xref: /openssh-portable/ssh_api.c (revision 04c091fc)
1 /* $OpenBSD: ssh_api.c,v 1.10 2019/01/19 21:43:56 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 "ssh_api.h"
21 #include "compat.h"
22 #include "log.h"
23 #include "authfile.h"
24 #include "sshkey.h"
25 #include "misc.h"
26 #include "ssh2.h"
27 #include "version.h"
28 #include "myproposal.h"
29 #include "ssherr.h"
30 #include "sshbuf.h"
31 
32 #include "openbsd-compat/openssl-compat.h"
33 
34 #include <string.h>
35 
36 int	_ssh_exchange_banner(struct ssh *);
37 int	_ssh_send_banner(struct ssh *, struct sshbuf *);
38 int	_ssh_read_banner(struct ssh *, struct sshbuf *);
39 int	_ssh_order_hostkeyalgs(struct ssh *);
40 int	_ssh_verify_host_key(struct sshkey *, struct ssh *);
41 struct sshkey *_ssh_host_public_key(int, int, struct ssh *);
42 struct sshkey *_ssh_host_private_key(int, int, struct ssh *);
43 int	_ssh_host_key_sign(struct ssh *, struct sshkey *, struct sshkey *,
44     u_char **, size_t *, const u_char *, size_t, const char *);
45 
46 /*
47  * stubs for the server side implementation of kex.
48  * disable privsep so our stubs will never be called.
49  */
50 int	use_privsep = 0;
51 int	mm_sshkey_sign(struct sshkey *, u_char **, u_int *,
52     u_char *, u_int, char *, u_int);
53 DH	*mm_choose_dh(int, int, int);
54 
55 /* Define these two variables here so that they are part of the library */
56 u_char *session_id2 = NULL;
57 u_int session_id2_len = 0;
58 
59 int
60 mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp,
61     u_char *data, u_int datalen, char *alg, u_int compat)
62 {
63 	return (-1);
64 }
65 
66 DH *
67 mm_choose_dh(int min, int nbits, int max)
68 {
69 	return (NULL);
70 }
71 
72 /* API */
73 
74 int
75 ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params)
76 {
77         char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
78 	struct ssh *ssh;
79 	char **proposal;
80 	static int called;
81 	int r;
82 
83 	if (!called) {
84 		seed_rng();
85 		called = 1;
86 	}
87 
88 	if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL)
89 		return SSH_ERR_ALLOC_FAIL;
90 	if (is_server)
91 		ssh_packet_set_server(ssh);
92 
93 	/* Initialize key exchange */
94 	proposal = kex_params ? kex_params->proposal : myproposal;
95 	if ((r = kex_ready(ssh, proposal)) != 0) {
96 		ssh_free(ssh);
97 		return r;
98 	}
99 	ssh->kex->server = is_server;
100 	if (is_server) {
101 #ifdef WITH_OPENSSL
102 		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kexdh_server;
103 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kexdh_server;
104 		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kexdh_server;
105 		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kexdh_server;
106 		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kexdh_server;
107 		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
108 		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
109 # ifdef OPENSSL_HAS_ECC
110 		ssh->kex->kex[KEX_ECDH_SHA2] = kexecdh_server;
111 # endif
112 #endif /* WITH_OPENSSL */
113 		ssh->kex->kex[KEX_C25519_SHA256] = kexc25519_server;
114 		ssh->kex->load_host_public_key=&_ssh_host_public_key;
115 		ssh->kex->load_host_private_key=&_ssh_host_private_key;
116 		ssh->kex->sign=&_ssh_host_key_sign;
117 	} else {
118 #ifdef WITH_OPENSSL
119 		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kexdh_client;
120 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kexdh_client;
121 		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kexdh_client;
122 		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kexdh_client;
123 		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kexdh_client;
124 		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
125 		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
126 # ifdef OPENSSL_HAS_ECC
127 		ssh->kex->kex[KEX_ECDH_SHA2] = kexecdh_client;
128 # endif
129 #endif /* WITH_OPENSSL */
130 		ssh->kex->kex[KEX_C25519_SHA256] = kexc25519_client;
131 		ssh->kex->verify_host_key =&_ssh_verify_host_key;
132 	}
133 	*sshp = ssh;
134 	return 0;
135 }
136 
137 void
138 ssh_free(struct ssh *ssh)
139 {
140 	struct key_entry *k;
141 
142 	ssh_packet_close(ssh);
143 	/*
144 	 * we've only created the public keys variants in case we
145 	 * are a acting as a server.
146 	 */
147 	while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
148 		TAILQ_REMOVE(&ssh->public_keys, k, next);
149 		if (ssh->kex && ssh->kex->server)
150 			sshkey_free(k->key);
151 		free(k);
152 	}
153 	while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
154 		TAILQ_REMOVE(&ssh->private_keys, k, next);
155 		free(k);
156 	}
157 	if (ssh->kex)
158 		kex_free(ssh->kex);
159 	free(ssh);
160 }
161 
162 void
163 ssh_set_app_data(struct ssh *ssh, void *app_data)
164 {
165 	ssh->app_data = app_data;
166 }
167 
168 void *
169 ssh_get_app_data(struct ssh *ssh)
170 {
171 	return ssh->app_data;
172 }
173 
174 /* Returns < 0 on error, 0 otherwise */
175 int
176 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
177 {
178 	struct sshkey *pubkey = NULL;
179 	struct key_entry *k = NULL, *k_prv = NULL;
180 	int r;
181 
182 	if (ssh->kex->server) {
183 		if ((r = sshkey_from_private(key, &pubkey)) != 0)
184 			return r;
185 		if ((k = malloc(sizeof(*k))) == NULL ||
186 		    (k_prv = malloc(sizeof(*k_prv))) == NULL) {
187 			free(k);
188 			sshkey_free(pubkey);
189 			return SSH_ERR_ALLOC_FAIL;
190 		}
191 		k_prv->key = key;
192 		TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
193 
194 		/* add the public key, too */
195 		k->key = pubkey;
196 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
197 		r = 0;
198 	} else {
199 		if ((k = malloc(sizeof(*k))) == NULL)
200 			return SSH_ERR_ALLOC_FAIL;
201 		k->key = key;
202 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
203 		r = 0;
204 	}
205 
206 	return r;
207 }
208 
209 int
210 ssh_set_verify_host_key_callback(struct ssh *ssh,
211     int (*cb)(struct sshkey *, struct ssh *))
212 {
213 	if (cb == NULL || ssh->kex == NULL)
214 		return SSH_ERR_INVALID_ARGUMENT;
215 
216 	ssh->kex->verify_host_key = cb;
217 
218 	return 0;
219 }
220 
221 int
222 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
223 {
224 	return sshbuf_put(ssh_packet_get_input(ssh), data, len);
225 }
226 
227 int
228 ssh_packet_next(struct ssh *ssh, u_char *typep)
229 {
230 	int r;
231 	u_int32_t seqnr;
232 	u_char type;
233 
234 	/*
235 	 * Try to read a packet. Return SSH_MSG_NONE if no packet or not
236 	 * enough data.
237 	 */
238 	*typep = SSH_MSG_NONE;
239 	if (sshbuf_len(ssh->kex->client_version) == 0 ||
240 	    sshbuf_len(ssh->kex->server_version) == 0)
241 		return _ssh_exchange_banner(ssh);
242 	/*
243 	 * If we enough data and a dispatch function then
244 	 * call the function and get the next packet.
245 	 * Otherwise return the packet type to the caller so it
246 	 * can decide how to go on.
247 	 *
248 	 * We will only call the dispatch function for:
249 	 *     20-29    Algorithm negotiation
250 	 *     30-49    Key exchange method specific (numbers can be reused for
251 	 *              different authentication methods)
252 	 */
253 	for (;;) {
254 		if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
255 			return r;
256 		if (type > 0 && type < DISPATCH_MAX &&
257 		    type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
258 		    ssh->dispatch[type] != NULL) {
259 			if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
260 				return r;
261 		} else {
262 			*typep = type;
263 			return 0;
264 		}
265 	}
266 }
267 
268 const u_char *
269 ssh_packet_payload(struct ssh *ssh, size_t *lenp)
270 {
271 	return sshpkt_ptr(ssh, lenp);
272 }
273 
274 int
275 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
276 {
277 	int r;
278 
279 	if ((r = sshpkt_start(ssh, type)) != 0 ||
280 	    (r = sshpkt_put(ssh, data, len)) != 0 ||
281 	    (r = sshpkt_send(ssh)) != 0)
282 		return r;
283 	return 0;
284 }
285 
286 const u_char *
287 ssh_output_ptr(struct ssh *ssh, size_t *len)
288 {
289 	struct sshbuf *output = ssh_packet_get_output(ssh);
290 
291 	*len = sshbuf_len(output);
292 	return sshbuf_ptr(output);
293 }
294 
295 int
296 ssh_output_consume(struct ssh *ssh, size_t len)
297 {
298 	return sshbuf_consume(ssh_packet_get_output(ssh), len);
299 }
300 
301 int
302 ssh_output_space(struct ssh *ssh, size_t len)
303 {
304 	return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
305 }
306 
307 int
308 ssh_input_space(struct ssh *ssh, size_t len)
309 {
310 	return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
311 }
312 
313 /* Read other side's version identification. */
314 int
315 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner)
316 {
317 	struct sshbuf *input = ssh_packet_get_input(ssh);
318 	const char *mismatch = "Protocol mismatch.\r\n";
319 	const u_char *s = sshbuf_ptr(input);
320 	u_char c;
321 	char *cp, *remote_version;
322 	int r, remote_major, remote_minor, expect_nl;
323 	size_t n, j;
324 
325 	for (j = n = 0;;) {
326 		sshbuf_reset(banner);
327 		expect_nl = 0;
328 		for (;;) {
329 			if (j >= sshbuf_len(input))
330 				return 0; /* insufficient data in input buf */
331 			c = s[j++];
332 			if (c == '\r') {
333 				expect_nl = 1;
334 				continue;
335 			}
336 			if (c == '\n')
337 				break;
338 			if (expect_nl)
339 				goto bad;
340 			if ((r = sshbuf_put_u8(banner, c)) != 0)
341 				return r;
342 			if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN)
343 				goto bad;
344 		}
345 		if (sshbuf_len(banner) >= 4 &&
346 		    memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0)
347 			break;
348 		if ((cp = sshbuf_dup_string(banner)) == NULL)
349 			return SSH_ERR_ALLOC_FAIL;
350 		debug("%s: %s", __func__, cp);
351 		free(cp);
352 		/* Accept lines before banner only on client */
353 		if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) {
354   bad:
355 			if ((r = sshbuf_put(ssh_packet_get_output(ssh),
356 			   mismatch, strlen(mismatch))) != 0)
357 				return r;
358 			return SSH_ERR_NO_PROTOCOL_VERSION;
359 		}
360 	}
361 	if ((r = sshbuf_consume(input, j)) != 0)
362 		return r;
363 
364 	if ((cp = sshbuf_dup_string(banner)) == NULL)
365 		return SSH_ERR_ALLOC_FAIL;
366 	/* XXX remote version must be the same size as banner for sscanf */
367 	if ((remote_version = calloc(1, sshbuf_len(banner))) == NULL)
368 		return SSH_ERR_ALLOC_FAIL;
369 
370 	/*
371 	 * Check that the versions match.  In future this might accept
372 	 * several versions and set appropriate flags to handle them.
373 	 */
374 	if (sscanf(cp, "SSH-%d.%d-%[^\n]\n",
375 	    &remote_major, &remote_minor, remote_version) != 3)
376 		return SSH_ERR_INVALID_FORMAT;
377 	debug("Remote protocol version %d.%d, remote software version %.100s",
378 	    remote_major, remote_minor, remote_version);
379 
380 	ssh->compat = compat_datafellows(remote_version);
381 	if  (remote_major == 1 && remote_minor == 99) {
382 		remote_major = 2;
383 		remote_minor = 0;
384 	}
385 	if (remote_major != 2)
386 		return SSH_ERR_PROTOCOL_MISMATCH;
387 	debug("Remote version string %.100s", cp);
388 	free(cp);
389 	return 0;
390 }
391 
392 /* Send our own protocol version identification. */
393 int
394 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner)
395 {
396 	char *cp;
397 	int r;
398 
399 	if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0)
400 		return r;
401 	if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0)
402 		return r;
403 	/* Remove trailing \r\n */
404 	if ((r = sshbuf_consume_end(banner, 2)) != 0)
405 		return r;
406 	if ((cp = sshbuf_dup_string(banner)) == NULL)
407 		return SSH_ERR_ALLOC_FAIL;
408 	debug("Local version string %.100s", cp);
409 	free(cp);
410 	return 0;
411 }
412 
413 int
414 _ssh_exchange_banner(struct ssh *ssh)
415 {
416 	struct kex *kex = ssh->kex;
417 	int r;
418 
419 	/*
420 	 * if _ssh_read_banner() cannot parse a full version string
421 	 * it will return NULL and we end up calling it again.
422 	 */
423 
424 	r = 0;
425 	if (kex->server) {
426 		if (sshbuf_len(ssh->kex->server_version) == 0)
427 			r = _ssh_send_banner(ssh, ssh->kex->server_version);
428 		if (r == 0 &&
429 		    sshbuf_len(ssh->kex->server_version) != 0 &&
430 		    sshbuf_len(ssh->kex->client_version) == 0)
431 			r = _ssh_read_banner(ssh, ssh->kex->client_version);
432 	} else {
433 		if (sshbuf_len(ssh->kex->server_version) == 0)
434 			r = _ssh_read_banner(ssh, ssh->kex->server_version);
435 		if (r == 0 &&
436 		    sshbuf_len(ssh->kex->server_version) != 0 &&
437 		    sshbuf_len(ssh->kex->client_version) == 0)
438 			r = _ssh_send_banner(ssh, ssh->kex->client_version);
439 	}
440 	if (r != 0)
441 		return r;
442 	/* start initial kex as soon as we have exchanged the banners */
443 	if (sshbuf_len(ssh->kex->server_version) != 0 &&
444 	    sshbuf_len(ssh->kex->client_version) != 0) {
445 		if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
446 		    (r = kex_send_kexinit(ssh)) != 0)
447 			return r;
448 	}
449 	return 0;
450 }
451 
452 struct sshkey *
453 _ssh_host_public_key(int type, int nid, struct ssh *ssh)
454 {
455 	struct key_entry *k;
456 
457 	debug3("%s: need %d", __func__, type);
458 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
459 		debug3("%s: check %s", __func__, sshkey_type(k->key));
460 		if (k->key->type == type &&
461 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
462 			return (k->key);
463 	}
464 	return (NULL);
465 }
466 
467 struct sshkey *
468 _ssh_host_private_key(int type, int nid, struct ssh *ssh)
469 {
470 	struct key_entry *k;
471 
472 	debug3("%s: need %d", __func__, type);
473 	TAILQ_FOREACH(k, &ssh->private_keys, next) {
474 		debug3("%s: check %s", __func__, sshkey_type(k->key));
475 		if (k->key->type == type &&
476 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
477 			return (k->key);
478 	}
479 	return (NULL);
480 }
481 
482 int
483 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
484 {
485 	struct key_entry *k;
486 
487 	debug3("%s: need %s", __func__, sshkey_type(hostkey));
488 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
489 		debug3("%s: check %s", __func__, sshkey_type(k->key));
490 		if (sshkey_equal_public(hostkey, k->key))
491 			return (0);	/* ok */
492 	}
493 	return (-1);	/* failed */
494 }
495 
496 /* offer hostkey algorithms in kexinit depending on registered keys */
497 int
498 _ssh_order_hostkeyalgs(struct ssh *ssh)
499 {
500 	struct key_entry *k;
501 	char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
502 	char **proposal;
503 	size_t maxlen;
504 	int ktype, r;
505 
506 	/* XXX we de-serialize ssh->kex->my, modify it, and change it */
507 	if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
508 		return r;
509 	orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
510 	if ((oavail = avail = strdup(orig)) == NULL) {
511 		r = SSH_ERR_ALLOC_FAIL;
512 		goto out;
513 	}
514 	maxlen = strlen(avail) + 1;
515 	if ((replace = calloc(1, maxlen)) == NULL) {
516 		r = SSH_ERR_ALLOC_FAIL;
517 		goto out;
518 	}
519 	*replace = '\0';
520 	while ((alg = strsep(&avail, ",")) && *alg != '\0') {
521 		if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
522 			continue;
523 		TAILQ_FOREACH(k, &ssh->public_keys, next) {
524 			if (k->key->type == ktype ||
525 			    (sshkey_is_cert(k->key) && k->key->type ==
526 			    sshkey_type_plain(ktype))) {
527 				if (*replace != '\0')
528 					strlcat(replace, ",", maxlen);
529 				strlcat(replace, alg, maxlen);
530 				break;
531 			}
532 		}
533 	}
534 	if (*replace != '\0') {
535 		debug2("%s: orig/%d    %s", __func__, ssh->kex->server, orig);
536 		debug2("%s: replace/%d %s", __func__, ssh->kex->server, replace);
537 		free(orig);
538 		proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
539 		replace = NULL;	/* owned by proposal */
540 		r = kex_prop2buf(ssh->kex->my, proposal);
541 	}
542  out:
543 	free(oavail);
544 	free(replace);
545 	kex_prop_free(proposal);
546 	return r;
547 }
548 
549 int
550 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey,
551     struct sshkey *pubkey, u_char **signature, size_t *slen,
552     const u_char *data, size_t dlen, const char *alg)
553 {
554 	return sshkey_sign(privkey, signature, slen, data, dlen,
555 	    alg, ssh->compat);
556 }
557