ssh_api.c revision 323129 
1/* $OpenBSD: ssh_api.c,v 1.7 2016/05/04 14:22:33 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 "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 <string.h>
33
34int	_ssh_exchange_banner(struct ssh *);
35int	_ssh_send_banner(struct ssh *, char **);
36int	_ssh_read_banner(struct ssh *, char **);
37int	_ssh_order_hostkeyalgs(struct ssh *);
38int	_ssh_verify_host_key(struct sshkey *, struct ssh *);
39struct sshkey *_ssh_host_public_key(int, int, struct ssh *);
40struct sshkey *_ssh_host_private_key(int, int, struct ssh *);
41int	_ssh_host_key_sign(struct sshkey *, struct sshkey *,
42    u_char **, size_t *, const u_char *, size_t, const char *, u_int);
43
44/*
45 * stubs for the server side implementation of kex.
46 * disable privsep so our stubs will never be called.
47 */
48int	use_privsep = 0;
49int	mm_sshkey_sign(struct sshkey *, u_char **, u_int *,
50    u_char *, u_int, char *, u_int);
51DH	*mm_choose_dh(int, int, int);
52
53/* Define these two variables here so that they are part of the library */
54u_char *session_id2 = NULL;
55u_int session_id2_len = 0;
56
57int
58mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp,
59    u_char *data, u_int datalen, char *alg, u_int compat)
60{
61	return (-1);
62}
63
64DH *
65mm_choose_dh(int min, int nbits, int max)
66{
67	return (NULL);
68}
69
70/* API */
71
72int
73ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params)
74{
75        char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
76	struct ssh *ssh;
77	char **proposal;
78	static int called;
79	int r;
80
81	if (!called) {
82#ifdef WITH_OPENSSL
83		OpenSSL_add_all_algorithms();
84#endif /* WITH_OPENSSL */
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_new(ssh, proposal, &ssh->kex)) != 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
137void
138ssh_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
162void
163ssh_set_app_data(struct ssh *ssh, void *app_data)
164{
165	ssh->app_data = app_data;
166}
167
168void *
169ssh_get_app_data(struct ssh *ssh)
170{
171	return ssh->app_data;
172}
173
174/* Returns < 0 on error, 0 otherwise */
175int
176ssh_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
209int
210ssh_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
221int
222ssh_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
227int
228ssh_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 (ssh->kex->client_version_string == NULL ||
240	    ssh->kex->server_version_string == NULL)
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
268const u_char *
269ssh_packet_payload(struct ssh *ssh, size_t *lenp)
270{
271	return sshpkt_ptr(ssh, lenp);
272}
273
274int
275ssh_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
286const u_char *
287ssh_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
295int
296ssh_output_consume(struct ssh *ssh, size_t len)
297{
298	return sshbuf_consume(ssh_packet_get_output(ssh), len);
299}
300
301int
302ssh_output_space(struct ssh *ssh, size_t len)
303{
304	return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
305}
306
307int
308ssh_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. */
314int
315_ssh_read_banner(struct ssh *ssh, char **bannerp)
316{
317	struct sshbuf *input;
318	const char *s;
319	char buf[256], remote_version[256];	/* must be same size! */
320	const char *mismatch = "Protocol mismatch.\r\n";
321	int r, remote_major, remote_minor;
322	size_t i, n, j, len;
323
324	*bannerp = NULL;
325	input = ssh_packet_get_input(ssh);
326	len = sshbuf_len(input);
327	s = (const char *)sshbuf_ptr(input);
328	for (j = n = 0;;) {
329		for (i = 0; i < sizeof(buf) - 1; i++) {
330			if (j >= len)
331				return (0);
332			buf[i] = s[j++];
333			if (buf[i] == '\r') {
334				buf[i] = '\n';
335				buf[i + 1] = 0;
336				continue;		/**XXX wait for \n */
337			}
338			if (buf[i] == '\n') {
339				buf[i + 1] = 0;
340				break;
341			}
342		}
343		buf[sizeof(buf) - 1] = 0;
344		if (strncmp(buf, "SSH-", 4) == 0)
345			break;
346		debug("ssh_exchange_identification: %s", buf);
347		if (ssh->kex->server || ++n > 65536) {
348			if ((r = sshbuf_put(ssh_packet_get_output(ssh),
349			   mismatch, strlen(mismatch))) != 0)
350				return r;
351			return SSH_ERR_NO_PROTOCOL_VERSION;
352		}
353	}
354	if ((r = sshbuf_consume(input, j)) != 0)
355		return r;
356
357	/*
358	 * Check that the versions match.  In future this might accept
359	 * several versions and set appropriate flags to handle them.
360	 */
361	if (sscanf(buf, "SSH-%d.%d-%[^\n]\n",
362	    &remote_major, &remote_minor, remote_version) != 3)
363		return SSH_ERR_INVALID_FORMAT;
364	debug("Remote protocol version %d.%d, remote software version %.100s",
365	    remote_major, remote_minor, remote_version);
366
367	ssh->compat = compat_datafellows(remote_version);
368	if  (remote_major == 1 && remote_minor == 99) {
369		remote_major = 2;
370		remote_minor = 0;
371	}
372	if (remote_major != 2)
373		return SSH_ERR_PROTOCOL_MISMATCH;
374	enable_compat20();
375	chop(buf);
376	debug("Remote version string %.100s", buf);
377	if ((*bannerp = strdup(buf)) == NULL)
378		return SSH_ERR_ALLOC_FAIL;
379	return 0;
380}
381
382/* Send our own protocol version identification. */
383int
384_ssh_send_banner(struct ssh *ssh, char **bannerp)
385{
386	char buf[256];
387	int r;
388
389	snprintf(buf, sizeof buf, "SSH-2.0-%.100s\r\n", SSH_VERSION);
390	if ((r = sshbuf_put(ssh_packet_get_output(ssh), buf, strlen(buf))) != 0)
391		return r;
392	chop(buf);
393	debug("Local version string %.100s", buf);
394	if ((*bannerp = strdup(buf)) == NULL)
395		return SSH_ERR_ALLOC_FAIL;
396	return 0;
397}
398
399int
400_ssh_exchange_banner(struct ssh *ssh)
401{
402	struct kex *kex = ssh->kex;
403	int r;
404
405	/*
406	 * if _ssh_read_banner() cannot parse a full version string
407	 * it will return NULL and we end up calling it again.
408	 */
409
410	r = 0;
411	if (kex->server) {
412		if (kex->server_version_string == NULL)
413			r = _ssh_send_banner(ssh, &kex->server_version_string);
414		if (r == 0 &&
415		    kex->server_version_string != NULL &&
416		    kex->client_version_string == NULL)
417			r = _ssh_read_banner(ssh, &kex->client_version_string);
418	} else {
419		if (kex->server_version_string == NULL)
420			r = _ssh_read_banner(ssh, &kex->server_version_string);
421		if (r == 0 &&
422		    kex->server_version_string != NULL &&
423		    kex->client_version_string == NULL)
424			r = _ssh_send_banner(ssh, &kex->client_version_string);
425	}
426	if (r != 0)
427		return r;
428	/* start initial kex as soon as we have exchanged the banners */
429	if (kex->server_version_string != NULL &&
430	    kex->client_version_string != NULL) {
431		if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
432		    (r = kex_send_kexinit(ssh)) != 0)
433			return r;
434	}
435	return 0;
436}
437
438struct sshkey *
439_ssh_host_public_key(int type, int nid, struct ssh *ssh)
440{
441	struct key_entry *k;
442
443	debug3("%s: need %d", __func__, type);
444	TAILQ_FOREACH(k, &ssh->public_keys, next) {
445		debug3("%s: check %s", __func__, sshkey_type(k->key));
446		if (k->key->type == type &&
447		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
448			return (k->key);
449	}
450	return (NULL);
451}
452
453struct sshkey *
454_ssh_host_private_key(int type, int nid, struct ssh *ssh)
455{
456	struct key_entry *k;
457
458	debug3("%s: need %d", __func__, type);
459	TAILQ_FOREACH(k, &ssh->private_keys, next) {
460		debug3("%s: check %s", __func__, sshkey_type(k->key));
461		if (k->key->type == type &&
462		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
463			return (k->key);
464	}
465	return (NULL);
466}
467
468int
469_ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
470{
471	struct key_entry *k;
472
473	debug3("%s: need %s", __func__, sshkey_type(hostkey));
474	TAILQ_FOREACH(k, &ssh->public_keys, next) {
475		debug3("%s: check %s", __func__, sshkey_type(k->key));
476		if (sshkey_equal_public(hostkey, k->key))
477			return (0);	/* ok */
478	}
479	return (-1);	/* failed */
480}
481
482/* offer hostkey algorithms in kexinit depending on registered keys */
483int
484_ssh_order_hostkeyalgs(struct ssh *ssh)
485{
486	struct key_entry *k;
487	char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
488	char **proposal;
489	size_t maxlen;
490	int ktype, r;
491
492	/* XXX we de-serialize ssh->kex->my, modify it, and change it */
493	if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
494		return r;
495	orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
496	if ((oavail = avail = strdup(orig)) == NULL) {
497		r = SSH_ERR_ALLOC_FAIL;
498		goto out;
499	}
500	maxlen = strlen(avail) + 1;
501	if ((replace = calloc(1, maxlen)) == NULL) {
502		r = SSH_ERR_ALLOC_FAIL;
503		goto out;
504	}
505	*replace = '\0';
506	while ((alg = strsep(&avail, ",")) && *alg != '\0') {
507		if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
508			continue;
509		TAILQ_FOREACH(k, &ssh->public_keys, next) {
510			if (k->key->type == ktype ||
511			    (sshkey_is_cert(k->key) && k->key->type ==
512			    sshkey_type_plain(ktype))) {
513				if (*replace != '\0')
514					strlcat(replace, ",", maxlen);
515				strlcat(replace, alg, maxlen);
516				break;
517			}
518		}
519	}
520	if (*replace != '\0') {
521		debug2("%s: orig/%d    %s", __func__, ssh->kex->server, orig);
522		debug2("%s: replace/%d %s", __func__, ssh->kex->server, replace);
523		free(orig);
524		proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
525		replace = NULL;	/* owned by proposal */
526		r = kex_prop2buf(ssh->kex->my, proposal);
527	}
528 out:
529	free(oavail);
530	free(replace);
531	kex_prop_free(proposal);
532	return r;
533}
534
535int
536_ssh_host_key_sign(struct sshkey *privkey, struct sshkey *pubkey,
537    u_char **signature, size_t *slen, const u_char *data, size_t dlen,
538    const char *alg, u_int compat)
539{
540	return sshkey_sign(privkey, signature, slen, data, dlen, alg, compat);
541}
542