xref: /openssh-portable/ssh_api.c (revision 76c9fbbe)
1 /* $OpenBSD: ssh_api.c,v 1.5 2015/12/04 16:41:28 markus 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 "ssh1.h" /* For SSH_MSG_NONE */
21 #include "ssh_api.h"
22 #include "compat.h"
23 #include "log.h"
24 #include "authfile.h"
25 #include "sshkey.h"
26 #include "misc.h"
27 #include "ssh1.h"
28 #include "ssh2.h"
29 #include "version.h"
30 #include "myproposal.h"
31 #include "ssherr.h"
32 #include "sshbuf.h"
33 
34 #include <string.h>
35 
36 int	_ssh_exchange_banner(struct ssh *);
37 int	_ssh_send_banner(struct ssh *, char **);
38 int	_ssh_read_banner(struct ssh *, char **);
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 sshkey *, struct sshkey *,
44     u_char **, size_t *, const u_char *, size_t, const char *, u_int);
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 #ifdef WITH_OPENSSL
85 		OpenSSL_add_all_algorithms();
86 #endif /* WITH_OPENSSL */
87 		called = 1;
88 	}
89 
90 	if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL)
91 		return SSH_ERR_ALLOC_FAIL;
92 	if (is_server)
93 		ssh_packet_set_server(ssh);
94 
95 	/* Initialize key exchange */
96 	proposal = kex_params ? kex_params->proposal : myproposal;
97 	if ((r = kex_new(ssh, proposal, &ssh->kex)) != 0) {
98 		ssh_free(ssh);
99 		return r;
100 	}
101 	ssh->kex->server = is_server;
102 	if (is_server) {
103 #ifdef WITH_OPENSSL
104 		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kexdh_server;
105 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kexdh_server;
106 		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
107 		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
108 # ifdef OPENSSL_HAS_ECC
109 		ssh->kex->kex[KEX_ECDH_SHA2] = kexecdh_server;
110 # endif
111 #endif /* WITH_OPENSSL */
112 		ssh->kex->kex[KEX_C25519_SHA256] = kexc25519_server;
113 		ssh->kex->load_host_public_key=&_ssh_host_public_key;
114 		ssh->kex->load_host_private_key=&_ssh_host_private_key;
115 		ssh->kex->sign=&_ssh_host_key_sign;
116 	} else {
117 #ifdef WITH_OPENSSL
118 		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kexdh_client;
119 		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kexdh_client;
120 		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
121 		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
122 # ifdef OPENSSL_HAS_ECC
123 		ssh->kex->kex[KEX_ECDH_SHA2] = kexecdh_client;
124 # endif
125 #endif /* WITH_OPENSSL */
126 		ssh->kex->kex[KEX_C25519_SHA256] = kexc25519_client;
127 		ssh->kex->verify_host_key =&_ssh_verify_host_key;
128 	}
129 	*sshp = ssh;
130 	return 0;
131 }
132 
133 void
134 ssh_free(struct ssh *ssh)
135 {
136 	struct key_entry *k;
137 
138 	ssh_packet_close(ssh);
139 	/*
140 	 * we've only created the public keys variants in case we
141 	 * are a acting as a server.
142 	 */
143 	while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
144 		TAILQ_REMOVE(&ssh->public_keys, k, next);
145 		if (ssh->kex && ssh->kex->server)
146 			sshkey_free(k->key);
147 		free(k);
148 	}
149 	while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
150 		TAILQ_REMOVE(&ssh->private_keys, k, next);
151 		free(k);
152 	}
153 	if (ssh->kex)
154 		kex_free(ssh->kex);
155 	free(ssh);
156 }
157 
158 void
159 ssh_set_app_data(struct ssh *ssh, void *app_data)
160 {
161 	ssh->app_data = app_data;
162 }
163 
164 void *
165 ssh_get_app_data(struct ssh *ssh)
166 {
167 	return ssh->app_data;
168 }
169 
170 /* Returns < 0 on error, 0 otherwise */
171 int
172 ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
173 {
174 	struct sshkey *pubkey = NULL;
175 	struct key_entry *k = NULL, *k_prv = NULL;
176 	int r;
177 
178 	if (ssh->kex->server) {
179 		if ((r = sshkey_from_private(key, &pubkey)) != 0)
180 			return r;
181 		if ((k = malloc(sizeof(*k))) == NULL ||
182 		    (k_prv = malloc(sizeof(*k_prv))) == NULL) {
183 			free(k);
184 			sshkey_free(pubkey);
185 			return SSH_ERR_ALLOC_FAIL;
186 		}
187 		k_prv->key = key;
188 		TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
189 
190 		/* add the public key, too */
191 		k->key = pubkey;
192 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
193 		r = 0;
194 	} else {
195 		if ((k = malloc(sizeof(*k))) == NULL)
196 			return SSH_ERR_ALLOC_FAIL;
197 		k->key = key;
198 		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
199 		r = 0;
200 	}
201 
202 	return r;
203 }
204 
205 int
206 ssh_set_verify_host_key_callback(struct ssh *ssh,
207     int (*cb)(struct sshkey *, struct ssh *))
208 {
209 	if (cb == NULL || ssh->kex == NULL)
210 		return SSH_ERR_INVALID_ARGUMENT;
211 
212 	ssh->kex->verify_host_key = cb;
213 
214 	return 0;
215 }
216 
217 int
218 ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
219 {
220 	return sshbuf_put(ssh_packet_get_input(ssh), data, len);
221 }
222 
223 int
224 ssh_packet_next(struct ssh *ssh, u_char *typep)
225 {
226 	int r;
227 	u_int32_t seqnr;
228 	u_char type;
229 
230 	/*
231 	 * Try to read a packet. Return SSH_MSG_NONE if no packet or not
232 	 * enough data.
233 	 */
234 	*typep = SSH_MSG_NONE;
235 	if (ssh->kex->client_version_string == NULL ||
236 	    ssh->kex->server_version_string == NULL)
237 		return _ssh_exchange_banner(ssh);
238 	/*
239 	 * If we enough data and a dispatch function then
240 	 * call the function and get the next packet.
241 	 * Otherwise return the packet type to the caller so it
242 	 * can decide how to go on.
243 	 *
244 	 * We will only call the dispatch function for:
245 	 *     20-29    Algorithm negotiation
246 	 *     30-49    Key exchange method specific (numbers can be reused for
247 	 *              different authentication methods)
248 	 */
249 	for (;;) {
250 		if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
251 			return r;
252 		if (type > 0 && type < DISPATCH_MAX &&
253 		    type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
254 		    ssh->dispatch[type] != NULL) {
255 			if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
256 				return r;
257 		} else {
258 			*typep = type;
259 			return 0;
260 		}
261 	}
262 }
263 
264 const u_char *
265 ssh_packet_payload(struct ssh *ssh, size_t *lenp)
266 {
267 	return sshpkt_ptr(ssh, lenp);
268 }
269 
270 int
271 ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
272 {
273 	int r;
274 
275 	if ((r = sshpkt_start(ssh, type)) != 0 ||
276 	    (r = sshpkt_put(ssh, data, len)) != 0 ||
277 	    (r = sshpkt_send(ssh)) != 0)
278 		return r;
279 	return 0;
280 }
281 
282 const u_char *
283 ssh_output_ptr(struct ssh *ssh, size_t *len)
284 {
285 	struct sshbuf *output = ssh_packet_get_output(ssh);
286 
287 	*len = sshbuf_len(output);
288 	return sshbuf_ptr(output);
289 }
290 
291 int
292 ssh_output_consume(struct ssh *ssh, size_t len)
293 {
294 	return sshbuf_consume(ssh_packet_get_output(ssh), len);
295 }
296 
297 int
298 ssh_output_space(struct ssh *ssh, size_t len)
299 {
300 	return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
301 }
302 
303 int
304 ssh_input_space(struct ssh *ssh, size_t len)
305 {
306 	return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
307 }
308 
309 /* Read other side's version identification. */
310 int
311 _ssh_read_banner(struct ssh *ssh, char **bannerp)
312 {
313 	struct sshbuf *input;
314 	const char *s;
315 	char buf[256], remote_version[256];	/* must be same size! */
316 	const char *mismatch = "Protocol mismatch.\r\n";
317 	int r, remote_major, remote_minor;
318 	size_t i, n, j, len;
319 
320 	*bannerp = NULL;
321 	input = ssh_packet_get_input(ssh);
322 	len = sshbuf_len(input);
323 	s = (const char *)sshbuf_ptr(input);
324 	for (j = n = 0;;) {
325 		for (i = 0; i < sizeof(buf) - 1; i++) {
326 			if (j >= len)
327 				return (0);
328 			buf[i] = s[j++];
329 			if (buf[i] == '\r') {
330 				buf[i] = '\n';
331 				buf[i + 1] = 0;
332 				continue;		/**XXX wait for \n */
333 			}
334 			if (buf[i] == '\n') {
335 				buf[i + 1] = 0;
336 				break;
337 			}
338 		}
339 		buf[sizeof(buf) - 1] = 0;
340 		if (strncmp(buf, "SSH-", 4) == 0)
341 			break;
342 		debug("ssh_exchange_identification: %s", buf);
343 		if (ssh->kex->server || ++n > 65536) {
344 			if ((r = sshbuf_put(ssh_packet_get_output(ssh),
345 			   mismatch, strlen(mismatch))) != 0)
346 				return r;
347 			return SSH_ERR_NO_PROTOCOL_VERSION;
348 		}
349 	}
350 	if ((r = sshbuf_consume(input, j)) != 0)
351 		return r;
352 
353 	/*
354 	 * Check that the versions match.  In future this might accept
355 	 * several versions and set appropriate flags to handle them.
356 	 */
357 	if (sscanf(buf, "SSH-%d.%d-%[^\n]\n",
358 	    &remote_major, &remote_minor, remote_version) != 3)
359 		return SSH_ERR_INVALID_FORMAT;
360 	debug("Remote protocol version %d.%d, remote software version %.100s",
361 	    remote_major, remote_minor, remote_version);
362 
363 	ssh->compat = compat_datafellows(remote_version);
364 	if  (remote_major == 1 && remote_minor == 99) {
365 		remote_major = 2;
366 		remote_minor = 0;
367 	}
368 	if (remote_major != 2)
369 		return SSH_ERR_PROTOCOL_MISMATCH;
370 	enable_compat20();
371 	chop(buf);
372 	debug("Remote version string %.100s", buf);
373 	if ((*bannerp = strdup(buf)) == NULL)
374 		return SSH_ERR_ALLOC_FAIL;
375 	return 0;
376 }
377 
378 /* Send our own protocol version identification. */
379 int
380 _ssh_send_banner(struct ssh *ssh, char **bannerp)
381 {
382 	char buf[256];
383 	int r;
384 
385 	snprintf(buf, sizeof buf, "SSH-2.0-%.100s\r\n", SSH_VERSION);
386 	if ((r = sshbuf_put(ssh_packet_get_output(ssh), buf, strlen(buf))) != 0)
387 		return r;
388 	chop(buf);
389 	debug("Local version string %.100s", buf);
390 	if ((*bannerp = strdup(buf)) == NULL)
391 		return SSH_ERR_ALLOC_FAIL;
392 	return 0;
393 }
394 
395 int
396 _ssh_exchange_banner(struct ssh *ssh)
397 {
398 	struct kex *kex = ssh->kex;
399 	int r;
400 
401 	/*
402 	 * if _ssh_read_banner() cannot parse a full version string
403 	 * it will return NULL and we end up calling it again.
404 	 */
405 
406 	r = 0;
407 	if (kex->server) {
408 		if (kex->server_version_string == NULL)
409 			r = _ssh_send_banner(ssh, &kex->server_version_string);
410 		if (r == 0 &&
411 		    kex->server_version_string != NULL &&
412 		    kex->client_version_string == NULL)
413 			r = _ssh_read_banner(ssh, &kex->client_version_string);
414 	} else {
415 		if (kex->server_version_string == NULL)
416 			r = _ssh_read_banner(ssh, &kex->server_version_string);
417 		if (r == 0 &&
418 		    kex->server_version_string != NULL &&
419 		    kex->client_version_string == NULL)
420 			r = _ssh_send_banner(ssh, &kex->client_version_string);
421 	}
422 	if (r != 0)
423 		return r;
424 	/* start initial kex as soon as we have exchanged the banners */
425 	if (kex->server_version_string != NULL &&
426 	    kex->client_version_string != NULL) {
427 		if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
428 		    (r = kex_send_kexinit(ssh)) != 0)
429 			return r;
430 	}
431 	return 0;
432 }
433 
434 struct sshkey *
435 _ssh_host_public_key(int type, int nid, struct ssh *ssh)
436 {
437 	struct key_entry *k;
438 
439 	debug3("%s: need %d", __func__, type);
440 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
441 		debug3("%s: check %s", __func__, sshkey_type(k->key));
442 		if (k->key->type == type &&
443 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
444 			return (k->key);
445 	}
446 	return (NULL);
447 }
448 
449 struct sshkey *
450 _ssh_host_private_key(int type, int nid, struct ssh *ssh)
451 {
452 	struct key_entry *k;
453 
454 	debug3("%s: need %d", __func__, type);
455 	TAILQ_FOREACH(k, &ssh->private_keys, next) {
456 		debug3("%s: check %s", __func__, sshkey_type(k->key));
457 		if (k->key->type == type &&
458 		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
459 			return (k->key);
460 	}
461 	return (NULL);
462 }
463 
464 int
465 _ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
466 {
467 	struct key_entry *k;
468 
469 	debug3("%s: need %s", __func__, sshkey_type(hostkey));
470 	TAILQ_FOREACH(k, &ssh->public_keys, next) {
471 		debug3("%s: check %s", __func__, sshkey_type(k->key));
472 		if (sshkey_equal_public(hostkey, k->key))
473 			return (0);	/* ok */
474 	}
475 	return (-1);	/* failed */
476 }
477 
478 /* offer hostkey algorithms in kexinit depending on registered keys */
479 int
480 _ssh_order_hostkeyalgs(struct ssh *ssh)
481 {
482 	struct key_entry *k;
483 	char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
484 	char **proposal;
485 	size_t maxlen;
486 	int ktype, r;
487 
488 	/* XXX we de-serialize ssh->kex->my, modify it, and change it */
489 	if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
490 		return r;
491 	orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
492 	if ((oavail = avail = strdup(orig)) == NULL) {
493 		r = SSH_ERR_ALLOC_FAIL;
494 		goto out;
495 	}
496 	maxlen = strlen(avail) + 1;
497 	if ((replace = calloc(1, maxlen)) == NULL) {
498 		r = SSH_ERR_ALLOC_FAIL;
499 		goto out;
500 	}
501 	*replace = '\0';
502 	while ((alg = strsep(&avail, ",")) && *alg != '\0') {
503 		if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
504 			continue;
505 		TAILQ_FOREACH(k, &ssh->public_keys, next) {
506 			if (k->key->type == ktype ||
507 			    (sshkey_is_cert(k->key) && k->key->type ==
508 			    sshkey_type_plain(ktype))) {
509 				if (*replace != '\0')
510 					strlcat(replace, ",", maxlen);
511 				strlcat(replace, alg, maxlen);
512 				break;
513 			}
514 		}
515 	}
516 	if (*replace != '\0') {
517 		debug2("%s: orig/%d    %s", __func__, ssh->kex->server, orig);
518 		debug2("%s: replace/%d %s", __func__, ssh->kex->server, replace);
519 		free(orig);
520 		proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
521 		replace = NULL;	/* owned by proposal */
522 		r = kex_prop2buf(ssh->kex->my, proposal);
523 	}
524  out:
525 	free(oavail);
526 	free(replace);
527 	kex_prop_free(proposal);
528 	return r;
529 }
530 
531 int
532 _ssh_host_key_sign(struct sshkey *privkey, struct sshkey *pubkey,
533     u_char **signature, size_t *slen, const u_char *data, size_t dlen,
534     const char *alg, u_int compat)
535 {
536 	return sshkey_sign(privkey, signature, slen, data, dlen, alg, compat);
537 }
538