1 /* $OpenBSD: ssh_api.c,v 1.19 2019/10/31 21:23:19 djm Exp $ */
2 /*
3 * Copyright (c) 2012 Markus Friedl. All rights reserved.
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18 #include "includes.h"
19
20 #include <sys/types.h>
21
22 #include <stdio.h>
23 #include <stdlib.h>
24
25 #include "ssh_api.h"
26 #include "compat.h"
27 #include "log.h"
28 #include "authfile.h"
29 #include "sshkey.h"
30 #include "misc.h"
31 #include "ssh2.h"
32 #include "version.h"
33 #include "myproposal.h"
34 #include "ssherr.h"
35 #include "sshbuf.h"
36
37 #include "openbsd-compat/openssl-compat.h"
38
39 #include <string.h>
40
41 int _ssh_exchange_banner(struct ssh *);
42 int _ssh_send_banner(struct ssh *, struct sshbuf *);
43 int _ssh_read_banner(struct ssh *, struct sshbuf *);
44 int _ssh_order_hostkeyalgs(struct ssh *);
45 int _ssh_verify_host_key(struct sshkey *, struct ssh *);
46 struct sshkey *_ssh_host_public_key(int, int, struct ssh *);
47 struct sshkey *_ssh_host_private_key(int, int, struct ssh *);
48 int _ssh_host_key_sign(struct ssh *, struct sshkey *, struct sshkey *,
49 u_char **, size_t *, const u_char *, size_t, const char *);
50
51 /*
52 * stubs for the server side implementation of kex.
53 * disable privsep so our stubs will never be called.
54 */
55 int use_privsep = 0;
56 int mm_sshkey_sign(struct sshkey *, u_char **, u_int *,
57 const u_char *, u_int, const char *, const char *, u_int);
58
59 #ifdef WITH_OPENSSL
60 DH *mm_choose_dh(int, int, int);
61 #endif
62
63 /* Define these two variables here so that they are part of the library */
64 u_char *session_id2 = NULL;
65 u_int session_id2_len = 0;
66
67 int
mm_sshkey_sign(struct sshkey * key,u_char ** sigp,u_int * lenp,const u_char * data,u_int datalen,const char * alg,const char * sk_provider,u_int compat)68 mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp,
69 const u_char *data, u_int datalen, const char *alg, const char *sk_provider,
70 u_int compat)
71 {
72 return (-1);
73 }
74
75 #ifdef WITH_OPENSSL
76 DH *
mm_choose_dh(int min,int nbits,int max)77 mm_choose_dh(int min, int nbits, int max)
78 {
79 return (NULL);
80 }
81 #endif
82
83 /* API */
84
85 int
ssh_init(struct ssh ** sshp,int is_server,struct kex_params * kex_params)86 ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params)
87 {
88 char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
89 struct ssh *ssh;
90 char **proposal;
91 static int called;
92 int r;
93
94 if (!called) {
95 seed_rng();
96 called = 1;
97 }
98
99 if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL)
100 return SSH_ERR_ALLOC_FAIL;
101 if (is_server)
102 ssh_packet_set_server(ssh);
103
104 /* Initialize key exchange */
105 proposal = kex_params ? kex_params->proposal : myproposal;
106 if ((r = kex_ready(ssh, proposal)) != 0) {
107 ssh_free(ssh);
108 return r;
109 }
110 ssh->kex->server = is_server;
111 if (is_server) {
112 #ifdef WITH_OPENSSL
113 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server;
114 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server;
115 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server;
116 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server;
117 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server;
118 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
119 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
120 # ifdef OPENSSL_HAS_ECC
121 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server;
122 # endif
123 #endif /* WITH_OPENSSL */
124 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server;
125 ssh->kex->kex[KEX_KEM_SNTRUP4591761X25519_SHA512] = kex_gen_server;
126 ssh->kex->load_host_public_key=&_ssh_host_public_key;
127 ssh->kex->load_host_private_key=&_ssh_host_private_key;
128 ssh->kex->sign=&_ssh_host_key_sign;
129 } else {
130 #ifdef WITH_OPENSSL
131 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client;
132 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client;
133 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client;
134 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client;
135 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client;
136 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
137 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
138 # ifdef OPENSSL_HAS_ECC
139 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
140 # endif
141 #endif /* WITH_OPENSSL */
142 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
143 ssh->kex->kex[KEX_KEM_SNTRUP4591761X25519_SHA512] = kex_gen_client;
144 ssh->kex->verify_host_key =&_ssh_verify_host_key;
145 }
146 *sshp = ssh;
147 return 0;
148 }
149
150 void
ssh_free(struct ssh * ssh)151 ssh_free(struct ssh *ssh)
152 {
153 struct key_entry *k;
154
155 ssh_packet_close(ssh);
156 /*
157 * we've only created the public keys variants in case we
158 * are a acting as a server.
159 */
160 while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
161 TAILQ_REMOVE(&ssh->public_keys, k, next);
162 if (ssh->kex && ssh->kex->server)
163 sshkey_free(k->key);
164 free(k);
165 }
166 while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
167 TAILQ_REMOVE(&ssh->private_keys, k, next);
168 free(k);
169 }
170 if (ssh->kex)
171 kex_free(ssh->kex);
172 free(ssh);
173 }
174
175 void
ssh_set_app_data(struct ssh * ssh,void * app_data)176 ssh_set_app_data(struct ssh *ssh, void *app_data)
177 {
178 ssh->app_data = app_data;
179 }
180
181 void *
ssh_get_app_data(struct ssh * ssh)182 ssh_get_app_data(struct ssh *ssh)
183 {
184 return ssh->app_data;
185 }
186
187 /* Returns < 0 on error, 0 otherwise */
188 int
ssh_add_hostkey(struct ssh * ssh,struct sshkey * key)189 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
190 {
191 struct sshkey *pubkey = NULL;
192 struct key_entry *k = NULL, *k_prv = NULL;
193 int r;
194
195 if (ssh->kex->server) {
196 if ((r = sshkey_from_private(key, &pubkey)) != 0)
197 return r;
198 if ((k = malloc(sizeof(*k))) == NULL ||
199 (k_prv = malloc(sizeof(*k_prv))) == NULL) {
200 free(k);
201 sshkey_free(pubkey);
202 return SSH_ERR_ALLOC_FAIL;
203 }
204 k_prv->key = key;
205 TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
206
207 /* add the public key, too */
208 k->key = pubkey;
209 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
210 r = 0;
211 } else {
212 if ((k = malloc(sizeof(*k))) == NULL)
213 return SSH_ERR_ALLOC_FAIL;
214 k->key = key;
215 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
216 r = 0;
217 }
218
219 return r;
220 }
221
222 int
ssh_set_verify_host_key_callback(struct ssh * ssh,int (* cb)(struct sshkey *,struct ssh *))223 ssh_set_verify_host_key_callback(struct ssh *ssh,
224 int (*cb)(struct sshkey *, struct ssh *))
225 {
226 if (cb == NULL || ssh->kex == NULL)
227 return SSH_ERR_INVALID_ARGUMENT;
228
229 ssh->kex->verify_host_key = cb;
230
231 return 0;
232 }
233
234 int
ssh_input_append(struct ssh * ssh,const u_char * data,size_t len)235 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
236 {
237 return sshbuf_put(ssh_packet_get_input(ssh), data, len);
238 }
239
240 int
ssh_packet_next(struct ssh * ssh,u_char * typep)241 ssh_packet_next(struct ssh *ssh, u_char *typep)
242 {
243 int r;
244 u_int32_t seqnr;
245 u_char type;
246
247 /*
248 * Try to read a packet. Return SSH_MSG_NONE if no packet or not
249 * enough data.
250 */
251 *typep = SSH_MSG_NONE;
252 if (sshbuf_len(ssh->kex->client_version) == 0 ||
253 sshbuf_len(ssh->kex->server_version) == 0)
254 return _ssh_exchange_banner(ssh);
255 /*
256 * If we enough data and a dispatch function then
257 * call the function and get the next packet.
258 * Otherwise return the packet type to the caller so it
259 * can decide how to go on.
260 *
261 * We will only call the dispatch function for:
262 * 20-29 Algorithm negotiation
263 * 30-49 Key exchange method specific (numbers can be reused for
264 * different authentication methods)
265 */
266 for (;;) {
267 if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
268 return r;
269 if (type > 0 && type < DISPATCH_MAX &&
270 type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
271 ssh->dispatch[type] != NULL) {
272 if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
273 return r;
274 } else {
275 *typep = type;
276 return 0;
277 }
278 }
279 }
280
281 const u_char *
ssh_packet_payload(struct ssh * ssh,size_t * lenp)282 ssh_packet_payload(struct ssh *ssh, size_t *lenp)
283 {
284 return sshpkt_ptr(ssh, lenp);
285 }
286
287 int
ssh_packet_put(struct ssh * ssh,int type,const u_char * data,size_t len)288 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
289 {
290 int r;
291
292 if ((r = sshpkt_start(ssh, type)) != 0 ||
293 (r = sshpkt_put(ssh, data, len)) != 0 ||
294 (r = sshpkt_send(ssh)) != 0)
295 return r;
296 return 0;
297 }
298
299 const u_char *
ssh_output_ptr(struct ssh * ssh,size_t * len)300 ssh_output_ptr(struct ssh *ssh, size_t *len)
301 {
302 struct sshbuf *output = ssh_packet_get_output(ssh);
303
304 *len = sshbuf_len(output);
305 return sshbuf_ptr(output);
306 }
307
308 int
ssh_output_consume(struct ssh * ssh,size_t len)309 ssh_output_consume(struct ssh *ssh, size_t len)
310 {
311 return sshbuf_consume(ssh_packet_get_output(ssh), len);
312 }
313
314 int
ssh_output_space(struct ssh * ssh,size_t len)315 ssh_output_space(struct ssh *ssh, size_t len)
316 {
317 return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
318 }
319
320 int
ssh_input_space(struct ssh * ssh,size_t len)321 ssh_input_space(struct ssh *ssh, size_t len)
322 {
323 return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
324 }
325
326 /* Read other side's version identification. */
327 int
_ssh_read_banner(struct ssh * ssh,struct sshbuf * banner)328 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner)
329 {
330 struct sshbuf *input = ssh_packet_get_input(ssh);
331 const char *mismatch = "Protocol mismatch.\r\n";
332 const u_char *s = sshbuf_ptr(input);
333 u_char c;
334 char *cp = NULL, *remote_version = NULL;
335 int r = 0, remote_major, remote_minor, expect_nl;
336 size_t n, j;
337
338 for (j = n = 0;;) {
339 sshbuf_reset(banner);
340 expect_nl = 0;
341 for (;;) {
342 if (j >= sshbuf_len(input))
343 return 0; /* insufficient data in input buf */
344 c = s[j++];
345 if (c == '\r') {
346 expect_nl = 1;
347 continue;
348 }
349 if (c == '\n')
350 break;
351 if (expect_nl)
352 goto bad;
353 if ((r = sshbuf_put_u8(banner, c)) != 0)
354 return r;
355 if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN)
356 goto bad;
357 }
358 if (sshbuf_len(banner) >= 4 &&
359 memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0)
360 break;
361 debug("%s: %.*s", __func__, (int)sshbuf_len(banner),
362 sshbuf_ptr(banner));
363 /* Accept lines before banner only on client */
364 if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) {
365 bad:
366 if ((r = sshbuf_put(ssh_packet_get_output(ssh),
367 mismatch, strlen(mismatch))) != 0)
368 return r;
369 return SSH_ERR_NO_PROTOCOL_VERSION;
370 }
371 }
372 if ((r = sshbuf_consume(input, j)) != 0)
373 return r;
374
375 /* XXX remote version must be the same size as banner for sscanf */
376 if ((cp = sshbuf_dup_string(banner)) == NULL ||
377 (remote_version = calloc(1, sshbuf_len(banner))) == NULL) {
378 r = SSH_ERR_ALLOC_FAIL;
379 goto out;
380 }
381
382 /*
383 * Check that the versions match. In future this might accept
384 * several versions and set appropriate flags to handle them.
385 */
386 if (sscanf(cp, "SSH-%d.%d-%[^\n]\n",
387 &remote_major, &remote_minor, remote_version) != 3) {
388 r = SSH_ERR_INVALID_FORMAT;
389 goto out;
390 }
391 debug("Remote protocol version %d.%d, remote software version %.100s",
392 remote_major, remote_minor, remote_version);
393
394 ssh->compat = compat_datafellows(remote_version);
395 if (remote_major == 1 && remote_minor == 99) {
396 remote_major = 2;
397 remote_minor = 0;
398 }
399 if (remote_major != 2)
400 r = SSH_ERR_PROTOCOL_MISMATCH;
401
402 debug("Remote version string %.100s", cp);
403 out:
404 free(cp);
405 free(remote_version);
406 return r;
407 }
408
409 /* Send our own protocol version identification. */
410 int
_ssh_send_banner(struct ssh * ssh,struct sshbuf * banner)411 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner)
412 {
413 char *cp;
414 int r;
415
416 if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0)
417 return r;
418 if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0)
419 return r;
420 /* Remove trailing \r\n */
421 if ((r = sshbuf_consume_end(banner, 2)) != 0)
422 return r;
423 if ((cp = sshbuf_dup_string(banner)) == NULL)
424 return SSH_ERR_ALLOC_FAIL;
425 debug("Local version string %.100s", cp);
426 free(cp);
427 return 0;
428 }
429
430 int
_ssh_exchange_banner(struct ssh * ssh)431 _ssh_exchange_banner(struct ssh *ssh)
432 {
433 struct kex *kex = ssh->kex;
434 int r;
435
436 /*
437 * if _ssh_read_banner() cannot parse a full version string
438 * it will return NULL and we end up calling it again.
439 */
440
441 r = 0;
442 if (kex->server) {
443 if (sshbuf_len(ssh->kex->server_version) == 0)
444 r = _ssh_send_banner(ssh, ssh->kex->server_version);
445 if (r == 0 &&
446 sshbuf_len(ssh->kex->server_version) != 0 &&
447 sshbuf_len(ssh->kex->client_version) == 0)
448 r = _ssh_read_banner(ssh, ssh->kex->client_version);
449 } else {
450 if (sshbuf_len(ssh->kex->server_version) == 0)
451 r = _ssh_read_banner(ssh, ssh->kex->server_version);
452 if (r == 0 &&
453 sshbuf_len(ssh->kex->server_version) != 0 &&
454 sshbuf_len(ssh->kex->client_version) == 0)
455 r = _ssh_send_banner(ssh, ssh->kex->client_version);
456 }
457 if (r != 0)
458 return r;
459 /* start initial kex as soon as we have exchanged the banners */
460 if (sshbuf_len(ssh->kex->server_version) != 0 &&
461 sshbuf_len(ssh->kex->client_version) != 0) {
462 if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
463 (r = kex_send_kexinit(ssh)) != 0)
464 return r;
465 }
466 return 0;
467 }
468
469 struct sshkey *
_ssh_host_public_key(int type,int nid,struct ssh * ssh)470 _ssh_host_public_key(int type, int nid, struct ssh *ssh)
471 {
472 struct key_entry *k;
473
474 debug3("%s: need %d", __func__, type);
475 TAILQ_FOREACH(k, &ssh->public_keys, next) {
476 debug3("%s: check %s", __func__, sshkey_type(k->key));
477 if (k->key->type == type &&
478 (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
479 return (k->key);
480 }
481 return (NULL);
482 }
483
484 struct sshkey *
_ssh_host_private_key(int type,int nid,struct ssh * ssh)485 _ssh_host_private_key(int type, int nid, struct ssh *ssh)
486 {
487 struct key_entry *k;
488
489 debug3("%s: need %d", __func__, type);
490 TAILQ_FOREACH(k, &ssh->private_keys, next) {
491 debug3("%s: check %s", __func__, sshkey_type(k->key));
492 if (k->key->type == type &&
493 (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
494 return (k->key);
495 }
496 return (NULL);
497 }
498
499 int
_ssh_verify_host_key(struct sshkey * hostkey,struct ssh * ssh)500 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
501 {
502 struct key_entry *k;
503
504 debug3("%s: need %s", __func__, sshkey_type(hostkey));
505 TAILQ_FOREACH(k, &ssh->public_keys, next) {
506 debug3("%s: check %s", __func__, sshkey_type(k->key));
507 if (sshkey_equal_public(hostkey, k->key))
508 return (0); /* ok */
509 }
510 return (-1); /* failed */
511 }
512
513 /* offer hostkey algorithms in kexinit depending on registered keys */
514 int
_ssh_order_hostkeyalgs(struct ssh * ssh)515 _ssh_order_hostkeyalgs(struct ssh *ssh)
516 {
517 struct key_entry *k;
518 char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
519 char **proposal;
520 size_t maxlen;
521 int ktype, r;
522
523 /* XXX we de-serialize ssh->kex->my, modify it, and change it */
524 if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
525 return r;
526 orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
527 if ((oavail = avail = strdup(orig)) == NULL) {
528 r = SSH_ERR_ALLOC_FAIL;
529 goto out;
530 }
531 maxlen = strlen(avail) + 1;
532 if ((replace = calloc(1, maxlen)) == NULL) {
533 r = SSH_ERR_ALLOC_FAIL;
534 goto out;
535 }
536 *replace = '\0';
537 while ((alg = strsep(&avail, ",")) && *alg != '\0') {
538 if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
539 continue;
540 TAILQ_FOREACH(k, &ssh->public_keys, next) {
541 if (k->key->type == ktype ||
542 (sshkey_is_cert(k->key) && k->key->type ==
543 sshkey_type_plain(ktype))) {
544 if (*replace != '\0')
545 strlcat(replace, ",", maxlen);
546 strlcat(replace, alg, maxlen);
547 break;
548 }
549 }
550 }
551 if (*replace != '\0') {
552 debug2("%s: orig/%d %s", __func__, ssh->kex->server, orig);
553 debug2("%s: replace/%d %s", __func__, ssh->kex->server, replace);
554 free(orig);
555 proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
556 replace = NULL; /* owned by proposal */
557 r = kex_prop2buf(ssh->kex->my, proposal);
558 }
559 out:
560 free(oavail);
561 free(replace);
562 kex_prop_free(proposal);
563 return r;
564 }
565
566 int
_ssh_host_key_sign(struct ssh * ssh,struct sshkey * privkey,struct sshkey * pubkey,u_char ** signature,size_t * slen,const u_char * data,size_t dlen,const char * alg)567 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey,
568 struct sshkey *pubkey, u_char **signature, size_t *slen,
569 const u_char *data, size_t dlen, const char *alg)
570 {
571 return sshkey_sign(privkey, signature, slen, data, dlen,
572 alg, NULL, ssh->compat);
573 }
574