1 /* $OpenBSD: ssh_api.c,v 1.28 2024/01/09 21:39:14 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 *, const char *, u_int);
58
59 #ifdef WITH_OPENSSL
60 DH *mm_choose_dh(int, int, int);
61 #endif
62
63 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,const char * sk_pin,u_int compat)64 mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp,
65 const u_char *data, u_int datalen, const char *alg,
66 const char *sk_provider, const char *sk_pin, u_int compat)
67 {
68 return (-1);
69 }
70
71 #ifdef WITH_OPENSSL
72 DH *
mm_choose_dh(int min,int nbits,int max)73 mm_choose_dh(int min, int nbits, int max)
74 {
75 return (NULL);
76 }
77 #endif
78
79 /* API */
80
81 int
ssh_init(struct ssh ** sshp,int is_server,struct kex_params * kex_params)82 ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params)
83 {
84 char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
85 char *populated[PROPOSAL_MAX];
86 struct ssh *ssh;
87 char **proposal;
88 static int called;
89 int r;
90
91 if (!called) {
92 seed_rng();
93 called = 1;
94 }
95
96 if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL)
97 return SSH_ERR_ALLOC_FAIL;
98 if (is_server)
99 ssh_packet_set_server(ssh);
100
101 /* Initialize key exchange */
102 proposal = kex_params ? kex_params->proposal : myproposal;
103 kex_proposal_populate_entries(ssh, populated,
104 proposal[PROPOSAL_KEX_ALGS],
105 proposal[PROPOSAL_ENC_ALGS_CTOS],
106 proposal[PROPOSAL_MAC_ALGS_CTOS],
107 proposal[PROPOSAL_COMP_ALGS_CTOS],
108 proposal[PROPOSAL_SERVER_HOST_KEY_ALGS]);
109 r = kex_ready(ssh, populated);
110 kex_proposal_free_entries(populated);
111 if (r != 0) {
112 ssh_free(ssh);
113 return r;
114 }
115
116 ssh->kex->server = is_server;
117 if (is_server) {
118 #ifdef WITH_OPENSSL
119 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server;
120 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server;
121 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server;
122 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server;
123 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server;
124 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
125 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
126 # ifdef OPENSSL_HAS_ECC
127 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server;
128 # endif
129 #endif /* WITH_OPENSSL */
130 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server;
131 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_server;
132 ssh->kex->load_host_public_key=&_ssh_host_public_key;
133 ssh->kex->load_host_private_key=&_ssh_host_private_key;
134 ssh->kex->sign=&_ssh_host_key_sign;
135 } else {
136 #ifdef WITH_OPENSSL
137 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client;
138 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client;
139 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client;
140 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client;
141 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client;
142 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
143 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
144 # ifdef OPENSSL_HAS_ECC
145 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
146 # endif
147 #endif /* WITH_OPENSSL */
148 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
149 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client;
150 ssh->kex->verify_host_key =&_ssh_verify_host_key;
151 }
152 *sshp = ssh;
153 return 0;
154 }
155
156 void
ssh_free(struct ssh * ssh)157 ssh_free(struct ssh *ssh)
158 {
159 struct key_entry *k;
160
161 if (ssh == NULL)
162 return;
163
164 /*
165 * we've only created the public keys variants in case we
166 * are a acting as a server.
167 */
168 while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
169 TAILQ_REMOVE(&ssh->public_keys, k, next);
170 if (ssh->kex && ssh->kex->server)
171 sshkey_free(k->key);
172 free(k);
173 }
174 while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
175 TAILQ_REMOVE(&ssh->private_keys, k, next);
176 free(k);
177 }
178 ssh_packet_close(ssh);
179 free(ssh);
180 }
181
182 void
ssh_set_app_data(struct ssh * ssh,void * app_data)183 ssh_set_app_data(struct ssh *ssh, void *app_data)
184 {
185 ssh->app_data = app_data;
186 }
187
188 void *
ssh_get_app_data(struct ssh * ssh)189 ssh_get_app_data(struct ssh *ssh)
190 {
191 return ssh->app_data;
192 }
193
194 /* Returns < 0 on error, 0 otherwise */
195 int
ssh_add_hostkey(struct ssh * ssh,struct sshkey * key)196 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
197 {
198 struct sshkey *pubkey = NULL;
199 struct key_entry *k = NULL, *k_prv = NULL;
200 int r;
201
202 if (ssh->kex->server) {
203 if ((r = sshkey_from_private(key, &pubkey)) != 0)
204 return r;
205 if ((k = malloc(sizeof(*k))) == NULL ||
206 (k_prv = malloc(sizeof(*k_prv))) == NULL) {
207 free(k);
208 sshkey_free(pubkey);
209 return SSH_ERR_ALLOC_FAIL;
210 }
211 k_prv->key = key;
212 TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
213
214 /* add the public key, too */
215 k->key = pubkey;
216 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
217 r = 0;
218 } else {
219 if ((k = malloc(sizeof(*k))) == NULL)
220 return SSH_ERR_ALLOC_FAIL;
221 k->key = key;
222 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
223 r = 0;
224 }
225
226 return r;
227 }
228
229 int
ssh_set_verify_host_key_callback(struct ssh * ssh,int (* cb)(struct sshkey *,struct ssh *))230 ssh_set_verify_host_key_callback(struct ssh *ssh,
231 int (*cb)(struct sshkey *, struct ssh *))
232 {
233 if (cb == NULL || ssh->kex == NULL)
234 return SSH_ERR_INVALID_ARGUMENT;
235
236 ssh->kex->verify_host_key = cb;
237
238 return 0;
239 }
240
241 int
ssh_input_append(struct ssh * ssh,const u_char * data,size_t len)242 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
243 {
244 return sshbuf_put(ssh_packet_get_input(ssh), data, len);
245 }
246
247 int
ssh_packet_next(struct ssh * ssh,u_char * typep)248 ssh_packet_next(struct ssh *ssh, u_char *typep)
249 {
250 int r;
251 u_int32_t seqnr;
252 u_char type;
253
254 /*
255 * Try to read a packet. Return SSH_MSG_NONE if no packet or not
256 * enough data.
257 */
258 *typep = SSH_MSG_NONE;
259 if (sshbuf_len(ssh->kex->client_version) == 0 ||
260 sshbuf_len(ssh->kex->server_version) == 0)
261 return _ssh_exchange_banner(ssh);
262 /*
263 * If we enough data and a dispatch function then
264 * call the function and get the next packet.
265 * Otherwise return the packet type to the caller so it
266 * can decide how to go on.
267 *
268 * We will only call the dispatch function for:
269 * 20-29 Algorithm negotiation
270 * 30-49 Key exchange method specific (numbers can be reused for
271 * different authentication methods)
272 */
273 for (;;) {
274 if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
275 return r;
276 if (type > 0 && type < DISPATCH_MAX &&
277 type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
278 ssh->dispatch[type] != NULL) {
279 if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
280 return r;
281 } else {
282 *typep = type;
283 return 0;
284 }
285 }
286 }
287
288 const u_char *
ssh_packet_payload(struct ssh * ssh,size_t * lenp)289 ssh_packet_payload(struct ssh *ssh, size_t *lenp)
290 {
291 return sshpkt_ptr(ssh, lenp);
292 }
293
294 int
ssh_packet_put(struct ssh * ssh,int type,const u_char * data,size_t len)295 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
296 {
297 int r;
298
299 if ((r = sshpkt_start(ssh, type)) != 0 ||
300 (r = sshpkt_put(ssh, data, len)) != 0 ||
301 (r = sshpkt_send(ssh)) != 0)
302 return r;
303 return 0;
304 }
305
306 const u_char *
ssh_output_ptr(struct ssh * ssh,size_t * len)307 ssh_output_ptr(struct ssh *ssh, size_t *len)
308 {
309 struct sshbuf *output = ssh_packet_get_output(ssh);
310
311 *len = sshbuf_len(output);
312 return sshbuf_ptr(output);
313 }
314
315 int
ssh_output_consume(struct ssh * ssh,size_t len)316 ssh_output_consume(struct ssh *ssh, size_t len)
317 {
318 return sshbuf_consume(ssh_packet_get_output(ssh), len);
319 }
320
321 int
ssh_output_space(struct ssh * ssh,size_t len)322 ssh_output_space(struct ssh *ssh, size_t len)
323 {
324 return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
325 }
326
327 int
ssh_input_space(struct ssh * ssh,size_t len)328 ssh_input_space(struct ssh *ssh, size_t len)
329 {
330 return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
331 }
332
333 /* Read other side's version identification. */
334 int
_ssh_read_banner(struct ssh * ssh,struct sshbuf * banner)335 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner)
336 {
337 struct sshbuf *input = ssh_packet_get_input(ssh);
338 const char *mismatch = "Protocol mismatch.\r\n";
339 const u_char *s = sshbuf_ptr(input);
340 u_char c;
341 char *cp = NULL, *remote_version = NULL;
342 int r = 0, remote_major, remote_minor, expect_nl;
343 size_t n, j;
344
345 for (j = n = 0;;) {
346 sshbuf_reset(banner);
347 expect_nl = 0;
348 for (;;) {
349 if (j >= sshbuf_len(input))
350 return 0; /* insufficient data in input buf */
351 c = s[j++];
352 if (c == '\r') {
353 expect_nl = 1;
354 continue;
355 }
356 if (c == '\n')
357 break;
358 if (expect_nl)
359 goto bad;
360 if ((r = sshbuf_put_u8(banner, c)) != 0)
361 return r;
362 if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN)
363 goto bad;
364 }
365 if (sshbuf_len(banner) >= 4 &&
366 memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0)
367 break;
368 debug_f("%.*s", (int)sshbuf_len(banner),
369 sshbuf_ptr(banner));
370 /* Accept lines before banner only on client */
371 if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) {
372 bad:
373 if ((r = sshbuf_put(ssh_packet_get_output(ssh),
374 mismatch, strlen(mismatch))) != 0)
375 return r;
376 return SSH_ERR_NO_PROTOCOL_VERSION;
377 }
378 }
379 if ((r = sshbuf_consume(input, j)) != 0)
380 return r;
381
382 /* XXX remote version must be the same size as banner for sscanf */
383 if ((cp = sshbuf_dup_string(banner)) == NULL ||
384 (remote_version = calloc(1, sshbuf_len(banner))) == NULL) {
385 r = SSH_ERR_ALLOC_FAIL;
386 goto out;
387 }
388
389 /*
390 * Check that the versions match. In future this might accept
391 * several versions and set appropriate flags to handle them.
392 */
393 if (sscanf(cp, "SSH-%d.%d-%[^\n]\n",
394 &remote_major, &remote_minor, remote_version) != 3) {
395 r = SSH_ERR_INVALID_FORMAT;
396 goto out;
397 }
398 debug("Remote protocol version %d.%d, remote software version %.100s",
399 remote_major, remote_minor, remote_version);
400
401 compat_banner(ssh, remote_version);
402 if (remote_major == 1 && remote_minor == 99) {
403 remote_major = 2;
404 remote_minor = 0;
405 }
406 if (remote_major != 2)
407 r = SSH_ERR_PROTOCOL_MISMATCH;
408
409 debug("Remote version string %.100s", cp);
410 out:
411 free(cp);
412 free(remote_version);
413 return r;
414 }
415
416 /* Send our own protocol version identification. */
417 int
_ssh_send_banner(struct ssh * ssh,struct sshbuf * banner)418 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner)
419 {
420 char *cp;
421 int r;
422
423 if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0)
424 return r;
425 if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0)
426 return r;
427 /* Remove trailing \r\n */
428 if ((r = sshbuf_consume_end(banner, 2)) != 0)
429 return r;
430 if ((cp = sshbuf_dup_string(banner)) == NULL)
431 return SSH_ERR_ALLOC_FAIL;
432 debug("Local version string %.100s", cp);
433 free(cp);
434 return 0;
435 }
436
437 int
_ssh_exchange_banner(struct ssh * ssh)438 _ssh_exchange_banner(struct ssh *ssh)
439 {
440 struct kex *kex = ssh->kex;
441 int r;
442
443 /*
444 * if _ssh_read_banner() cannot parse a full version string
445 * it will return NULL and we end up calling it again.
446 */
447
448 r = 0;
449 if (kex->server) {
450 if (sshbuf_len(ssh->kex->server_version) == 0)
451 r = _ssh_send_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_read_banner(ssh, ssh->kex->client_version);
456 } else {
457 if (sshbuf_len(ssh->kex->server_version) == 0)
458 r = _ssh_read_banner(ssh, ssh->kex->server_version);
459 if (r == 0 &&
460 sshbuf_len(ssh->kex->server_version) != 0 &&
461 sshbuf_len(ssh->kex->client_version) == 0)
462 r = _ssh_send_banner(ssh, ssh->kex->client_version);
463 }
464 if (r != 0)
465 return r;
466 /* start initial kex as soon as we have exchanged the banners */
467 if (sshbuf_len(ssh->kex->server_version) != 0 &&
468 sshbuf_len(ssh->kex->client_version) != 0) {
469 if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
470 (r = kex_send_kexinit(ssh)) != 0)
471 return r;
472 }
473 return 0;
474 }
475
476 struct sshkey *
_ssh_host_public_key(int type,int nid,struct ssh * ssh)477 _ssh_host_public_key(int type, int nid, struct ssh *ssh)
478 {
479 struct key_entry *k;
480
481 debug3_f("need %d", type);
482 TAILQ_FOREACH(k, &ssh->public_keys, next) {
483 debug3_f("check %s", sshkey_type(k->key));
484 if (k->key->type == type &&
485 (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
486 return (k->key);
487 }
488 return (NULL);
489 }
490
491 struct sshkey *
_ssh_host_private_key(int type,int nid,struct ssh * ssh)492 _ssh_host_private_key(int type, int nid, struct ssh *ssh)
493 {
494 struct key_entry *k;
495
496 debug3_f("need %d", type);
497 TAILQ_FOREACH(k, &ssh->private_keys, next) {
498 debug3_f("check %s", sshkey_type(k->key));
499 if (k->key->type == type &&
500 (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
501 return (k->key);
502 }
503 return (NULL);
504 }
505
506 int
_ssh_verify_host_key(struct sshkey * hostkey,struct ssh * ssh)507 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
508 {
509 struct key_entry *k;
510
511 debug3_f("need %s", sshkey_type(hostkey));
512 TAILQ_FOREACH(k, &ssh->public_keys, next) {
513 debug3_f("check %s", sshkey_type(k->key));
514 if (sshkey_equal_public(hostkey, k->key))
515 return (0); /* ok */
516 }
517 return (-1); /* failed */
518 }
519
520 /* offer hostkey algorithms in kexinit depending on registered keys */
521 int
_ssh_order_hostkeyalgs(struct ssh * ssh)522 _ssh_order_hostkeyalgs(struct ssh *ssh)
523 {
524 struct key_entry *k;
525 char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
526 char **proposal;
527 size_t maxlen;
528 int ktype, r;
529
530 /* XXX we de-serialize ssh->kex->my, modify it, and change it */
531 if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
532 return r;
533 orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
534 if ((oavail = avail = strdup(orig)) == NULL) {
535 r = SSH_ERR_ALLOC_FAIL;
536 goto out;
537 }
538 maxlen = strlen(avail) + 1;
539 if ((replace = calloc(1, maxlen)) == NULL) {
540 r = SSH_ERR_ALLOC_FAIL;
541 goto out;
542 }
543 *replace = '\0';
544 while ((alg = strsep(&avail, ",")) && *alg != '\0') {
545 if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
546 continue;
547 TAILQ_FOREACH(k, &ssh->public_keys, next) {
548 if (k->key->type == ktype ||
549 (sshkey_is_cert(k->key) && k->key->type ==
550 sshkey_type_plain(ktype))) {
551 if (*replace != '\0')
552 strlcat(replace, ",", maxlen);
553 strlcat(replace, alg, maxlen);
554 break;
555 }
556 }
557 }
558 if (*replace != '\0') {
559 debug2_f("orig/%d %s", ssh->kex->server, orig);
560 debug2_f("replace/%d %s", ssh->kex->server, replace);
561 free(orig);
562 proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
563 replace = NULL; /* owned by proposal */
564 r = kex_prop2buf(ssh->kex->my, proposal);
565 }
566 out:
567 free(oavail);
568 free(replace);
569 kex_prop_free(proposal);
570 return r;
571 }
572
573 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)574 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey,
575 struct sshkey *pubkey, u_char **signature, size_t *slen,
576 const u_char *data, size_t dlen, const char *alg)
577 {
578 return sshkey_sign(privkey, signature, slen, data, dlen,
579 alg, NULL, NULL, ssh->compat);
580 }
581