ssh_api.c revision 296853 
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
36int	_ssh_exchange_banner(struct ssh *);
37int	_ssh_send_banner(struct ssh *, char **);
38int	_ssh_read_banner(struct ssh *, char **);
39int	_ssh_order_hostkeyalgs(struct ssh *);
40int	_ssh_verify_host_key(struct sshkey *, struct ssh *);
41struct sshkey *_ssh_host_public_key(int, int, struct ssh *);
42struct sshkey *_ssh_host_private_key(int, int, struct ssh *);
43int	_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 */
50int	use_privsep = 0;
51int	mm_sshkey_sign(struct sshkey *, u_char **, u_int *,
52    u_char *, u_int, char *, u_int);
53DH	*mm_choose_dh(int, int, int);
54
55/* Define these two variables here so that they are part of the library */
56u_char *session_id2 = NULL;
57u_int session_id2_len = 0;
58
59int
60mm_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
66DH *
67mm_choose_dh(int min, int nbits, int max)
68{
69	return (NULL);
70}
71
72/* API */
73
74int
75ssh_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
133void
134ssh_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
158void
159ssh_set_app_data(struct ssh *ssh, void *app_data)
160{
161	ssh->app_data = app_data;
162}
163
164void *
165ssh_get_app_data(struct ssh *ssh)
166{
167	return ssh->app_data;
168}
169
170/* Returns < 0 on error, 0 otherwise */
171int
172ssh_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
205int
206ssh_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
217int
218ssh_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
223int
224ssh_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
264const u_char *
265ssh_packet_payload(struct ssh *ssh, size_t *lenp)
266{
267	return sshpkt_ptr(ssh, lenp);
268}
269
270int
271ssh_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
282const u_char *
283ssh_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
291int
292ssh_output_consume(struct ssh *ssh, size_t len)
293{
294	return sshbuf_consume(ssh_packet_get_output(ssh), len);
295}
296
297int
298ssh_output_space(struct ssh *ssh, size_t len)
299{
300	return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
301}
302
303int
304ssh_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. */
310int
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. */
379int
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
395int
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
434struct 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
449struct 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
464int
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 */
479int
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
531int
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