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1/* $OpenBSD: ssh_api.c,v 1.33 2025/11/13 10:35:14 dtucker 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 <sys/types.h>
19
20#include <stdio.h>
21#include <stdlib.h>
22
23#include "ssh_api.h"
24#include "compat.h"
25#include "log.h"
26#include "authfile.h"
27#include "sshkey.h"
28#include "dh.h"
29#include "misc.h"
30#include "ssh2.h"
31#include "version.h"
32#include "myproposal.h"
33#include "ssherr.h"
34#include "sshbuf.h"
35
36#include <string.h>
37
38int _ssh_exchange_banner(struct ssh *);
39int _ssh_send_banner(struct ssh *, struct sshbuf *);
40int _ssh_read_banner(struct ssh *, struct sshbuf *);
41int _ssh_order_hostkeyalgs(struct ssh *);
42int _ssh_verify_host_key(struct sshkey *, struct ssh *);
43struct sshkey *_ssh_host_public_key(int, int, struct ssh *);
44struct sshkey *_ssh_host_private_key(int, int, struct ssh *);
45int _ssh_host_key_sign(struct ssh *, struct sshkey *, struct sshkey *,
46 u_char **, size_t *, const u_char *, size_t, const char *);
47
48/*
49 * stubs for privsep calls in the server side implementation of kex.
50 */
51int mm_sshkey_sign(struct sshkey *, u_char **, u_int *,
52 const u_char *, u_int, const char *, const char *, const char *, u_int);
53
54#ifdef WITH_OPENSSL
55DH *mm_choose_dh(int, int, int);
56#endif
57
58int
59mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp,
60 const u_char *data, u_int datalen, const char *alg,
61 const char *sk_provider, const char *sk_pin, u_int compat)
62{
63 size_t slen = 0;
64 int ret;
65
66 ret = sshkey_sign(key, sigp, &slen, data, datalen, alg,
67 sk_provider, sk_pin, compat);
68 *lenp = slen;
69 return ret;
70}
71
72#ifdef WITH_OPENSSL
73DH *
74mm_choose_dh(int min, int nbits, int max)
75{
76 return choose_dh(min, nbits, max);
77}
78#endif
79
80/* API */
81
82int
83ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params)
84{
85 char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
86 char *populated[PROPOSAL_MAX];
87 struct ssh *ssh;
88 char **proposal;
89 static int called;
90 int r;
91
92 if (!called) {
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 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server;
127#endif /* WITH_OPENSSL */
128 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server;
129 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_server;
130 ssh->kex->kex[KEX_KEM_MLKEM768X25519_SHA256] = kex_gen_server;
131 ssh->kex->load_host_public_key=&_ssh_host_public_key;
132 ssh->kex->load_host_private_key=&_ssh_host_private_key;
133 ssh->kex->sign=&_ssh_host_key_sign;
134 } else {
135#ifdef WITH_OPENSSL
136 ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client;
137 ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client;
138 ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client;
139 ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client;
140 ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client;
141 ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
142 ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
143 ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
144#endif /* WITH_OPENSSL */
145 ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
146 ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client;
147 ssh->kex->kex[KEX_KEM_MLKEM768X25519_SHA256] = kex_gen_client;
148 ssh->kex->verify_host_key =&_ssh_verify_host_key;
149 }
150 *sshp = ssh;
151 return 0;
152}
153
154void
155ssh_free(struct ssh *ssh)
156{
157 struct key_entry *k;
158
159 if (ssh == NULL)
160 return;
161
162 /*
163 * we've only created the public keys variants in case we
164 * are a acting as a server.
165 */
166 while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
167 TAILQ_REMOVE(&ssh->public_keys, k, next);
168 if (ssh->kex && ssh->kex->server)
169 sshkey_free(k->key);
170 free(k);
171 }
172 while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
173 TAILQ_REMOVE(&ssh->private_keys, k, next);
174 free(k);
175 }
176 ssh_packet_close(ssh);
177 free(ssh);
178}
179
180void
181ssh_set_app_data(struct ssh *ssh, void *app_data)
182{
183 ssh->app_data = app_data;
184}
185
186void *
187ssh_get_app_data(struct ssh *ssh)
188{
189 return ssh->app_data;
190}
191
192/* Returns < 0 on error, 0 otherwise */
193int
194ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
195{
196 struct sshkey *pubkey = NULL;
197 struct key_entry *k = NULL, *k_prv = NULL;
198 int r;
199
200 if (ssh->kex->server) {
201 if ((r = sshkey_from_private(key, &pubkey)) != 0)
202 return r;
203 if ((k = malloc(sizeof(*k))) == NULL ||
204 (k_prv = malloc(sizeof(*k_prv))) == NULL) {
205 free(k);
206 sshkey_free(pubkey);
207 return SSH_ERR_ALLOC_FAIL;
208 }
209 k_prv->key = key;
210 TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
211
212 /* add the public key, too */
213 k->key = pubkey;
214 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
215 r = 0;
216 } else {
217 if ((k = malloc(sizeof(*k))) == NULL)
218 return SSH_ERR_ALLOC_FAIL;
219 k->key = key;
220 TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
221 r = 0;
222 }
223
224 return r;
225}
226
227int
228ssh_set_verify_host_key_callback(struct ssh *ssh,
229 int (*cb)(struct sshkey *, struct ssh *))
230{
231 if (cb == NULL || ssh->kex == NULL)
232 return SSH_ERR_INVALID_ARGUMENT;
233
234 ssh->kex->verify_host_key = cb;
235
236 return 0;
237}
238
239int
240ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
241{
242 return sshbuf_put(ssh_packet_get_input(ssh), data, len);
243}
244
245int
246ssh_packet_next(struct ssh *ssh, u_char *typep)
247{
248 int r;
249 u_int32_t seqnr;
250 u_char type;
251
252 /*
253 * Try to read a packet. Return SSH_MSG_NONE if no packet or not
254 * enough data.
255 */
256 *typep = SSH_MSG_NONE;
257 if (sshbuf_len(ssh->kex->client_version) == 0 ||
258 sshbuf_len(ssh->kex->server_version) == 0)
259 return _ssh_exchange_banner(ssh);
260 /*
261 * If we enough data and a dispatch function then
262 * call the function and get the next packet.
263 * Otherwise return the packet type to the caller so it
264 * can decide how to go on.
265 *
266 * We will only call the dispatch function for:
267 * 20-29 Algorithm negotiation
268 * 30-49 Key exchange method specific (numbers can be reused for
269 * different authentication methods)
270 */
271 for (;;) {
272 if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
273 return r;
274 if (type > 0 && type < DISPATCH_MAX &&
275 type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
276 ssh->dispatch[type] != NULL) {
277 if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
278 return r;
279 } else {
280 *typep = type;
281 return 0;
282 }
283 }
284}
285
286const u_char *
287ssh_packet_payload(struct ssh *ssh, size_t *lenp)
288{
289 return sshpkt_ptr(ssh, lenp);
290}
291
292int
293ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
294{
295 int r;
296
297 if ((r = sshpkt_start(ssh, type)) != 0 ||
298 (r = sshpkt_put(ssh, data, len)) != 0 ||
299 (r = sshpkt_send(ssh)) != 0)
300 return r;
301 return 0;
302}
303
304const u_char *
305ssh_output_ptr(struct ssh *ssh, size_t *len)
306{
307 struct sshbuf *output = ssh_packet_get_output(ssh);
308
309 *len = sshbuf_len(output);
310 return sshbuf_ptr(output);
311}
312
313int
314ssh_output_consume(struct ssh *ssh, size_t len)
315{
316 return sshbuf_consume(ssh_packet_get_output(ssh), len);
317}
318
319int
320ssh_output_space(struct ssh *ssh, size_t len)
321{
322 return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
323}
324
325int
326ssh_input_space(struct ssh *ssh, size_t len)
327{
328 return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
329}
330
331/* Read other side's version identification. */
332int
333_ssh_read_banner(struct ssh *ssh, struct sshbuf *banner)
334{
335 struct sshbuf *input = ssh_packet_get_input(ssh);
336 const char *mismatch = "Protocol mismatch.\r\n";
337 const u_char *s = sshbuf_ptr(input);
338 u_char c;
339 char *cp = NULL, *remote_version = NULL;
340 int r = 0, remote_major, remote_minor, expect_nl;
341 size_t n, j;
342
343 for (j = n = 0;;) {
344 sshbuf_reset(banner);
345 expect_nl = 0;
346 for (;;) {
347 if (j >= sshbuf_len(input))
348 return 0; /* insufficient data in input buf */
349 c = s[j++];
350 if (c == '\r') {
351 expect_nl = 1;
352 continue;
353 }
354 if (c == '\n')
355 break;
356 if (expect_nl)
357 goto bad;
358 if ((r = sshbuf_put_u8(banner, c)) != 0)
359 return r;
360 if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN)
361 goto bad;
362 }
363 if (sshbuf_len(banner) >= 4 &&
364 memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0)
365 break;
366 debug_f("%.*s", (int)sshbuf_len(banner),
367 sshbuf_ptr(banner));
368 /* Accept lines before banner only on client */
369 if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) {
370 bad:
371 if ((r = sshbuf_put(ssh_packet_get_output(ssh),
372 mismatch, strlen(mismatch))) != 0)
373 return r;
374 return SSH_ERR_NO_PROTOCOL_VERSION;
375 }
376 }
377 if ((r = sshbuf_consume(input, j)) != 0)
378 return r;
379
380 /* XXX remote version must be the same size as banner for sscanf */
381 if ((cp = sshbuf_dup_string(banner)) == NULL ||
382 (remote_version = calloc(1, sshbuf_len(banner))) == NULL) {
383 r = SSH_ERR_ALLOC_FAIL;
384 goto out;
385 }
386
387 /*
388 * Check that the versions match. In future this might accept
389 * several versions and set appropriate flags to handle them.
390 */
391 if (sscanf(cp, "SSH-%d.%d-%[^\n]\n",
392 &remote_major, &remote_minor, remote_version) != 3) {
393 r = SSH_ERR_INVALID_FORMAT;
394 goto out;
395 }
396 debug("Remote protocol version %d.%d, remote software version %.100s",
397 remote_major, remote_minor, remote_version);
398
399 compat_banner(ssh, remote_version);
400 if (remote_major == 1 && remote_minor == 99) {
401 remote_major = 2;
402 remote_minor = 0;
403 }
404 if (remote_major != 2)
405 r = SSH_ERR_PROTOCOL_MISMATCH;
406
407 debug("Remote version string %.100s", cp);
408 out:
409 free(cp);
410 free(remote_version);
411 return r;
412}
413
414/* Send our own protocol version identification. */
415int
416_ssh_send_banner(struct ssh *ssh, struct sshbuf *banner)
417{
418 char *cp;
419 int r;
420
421 if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0)
422 return r;
423 if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0)
424 return r;
425 /* Remove trailing \r\n */
426 if ((r = sshbuf_consume_end(banner, 2)) != 0)
427 return r;
428 if ((cp = sshbuf_dup_string(banner)) == NULL)
429 return SSH_ERR_ALLOC_FAIL;
430 debug("Local version string %.100s", cp);
431 free(cp);
432 return 0;
433}
434
435int
436_ssh_exchange_banner(struct ssh *ssh)
437{
438 struct kex *kex = ssh->kex;
439 int r;
440
441 /*
442 * if _ssh_read_banner() cannot parse a full version string
443 * it will return NULL and we end up calling it again.
444 */
445
446 r = 0;
447 if (kex->server) {
448 if (sshbuf_len(ssh->kex->server_version) == 0)
449 r = _ssh_send_banner(ssh, ssh->kex->server_version);
450 if (r == 0 &&
451 sshbuf_len(ssh->kex->server_version) != 0 &&
452 sshbuf_len(ssh->kex->client_version) == 0)
453 r = _ssh_read_banner(ssh, ssh->kex->client_version);
454 } else {
455 if (sshbuf_len(ssh->kex->server_version) == 0)
456 r = _ssh_read_banner(ssh, ssh->kex->server_version);
457 if (r == 0 &&
458 sshbuf_len(ssh->kex->server_version) != 0 &&
459 sshbuf_len(ssh->kex->client_version) == 0)
460 r = _ssh_send_banner(ssh, ssh->kex->client_version);
461 }
462 if (r != 0)
463 return r;
464 /* start initial kex as soon as we have exchanged the banners */
465 if (sshbuf_len(ssh->kex->server_version) != 0 &&
466 sshbuf_len(ssh->kex->client_version) != 0) {
467 if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
468 (r = kex_send_kexinit(ssh)) != 0)
469 return r;
470 }
471 return 0;
472}
473
474struct sshkey *
475_ssh_host_public_key(int type, int nid, struct ssh *ssh)
476{
477 struct key_entry *k;
478
479 debug3_f("need %d", type);
480 TAILQ_FOREACH(k, &ssh->public_keys, next) {
481 debug3_f("check %s", sshkey_type(k->key));
482 if (k->key->type == type &&
483 (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
484 return (k->key);
485 }
486 return (NULL);
487}
488
489struct sshkey *
490_ssh_host_private_key(int type, int nid, struct ssh *ssh)
491{
492 struct key_entry *k;
493
494 debug3_f("need %d", type);
495 TAILQ_FOREACH(k, &ssh->private_keys, next) {
496 debug3_f("check %s", sshkey_type(k->key));
497 if (k->key->type == type &&
498 (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
499 return (k->key);
500 }
501 return (NULL);
502}
503
504int
505_ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
506{
507 struct key_entry *k;
508
509 debug3_f("need %s", sshkey_type(hostkey));
510 TAILQ_FOREACH(k, &ssh->public_keys, next) {
511 debug3_f("check %s", sshkey_type(k->key));
512 if (sshkey_equal_public(hostkey, k->key))
513 return (0); /* ok */
514 }
515 return (-1); /* failed */
516}
517
518/* offer hostkey algorithms in kexinit depending on registered keys */
519int
520_ssh_order_hostkeyalgs(struct ssh *ssh)
521{
522 struct key_entry *k;
523 char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
524 char **proposal;
525 size_t maxlen;
526 int ktype, nid, r;
527
528 /* XXX we de-serialize ssh->kex->my, modify it, and change it */
529 if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
530 return r;
531 orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
532 if ((oavail = avail = strdup(orig)) == NULL) {
533 r = SSH_ERR_ALLOC_FAIL;
534 goto out;
535 }
536 maxlen = strlen(avail) + 1;
537 if ((replace = calloc(1, maxlen)) == NULL) {
538 r = SSH_ERR_ALLOC_FAIL;
539 goto out;
540 }
541 *replace = '\0';
542 while ((alg = strsep(&avail, ",")) && *alg != '\0') {
543 if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
544 continue;
545 nid = sshkey_ecdsa_nid_from_name(alg);
546 TAILQ_FOREACH(k, &ssh->public_keys, next) {
547 if (k->key->type != ktype &&
548 (!sshkey_is_cert(k->key) ||
549 k->key->type != sshkey_type_plain(ktype)))
550 continue;
551 if (sshkey_type_plain(k->key->type) == KEY_ECDSA &&
552 k->key->ecdsa_nid != nid)
553 continue;
554 /* Candidate */
555 if (*replace != '\0')
556 strlcat(replace, ",", maxlen);
557 strlcat(replace, alg, maxlen);
558 break;
559 }
560 }
561 if (*replace != '\0') {
562 debug2_f("orig/%d %s", ssh->kex->server, orig);
563 debug2_f("replace/%d %s", ssh->kex->server, replace);
564 free(orig);
565 proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
566 replace = NULL; /* owned by proposal */
567 r = kex_prop2buf(ssh->kex->my, proposal);
568 }
569 out:
570 free(oavail);
571 free(replace);
572 kex_prop_free(proposal);
573 return r;
574}
575
576int
577_ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey,
578 struct sshkey *pubkey, u_char **signature, size_t *slen,
579 const u_char *data, size_t dlen, const char *alg)
580{
581 return sshkey_sign(privkey, signature, slen, data, dlen,
582 alg, NULL, NULL, ssh->compat);
583}