xref: /openssh-portable/ssh_api.c (revision 670104b9)
1 /* $OpenBSD: ssh_api.c,v 1.17 2019/09/06 05:23:55 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     u_char *, u_int, 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
68 mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp,
69     u_char *data, u_int datalen, char *alg, u_int compat)
70 {
71 	return (-1);
72 }
73 
74 #ifdef WITH_OPENSSL
75 DH *
76 mm_choose_dh(int min, int nbits, int max)
77 {
78 	return (NULL);
79 }
80 #endif
81 
82 /* API */
83 
84 int
85 ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params)
86 {
87         char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
88 	struct ssh *ssh;
89 	char **proposal;
90 	static int called;
91 	int r;
92 
93 	if (!called) {
94 		seed_rng();
95 		called = 1;
96 	}
97 
98 	if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL)
99 		return SSH_ERR_ALLOC_FAIL;
100 	if (is_server)
101 		ssh_packet_set_server(ssh);
102 
103 	/* Initialize key exchange */
104 	proposal = kex_params ? kex_params->proposal : myproposal;
105 	if ((r = kex_ready(ssh, proposal)) != 0) {
106 		ssh_free(ssh);
107 		return r;
108 	}
109 	ssh->kex->server = is_server;
110 	if (is_server) {
111 #ifdef WITH_OPENSSL
112 		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server;
113 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server;
114 		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server;
115 		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server;
116 		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server;
117 		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
118 		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
119 # ifdef OPENSSL_HAS_ECC
120 		ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server;
121 # endif
122 #endif /* WITH_OPENSSL */
123 		ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server;
124 		ssh->kex->kex[KEX_KEM_SNTRUP4591761X25519_SHA512] = kex_gen_server;
125 		ssh->kex->load_host_public_key=&_ssh_host_public_key;
126 		ssh->kex->load_host_private_key=&_ssh_host_private_key;
127 		ssh->kex->sign=&_ssh_host_key_sign;
128 	} else {
129 #ifdef WITH_OPENSSL
130 		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client;
131 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client;
132 		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client;
133 		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client;
134 		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client;
135 		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
136 		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
137 # ifdef OPENSSL_HAS_ECC
138 		ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
139 # endif
140 #endif /* WITH_OPENSSL */
141 		ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
142 		ssh->kex->kex[KEX_KEM_SNTRUP4591761X25519_SHA512] = kex_gen_client;
143 		ssh->kex->verify_host_key =&_ssh_verify_host_key;
144 	}
145 	*sshp = ssh;
146 	return 0;
147 }
148 
149 void
150 ssh_free(struct ssh *ssh)
151 {
152 	struct key_entry *k;
153 
154 	ssh_packet_close(ssh);
155 	/*
156 	 * we've only created the public keys variants in case we
157 	 * are a acting as a server.
158 	 */
159 	while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
160 		TAILQ_REMOVE(&ssh->public_keys, k, next);
161 		if (ssh->kex && ssh->kex->server)
162 			sshkey_free(k->key);
163 		free(k);
164 	}
165 	while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
166 		TAILQ_REMOVE(&ssh->private_keys, k, next);
167 		free(k);
168 	}
169 	if (ssh->kex)
170 		kex_free(ssh->kex);
171 	free(ssh);
172 }
173 
174 void
175 ssh_set_app_data(struct ssh *ssh, void *app_data)
176 {
177 	ssh->app_data = app_data;
178 }
179 
180 void *
181 ssh_get_app_data(struct ssh *ssh)
182 {
183 	return ssh->app_data;
184 }
185 
186 /* Returns < 0 on error, 0 otherwise */
187 int
188 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
189 {
190 	struct sshkey *pubkey = NULL;
191 	struct key_entry *k = NULL, *k_prv = NULL;
192 	int r;
193 
194 	if (ssh->kex->server) {
195 		if ((r = sshkey_from_private(key, &pubkey)) != 0)
196 			return r;
197 		if ((k = malloc(sizeof(*k))) == NULL ||
198 		    (k_prv = malloc(sizeof(*k_prv))) == NULL) {
199 			free(k);
200 			sshkey_free(pubkey);
201 			return SSH_ERR_ALLOC_FAIL;
202 		}
203 		k_prv->key = key;
204 		TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
205 
206 		/* add the public key, too */
207 		k->key = pubkey;
208 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
209 		r = 0;
210 	} else {
211 		if ((k = malloc(sizeof(*k))) == NULL)
212 			return SSH_ERR_ALLOC_FAIL;
213 		k->key = key;
214 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
215 		r = 0;
216 	}
217 
218 	return r;
219 }
220 
221 int
222 ssh_set_verify_host_key_callback(struct ssh *ssh,
223     int (*cb)(struct sshkey *, struct ssh *))
224 {
225 	if (cb == NULL || ssh->kex == NULL)
226 		return SSH_ERR_INVALID_ARGUMENT;
227 
228 	ssh->kex->verify_host_key = cb;
229 
230 	return 0;
231 }
232 
233 int
234 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
235 {
236 	return sshbuf_put(ssh_packet_get_input(ssh), data, len);
237 }
238 
239 int
240 ssh_packet_next(struct ssh *ssh, u_char *typep)
241 {
242 	int r;
243 	u_int32_t seqnr;
244 	u_char type;
245 
246 	/*
247 	 * Try to read a packet. Return SSH_MSG_NONE if no packet or not
248 	 * enough data.
249 	 */
250 	*typep = SSH_MSG_NONE;
251 	if (sshbuf_len(ssh->kex->client_version) == 0 ||
252 	    sshbuf_len(ssh->kex->server_version) == 0)
253 		return _ssh_exchange_banner(ssh);
254 	/*
255 	 * If we enough data and a dispatch function then
256 	 * call the function and get the next packet.
257 	 * Otherwise return the packet type to the caller so it
258 	 * can decide how to go on.
259 	 *
260 	 * We will only call the dispatch function for:
261 	 *     20-29    Algorithm negotiation
262 	 *     30-49    Key exchange method specific (numbers can be reused for
263 	 *              different authentication methods)
264 	 */
265 	for (;;) {
266 		if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
267 			return r;
268 		if (type > 0 && type < DISPATCH_MAX &&
269 		    type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
270 		    ssh->dispatch[type] != NULL) {
271 			if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
272 				return r;
273 		} else {
274 			*typep = type;
275 			return 0;
276 		}
277 	}
278 }
279 
280 const u_char *
281 ssh_packet_payload(struct ssh *ssh, size_t *lenp)
282 {
283 	return sshpkt_ptr(ssh, lenp);
284 }
285 
286 int
287 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
288 {
289 	int r;
290 
291 	if ((r = sshpkt_start(ssh, type)) != 0 ||
292 	    (r = sshpkt_put(ssh, data, len)) != 0 ||
293 	    (r = sshpkt_send(ssh)) != 0)
294 		return r;
295 	return 0;
296 }
297 
298 const u_char *
299 ssh_output_ptr(struct ssh *ssh, size_t *len)
300 {
301 	struct sshbuf *output = ssh_packet_get_output(ssh);
302 
303 	*len = sshbuf_len(output);
304 	return sshbuf_ptr(output);
305 }
306 
307 int
308 ssh_output_consume(struct ssh *ssh, size_t len)
309 {
310 	return sshbuf_consume(ssh_packet_get_output(ssh), len);
311 }
312 
313 int
314 ssh_output_space(struct ssh *ssh, size_t len)
315 {
316 	return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
317 }
318 
319 int
320 ssh_input_space(struct ssh *ssh, size_t len)
321 {
322 	return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
323 }
324 
325 /* Read other side's version identification. */
326 int
327 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner)
328 {
329 	struct sshbuf *input = ssh_packet_get_input(ssh);
330 	const char *mismatch = "Protocol mismatch.\r\n";
331 	const u_char *s = sshbuf_ptr(input);
332 	u_char c;
333 	char *cp, *remote_version;
334 	int r, remote_major, remote_minor, expect_nl;
335 	size_t n, j;
336 
337 	for (j = n = 0;;) {
338 		sshbuf_reset(banner);
339 		expect_nl = 0;
340 		for (;;) {
341 			if (j >= sshbuf_len(input))
342 				return 0; /* insufficient data in input buf */
343 			c = s[j++];
344 			if (c == '\r') {
345 				expect_nl = 1;
346 				continue;
347 			}
348 			if (c == '\n')
349 				break;
350 			if (expect_nl)
351 				goto bad;
352 			if ((r = sshbuf_put_u8(banner, c)) != 0)
353 				return r;
354 			if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN)
355 				goto bad;
356 		}
357 		if (sshbuf_len(banner) >= 4 &&
358 		    memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0)
359 			break;
360 		if ((cp = sshbuf_dup_string(banner)) == NULL)
361 			return SSH_ERR_ALLOC_FAIL;
362 		debug("%s: %s", __func__, cp);
363 		free(cp);
364 		/* Accept lines before banner only on client */
365 		if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) {
366   bad:
367 			if ((r = sshbuf_put(ssh_packet_get_output(ssh),
368 			   mismatch, strlen(mismatch))) != 0)
369 				return r;
370 			return SSH_ERR_NO_PROTOCOL_VERSION;
371 		}
372 	}
373 	if ((r = sshbuf_consume(input, j)) != 0)
374 		return r;
375 
376 	if ((cp = sshbuf_dup_string(banner)) == NULL)
377 		return SSH_ERR_ALLOC_FAIL;
378 	/* XXX remote version must be the same size as banner for sscanf */
379 	if ((remote_version = calloc(1, sshbuf_len(banner))) == NULL)
380 		return SSH_ERR_ALLOC_FAIL;
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 		return SSH_ERR_INVALID_FORMAT;
389 	debug("Remote protocol version %d.%d, remote software version %.100s",
390 	    remote_major, remote_minor, remote_version);
391 
392 	ssh->compat = compat_datafellows(remote_version);
393 	if  (remote_major == 1 && remote_minor == 99) {
394 		remote_major = 2;
395 		remote_minor = 0;
396 	}
397 	if (remote_major != 2)
398 		return SSH_ERR_PROTOCOL_MISMATCH;
399 	debug("Remote version string %.100s", cp);
400 	free(cp);
401 	return 0;
402 }
403 
404 /* Send our own protocol version identification. */
405 int
406 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner)
407 {
408 	char *cp;
409 	int r;
410 
411 	if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0)
412 		return r;
413 	if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0)
414 		return r;
415 	/* Remove trailing \r\n */
416 	if ((r = sshbuf_consume_end(banner, 2)) != 0)
417 		return r;
418 	if ((cp = sshbuf_dup_string(banner)) == NULL)
419 		return SSH_ERR_ALLOC_FAIL;
420 	debug("Local version string %.100s", cp);
421 	free(cp);
422 	return 0;
423 }
424 
425 int
426 _ssh_exchange_banner(struct ssh *ssh)
427 {
428 	struct kex *kex = ssh->kex;
429 	int r;
430 
431 	/*
432 	 * if _ssh_read_banner() cannot parse a full version string
433 	 * it will return NULL and we end up calling it again.
434 	 */
435 
436 	r = 0;
437 	if (kex->server) {
438 		if (sshbuf_len(ssh->kex->server_version) == 0)
439 			r = _ssh_send_banner(ssh, ssh->kex->server_version);
440 		if (r == 0 &&
441 		    sshbuf_len(ssh->kex->server_version) != 0 &&
442 		    sshbuf_len(ssh->kex->client_version) == 0)
443 			r = _ssh_read_banner(ssh, ssh->kex->client_version);
444 	} else {
445 		if (sshbuf_len(ssh->kex->server_version) == 0)
446 			r = _ssh_read_banner(ssh, ssh->kex->server_version);
447 		if (r == 0 &&
448 		    sshbuf_len(ssh->kex->server_version) != 0 &&
449 		    sshbuf_len(ssh->kex->client_version) == 0)
450 			r = _ssh_send_banner(ssh, ssh->kex->client_version);
451 	}
452 	if (r != 0)
453 		return r;
454 	/* start initial kex as soon as we have exchanged the banners */
455 	if (sshbuf_len(ssh->kex->server_version) != 0 &&
456 	    sshbuf_len(ssh->kex->client_version) != 0) {
457 		if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
458 		    (r = kex_send_kexinit(ssh)) != 0)
459 			return r;
460 	}
461 	return 0;
462 }
463 
464 struct sshkey *
465 _ssh_host_public_key(int type, int nid, struct ssh *ssh)
466 {
467 	struct key_entry *k;
468 
469 	debug3("%s: need %d", __func__, type);
470 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
471 		debug3("%s: check %s", __func__, sshkey_type(k->key));
472 		if (k->key->type == type &&
473 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
474 			return (k->key);
475 	}
476 	return (NULL);
477 }
478 
479 struct sshkey *
480 _ssh_host_private_key(int type, int nid, struct ssh *ssh)
481 {
482 	struct key_entry *k;
483 
484 	debug3("%s: need %d", __func__, type);
485 	TAILQ_FOREACH(k, &ssh->private_keys, next) {
486 		debug3("%s: check %s", __func__, sshkey_type(k->key));
487 		if (k->key->type == type &&
488 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
489 			return (k->key);
490 	}
491 	return (NULL);
492 }
493 
494 int
495 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
496 {
497 	struct key_entry *k;
498 
499 	debug3("%s: need %s", __func__, sshkey_type(hostkey));
500 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
501 		debug3("%s: check %s", __func__, sshkey_type(k->key));
502 		if (sshkey_equal_public(hostkey, k->key))
503 			return (0);	/* ok */
504 	}
505 	return (-1);	/* failed */
506 }
507 
508 /* offer hostkey algorithms in kexinit depending on registered keys */
509 int
510 _ssh_order_hostkeyalgs(struct ssh *ssh)
511 {
512 	struct key_entry *k;
513 	char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
514 	char **proposal;
515 	size_t maxlen;
516 	int ktype, r;
517 
518 	/* XXX we de-serialize ssh->kex->my, modify it, and change it */
519 	if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
520 		return r;
521 	orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
522 	if ((oavail = avail = strdup(orig)) == NULL) {
523 		r = SSH_ERR_ALLOC_FAIL;
524 		goto out;
525 	}
526 	maxlen = strlen(avail) + 1;
527 	if ((replace = calloc(1, maxlen)) == NULL) {
528 		r = SSH_ERR_ALLOC_FAIL;
529 		goto out;
530 	}
531 	*replace = '\0';
532 	while ((alg = strsep(&avail, ",")) && *alg != '\0') {
533 		if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
534 			continue;
535 		TAILQ_FOREACH(k, &ssh->public_keys, next) {
536 			if (k->key->type == ktype ||
537 			    (sshkey_is_cert(k->key) && k->key->type ==
538 			    sshkey_type_plain(ktype))) {
539 				if (*replace != '\0')
540 					strlcat(replace, ",", maxlen);
541 				strlcat(replace, alg, maxlen);
542 				break;
543 			}
544 		}
545 	}
546 	if (*replace != '\0') {
547 		debug2("%s: orig/%d    %s", __func__, ssh->kex->server, orig);
548 		debug2("%s: replace/%d %s", __func__, ssh->kex->server, replace);
549 		free(orig);
550 		proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
551 		replace = NULL;	/* owned by proposal */
552 		r = kex_prop2buf(ssh->kex->my, proposal);
553 	}
554  out:
555 	free(oavail);
556 	free(replace);
557 	kex_prop_free(proposal);
558 	return r;
559 }
560 
561 int
562 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey,
563     struct sshkey *pubkey, u_char **signature, size_t *slen,
564     const u_char *data, size_t dlen, const char *alg)
565 {
566 	return sshkey_sign(privkey, signature, slen, data, dlen,
567 	    alg, ssh->compat);
568 }
569