xref: /openssh-portable/ssh_api.c (revision 39be3dc2)
1 /* $OpenBSD: ssh_api.c,v 1.26 2021/01/27 10:05:28 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
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 *
73 mm_choose_dh(int min, int nbits, int max)
74 {
75 	return (NULL);
76 }
77 #endif
78 
79 /* API */
80 
81 int
82 ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params)
83 {
84         char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
85 	struct ssh *ssh;
86 	char **proposal;
87 	static int called;
88 	int r;
89 
90 	if (!called) {
91 		seed_rng();
92 		called = 1;
93 	}
94 
95 	if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL)
96 		return SSH_ERR_ALLOC_FAIL;
97 	if (is_server)
98 		ssh_packet_set_server(ssh);
99 
100 	/* Initialize key exchange */
101 	proposal = kex_params ? kex_params->proposal : myproposal;
102 	if ((r = kex_ready(ssh, proposal)) != 0) {
103 		ssh_free(ssh);
104 		return r;
105 	}
106 	ssh->kex->server = is_server;
107 	if (is_server) {
108 #ifdef WITH_OPENSSL
109 		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server;
110 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server;
111 		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server;
112 		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server;
113 		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server;
114 		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
115 		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
116 # ifdef OPENSSL_HAS_ECC
117 		ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server;
118 # endif
119 #endif /* WITH_OPENSSL */
120 		ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server;
121 		ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_server;
122 		ssh->kex->load_host_public_key=&_ssh_host_public_key;
123 		ssh->kex->load_host_private_key=&_ssh_host_private_key;
124 		ssh->kex->sign=&_ssh_host_key_sign;
125 	} else {
126 #ifdef WITH_OPENSSL
127 		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client;
128 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client;
129 		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client;
130 		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client;
131 		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client;
132 		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
133 		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
134 # ifdef OPENSSL_HAS_ECC
135 		ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
136 # endif
137 #endif /* WITH_OPENSSL */
138 		ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
139 		ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client;
140 		ssh->kex->verify_host_key =&_ssh_verify_host_key;
141 	}
142 	*sshp = ssh;
143 	return 0;
144 }
145 
146 void
147 ssh_free(struct ssh *ssh)
148 {
149 	struct key_entry *k;
150 
151 	if (ssh == NULL)
152 		return;
153 
154 	/*
155 	 * we've only created the public keys variants in case we
156 	 * are a acting as a server.
157 	 */
158 	while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
159 		TAILQ_REMOVE(&ssh->public_keys, k, next);
160 		if (ssh->kex && ssh->kex->server)
161 			sshkey_free(k->key);
162 		free(k);
163 	}
164 	while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
165 		TAILQ_REMOVE(&ssh->private_keys, k, next);
166 		free(k);
167 	}
168 	ssh_packet_close(ssh);
169 	free(ssh);
170 }
171 
172 void
173 ssh_set_app_data(struct ssh *ssh, void *app_data)
174 {
175 	ssh->app_data = app_data;
176 }
177 
178 void *
179 ssh_get_app_data(struct ssh *ssh)
180 {
181 	return ssh->app_data;
182 }
183 
184 /* Returns < 0 on error, 0 otherwise */
185 int
186 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
187 {
188 	struct sshkey *pubkey = NULL;
189 	struct key_entry *k = NULL, *k_prv = NULL;
190 	int r;
191 
192 	if (ssh->kex->server) {
193 		if ((r = sshkey_from_private(key, &pubkey)) != 0)
194 			return r;
195 		if ((k = malloc(sizeof(*k))) == NULL ||
196 		    (k_prv = malloc(sizeof(*k_prv))) == NULL) {
197 			free(k);
198 			sshkey_free(pubkey);
199 			return SSH_ERR_ALLOC_FAIL;
200 		}
201 		k_prv->key = key;
202 		TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
203 
204 		/* add the public key, too */
205 		k->key = pubkey;
206 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
207 		r = 0;
208 	} else {
209 		if ((k = malloc(sizeof(*k))) == NULL)
210 			return SSH_ERR_ALLOC_FAIL;
211 		k->key = key;
212 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
213 		r = 0;
214 	}
215 
216 	return r;
217 }
218 
219 int
220 ssh_set_verify_host_key_callback(struct ssh *ssh,
221     int (*cb)(struct sshkey *, struct ssh *))
222 {
223 	if (cb == NULL || ssh->kex == NULL)
224 		return SSH_ERR_INVALID_ARGUMENT;
225 
226 	ssh->kex->verify_host_key = cb;
227 
228 	return 0;
229 }
230 
231 int
232 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
233 {
234 	return sshbuf_put(ssh_packet_get_input(ssh), data, len);
235 }
236 
237 int
238 ssh_packet_next(struct ssh *ssh, u_char *typep)
239 {
240 	int r;
241 	u_int32_t seqnr;
242 	u_char type;
243 
244 	/*
245 	 * Try to read a packet. Return SSH_MSG_NONE if no packet or not
246 	 * enough data.
247 	 */
248 	*typep = SSH_MSG_NONE;
249 	if (sshbuf_len(ssh->kex->client_version) == 0 ||
250 	    sshbuf_len(ssh->kex->server_version) == 0)
251 		return _ssh_exchange_banner(ssh);
252 	/*
253 	 * If we enough data and a dispatch function then
254 	 * call the function and get the next packet.
255 	 * Otherwise return the packet type to the caller so it
256 	 * can decide how to go on.
257 	 *
258 	 * We will only call the dispatch function for:
259 	 *     20-29    Algorithm negotiation
260 	 *     30-49    Key exchange method specific (numbers can be reused for
261 	 *              different authentication methods)
262 	 */
263 	for (;;) {
264 		if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
265 			return r;
266 		if (type > 0 && type < DISPATCH_MAX &&
267 		    type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
268 		    ssh->dispatch[type] != NULL) {
269 			if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
270 				return r;
271 		} else {
272 			*typep = type;
273 			return 0;
274 		}
275 	}
276 }
277 
278 const u_char *
279 ssh_packet_payload(struct ssh *ssh, size_t *lenp)
280 {
281 	return sshpkt_ptr(ssh, lenp);
282 }
283 
284 int
285 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
286 {
287 	int r;
288 
289 	if ((r = sshpkt_start(ssh, type)) != 0 ||
290 	    (r = sshpkt_put(ssh, data, len)) != 0 ||
291 	    (r = sshpkt_send(ssh)) != 0)
292 		return r;
293 	return 0;
294 }
295 
296 const u_char *
297 ssh_output_ptr(struct ssh *ssh, size_t *len)
298 {
299 	struct sshbuf *output = ssh_packet_get_output(ssh);
300 
301 	*len = sshbuf_len(output);
302 	return sshbuf_ptr(output);
303 }
304 
305 int
306 ssh_output_consume(struct ssh *ssh, size_t len)
307 {
308 	return sshbuf_consume(ssh_packet_get_output(ssh), len);
309 }
310 
311 int
312 ssh_output_space(struct ssh *ssh, size_t len)
313 {
314 	return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
315 }
316 
317 int
318 ssh_input_space(struct ssh *ssh, size_t len)
319 {
320 	return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
321 }
322 
323 /* Read other side's version identification. */
324 int
325 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner)
326 {
327 	struct sshbuf *input = ssh_packet_get_input(ssh);
328 	const char *mismatch = "Protocol mismatch.\r\n";
329 	const u_char *s = sshbuf_ptr(input);
330 	u_char c;
331 	char *cp = NULL, *remote_version = NULL;
332 	int r = 0, remote_major, remote_minor, expect_nl;
333 	size_t n, j;
334 
335 	for (j = n = 0;;) {
336 		sshbuf_reset(banner);
337 		expect_nl = 0;
338 		for (;;) {
339 			if (j >= sshbuf_len(input))
340 				return 0; /* insufficient data in input buf */
341 			c = s[j++];
342 			if (c == '\r') {
343 				expect_nl = 1;
344 				continue;
345 			}
346 			if (c == '\n')
347 				break;
348 			if (expect_nl)
349 				goto bad;
350 			if ((r = sshbuf_put_u8(banner, c)) != 0)
351 				return r;
352 			if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN)
353 				goto bad;
354 		}
355 		if (sshbuf_len(banner) >= 4 &&
356 		    memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0)
357 			break;
358 		debug_f("%.*s", (int)sshbuf_len(banner),
359 		    sshbuf_ptr(banner));
360 		/* Accept lines before banner only on client */
361 		if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) {
362   bad:
363 			if ((r = sshbuf_put(ssh_packet_get_output(ssh),
364 			   mismatch, strlen(mismatch))) != 0)
365 				return r;
366 			return SSH_ERR_NO_PROTOCOL_VERSION;
367 		}
368 	}
369 	if ((r = sshbuf_consume(input, j)) != 0)
370 		return r;
371 
372 	/* XXX remote version must be the same size as banner for sscanf */
373 	if ((cp = sshbuf_dup_string(banner)) == NULL ||
374 	    (remote_version = calloc(1, sshbuf_len(banner))) == NULL) {
375 		r = SSH_ERR_ALLOC_FAIL;
376 		goto out;
377 	}
378 
379 	/*
380 	 * Check that the versions match.  In future this might accept
381 	 * several versions and set appropriate flags to handle them.
382 	 */
383 	if (sscanf(cp, "SSH-%d.%d-%[^\n]\n",
384 	    &remote_major, &remote_minor, remote_version) != 3) {
385 		r = SSH_ERR_INVALID_FORMAT;
386 		goto out;
387 	}
388 	debug("Remote protocol version %d.%d, remote software version %.100s",
389 	    remote_major, remote_minor, remote_version);
390 
391 	compat_banner(ssh, remote_version);
392 	if  (remote_major == 1 && remote_minor == 99) {
393 		remote_major = 2;
394 		remote_minor = 0;
395 	}
396 	if (remote_major != 2)
397 		r = SSH_ERR_PROTOCOL_MISMATCH;
398 
399 	debug("Remote version string %.100s", cp);
400  out:
401 	free(cp);
402 	free(remote_version);
403 	return r;
404 }
405 
406 /* Send our own protocol version identification. */
407 int
408 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner)
409 {
410 	char *cp;
411 	int r;
412 
413 	if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0)
414 		return r;
415 	if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0)
416 		return r;
417 	/* Remove trailing \r\n */
418 	if ((r = sshbuf_consume_end(banner, 2)) != 0)
419 		return r;
420 	if ((cp = sshbuf_dup_string(banner)) == NULL)
421 		return SSH_ERR_ALLOC_FAIL;
422 	debug("Local version string %.100s", cp);
423 	free(cp);
424 	return 0;
425 }
426 
427 int
428 _ssh_exchange_banner(struct ssh *ssh)
429 {
430 	struct kex *kex = ssh->kex;
431 	int r;
432 
433 	/*
434 	 * if _ssh_read_banner() cannot parse a full version string
435 	 * it will return NULL and we end up calling it again.
436 	 */
437 
438 	r = 0;
439 	if (kex->server) {
440 		if (sshbuf_len(ssh->kex->server_version) == 0)
441 			r = _ssh_send_banner(ssh, ssh->kex->server_version);
442 		if (r == 0 &&
443 		    sshbuf_len(ssh->kex->server_version) != 0 &&
444 		    sshbuf_len(ssh->kex->client_version) == 0)
445 			r = _ssh_read_banner(ssh, ssh->kex->client_version);
446 	} else {
447 		if (sshbuf_len(ssh->kex->server_version) == 0)
448 			r = _ssh_read_banner(ssh, ssh->kex->server_version);
449 		if (r == 0 &&
450 		    sshbuf_len(ssh->kex->server_version) != 0 &&
451 		    sshbuf_len(ssh->kex->client_version) == 0)
452 			r = _ssh_send_banner(ssh, ssh->kex->client_version);
453 	}
454 	if (r != 0)
455 		return r;
456 	/* start initial kex as soon as we have exchanged the banners */
457 	if (sshbuf_len(ssh->kex->server_version) != 0 &&
458 	    sshbuf_len(ssh->kex->client_version) != 0) {
459 		if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
460 		    (r = kex_send_kexinit(ssh)) != 0)
461 			return r;
462 	}
463 	return 0;
464 }
465 
466 struct sshkey *
467 _ssh_host_public_key(int type, int nid, struct ssh *ssh)
468 {
469 	struct key_entry *k;
470 
471 	debug3_f("need %d", type);
472 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
473 		debug3_f("check %s", sshkey_type(k->key));
474 		if (k->key->type == type &&
475 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
476 			return (k->key);
477 	}
478 	return (NULL);
479 }
480 
481 struct sshkey *
482 _ssh_host_private_key(int type, int nid, struct ssh *ssh)
483 {
484 	struct key_entry *k;
485 
486 	debug3_f("need %d", type);
487 	TAILQ_FOREACH(k, &ssh->private_keys, next) {
488 		debug3_f("check %s", sshkey_type(k->key));
489 		if (k->key->type == type &&
490 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
491 			return (k->key);
492 	}
493 	return (NULL);
494 }
495 
496 int
497 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
498 {
499 	struct key_entry *k;
500 
501 	debug3_f("need %s", sshkey_type(hostkey));
502 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
503 		debug3_f("check %s", sshkey_type(k->key));
504 		if (sshkey_equal_public(hostkey, k->key))
505 			return (0);	/* ok */
506 	}
507 	return (-1);	/* failed */
508 }
509 
510 /* offer hostkey algorithms in kexinit depending on registered keys */
511 int
512 _ssh_order_hostkeyalgs(struct ssh *ssh)
513 {
514 	struct key_entry *k;
515 	char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
516 	char **proposal;
517 	size_t maxlen;
518 	int ktype, r;
519 
520 	/* XXX we de-serialize ssh->kex->my, modify it, and change it */
521 	if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
522 		return r;
523 	orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
524 	if ((oavail = avail = strdup(orig)) == NULL) {
525 		r = SSH_ERR_ALLOC_FAIL;
526 		goto out;
527 	}
528 	maxlen = strlen(avail) + 1;
529 	if ((replace = calloc(1, maxlen)) == NULL) {
530 		r = SSH_ERR_ALLOC_FAIL;
531 		goto out;
532 	}
533 	*replace = '\0';
534 	while ((alg = strsep(&avail, ",")) && *alg != '\0') {
535 		if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
536 			continue;
537 		TAILQ_FOREACH(k, &ssh->public_keys, next) {
538 			if (k->key->type == ktype ||
539 			    (sshkey_is_cert(k->key) && k->key->type ==
540 			    sshkey_type_plain(ktype))) {
541 				if (*replace != '\0')
542 					strlcat(replace, ",", maxlen);
543 				strlcat(replace, alg, maxlen);
544 				break;
545 			}
546 		}
547 	}
548 	if (*replace != '\0') {
549 		debug2_f("orig/%d    %s", ssh->kex->server, orig);
550 		debug2_f("replace/%d %s", ssh->kex->server, replace);
551 		free(orig);
552 		proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
553 		replace = NULL;	/* owned by proposal */
554 		r = kex_prop2buf(ssh->kex->my, proposal);
555 	}
556  out:
557 	free(oavail);
558 	free(replace);
559 	kex_prop_free(proposal);
560 	return r;
561 }
562 
563 int
564 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey,
565     struct sshkey *pubkey, u_char **signature, size_t *slen,
566     const u_char *data, size_t dlen, const char *alg)
567 {
568 	return sshkey_sign(privkey, signature, slen, data, dlen,
569 	    alg, NULL, NULL, ssh->compat);
570 }
571