_COOKIE_KEY_LABEL "cookie--"
25 #define COOKIE_SECRET_MAX_AGE 120
26 #define COOKIE_SECRET_LATENCY 5
27
28 /* Constants for initiation rate limiting */
29 #define RATELIMIT_SIZE (1 << 13)
30 #define RATELIMIT_MASK (RATELIMIT_SIZE - 1)
31 #define RATELIMIT_SIZE_MAX (RATELIMIT_SIZE * 8)
32 #define INITIATIONS_PER_SECOND 20
33 #define INITIATIONS_BURSTABLE 5
34 #define INITIATION_COST (SBT_1S / INITIATIONS_PER_SECOND)
35 #define TOKEN_MAX (INITIATION_COST * INITIATIONS_BURSTABLE)
36 #define ELEMENT_TIMEOUT 1
37 #define IPV4_MASK_SIZE 4 /* Use all 4 bytes of IPv4 address */
38 #define IPV6_MASK_SIZE 8 /* Use top 8 bytes (/64) of IPv6 address */
39
40 struct ratelimit_key {
41 struct vnet *vnet;
42 uint8_t ip[IPV6_MASK_SIZE];
43 };
44
45 struct ratelimit_entry {
46 LIST_ENTRY(ratelimit_entry) r_entry;
47 struct ratelimit_key r_key;
48 sbintime_t r_last_time; /* sbinuptime */
49 uint64_t r_tokens;
50 };
51
52 struct ratelimit {
53 uint8_t rl_secret[SIPHASH_KEY_LENGTH];
54 struct mtx rl_mtx;
55 struct callout rl_gc;
56 LIST_HEAD(, ratelimit_entry) rl_table[RATELIMIT_SIZE];
57 size_t rl_table_num;
58 bool rl_initialized;
59 };
60
61 static void precompute_key(uint8_t *,
62 const uint8_t[COOKIE_INPUT_SIZE], const char *);
63 static void macs_mac1(struct cookie_macs *, const void *, size_t,
64 const uint8_t[COOKIE_KEY_SIZE]);
65 static void macs_mac2(struct cookie_macs *, const void *, size_t,
66 const uint8_t[COOKIE_COOKIE_SIZE]);
67 static int timer_expired(sbintime_t, uint32_t, uint32_t);
68 static void make_cookie(struct cookie_checker *,
69 uint8_t[COOKIE_COOKIE_SIZE], struct sockaddr *);
70 static void ratelimit_init(struct ratelimit *);
71 static void ratelimit_deinit(struct ratelimit *);
72 static void ratelimit_gc_callout(void *);
73 static void ratelimit_gc_schedule(struct ratelimit *);
74 static void ratelimit_gc(struct ratelimit *, bool);
75 static int ratelimit_allow(struct ratelimit *, struct sockaddr *, struct vnet *);
76 static uint64_t siphash13(const uint8_t [SIPHASH_KEY_LENGTH], const void *, size_t);
77
78 static struct ratelimit ratelimit_v4;
79 #ifdef INET6
80 static struct ratelimit ratelimit_v6;
81 #endif
82 static uma_zone_t ratelimit_zone;
83
84 /* Public Functions */
85 int
cookie_init(void)86 cookie_init(void)
87 {
88 ratelimit_zone = uma_zcreate("wg ratelimit",
89 sizeof(struct ratelimit_entry), NULL, NULL, NULL, NULL, 0, 0);
90
91 ratelimit_init(&ratelimit_v4);
92 #ifdef INET6
93 ratelimit_init(&ratelimit_v6);
94 #endif
95 return (0);
96 }
97
98 void
cookie_deinit(void)99 cookie_deinit(void)
100 {
101 ratelimit_deinit(&ratelimit_v4);
102 #ifdef INET6
103 ratelimit_deinit(&ratelimit_v6);
104 #endif
105 if (ratelimit_zone != NULL)
106 uma_zdestroy(ratelimit_zone);
107 }
108
109 void
cookie_checker_init(struct cookie_checker * cc)110 cookie_checker_init(struct cookie_checker *cc)
111 {
112 bzero(cc, sizeof(*cc));
113
114 rw_init(&cc->cc_key_lock, "cookie_checker_key");
115 mtx_init(&cc->cc_secret_mtx, "cookie_checker_secret", NULL, MTX_DEF);
116 }
117
118 void
cookie_checker_free(struct cookie_checker * cc)119 cookie_checker_free(struct cookie_checker *cc)
120 {
121 rw_destroy(&cc->cc_key_lock);
122 mtx_destroy(&cc->cc_secret_mtx);
123 explicit_bzero(cc, sizeof(*cc));
124 }
125
126 void
cookie_checker_update(struct cookie_checker * cc,const uint8_t key[COOKIE_INPUT_SIZE])127 cookie_checker_update(struct cookie_checker *cc,
128 const uint8_t key[COOKIE_INPUT_SIZE])
129 {
130 rw_wlock(&cc->cc_key_lock);
131 if (key) {
132 precompute_key(cc->cc_mac1_key, key, COOKIE_MAC1_KEY_LABEL);
133 precompute_key(cc->cc_cookie_key, key, COOKIE_COOKIE_KEY_LABEL);
134 } else {
135 bzero(cc->cc_mac1_key, sizeof(cc->cc_mac1_key));
136 bzero(cc->cc_cookie_key, sizeof(cc->cc_cookie_key));
137 }
138 rw_wunlock(&cc->cc_key_lock);
139 }
140
141 void
cookie_checker_create_payload(struct cookie_checker * cc,struct cookie_macs * macs,uint8_t nonce[COOKIE_NONCE_SIZE],uint8_t ecookie[COOKIE_ENCRYPTED_SIZE],struct sockaddr * sa)142 cookie_checker_create_payload(struct cookie_checker *cc,
143 struct cookie_macs *macs, uint8_t nonce[COOKIE_NONCE_SIZE],
144 uint8_t ecookie[COOKIE_ENCRYPTED_SIZE], struct sockaddr *sa)
145 {
146 uint8_t cookie[COOKIE_COOKIE_SIZE];
147
148 make_cookie(cc, cookie, sa);
149 arc4random_buf(nonce, COOKIE_NONCE_SIZE);
150
151 rw_rlock(&cc->cc_key_lock);
152 xchacha20poly1305_encrypt(ecookie, cookie, COOKIE_COOKIE_SIZE,
153 macs->mac1, COOKIE_MAC_SIZE, nonce, cc->cc_cookie_key);
154 rw_runlock(&cc->cc_key_lock);
155
156 explicit_bzero(cookie, sizeof(cookie));
157 }
158
159 void
cookie_maker_init(struct cookie_maker * cm,const uint8_t key[COOKIE_INPUT_SIZE])160 cookie_maker_init(struct cookie_maker *cm, const uint8_t key[COOKIE_INPUT_SIZE])
161 {
162 bzero(cm, sizeof(*cm));
163 precompute_key(cm->cm_mac1_key, key, COOKIE_MAC1_KEY_LABEL);
164 precompute_key(cm->cm_cookie_key, key, COOKIE_COOKIE_KEY_LABEL);
165 rw_init(&cm->cm_lock, "cookie_maker");
166 }
167
168 void
cookie_maker_free(struct cookie_maker * cm)169 cookie_maker_free(struct cookie_maker *cm)
170 {
171 rw_destroy(&cm->cm_lock);
172 explicit_bzero(cm, sizeof(*cm));
173 }
174
175 int
cookie_maker_consume_payload(struct cookie_maker * cm,uint8_t nonce[COOKIE_NONCE_SIZE],uint8_t ecookie[COOKIE_ENCRYPTED_SIZE])176 cookie_maker_consume_payload(struct cookie_maker *cm,
177 uint8_t nonce[COOKIE_NONCE_SIZE], uint8_t ecookie[COOKIE_ENCRYPTED_SIZE])
178 {
179 uint8_t cookie[COOKIE_COOKIE_SIZE];
180 int ret;
181
182 rw_rlock(&cm->cm_lock);
183 if (!cm->cm_mac1_sent) {
184 ret = ETIMEDOUT;
185 goto error;
186 }
187
188 if (!xchacha20poly1305_decrypt(cookie, ecookie, COOKIE_ENCRYPTED_SIZE,
189 cm->cm_mac1_last, COOKIE_MAC_SIZE, nonce, cm->cm_cookie_key)) {
190 ret = EINVAL;
191 goto error;
192 }
193 rw_runlock(&cm->cm_lock);
194
195 rw_wlock(&cm->cm_lock);
196 memcpy(cm->cm_cookie, cookie, COOKIE_COOKIE_SIZE);
197 cm->cm_cookie_birthdate = getsbinuptime();
198 cm->cm_cookie_valid = true;
199 cm->cm_mac1_sent = false;
200 rw_wunlock(&cm->cm_lock);
201
202 return 0;
203 error:
204 rw_runlock(&cm->cm_lock);
205 return ret;
206 }
207
208 void
cookie_maker_mac(struct cookie_maker * cm,struct cookie_macs * macs,void * buf,size_t len)209 cookie_maker_mac(struct cookie_maker *cm, struct cookie_macs *macs, void *buf,
210 size_t len)
211 {
212 rw_wlock(&cm->cm_lock);
213 macs_mac1(macs, buf, len, cm->cm_mac1_key);
214 memcpy(cm->cm_mac1_last, macs->mac1, COOKIE_MAC_SIZE);
215 cm->cm_mac1_sent = true;
216
217 if (cm->cm_cookie_valid &&
218 !timer_expired(cm->cm_cookie_birthdate,
219 COOKIE_SECRET_MAX_AGE - COOKIE_SECRET_LATENCY, 0)) {
220 macs_mac2(macs, buf, len, cm->cm_cookie);
221 } else {
222 bzero(macs->mac2, COOKIE_MAC_SIZE);
223 cm->cm_cookie_valid = false;
224 }
225 rw_wunlock(&cm->cm_lock);
226 }
227
228 int
cookie_checker_validate_macs(struct cookie_checker * cc,struct cookie_macs * macs,void * buf,size_t len,bool check_cookie,struct sockaddr * sa,struct vnet * vnet)229 cookie_checker_validate_macs(struct cookie_checker *cc, struct cookie_macs *macs,
230 void *buf, size_t len, bool check_cookie, struct sockaddr *sa, struct vnet *vnet)
231 {
232 struct cookie_macs our_macs;
233 uint8_t cookie[COOKIE_COOKIE_SIZE];
234
235 /* Validate incoming MACs */
236 rw_rlock(&cc->cc_key_lock);
237 macs_mac1(&our_macs, buf, len, cc->cc_mac1_key);
238 rw_runlock(&cc->cc_key_lock);
239
240 /* If mac1 is invald, we want to drop the packet */
241 if (timingsafe_bcmp(our_macs.mac1, macs->mac1, COOKIE_MAC_SIZE) != 0)
242 return EINVAL;
243
244 if (check_cookie) {
245 make_cookie(cc, cookie, sa);
246 macs_mac2(&our_macs, buf, len, cookie);
247
248 /* If the mac2 is invalid, we want to send a cookie response */
249 if (timingsafe_bcmp(our_macs.mac2, macs->mac2, COOKIE_MAC_SIZE) != 0)
250 return EAGAIN;
251
252 /* If the mac2 is valid, we may want rate limit the peer.
253 * ratelimit_allow will return either 0 or ECONNREFUSED,
254 * implying there is no ratelimiting, or we should ratelimit
255 * (refuse) respectively. */
256 if (sa->sa_family == AF_INET)
257 return ratelimit_allow(&ratelimit_v4, sa, vnet);
258 #ifdef INET6
259 else if (sa->sa_family == AF_INET6)
260 return ratelimit_allow(&ratelimit_v6, sa, vnet);
261 #endif
262 else
263 return EAFNOSUPPORT;
264 }
265
266 return 0;
267 }
268
269 /* Private functions */
270 static void
precompute_key(uint8_t * key,const uint8_t input[COOKIE_INPUT_SIZE],const char * label)271 precompute_key(uint8_t *key, const uint8_t input[COOKIE_INPUT_SIZE],
272 const char *label)
273 {
274 struct blake2s_state blake;
275 blake2s_init(&blake, COOKIE_KEY_SIZE);
276 blake2s_update(&blake, label, strlen(label));
277 blake2s_update(&blake, input, COOKIE_INPUT_SIZE);
278 blake2s_final(&blake, key);
279 }
280
281 static void
macs_mac1(struct cookie_macs * macs,const void * buf,size_t len,const uint8_t key[COOKIE_KEY_SIZE])282 macs_mac1(struct cookie_macs *macs, const void *buf, size_t len,
283 const uint8_t key[COOKIE_KEY_SIZE])
284 {
285 struct blake2s_state state;
286 blake2s_init_key(&state, COOKIE_MAC_SIZE, key, COOKIE_KEY_SIZE);
287 blake2s_update(&state, buf, len);
288 blake2s_final(&state, macs->mac1);
289 }
290
291 static void
macs_mac2(struct cookie_macs * macs,const void * buf,size_t len,const uint8_t key[COOKIE_COOKIE_SIZE])292 macs_mac2(struct cookie_macs *macs, const void *buf, size_t len,
293 const uint8_t key[COOKIE_COOKIE_SIZE])
294 {
295 struct blake2s_state state;
296 blake2s_init_key(&state, COOKIE_MAC_SIZE, key, COOKIE_COOKIE_SIZE);
297 blake2s_update(&state, buf, len);
298 blake2s_update(&state, macs->mac1, COOKIE_MAC_SIZE);
299 blake2s_final(&state, macs->mac2);
300 }
301
302 static __inline int
timer_expired(sbintime_t timer,uint32_t sec,uint32_t nsec)303 timer_expired(sbintime_t timer, uint32_t sec, uint32_t nsec)
304 {
305 sbintime_t now = getsbinuptime();
306 return (now > (timer + sec * SBT_1S + nstosbt(nsec))) ? ETIMEDOUT : 0;
307 }
308
309 static void
make_cookie(struct cookie_checker * cc,uint8_t cookie[COOKIE_COOKIE_SIZE],struct sockaddr * sa)310 make_cookie(struct cookie_checker *cc, uint8_t cookie[COOKIE_COOKIE_SIZE],
311 struct sockaddr *sa)
312 {
313 struct blake2s_state state;
314
315 mtx_lock(&cc->cc_secret_mtx);
316 if (timer_expired(cc->cc_secret_birthdate,
317 COOKIE_SECRET_MAX_AGE, 0)) {
318 arc4random_buf(cc->cc_secret, COOKIE_SECRET_SIZE);
319 cc->cc_secret_birthdate = getsbinuptime();
320 }
321 blake2s_init_key(&state, COOKIE_COOKIE_SIZE, cc->cc_secret,
322 COOKIE_SECRET_SIZE);
323 mtx_unlock(&cc->cc_secret_mtx);
324
325 if (sa->sa_family == AF_INET) {
326 blake2s_update(&state, (uint8_t *)&satosin(sa)->sin_addr,
327 sizeof(struct in_addr));
328 blake2s_update(&state, (uint8_t *)&satosin(sa)->sin_port,
329 sizeof(in_port_t));
330 blake2s_final(&state, cookie);
331 #ifdef INET6
332 } else if (sa->sa_family == AF_INET6) {
333 blake2s_update(&state, (uint8_t *)&satosin6(sa)->sin6_addr,
334 sizeof(struct in6_addr));
335 blake2s_update(&state, (uint8_t *)&satosin6(sa)->sin6_port,
336 sizeof(in_port_t));
337 blake2s_final(&state, cookie);
338 #endif
339 } else {
340 arc4random_buf(cookie, COOKIE_COOKIE_SIZE);
341 }
342 }
343
344 static void
ratelimit_init(struct ratelimit * rl)345 ratelimit_init(struct ratelimit *rl)
346 {
347 size_t i;
348 mtx_init(&rl->rl_mtx, "ratelimit_lock", NULL, MTX_DEF);
349 callout_init_mtx(&rl->rl_gc, &rl->rl_mtx, 0);
350 arc4random_buf(rl->rl_secret, sizeof(rl->rl_secret));
351 for (i = 0; i < RATELIMIT_SIZE; i++)
352 LIST_INIT(&rl->rl_table[i]);
353 rl->rl_table_num = 0;
354 rl->rl_initialized = true;
355 }
356
357 static void
ratelimit_deinit(struct ratelimit * rl)358 ratelimit_deinit(struct ratelimit *rl)
359 {
360 if (!rl->rl_initialized)
361 return;
362 mtx_lock(&rl->rl_mtx);
363 callout_stop(&rl->rl_gc);
364 ratelimit_gc(rl, true);
365 mtx_unlock(&rl->rl_mtx);
366 mtx_destroy(&rl->rl_mtx);
367
368 rl->rl_initialized = false;
369 }
370
371 static void
ratelimit_gc_callout(void * _rl)372 ratelimit_gc_callout(void *_rl)
373 {
374 /* callout will lock rl_mtx for us */
375 ratelimit_gc(_rl, false);
376 }
377
378 static void
ratelimit_gc_schedule(struct ratelimit * rl)379 ratelimit_gc_schedule(struct ratelimit *rl)
380 {
381 /* Trigger another GC if needed. There is no point calling GC if there
382 * are no entries in the table. We also want to ensure that GC occurs
383 * on a regular interval, so don't override a currently pending GC.
384 *
385 * In the case of a forced ratelimit_gc, there will be no entries left
386 * so we will will not schedule another GC. */
387 if (rl->rl_table_num > 0 && !callout_pending(&rl->rl_gc))
388 callout_reset(&rl->rl_gc, ELEMENT_TIMEOUT * hz,
389 ratelimit_gc_callout, rl);
390 }
391
392 static void
ratelimit_gc(struct ratelimit * rl,bool force)393 ratelimit_gc(struct ratelimit *rl, bool force)
394 {
395 size_t i;
396 struct ratelimit_entry *r, *tr;
397 sbintime_t expiry;
398
399 mtx_assert(&rl->rl_mtx, MA_OWNED);
400
401 if (rl->rl_table_num == 0)
402 return;
403
404 expiry = getsbinuptime() - ELEMENT_TIMEOUT * SBT_1S;
405
406 for (i = 0; i < RATELIMIT_SIZE; i++) {
407 LIST_FOREACH_SAFE(r, &rl->rl_table[i], r_entry, tr) {
408 if (r->r_last_time < expiry || force) {
409 rl->rl_table_num--;
410 LIST_REMOVE(r, r_entry);
411 uma_zfree(ratelimit_zone, r);
412 }
413 }
414 }
415
416 ratelimit_gc_schedule(rl);
417 }
418
419 static int
ratelimit_allow(struct ratelimit * rl,struct sockaddr * sa,struct vnet * vnet)420 ratelimit_allow(struct ratelimit *rl, struct sockaddr *sa, struct vnet *vnet)
421 {
422 uint64_t bucket, tokens;
423 sbintime_t diff, now;
424 struct ratelimit_entry *r;
425 int ret = ECONNREFUSED;
426 struct ratelimit_key key = { .vnet = vnet };
427 size_t len = sizeof(key);
428
429 if (sa->sa_family == AF_INET) {
430 memcpy(key.ip, &satosin(sa)->sin_addr, IPV4_MASK_SIZE);
431 len -= IPV6_MASK_SIZE - IPV4_MASK_SIZE;
432 }
433 #ifdef INET6
434 else if (sa->sa_family == AF_INET6)
435 memcpy(key.ip, &satosin6(sa)->sin6_addr, IPV6_MASK_SIZE);
436 #endif
437 else
438 return ret;
439
440 bucket = siphash13(rl->rl_secret, &key, len) & RATELIMIT_MASK;
441 mtx_lock(&rl->rl_mtx);
442
443 LIST_FOREACH(r, &rl->rl_table[bucket], r_entry) {
444 if (bcmp(&r->r_key, &key, len) != 0)
445 continue;
446
447 /* If we get to here, we've found an entry for the endpoint.
448 * We apply standard token bucket, by calculating the time
449 * lapsed since our last_time, adding that, ensuring that we
450 * cap the tokens at TOKEN_MAX. If the endpoint has no tokens
451 * left (that is tokens <= INITIATION_COST) then we block the
452 * request, otherwise we subtract the INITITIATION_COST and
453 * return OK. */
454 now = getsbinuptime();
455 diff = now - r->r_last_time;
456 r->r_last_time = now;
457
458 tokens = r->r_tokens + diff;
459
460 if (tokens > TOKEN_MAX)
461 tokens = TOKEN_MAX;
462
463 if (tokens >= INITIATION_COST) {
464 r->r_tokens = tokens - INITIATION_COST;
465 goto ok;
466 } else {
467 r->r_tokens = tokens;
468 goto error;
469 }
470 }
471
472 /* If we get to here, we didn't have an entry for the endpoint, let's
473 * add one if we have space. */
474 if (rl->rl_table_num >= RATELIMIT_SIZE_MAX)
475 goto error;
476
477 /* Goto error if out of memory */
478 if ((r = uma_zalloc(ratelimit_zone, M_NOWAIT | M_ZERO)) == NULL)
479 goto error;
480
481 rl->rl_table_num++;
482
483 /* Insert entry into the hashtable and ensure it's initialised */
484 LIST_INSERT_HEAD(&rl->rl_table[bucket], r, r_entry);
485 r->r_key = key;
486 r->r_last_time = getsbinuptime();
487 r->r_tokens = TOKEN_MAX - INITIATION_COST;
488
489 /* If we've added a new entry, let's trigger GC. */
490 ratelimit_gc_schedule(rl);
491 ok:
492 ret = 0;
493 error:
494 mtx_unlock(&rl->rl_mtx);
495 return ret;
496 }
497
siphash13(const uint8_t key[SIPHASH_KEY_LENGTH],const void * src,size_t len)498 static uint64_t siphash13(const uint8_t key[SIPHASH_KEY_LENGTH], const void *src, size_t len)
499 {
500 SIPHASH_CTX ctx;
501 return (SipHashX(&ctx, 1, 3, key, src, len));
502 }
503
504 #ifdef SELFTESTS
505 #include "selftest/cookie.c"
506 #endif /* SELFTESTS */
507