xref: /openssh-portable/ssh-sk-client.c (revision 3bf2a6ac)
1 /* $OpenBSD: ssh-sk-client.c,v 1.7 2020/01/23 07:10:22 dtucker Exp $ */
2 /*
3  * Copyright (c) 2019 Google LLC
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 <sys/types.h>
21 #include <sys/socket.h>
22 #include <sys/wait.h>
23 
24 #include <fcntl.h>
25 #include <limits.h>
26 #include <errno.h>
27 #include <signal.h>
28 #include <stdarg.h>
29 #include <stdio.h>
30 #include <stdlib.h>
31 #include <string.h>
32 #include <unistd.h>
33 
34 #include "log.h"
35 #include "ssherr.h"
36 #include "sshbuf.h"
37 #include "sshkey.h"
38 #include "msg.h"
39 #include "digest.h"
40 #include "pathnames.h"
41 #include "ssh-sk.h"
42 #include "misc.h"
43 
44 /* #define DEBUG_SK 1 */
45 
46 static int
start_helper(int * fdp,pid_t * pidp,void (** osigchldp)(int))47 start_helper(int *fdp, pid_t *pidp, void (**osigchldp)(int))
48 {
49 	void (*osigchld)(int);
50 	int oerrno, pair[2], r = SSH_ERR_INTERNAL_ERROR;
51 	pid_t pid;
52 	char *helper, *verbosity = NULL;
53 
54 	*fdp = -1;
55 	*pidp = 0;
56 	*osigchldp = SIG_DFL;
57 
58 	helper = getenv("SSH_SK_HELPER");
59 	if (helper == NULL || strlen(helper) == 0)
60 		helper = _PATH_SSH_SK_HELPER;
61 	if (access(helper, X_OK) != 0) {
62 		oerrno = errno;
63 		error("%s: helper \"%s\" unusable: %s", __func__, helper,
64 		    strerror(errno));
65 		errno = oerrno;
66 		return SSH_ERR_SYSTEM_ERROR;
67 	}
68 #ifdef DEBUG_SK
69 	verbosity = "-vvv";
70 #endif
71 
72 	/* Start helper */
73 	if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) == -1) {
74 		error("socketpair: %s", strerror(errno));
75 		return SSH_ERR_SYSTEM_ERROR;
76 	}
77 	osigchld = ssh_signal(SIGCHLD, SIG_DFL);
78 	if ((pid = fork()) == -1) {
79 		oerrno = errno;
80 		error("fork: %s", strerror(errno));
81 		close(pair[0]);
82 		close(pair[1]);
83 		ssh_signal(SIGCHLD, osigchld);
84 		errno = oerrno;
85 		return SSH_ERR_SYSTEM_ERROR;
86 	}
87 	if (pid == 0) {
88 		if ((dup2(pair[1], STDIN_FILENO) == -1) ||
89 		    (dup2(pair[1], STDOUT_FILENO) == -1)) {
90 			error("%s: dup2: %s", __func__, ssh_err(r));
91 			_exit(1);
92 		}
93 		close(pair[0]);
94 		close(pair[1]);
95 		closefrom(STDERR_FILENO + 1);
96 		debug("%s: starting %s %s", __func__, helper,
97 		    verbosity == NULL ? "" : verbosity);
98 		execlp(helper, helper, verbosity, (char *)NULL);
99 		error("%s: execlp: %s", __func__, strerror(errno));
100 		_exit(1);
101 	}
102 	close(pair[1]);
103 
104 	/* success */
105 	debug3("%s: started pid=%ld", __func__, (long)pid);
106 	*fdp = pair[0];
107 	*pidp = pid;
108 	*osigchldp = osigchld;
109 	return 0;
110 }
111 
112 static int
reap_helper(pid_t pid)113 reap_helper(pid_t pid)
114 {
115 	int status, oerrno;
116 
117 	debug3("%s: pid=%ld", __func__, (long)pid);
118 
119 	errno = 0;
120 	while (waitpid(pid, &status, 0) == -1) {
121 		if (errno == EINTR) {
122 			errno = 0;
123 			continue;
124 		}
125 		oerrno = errno;
126 		error("%s: waitpid: %s", __func__, strerror(errno));
127 		errno = oerrno;
128 		return SSH_ERR_SYSTEM_ERROR;
129 	}
130 	if (!WIFEXITED(status)) {
131 		error("%s: helper exited abnormally", __func__);
132 		return SSH_ERR_AGENT_FAILURE;
133 	} else if (WEXITSTATUS(status) != 0) {
134 		error("%s: helper exited with non-zero exit status", __func__);
135 		return SSH_ERR_AGENT_FAILURE;
136 	}
137 	return 0;
138 }
139 
140 static int
client_converse(struct sshbuf * msg,struct sshbuf ** respp,u_int type)141 client_converse(struct sshbuf *msg, struct sshbuf **respp, u_int type)
142 {
143 	int oerrno, fd, r2, ll, r = SSH_ERR_INTERNAL_ERROR;
144 	u_int rtype, rerr;
145 	pid_t pid;
146 	u_char version;
147 	void (*osigchld)(int);
148 	struct sshbuf *req = NULL, *resp = NULL;
149 	*respp = NULL;
150 
151 	if ((r = start_helper(&fd, &pid, &osigchld)) != 0)
152 		return r;
153 
154 	if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL) {
155 		r = SSH_ERR_ALLOC_FAIL;
156 		goto out;
157 	}
158 	/* Request preamble: type, log_on_stderr, log_level */
159 	ll = log_level_get();
160 	if ((r = sshbuf_put_u32(req, type)) != 0 ||
161 	   (r = sshbuf_put_u8(req, log_is_on_stderr() != 0)) != 0 ||
162 	   (r = sshbuf_put_u32(req, ll < 0 ? 0 : ll)) != 0 ||
163 	   (r = sshbuf_putb(req, msg)) != 0) {
164 		error("%s: build: %s", __func__, ssh_err(r));
165 		goto out;
166 	}
167 	if ((r = ssh_msg_send(fd, SSH_SK_HELPER_VERSION, req)) != 0) {
168 		error("%s: send: %s", __func__, ssh_err(r));
169 		goto out;
170 	}
171 	if ((r = ssh_msg_recv(fd, resp)) != 0) {
172 		error("%s: receive: %s", __func__, ssh_err(r));
173 		goto out;
174 	}
175 	if ((r = sshbuf_get_u8(resp, &version)) != 0) {
176 		error("%s: parse version: %s", __func__, ssh_err(r));
177 		goto out;
178 	}
179 	if (version != SSH_SK_HELPER_VERSION) {
180 		error("%s: unsupported version: got %u, expected %u",
181 		    __func__, version, SSH_SK_HELPER_VERSION);
182 		r = SSH_ERR_INVALID_FORMAT;
183 		goto out;
184 	}
185 	if ((r = sshbuf_get_u32(resp, &rtype)) != 0) {
186 		error("%s: parse message type: %s", __func__, ssh_err(r));
187 		goto out;
188 	}
189 	if (rtype == SSH_SK_HELPER_ERROR) {
190 		if ((r = sshbuf_get_u32(resp, &rerr)) != 0) {
191 			error("%s: parse error: %s", __func__, ssh_err(r));
192 			goto out;
193 		}
194 		debug("%s: helper returned error -%u", __func__, rerr);
195 		/* OpenSSH error values are negative; encoded as -err on wire */
196 		if (rerr == 0 || rerr >= INT_MAX)
197 			r = SSH_ERR_INTERNAL_ERROR;
198 		else
199 			r = -(int)rerr;
200 		goto out;
201 	} else if (rtype != type) {
202 		error("%s: helper returned incorrect message type %u, "
203 		    "expecting %u", __func__, rtype, type);
204 		r = SSH_ERR_INTERNAL_ERROR;
205 		goto out;
206 	}
207 	/* success */
208 	r = 0;
209  out:
210 	oerrno = errno;
211 	close(fd);
212 	if ((r2 = reap_helper(pid)) != 0) {
213 		if (r == 0) {
214 			r = r2;
215 			oerrno = errno;
216 		}
217 	}
218 	if (r == 0) {
219 		*respp = resp;
220 		resp = NULL;
221 	}
222 	sshbuf_free(req);
223 	sshbuf_free(resp);
224 	ssh_signal(SIGCHLD, osigchld);
225 	errno = oerrno;
226 	return r;
227 
228 }
229 
230 int
sshsk_sign(const char * provider,struct sshkey * key,u_char ** sigp,size_t * lenp,const u_char * data,size_t datalen,u_int compat,const char * pin)231 sshsk_sign(const char *provider, struct sshkey *key,
232     u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,
233     u_int compat, const char *pin)
234 {
235 	int oerrno, r = SSH_ERR_INTERNAL_ERROR;
236 	char *fp = NULL;
237 	struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;
238 
239 	*sigp = NULL;
240 	*lenp = 0;
241 
242 #ifndef ENABLE_SK
243 	return SSH_ERR_KEY_TYPE_UNKNOWN;
244 #endif
245 
246 	if ((kbuf = sshbuf_new()) == NULL ||
247 	    (req = sshbuf_new()) == NULL) {
248 		r = SSH_ERR_ALLOC_FAIL;
249 		goto out;
250 	}
251 
252 	if ((r = sshkey_private_serialize(key, kbuf)) != 0) {
253 		error("%s: serialize private key: %s", __func__, ssh_err(r));
254 		goto out;
255 	}
256 	if ((r = sshbuf_put_stringb(req, kbuf)) != 0 ||
257 	    (r = sshbuf_put_cstring(req, provider)) != 0 ||
258 	    (r = sshbuf_put_string(req, data, datalen)) != 0 ||
259 	    (r = sshbuf_put_cstring(req, NULL)) != 0 || /* alg */
260 	    (r = sshbuf_put_u32(req, compat)) != 0 ||
261 	    (r = sshbuf_put_cstring(req, pin)) != 0) {
262 		error("%s: compose: %s", __func__, ssh_err(r));
263 		goto out;
264 	}
265 
266 	if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
267 	    SSH_FP_DEFAULT)) == NULL) {
268 		error("%s: sshkey_fingerprint failed", __func__);
269 		r = SSH_ERR_ALLOC_FAIL;
270 		goto out;
271 	}
272 	if ((r = client_converse(req, &resp, SSH_SK_HELPER_SIGN)) != 0)
273 		goto out;
274 
275 	if ((r = sshbuf_get_string(resp, sigp, lenp)) != 0) {
276 		error("%s: parse signature: %s", __func__, ssh_err(r));
277 		r = SSH_ERR_INVALID_FORMAT;
278 		goto out;
279 	}
280 	if (sshbuf_len(resp) != 0) {
281 		error("%s: trailing data in response", __func__);
282 		r = SSH_ERR_INVALID_FORMAT;
283 		goto out;
284 	}
285 	/* success */
286 	r = 0;
287  out:
288 	oerrno = errno;
289 	if (r != 0) {
290 		freezero(*sigp, *lenp);
291 		*sigp = NULL;
292 		*lenp = 0;
293 	}
294 	sshbuf_free(kbuf);
295 	sshbuf_free(req);
296 	sshbuf_free(resp);
297 	errno = oerrno;
298 	return r;
299 }
300 
301 int
sshsk_enroll(int type,const char * provider_path,const char * device,const char * application,const char * userid,uint8_t flags,const char * pin,struct sshbuf * challenge_buf,struct sshkey ** keyp,struct sshbuf * attest)302 sshsk_enroll(int type, const char *provider_path, const char *device,
303     const char *application, const char *userid, uint8_t flags,
304     const char *pin, struct sshbuf *challenge_buf,
305     struct sshkey **keyp, struct sshbuf *attest)
306 {
307 	int oerrno, r = SSH_ERR_INTERNAL_ERROR;
308 	struct sshbuf *kbuf = NULL, *abuf = NULL, *req = NULL, *resp = NULL;
309 	struct sshkey *key = NULL;
310 
311 	*keyp = NULL;
312 	if (attest != NULL)
313 		sshbuf_reset(attest);
314 
315 #ifndef ENABLE_SK
316 	return SSH_ERR_KEY_TYPE_UNKNOWN;
317 #endif
318 
319 	if (type < 0)
320 		return SSH_ERR_INVALID_ARGUMENT;
321 
322 	if ((abuf = sshbuf_new()) == NULL ||
323 	    (kbuf = sshbuf_new()) == NULL ||
324 	    (req = sshbuf_new()) == NULL) {
325 		r = SSH_ERR_ALLOC_FAIL;
326 		goto out;
327 	}
328 
329 	if ((r = sshbuf_put_u32(req, (u_int)type)) != 0 ||
330 	    (r = sshbuf_put_cstring(req, provider_path)) != 0 ||
331 	    (r = sshbuf_put_cstring(req, device)) != 0 ||
332 	    (r = sshbuf_put_cstring(req, application)) != 0 ||
333 	    (r = sshbuf_put_cstring(req, userid)) != 0 ||
334 	    (r = sshbuf_put_u8(req, flags)) != 0 ||
335 	    (r = sshbuf_put_cstring(req, pin)) != 0 ||
336 	    (r = sshbuf_put_stringb(req, challenge_buf)) != 0) {
337 		error("%s: compose: %s", __func__, ssh_err(r));
338 		goto out;
339 	}
340 
341 	if ((r = client_converse(req, &resp, SSH_SK_HELPER_ENROLL)) != 0)
342 		goto out;
343 
344 	if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
345 	    (r = sshbuf_get_stringb(resp, abuf)) != 0) {
346 		error("%s: parse signature: %s", __func__, ssh_err(r));
347 		r = SSH_ERR_INVALID_FORMAT;
348 		goto out;
349 	}
350 	if (sshbuf_len(resp) != 0) {
351 		error("%s: trailing data in response", __func__);
352 		r = SSH_ERR_INVALID_FORMAT;
353 		goto out;
354 	}
355 	if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
356 		error("Unable to parse private key: %s", ssh_err(r));
357 		goto out;
358 	}
359 	if (attest != NULL && (r = sshbuf_putb(attest, abuf)) != 0) {
360 		error("%s: buffer error: %s", __func__, ssh_err(r));
361 		goto out;
362 	}
363 
364 	/* success */
365 	r = 0;
366 	*keyp = key;
367 	key = NULL;
368  out:
369 	oerrno = errno;
370 	sshkey_free(key);
371 	sshbuf_free(kbuf);
372 	sshbuf_free(abuf);
373 	sshbuf_free(req);
374 	sshbuf_free(resp);
375 	errno = oerrno;
376 	return r;
377 }
378 
379 int
sshsk_load_resident(const char * provider_path,const char * device,const char * pin,struct sshkey *** keysp,size_t * nkeysp)380 sshsk_load_resident(const char *provider_path, const char *device,
381     const char *pin, struct sshkey ***keysp, size_t *nkeysp)
382 {
383 	int oerrno, r = SSH_ERR_INTERNAL_ERROR;
384 	struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;
385 	struct sshkey *key = NULL, **keys = NULL, **tmp;
386 	size_t i, nkeys = 0;
387 
388 	*keysp = NULL;
389 	*nkeysp = 0;
390 
391 	if ((resp = sshbuf_new()) == NULL ||
392 	    (kbuf = sshbuf_new()) == NULL ||
393 	    (req = sshbuf_new()) == NULL) {
394 		r = SSH_ERR_ALLOC_FAIL;
395 		goto out;
396 	}
397 
398 	if ((r = sshbuf_put_cstring(req, provider_path)) != 0 ||
399 	    (r = sshbuf_put_cstring(req, device)) != 0 ||
400 	    (r = sshbuf_put_cstring(req, pin)) != 0) {
401 		error("%s: compose: %s", __func__, ssh_err(r));
402 		goto out;
403 	}
404 
405 	if ((r = client_converse(req, &resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0)
406 		goto out;
407 
408 	while (sshbuf_len(resp) != 0) {
409 		/* key, comment */
410 		if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
411 		    (r = sshbuf_get_cstring(resp, NULL, NULL)) != 0) {
412 			error("%s: parse signature: %s", __func__, ssh_err(r));
413 			r = SSH_ERR_INVALID_FORMAT;
414 			goto out;
415 		}
416 		if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
417 			error("Unable to parse private key: %s", ssh_err(r));
418 			goto out;
419 		}
420 		if ((tmp = recallocarray(keys, nkeys, nkeys + 1,
421 		    sizeof(*keys))) == NULL) {
422 			error("%s: recallocarray keys failed", __func__);
423 			goto out;
424 		}
425 		debug("%s: keys[%zu]: %s %s", __func__,
426 		    nkeys, sshkey_type(key), key->sk_application);
427 		keys = tmp;
428 		keys[nkeys++] = key;
429 		key = NULL;
430 	}
431 
432 	/* success */
433 	r = 0;
434 	*keysp = keys;
435 	*nkeysp = nkeys;
436 	keys = NULL;
437 	nkeys = 0;
438  out:
439 	oerrno = errno;
440 	for (i = 0; i < nkeys; i++)
441 		sshkey_free(keys[i]);
442 	free(keys);
443 	sshkey_free(key);
444 	sshbuf_free(kbuf);
445 	sshbuf_free(req);
446 	sshbuf_free(resp);
447 	errno = oerrno;
448 	return r;
449 }
450