1/*	$NetBSD: ssh_api.c,v 1.15 2023/07/28 04:58:27 rin Exp $	*/
2/* $OpenBSD: ssh_api.c,v 1.27 2021/04/03 06:18:41 djm Exp $ */
3
4/*
5 * Copyright (c) 2012 Markus Friedl.  All rights reserved.
6 *
7 * Permission to use, copy, modify, and distribute this software for any
8 * purpose with or without fee is hereby granted, provided that the above
9 * copyright notice and this permission notice appear in all copies.
10 *
11 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
12 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
13 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
14 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
15 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
16 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
17 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
18 */
19
20#include "includes.h"
21__RCSID("$NetBSD: ssh_api.c,v 1.15 2023/07/28 04:58:27 rin Exp $");
22
23#include <sys/types.h>
24
25#include <stdio.h>
26#include <stdlib.h>
27
28#include "ssh_api.h"
29#include "compat.h"
30#include "log.h"
31#include "authfile.h"
32#include "sshkey.h"
33#include "misc.h"
34#include "ssh2.h"
35#include "version.h"
36#include "myproposal.h"
37#include "ssherr.h"
38#include "sshbuf.h"
39
40#include <string.h>
41
42int	_ssh_exchange_banner(struct ssh *);
43int	_ssh_send_banner(struct ssh *, struct sshbuf *);
44int	_ssh_read_banner(struct ssh *, struct sshbuf *);
45int	_ssh_order_hostkeyalgs(struct ssh *);
46int	_ssh_verify_host_key(struct sshkey *, struct ssh *);
47struct sshkey *_ssh_host_public_key(int, int, struct ssh *);
48struct sshkey *_ssh_host_private_key(int, int, struct ssh *);
49int	_ssh_host_key_sign(struct ssh *, struct sshkey *, struct sshkey *,
50    u_char **, size_t *, const u_char *, size_t, const char *);
51
52/*
53 * stubs for the server side implementation of kex.
54 * disable privsep so our stubs will never be called.
55 */
56int	use_privsep = 0;
57int	mm_sshkey_sign(struct sshkey *, u_char **, u_int *,
58    const u_char *, u_int, const char *, const char *, const char *, u_int);
59
60#ifdef WITH_OPENSSL
61DH	*mm_choose_dh(int, int, int);
62#endif
63
64int
65mm_sshkey_sign(struct sshkey *key, u_char **sigp, u_int *lenp,
66    const u_char *data, u_int datalen, const char *alg,
67    const char *sk_provider, const char *sk_pin, u_int compat)
68{
69	return (-1);
70}
71
72#ifdef WITH_OPENSSL
73DH *
74mm_choose_dh(int min, int nbits, int max)
75{
76	return (NULL);
77}
78#endif
79
80/* API */
81
82int
83ssh_init(struct ssh **sshp, int is_server, struct kex_params *kex_params)
84{
85	const char *myproposal[PROPOSAL_MAX] = { KEX_CLIENT };
86	struct ssh *ssh;
87	const char **proposal;
88	static int called;
89	int r;
90
91	if (!called) {
92#ifdef WITH_OPENSSL
93		OpenSSL_add_all_algorithms();
94#endif
95		called = 1;
96	}
97
98	if ((ssh = ssh_packet_set_connection(NULL, -1, -1)) == NULL)
99		return SSH_ERR_ALLOC_FAIL;
100	if (is_server)
101		ssh_packet_set_server(ssh);
102
103	/* Initialize key exchange */
104	proposal = kex_params ? __UNCONST(kex_params->proposal) : myproposal;
105	if ((r = kex_ready(ssh, __UNCONST(proposal))) != 0) {
106		ssh_free(ssh);
107		return r;
108	}
109	ssh->kex->server = is_server;
110	if (is_server) {
111#ifdef WITH_OPENSSL
112		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server;
113		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server;
114		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server;
115		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server;
116		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server;
117		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
118		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
119		ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_server;
120#endif /* WITH_OPENSSL */
121		ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_server;
122		ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_server;
123		ssh->kex->load_host_public_key=&_ssh_host_public_key;
124		ssh->kex->load_host_private_key=&_ssh_host_private_key;
125		ssh->kex->sign=&_ssh_host_key_sign;
126	} else {
127#ifdef WITH_OPENSSL
128		ssh->kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_client;
129		ssh->kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_client;
130		ssh->kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_client;
131		ssh->kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_client;
132		ssh->kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_client;
133		ssh->kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
134		ssh->kex->kex[KEX_DH_GEX_SHA256] = kexgex_client;
135		ssh->kex->kex[KEX_ECDH_SHA2] = kex_gen_client;
136#endif /* WITH_OPENSSL */
137		ssh->kex->kex[KEX_C25519_SHA256] = kex_gen_client;
138		ssh->kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_client;
139		ssh->kex->verify_host_key =&_ssh_verify_host_key;
140	}
141	*sshp = ssh;
142	return 0;
143}
144
145void
146ssh_free(struct ssh *ssh)
147{
148	struct key_entry *k;
149
150	if (ssh == NULL)
151		return;
152
153	/*
154	 * we've only created the public keys variants in case we
155	 * are a acting as a server.
156	 */
157	while ((k = TAILQ_FIRST(&ssh->public_keys)) != NULL) {
158		TAILQ_REMOVE(&ssh->public_keys, k, next);
159		if (ssh->kex && ssh->kex->server)
160			sshkey_free(k->key);
161		free(k);
162	}
163	while ((k = TAILQ_FIRST(&ssh->private_keys)) != NULL) {
164		TAILQ_REMOVE(&ssh->private_keys, k, next);
165		free(k);
166	}
167	ssh_packet_close(ssh);
168	free(ssh);
169}
170
171void
172ssh_set_app_data(struct ssh *ssh, void *app_data)
173{
174	ssh->app_data = app_data;
175}
176
177void *
178ssh_get_app_data(struct ssh *ssh)
179{
180	return ssh->app_data;
181}
182
183/* Returns < 0 on error, 0 otherwise */
184int
185ssh_add_hostkey(struct ssh *ssh, struct sshkey *key)
186{
187	struct sshkey *pubkey = NULL;
188	struct key_entry *k = NULL, *k_prv = NULL;
189	int r;
190
191	if (ssh->kex->server) {
192		if ((r = sshkey_from_private(key, &pubkey)) != 0)
193			return r;
194		if ((k = malloc(sizeof(*k))) == NULL ||
195		    (k_prv = malloc(sizeof(*k_prv))) == NULL) {
196			free(k);
197			sshkey_free(pubkey);
198			return SSH_ERR_ALLOC_FAIL;
199		}
200		k_prv->key = key;
201		TAILQ_INSERT_TAIL(&ssh->private_keys, k_prv, next);
202
203		/* add the public key, too */
204		k->key = pubkey;
205		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
206		r = 0;
207	} else {
208		if ((k = malloc(sizeof(*k))) == NULL)
209			return SSH_ERR_ALLOC_FAIL;
210		k->key = key;
211		TAILQ_INSERT_TAIL(&ssh->public_keys, k, next);
212		r = 0;
213	}
214
215	return r;
216}
217
218int
219ssh_set_verify_host_key_callback(struct ssh *ssh,
220    int (*cb)(struct sshkey *, struct ssh *))
221{
222	if (cb == NULL || ssh->kex == NULL)
223		return SSH_ERR_INVALID_ARGUMENT;
224
225	ssh->kex->verify_host_key = cb;
226
227	return 0;
228}
229
230int
231ssh_input_append(struct ssh *ssh, const u_char *data, size_t len)
232{
233	return sshbuf_put(ssh_packet_get_input(ssh), data, len);
234}
235
236int
237ssh_packet_next(struct ssh *ssh, u_char *typep)
238{
239	int r;
240	u_int32_t seqnr;
241	u_char type;
242
243	/*
244	 * Try to read a packet. Return SSH_MSG_NONE if no packet or not
245	 * enough data.
246	 */
247	*typep = SSH_MSG_NONE;
248	if (sshbuf_len(ssh->kex->client_version) == 0 ||
249	    sshbuf_len(ssh->kex->server_version) == 0)
250		return _ssh_exchange_banner(ssh);
251	/*
252	 * If we enough data and a dispatch function then
253	 * call the function and get the next packet.
254	 * Otherwise return the packet type to the caller so it
255	 * can decide how to go on.
256	 *
257	 * We will only call the dispatch function for:
258	 *     20-29    Algorithm negotiation
259	 *     30-49    Key exchange method specific (numbers can be reused for
260	 *              different authentication methods)
261	 */
262	for (;;) {
263		if ((r = ssh_packet_read_poll2(ssh, &type, &seqnr)) != 0)
264			return r;
265		if (type > 0 && type < DISPATCH_MAX &&
266		    type >= SSH2_MSG_KEXINIT && type <= SSH2_MSG_TRANSPORT_MAX &&
267		    ssh->dispatch[type] != NULL) {
268			if ((r = (*ssh->dispatch[type])(type, seqnr, ssh)) != 0)
269				return r;
270		} else {
271			*typep = type;
272			return 0;
273		}
274	}
275}
276
277const u_char *
278ssh_packet_payload(struct ssh *ssh, size_t *lenp)
279{
280	return sshpkt_ptr(ssh, lenp);
281}
282
283int
284ssh_packet_put(struct ssh *ssh, int type, const u_char *data, size_t len)
285{
286	int r;
287
288	if ((r = sshpkt_start(ssh, type)) != 0 ||
289	    (r = sshpkt_put(ssh, data, len)) != 0 ||
290	    (r = sshpkt_send(ssh)) != 0)
291		return r;
292	return 0;
293}
294
295const u_char *
296ssh_output_ptr(struct ssh *ssh, size_t *len)
297{
298	struct sshbuf *output = ssh_packet_get_output(ssh);
299
300	*len = sshbuf_len(output);
301	return sshbuf_ptr(output);
302}
303
304int
305ssh_output_consume(struct ssh *ssh, size_t len)
306{
307	return sshbuf_consume(ssh_packet_get_output(ssh), len);
308}
309
310int
311ssh_output_space(struct ssh *ssh, size_t len)
312{
313	return (0 == sshbuf_check_reserve(ssh_packet_get_output(ssh), len));
314}
315
316int
317ssh_input_space(struct ssh *ssh, size_t len)
318{
319	return (0 == sshbuf_check_reserve(ssh_packet_get_input(ssh), len));
320}
321
322/* Read other side's version identification. */
323int
324_ssh_read_banner(struct ssh *ssh, struct sshbuf *banner)
325{
326	struct sshbuf *input = ssh_packet_get_input(ssh);
327	const char *mismatch = "Protocol mismatch.\r\n";
328	const u_char *s = sshbuf_ptr(input);
329	u_char c;
330	char *cp = NULL, *remote_version = NULL;
331	int r = 0, remote_major, remote_minor, expect_nl;
332	size_t n, j;
333
334	for (j = n = 0;;) {
335		sshbuf_reset(banner);
336		expect_nl = 0;
337		for (;;) {
338			if (j >= sshbuf_len(input))
339				return 0; /* insufficient data in input buf */
340			c = s[j++];
341			if (c == '\r') {
342				expect_nl = 1;
343				continue;
344			}
345			if (c == '\n')
346				break;
347			if (expect_nl)
348				goto bad;
349			if ((r = sshbuf_put_u8(banner, c)) != 0)
350				return r;
351			if (sshbuf_len(banner) > SSH_MAX_BANNER_LEN)
352				goto bad;
353		}
354		if (sshbuf_len(banner) >= 4 &&
355		    memcmp(sshbuf_ptr(banner), "SSH-", 4) == 0)
356			break;
357		debug_f("%.*s", (int)sshbuf_len(banner),
358		    sshbuf_ptr(banner));
359		/* Accept lines before banner only on client */
360		if (ssh->kex->server || ++n > SSH_MAX_PRE_BANNER_LINES) {
361  bad:
362			if ((r = sshbuf_put(ssh_packet_get_output(ssh),
363			    mismatch, strlen(mismatch))) != 0)
364				return r;
365			return SSH_ERR_NO_PROTOCOL_VERSION;
366		}
367	}
368	if ((r = sshbuf_consume(input, j)) != 0)
369		return r;
370
371	/* XXX remote version must be the same size as banner for sscanf */
372	if ((cp = sshbuf_dup_string(banner)) == NULL ||
373	    (remote_version = calloc(1, sshbuf_len(banner))) == NULL) {
374		r = SSH_ERR_ALLOC_FAIL;
375		goto out;
376	}
377
378	/*
379	 * Check that the versions match.  In future this might accept
380	 * several versions and set appropriate flags to handle them.
381	 */
382	if (sscanf(cp, "SSH-%d.%d-%[^\n]\n",
383	    &remote_major, &remote_minor, remote_version) != 3) {
384		r = SSH_ERR_INVALID_FORMAT;
385		goto out;
386	}
387	debug("Remote protocol version %d.%d, remote software version %.100s",
388	    remote_major, remote_minor, remote_version);
389
390	compat_banner(ssh, remote_version);
391	if  (remote_major == 1 && remote_minor == 99) {
392		remote_major = 2;
393		remote_minor = 0;
394	}
395	if (remote_major != 2)
396		r = SSH_ERR_PROTOCOL_MISMATCH;
397
398	debug("Remote version string %.100s", cp);
399 out:
400	free(cp);
401	free(remote_version);
402	return r;
403}
404
405/* Send our own protocol version identification. */
406int
407_ssh_send_banner(struct ssh *ssh, struct sshbuf *banner)
408{
409	char *cp;
410	int r;
411
412	if ((r = sshbuf_putf(banner, "SSH-2.0-%.100s\r\n", SSH_VERSION)) != 0)
413		return r;
414	if ((r = sshbuf_putb(ssh_packet_get_output(ssh), banner)) != 0)
415		return r;
416	/* Remove trailing \r\n */
417	if ((r = sshbuf_consume_end(banner, 2)) != 0)
418		return r;
419	if ((cp = sshbuf_dup_string(banner)) == NULL)
420		return SSH_ERR_ALLOC_FAIL;
421	debug("Local version string %.100s", cp);
422	free(cp);
423	return 0;
424}
425
426int
427_ssh_exchange_banner(struct ssh *ssh)
428{
429	struct kex *kex = ssh->kex;
430	int r;
431
432	/*
433	 * if _ssh_read_banner() cannot parse a full version string
434	 * it will return NULL and we end up calling it again.
435	 */
436
437	r = 0;
438	if (kex->server) {
439		if (sshbuf_len(ssh->kex->server_version) == 0)
440			r = _ssh_send_banner(ssh, ssh->kex->server_version);
441		if (r == 0 &&
442		    sshbuf_len(ssh->kex->server_version) != 0 &&
443		    sshbuf_len(ssh->kex->client_version) == 0)
444			r = _ssh_read_banner(ssh, ssh->kex->client_version);
445	} else {
446		if (sshbuf_len(ssh->kex->server_version) == 0)
447			r = _ssh_read_banner(ssh, ssh->kex->server_version);
448		if (r == 0 &&
449		    sshbuf_len(ssh->kex->server_version) != 0 &&
450		    sshbuf_len(ssh->kex->client_version) == 0)
451			r = _ssh_send_banner(ssh, ssh->kex->client_version);
452	}
453	if (r != 0)
454		return r;
455	/* start initial kex as soon as we have exchanged the banners */
456	if (sshbuf_len(ssh->kex->server_version) != 0 &&
457	    sshbuf_len(ssh->kex->client_version) != 0) {
458		if ((r = _ssh_order_hostkeyalgs(ssh)) != 0 ||
459		    (r = kex_send_kexinit(ssh)) != 0)
460			return r;
461	}
462	return 0;
463}
464
465struct sshkey *
466_ssh_host_public_key(int type, int nid, struct ssh *ssh)
467{
468	struct key_entry *k;
469
470	debug3_f("need %d", type);
471	TAILQ_FOREACH(k, &ssh->public_keys, next) {
472		debug3_f("check %s", sshkey_type(k->key));
473		if (k->key->type == type &&
474		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
475			return (k->key);
476	}
477	return (NULL);
478}
479
480struct sshkey *
481_ssh_host_private_key(int type, int nid, struct ssh *ssh)
482{
483	struct key_entry *k;
484
485	debug3_f("need %d", type);
486	TAILQ_FOREACH(k, &ssh->private_keys, next) {
487		debug3_f("check %s", sshkey_type(k->key));
488		if (k->key->type == type &&
489		    (type != KEY_ECDSA || k->key->ecdsa_nid == nid))
490			return (k->key);
491	}
492	return (NULL);
493}
494
495int
496_ssh_verify_host_key(struct sshkey *hostkey, struct ssh *ssh)
497{
498	struct key_entry *k;
499
500	debug3_f("need %s", sshkey_type(hostkey));
501	TAILQ_FOREACH(k, &ssh->public_keys, next) {
502		debug3_f("check %s", sshkey_type(k->key));
503		if (sshkey_equal_public(hostkey, k->key))
504			return (0);	/* ok */
505	}
506	return (-1);	/* failed */
507}
508
509/* offer hostkey algorithms in kexinit depending on registered keys */
510int
511_ssh_order_hostkeyalgs(struct ssh *ssh)
512{
513	struct key_entry *k;
514	char *orig, *avail, *oavail = NULL, *alg, *replace = NULL;
515	char **proposal;
516	size_t maxlen;
517	int ktype, r;
518
519	/* XXX we de-serialize ssh->kex->my, modify it, and change it */
520	if ((r = kex_buf2prop(ssh->kex->my, NULL, &proposal)) != 0)
521		return r;
522	orig = proposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
523	if ((oavail = avail = strdup(orig)) == NULL) {
524		r = SSH_ERR_ALLOC_FAIL;
525		goto out;
526	}
527	maxlen = strlen(avail) + 1;
528	if ((replace = calloc(1, maxlen)) == NULL) {
529		r = SSH_ERR_ALLOC_FAIL;
530		goto out;
531	}
532	*replace = '\0';
533	while ((alg = strsep(&avail, ",")) && *alg != '\0') {
534		if ((ktype = sshkey_type_from_name(alg)) == KEY_UNSPEC)
535			continue;
536		TAILQ_FOREACH(k, &ssh->public_keys, next) {
537			if (k->key->type == ktype ||
538			    (sshkey_is_cert(k->key) && k->key->type ==
539			    sshkey_type_plain(ktype))) {
540				if (*replace != '\0')
541					strlcat(replace, ",", maxlen);
542				strlcat(replace, alg, maxlen);
543				break;
544			}
545		}
546	}
547	if (*replace != '\0') {
548		debug2_f("orig/%d    %s", ssh->kex->server, orig);
549		debug2_f("replace/%d %s", ssh->kex->server, replace);
550		free(orig);
551		proposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = replace;
552		replace = NULL;	/* owned by proposal */
553		r = kex_prop2buf(ssh->kex->my, proposal);
554	}
555 out:
556	free(oavail);
557	free(replace);
558	kex_prop_free(proposal);
559	return r;
560}
561
562int
563_ssh_host_key_sign(struct ssh *ssh, struct sshkey *privkey,
564    struct sshkey *pubkey, u_char **signature, size_t *slen,
565    const u_char *data, size_t dlen, const char *alg)
566{
567	return sshkey_sign(privkey, signature, slen, data, dlen,
568	    alg, NULL, NULL, ssh->compat);
569}
570