xref: /openssh-portable/ssh_api.c (revision aaca72d6)
1 /* $OpenBSD: ssh_api.c,v 1.15 2019/01/21 10:38:54 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
mm_sshkey_sign(struct sshkey * key,u_char ** sigp,u_int * lenp,u_char * data,u_int datalen,char * alg,u_int compat)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 *
mm_choose_dh(int min,int nbits,int max)67 mm_choose_dh(int min, int nbits, int max)
68 {
69 	return (NULL);
70 }
71 
72 /* API */
73 
74 int
ssh_init(struct ssh ** sshp,int is_server,struct kex_params * kex_params)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] = kex_gen_server;
103 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server;
104 		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server;
105 		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server;
106 		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_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] = kex_gen_server;
111 # endif
112 #endif /* WITH_OPENSSL */
113 		ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server;
114 		ssh->kex->kex[KEX_KEM_SNTRUP4591761X25519_SHA512] = kex_gen_server;
115 		ssh->kex->load_host_public_key=&_ssh_host_public_key;
116 		ssh->kex->load_host_private_key=&_ssh_host_private_key;
117 		ssh->kex->sign=&_ssh_host_key_sign;
118 	} else {
119 #ifdef WITH_OPENSSL
120 		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client;
121 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client;
122 		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client;
123 		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client;
124 		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client;
125 		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
126 		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
127 # ifdef OPENSSL_HAS_ECC
128 		ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
129 # endif
130 #endif /* WITH_OPENSSL */
131 		ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
132 		ssh->kex->kex[KEX_KEM_SNTRUP4591761X25519_SHA512] = kex_gen_client;
133 		ssh->kex->verify_host_key =&_ssh_verify_host_key;
134 	}
135 	*sshp = ssh;
136 	return 0;
137 }
138 
139 void
ssh_free(struct ssh * ssh)140 ssh_free(struct ssh *ssh)
141 {
142 	struct key_entry *k;
143 
144 	ssh_packet_close(ssh);
145 	/*
146 	 * we've only created the public keys variants in case we
147 	 * are a acting as a server.
148 	 */
149 	while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
150 		TAILQ_REMOVE(&ssh->public_keys, k, next);
151 		if (ssh->kex && ssh->kex->server)
152 			sshkey_free(k->key);
153 		free(k);
154 	}
155 	while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
156 		TAILQ_REMOVE(&ssh->private_keys, k, next);
157 		free(k);
158 	}
159 	if (ssh->kex)
160 		kex_free(ssh->kex);
161 	free(ssh);
162 }
163 
164 void
ssh_set_app_data(struct ssh * ssh,void * app_data)165 ssh_set_app_data(struct ssh *ssh, void *app_data)
166 {
167 	ssh->app_data = app_data;
168 }
169 
170 void *
ssh_get_app_data(struct ssh * ssh)171 ssh_get_app_data(struct ssh *ssh)
172 {
173 	return ssh->app_data;
174 }
175 
176 /* Returns < 0 on error, 0 otherwise */
177 int
ssh_add_hostkey(struct ssh * ssh,struct sshkey * key)178 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
179 {
180 	struct sshkey *pubkey = NULL;
181 	struct key_entry *k = NULL, *k_prv = NULL;
182 	int r;
183 
184 	if (ssh->kex->server) {
185 		if ((r = sshkey_from_private(key, &pubkey)) != 0)
186 			return r;
187 		if ((k = malloc(sizeof(*k))) == NULL ||
188 		    (k_prv = malloc(sizeof(*k_prv))) == NULL) {
189 			free(k);
190 			sshkey_free(pubkey);
191 			return SSH_ERR_ALLOC_FAIL;
192 		}
193 		k_prv->key = key;
194 		TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
195 
196 		/* add the public key, too */
197 		k->key = pubkey;
198 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
199 		r = 0;
200 	} else {
201 		if ((k = malloc(sizeof(*k))) == NULL)
202 			return SSH_ERR_ALLOC_FAIL;
203 		k->key = key;
204 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
205 		r = 0;
206 	}
207 
208 	return r;
209 }
210 
211 int
ssh_set_verify_host_key_callback(struct ssh * ssh,int (* cb)(struct sshkey *,struct ssh *))212 ssh_set_verify_host_key_callback(struct ssh *ssh,
213     int (*cb)(struct sshkey *, struct ssh *))
214 {
215 	if (cb == NULL || ssh->kex == NULL)
216 		return SSH_ERR_INVALID_ARGUMENT;
217 
218 	ssh->kex->verify_host_key = cb;
219 
220 	return 0;
221 }
222 
223 int
ssh_input_append(struct ssh * ssh,const u_char * data,size_t len)224 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
225 {
226 	return sshbuf_put(ssh_packet_get_input(ssh), data, len);
227 }
228 
229 int
ssh_packet_next(struct ssh * ssh,u_char * typep)230 ssh_packet_next(struct ssh *ssh, u_char *typep)
231 {
232 	int r;
233 	u_int32_t seqnr;
234 	u_char type;
235 
236 	/*
237 	 * Try to read a packet. Return SSH_MSG_NONE if no packet or not
238 	 * enough data.
239 	 */
240 	*typep = SSH_MSG_NONE;
241 	if (sshbuf_len(ssh->kex->client_version) == 0 ||
242 	    sshbuf_len(ssh->kex->server_version) == 0)
243 		return _ssh_exchange_banner(ssh);
244 	/*
245 	 * If we enough data and a dispatch function then
246 	 * call the function and get the next packet.
247 	 * Otherwise return the packet type to the caller so it
248 	 * can decide how to go on.
249 	 *
250 	 * We will only call the dispatch function for:
251 	 *     20-29    Algorithm negotiation
252 	 *     30-49    Key exchange method specific (numbers can be reused for
253 	 *              different authentication methods)
254 	 */
255 	for (;;) {
256 		if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
257 			return r;
258 		if (type > 0 && type < DISPATCH_MAX &&
259 		    type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
260 		    ssh->dispatch[type] != NULL) {
261 			if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
262 				return r;
263 		} else {
264 			*typep = type;
265 			return 0;
266 		}
267 	}
268 }
269 
270 const u_char *
ssh_packet_payload(struct ssh * ssh,size_t * lenp)271 ssh_packet_payload(struct ssh *ssh, size_t *lenp)
272 {
273 	return sshpkt_ptr(ssh, lenp);
274 }
275 
276 int
ssh_packet_put(struct ssh * ssh,int type,const u_char * data,size_t len)277 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
278 {
279 	int r;
280 
281 	if ((r = sshpkt_start(ssh, type)) != 0 ||
282 	    (r = sshpkt_put(ssh, data, len)) != 0 ||
283 	    (r = sshpkt_send(ssh)) != 0)
284 		return r;
285 	return 0;
286 }
287 
288 const u_char *
ssh_output_ptr(struct ssh * ssh,size_t * len)289 ssh_output_ptr(struct ssh *ssh, size_t *len)
290 {
291 	struct sshbuf *output = ssh_packet_get_output(ssh);
292 
293 	*len = sshbuf_len(output);
294 	return sshbuf_ptr(output);
295 }
296 
297 int
ssh_output_consume(struct ssh * ssh,size_t len)298 ssh_output_consume(struct ssh *ssh, size_t len)
299 {
300 	return sshbuf_consume(ssh_packet_get_output(ssh), len);
301 }
302 
303 int
ssh_output_space(struct ssh * ssh,size_t len)304 ssh_output_space(struct ssh *ssh, size_t len)
305 {
306 	return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
307 }
308 
309 int
ssh_input_space(struct ssh * ssh,size_t len)310 ssh_input_space(struct ssh *ssh, size_t len)
311 {
312 	return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
313 }
314 
315 /* Read other side's version identification. */
316 int
_ssh_read_banner(struct ssh * ssh,struct sshbuf * banner)317 _ssh_read_banner(struct ssh *ssh, struct sshbuf *banner)
318 {
319 	struct sshbuf *input = ssh_packet_get_input(ssh);
320 	const char *mismatch = "Protocol mismatch.\r\n";
321 	const u_char *s = sshbuf_ptr(input);
322 	u_char c;
323 	char *cp, *remote_version;
324 	int r, remote_major, remote_minor, expect_nl;
325 	size_t n, j;
326 
327 	for (j = n = 0;;) {
328 		sshbuf_reset(banner);
329 		expect_nl = 0;
330 		for (;;) {
331 			if (j >= sshbuf_len(input))
332 				return 0; /* insufficient data in input buf */
333 			c = s[j++];
334 			if (c == '\r') {
335 				expect_nl = 1;
336 				continue;
337 			}
338 			if (c == '\n')
339 				break;
340 			if (expect_nl)
341 				goto bad;
342 			if ((r = sshbuf_put_u8(banner, c)) != 0)
343 				return r;
344 			if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN)
345 				goto bad;
346 		}
347 		if (sshbuf_len(banner) >= 4 &&
348 		    memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0)
349 			break;
350 		if ((cp = sshbuf_dup_string(banner)) == NULL)
351 			return SSH_ERR_ALLOC_FAIL;
352 		debug("%s: %s", __func__, cp);
353 		free(cp);
354 		/* Accept lines before banner only on client */
355 		if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) {
356   bad:
357 			if ((r = sshbuf_put(ssh_packet_get_output(ssh),
358 			   mismatch, strlen(mismatch))) != 0)
359 				return r;
360 			return SSH_ERR_NO_PROTOCOL_VERSION;
361 		}
362 	}
363 	if ((r = sshbuf_consume(input, j)) != 0)
364 		return r;
365 
366 	if ((cp = sshbuf_dup_string(banner)) == NULL)
367 		return SSH_ERR_ALLOC_FAIL;
368 	/* XXX remote version must be the same size as banner for sscanf */
369 	if ((remote_version = calloc(1, sshbuf_len(banner))) == NULL)
370 		return SSH_ERR_ALLOC_FAIL;
371 
372 	/*
373 	 * Check that the versions match.  In future this might accept
374 	 * several versions and set appropriate flags to handle them.
375 	 */
376 	if (sscanf(cp, "SSH-%d.%d-%[^\n]\n",
377 	    &remote_major, &remote_minor, remote_version) != 3)
378 		return SSH_ERR_INVALID_FORMAT;
379 	debug("Remote protocol version %d.%d, remote software version %.100s",
380 	    remote_major, remote_minor, remote_version);
381 
382 	ssh->compat = compat_datafellows(remote_version);
383 	if  (remote_major == 1 && remote_minor == 99) {
384 		remote_major = 2;
385 		remote_minor = 0;
386 	}
387 	if (remote_major != 2)
388 		return SSH_ERR_PROTOCOL_MISMATCH;
389 	debug("Remote version string %.100s", cp);
390 	free(cp);
391 	return 0;
392 }
393 
394 /* Send our own protocol version identification. */
395 int
_ssh_send_banner(struct ssh * ssh,struct sshbuf * banner)396 _ssh_send_banner(struct ssh *ssh, struct sshbuf *banner)
397 {
398 	char *cp;
399 	int r;
400 
401 	if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0)
402 		return r;
403 	if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0)
404 		return r;
405 	/* Remove trailing \r\n */
406 	if ((r = sshbuf_consume_end(banner, 2)) != 0)
407 		return r;
408 	if ((cp = sshbuf_dup_string(banner)) == NULL)
409 		return SSH_ERR_ALLOC_FAIL;
410 	debug("Local version string %.100s", cp);
411 	free(cp);
412 	return 0;
413 }
414 
415 int
_ssh_exchange_banner(struct ssh * ssh)416 _ssh_exchange_banner(struct ssh *ssh)
417 {
418 	struct kex *kex = ssh->kex;
419 	int r;
420 
421 	/*
422 	 * if _ssh_read_banner() cannot parse a full version string
423 	 * it will return NULL and we end up calling it again.
424 	 */
425 
426 	r = 0;
427 	if (kex->server) {
428 		if (sshbuf_len(ssh->kex->server_version) == 0)
429 			r = _ssh_send_banner(ssh, ssh->kex->server_version);
430 		if (r == 0 &&
431 		    sshbuf_len(ssh->kex->server_version) != 0 &&
432 		    sshbuf_len(ssh->kex->client_version) == 0)
433 			r = _ssh_read_banner(ssh, ssh->kex->client_version);
434 	} else {
435 		if (sshbuf_len(ssh->kex->server_version) == 0)
436 			r = _ssh_read_banner(ssh, ssh->kex->server_version);
437 		if (r == 0 &&
438 		    sshbuf_len(ssh->kex->server_version) != 0 &&
439 		    sshbuf_len(ssh->kex->client_version) == 0)
440 			r = _ssh_send_banner(ssh, ssh->kex->client_version);
441 	}
442 	if (r != 0)
443 		return r;
444 	/* start initial kex as soon as we have exchanged the banners */
445 	if (sshbuf_len(ssh->kex->server_version) != 0 &&
446 	    sshbuf_len(ssh->kex->client_version) != 0) {
447 		if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
448 		    (r = kex_send_kexinit(ssh)) != 0)
449 			return r;
450 	}
451 	return 0;
452 }
453 
454 struct sshkey *
_ssh_host_public_key(int type,int nid,struct ssh * ssh)455 _ssh_host_public_key(int type, int nid, struct ssh *ssh)
456 {
457 	struct key_entry *k;
458 
459 	debug3("%s: need %d", __func__, type);
460 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
461 		debug3("%s: check %s", __func__, sshkey_type(k->key));
462 		if (k->key->type == type &&
463 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
464 			return (k->key);
465 	}
466 	return (NULL);
467 }
468 
469 struct sshkey *
_ssh_host_private_key(int type,int nid,struct ssh * ssh)470 _ssh_host_private_key(int type, int nid, struct ssh *ssh)
471 {
472 	struct key_entry *k;
473 
474 	debug3("%s: need %d", __func__, type);
475 	TAILQ_FOREACH(k, &ssh->private_keys, next) {
476 		debug3("%s: check %s", __func__, sshkey_type(k->key));
477 		if (k->key->type == type &&
478 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
479 			return (k->key);
480 	}
481 	return (NULL);
482 }
483 
484 int
_ssh_verify_host_key(struct sshkey * hostkey,struct ssh * ssh)485 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
486 {
487 	struct key_entry *k;
488 
489 	debug3("%s: need %s", __func__, sshkey_type(hostkey));
490 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
491 		debug3("%s: check %s", __func__, sshkey_type(k->key));
492 		if (sshkey_equal_public(hostkey, k->key))
493 			return (0);	/* ok */
494 	}
495 	return (-1);	/* failed */
496 }
497 
498 /* offer hostkey algorithms in kexinit depending on registered keys */
499 int
_ssh_order_hostkeyalgs(struct ssh * ssh)500 _ssh_order_hostkeyalgs(struct ssh *ssh)
501 {
502 	struct key_entry *k;
503 	char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
504 	char **proposal;
505 	size_t maxlen;
506 	int ktype, r;
507 
508 	/* XXX we de-serialize ssh->kex->my, modify it, and change it */
509 	if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
510 		return r;
511 	orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
512 	if ((oavail = avail = strdup(orig)) == NULL) {
513 		r = SSH_ERR_ALLOC_FAIL;
514 		goto out;
515 	}
516 	maxlen = strlen(avail) + 1;
517 	if ((replace = calloc(1, maxlen)) == NULL) {
518 		r = SSH_ERR_ALLOC_FAIL;
519 		goto out;
520 	}
521 	*replace = '\0';
522 	while ((alg = strsep(&avail, ",")) && *alg != '\0') {
523 		if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
524 			continue;
525 		TAILQ_FOREACH(k, &ssh->public_keys, next) {
526 			if (k->key->type == ktype ||
527 			    (sshkey_is_cert(k->key) && k->key->type ==
528 			    sshkey_type_plain(ktype))) {
529 				if (*replace != '\0')
530 					strlcat(replace, ",", maxlen);
531 				strlcat(replace, alg, maxlen);
532 				break;
533 			}
534 		}
535 	}
536 	if (*replace != '\0') {
537 		debug2("%s: orig/%d    %s", __func__, ssh->kex->server, orig);
538 		debug2("%s: replace/%d %s", __func__, ssh->kex->server, replace);
539 		free(orig);
540 		proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
541 		replace = NULL;	/* owned by proposal */
542 		r = kex_prop2buf(ssh->kex->my, proposal);
543 	}
544  out:
545 	free(oavail);
546 	free(replace);
547 	kex_prop_free(proposal);
548 	return r;
549 }
550 
551 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)552 _ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey,
553     struct sshkey *pubkey, u_char **signature, size_t *slen,
554     const u_char *data, size_t dlen, const char *alg)
555 {
556 	return sshkey_sign(privkey, signature, slen, data, dlen,
557 	    alg, ssh->compat);
558 }
559