1 /* $OpenBSD: ssh-sk-client.c,v 1.9 2021/04/03 06:18:41 djm 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];
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_f("helper \"%s\" unusable: %s", helper, strerror(errno));
64 errno = oerrno;
65 return SSH_ERR_SYSTEM_ERROR;
66 }
67 #ifdef DEBUG_SK
68 verbosity = "-vvv";
69 #endif
70
71 /* Start helper */
72 if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) == -1) {
73 error("socketpair: %s", strerror(errno));
74 return SSH_ERR_SYSTEM_ERROR;
75 }
76 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
77 if ((pid = fork()) == -1) {
78 oerrno = errno;
79 error("fork: %s", strerror(errno));
80 close(pair[0]);
81 close(pair[1]);
82 ssh_signal(SIGCHLD, osigchld);
83 errno = oerrno;
84 return SSH_ERR_SYSTEM_ERROR;
85 }
86 if (pid == 0) {
87 if ((dup2(pair[1], STDIN_FILENO) == -1) ||
88 (dup2(pair[1], STDOUT_FILENO) == -1)) {
89 error_f("dup2: %s", strerror(errno));
90 _exit(1);
91 }
92 close(pair[0]);
93 close(pair[1]);
94 closefrom(STDERR_FILENO + 1);
95 debug_f("starting %s %s", helper,
96 verbosity == NULL ? "" : verbosity);
97 execlp(helper, helper, verbosity, (char *)NULL);
98 error_f("execlp: %s", strerror(errno));
99 _exit(1);
100 }
101 close(pair[1]);
102
103 /* success */
104 debug3_f("started pid=%ld", (long)pid);
105 *fdp = pair[0];
106 *pidp = pid;
107 *osigchldp = osigchld;
108 return 0;
109 }
110
111 static int
reap_helper(pid_t pid)112 reap_helper(pid_t pid)
113 {
114 int status, oerrno;
115
116 debug3_f("pid=%ld", (long)pid);
117
118 errno = 0;
119 while (waitpid(pid, &status, 0) == -1) {
120 if (errno == EINTR) {
121 errno = 0;
122 continue;
123 }
124 oerrno = errno;
125 error_f("waitpid: %s", strerror(errno));
126 errno = oerrno;
127 return SSH_ERR_SYSTEM_ERROR;
128 }
129 if (!WIFEXITED(status)) {
130 error_f("helper exited abnormally");
131 return SSH_ERR_AGENT_FAILURE;
132 } else if (WEXITSTATUS(status) != 0) {
133 error_f("helper exited with non-zero exit status");
134 return SSH_ERR_AGENT_FAILURE;
135 }
136 return 0;
137 }
138
139 static int
client_converse(struct sshbuf * msg,struct sshbuf ** respp,u_int type)140 client_converse(struct sshbuf *msg, struct sshbuf **respp, u_int type)
141 {
142 int oerrno, fd, r2, ll, r = SSH_ERR_INTERNAL_ERROR;
143 u_int rtype, rerr;
144 pid_t pid;
145 u_char version;
146 void (*osigchld)(int);
147 struct sshbuf *req = NULL, *resp = NULL;
148 *respp = NULL;
149
150 if ((r = start_helper(&fd, &pid, &osigchld)) != 0)
151 return r;
152
153 if ((req = sshbuf_new()) == NULL || (resp = sshbuf_new()) == NULL) {
154 r = SSH_ERR_ALLOC_FAIL;
155 goto out;
156 }
157 /* Request preamble: type, log_on_stderr, log_level */
158 ll = log_level_get();
159 if ((r = sshbuf_put_u32(req, type)) != 0 ||
160 (r = sshbuf_put_u8(req, log_is_on_stderr() != 0)) != 0 ||
161 (r = sshbuf_put_u32(req, ll < 0 ? 0 : ll)) != 0 ||
162 (r = sshbuf_putb(req, msg)) != 0) {
163 error_fr(r, "compose");
164 goto out;
165 }
166 if ((r = ssh_msg_send(fd, SSH_SK_HELPER_VERSION, req)) != 0) {
167 error_fr(r, "send");
168 goto out;
169 }
170 if ((r = ssh_msg_recv(fd, resp)) != 0) {
171 error_fr(r, "receive");
172 goto out;
173 }
174 if ((r = sshbuf_get_u8(resp, &version)) != 0) {
175 error_fr(r, "parse version");
176 goto out;
177 }
178 if (version != SSH_SK_HELPER_VERSION) {
179 error_f("unsupported version: got %u, expected %u",
180 version, SSH_SK_HELPER_VERSION);
181 r = SSH_ERR_INVALID_FORMAT;
182 goto out;
183 }
184 if ((r = sshbuf_get_u32(resp, &rtype)) != 0) {
185 error_fr(r, "parse message type");
186 goto out;
187 }
188 if (rtype == SSH_SK_HELPER_ERROR) {
189 if ((r = sshbuf_get_u32(resp, &rerr)) != 0) {
190 error_fr(r, "parse");
191 goto out;
192 }
193 debug_f("helper returned error -%u", rerr);
194 /* OpenSSH error values are negative; encoded as -err on wire */
195 if (rerr == 0 || rerr >= INT_MAX)
196 r = SSH_ERR_INTERNAL_ERROR;
197 else
198 r = -(int)rerr;
199 goto out;
200 } else if (rtype != type) {
201 error_f("helper returned incorrect message type %u, "
202 "expecting %u", rtype, type);
203 r = SSH_ERR_INTERNAL_ERROR;
204 goto out;
205 }
206 /* success */
207 r = 0;
208 out:
209 oerrno = errno;
210 close(fd);
211 if ((r2 = reap_helper(pid)) != 0) {
212 if (r == 0) {
213 r = r2;
214 oerrno = errno;
215 }
216 }
217 if (r == 0) {
218 *respp = resp;
219 resp = NULL;
220 }
221 sshbuf_free(req);
222 sshbuf_free(resp);
223 ssh_signal(SIGCHLD, osigchld);
224 errno = oerrno;
225 return r;
226
227 }
228
229 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)230 sshsk_sign(const char *provider, struct sshkey *key,
231 u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,
232 u_int compat, const char *pin)
233 {
234 int oerrno, r = SSH_ERR_INTERNAL_ERROR;
235 char *fp = NULL;
236 struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;
237
238 *sigp = NULL;
239 *lenp = 0;
240
241 #ifndef ENABLE_SK
242 return SSH_ERR_KEY_TYPE_UNKNOWN;
243 #endif
244
245 if ((kbuf = sshbuf_new()) == NULL ||
246 (req = sshbuf_new()) == NULL) {
247 r = SSH_ERR_ALLOC_FAIL;
248 goto out;
249 }
250
251 if ((r = sshkey_private_serialize(key, kbuf)) != 0) {
252 error_fr(r, "encode key");
253 goto out;
254 }
255 if ((r = sshbuf_put_stringb(req, kbuf)) != 0 ||
256 (r = sshbuf_put_cstring(req, provider)) != 0 ||
257 (r = sshbuf_put_string(req, data, datalen)) != 0 ||
258 (r = sshbuf_put_cstring(req, NULL)) != 0 || /* alg */
259 (r = sshbuf_put_u32(req, compat)) != 0 ||
260 (r = sshbuf_put_cstring(req, pin)) != 0) {
261 error_fr(r, "compose");
262 goto out;
263 }
264
265 if ((fp = sshkey_fingerprint(key, SSH_FP_HASH_DEFAULT,
266 SSH_FP_DEFAULT)) == NULL) {
267 error_f("sshkey_fingerprint failed");
268 r = SSH_ERR_ALLOC_FAIL;
269 goto out;
270 }
271 if ((r = client_converse(req, &resp, SSH_SK_HELPER_SIGN)) != 0)
272 goto out;
273
274 if ((r = sshbuf_get_string(resp, sigp, lenp)) != 0) {
275 error_fr(r, "parse signature");
276 r = SSH_ERR_INVALID_FORMAT;
277 goto out;
278 }
279 if (sshbuf_len(resp) != 0) {
280 error_f("trailing data in response");
281 r = SSH_ERR_INVALID_FORMAT;
282 goto out;
283 }
284 /* success */
285 r = 0;
286 out:
287 oerrno = errno;
288 if (r != 0) {
289 freezero(*sigp, *lenp);
290 *sigp = NULL;
291 *lenp = 0;
292 }
293 sshbuf_free(kbuf);
294 sshbuf_free(req);
295 sshbuf_free(resp);
296 errno = oerrno;
297 return r;
298 }
299
300 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)301 sshsk_enroll(int type, const char *provider_path, const char *device,
302 const char *application, const char *userid, uint8_t flags,
303 const char *pin, struct sshbuf *challenge_buf,
304 struct sshkey **keyp, struct sshbuf *attest)
305 {
306 int oerrno, r = SSH_ERR_INTERNAL_ERROR;
307 struct sshbuf *kbuf = NULL, *abuf = NULL, *req = NULL, *resp = NULL;
308 struct sshkey *key = NULL;
309
310 *keyp = NULL;
311 if (attest != NULL)
312 sshbuf_reset(attest);
313
314 #ifndef ENABLE_SK
315 return SSH_ERR_KEY_TYPE_UNKNOWN;
316 #endif
317
318 if (type < 0)
319 return SSH_ERR_INVALID_ARGUMENT;
320
321 if ((abuf = sshbuf_new()) == NULL ||
322 (kbuf = sshbuf_new()) == NULL ||
323 (req = sshbuf_new()) == NULL) {
324 r = SSH_ERR_ALLOC_FAIL;
325 goto out;
326 }
327
328 if ((r = sshbuf_put_u32(req, (u_int)type)) != 0 ||
329 (r = sshbuf_put_cstring(req, provider_path)) != 0 ||
330 (r = sshbuf_put_cstring(req, device)) != 0 ||
331 (r = sshbuf_put_cstring(req, application)) != 0 ||
332 (r = sshbuf_put_cstring(req, userid)) != 0 ||
333 (r = sshbuf_put_u8(req, flags)) != 0 ||
334 (r = sshbuf_put_cstring(req, pin)) != 0 ||
335 (r = sshbuf_put_stringb(req, challenge_buf)) != 0) {
336 error_fr(r, "compose");
337 goto out;
338 }
339
340 if ((r = client_converse(req, &resp, SSH_SK_HELPER_ENROLL)) != 0)
341 goto out;
342
343 if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
344 (r = sshbuf_get_stringb(resp, abuf)) != 0) {
345 error_fr(r, "parse");
346 r = SSH_ERR_INVALID_FORMAT;
347 goto out;
348 }
349 if (sshbuf_len(resp) != 0) {
350 error_f("trailing data in response");
351 r = SSH_ERR_INVALID_FORMAT;
352 goto out;
353 }
354 if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
355 error_fr(r, "encode");
356 goto out;
357 }
358 if (attest != NULL && (r = sshbuf_putb(attest, abuf)) != 0) {
359 error_fr(r, "encode attestation information");
360 goto out;
361 }
362
363 /* success */
364 r = 0;
365 *keyp = key;
366 key = NULL;
367 out:
368 oerrno = errno;
369 sshkey_free(key);
370 sshbuf_free(kbuf);
371 sshbuf_free(abuf);
372 sshbuf_free(req);
373 sshbuf_free(resp);
374 errno = oerrno;
375 return r;
376 }
377
378 int
sshsk_load_resident(const char * provider_path,const char * device,const char * pin,struct sshkey *** keysp,size_t * nkeysp)379 sshsk_load_resident(const char *provider_path, const char *device,
380 const char *pin, struct sshkey ***keysp, size_t *nkeysp)
381 {
382 int oerrno, r = SSH_ERR_INTERNAL_ERROR;
383 struct sshbuf *kbuf = NULL, *req = NULL, *resp = NULL;
384 struct sshkey *key = NULL, **keys = NULL, **tmp;
385 size_t i, nkeys = 0;
386
387 *keysp = NULL;
388 *nkeysp = 0;
389
390 if ((resp = sshbuf_new()) == NULL ||
391 (kbuf = sshbuf_new()) == NULL ||
392 (req = sshbuf_new()) == NULL) {
393 r = SSH_ERR_ALLOC_FAIL;
394 goto out;
395 }
396
397 if ((r = sshbuf_put_cstring(req, provider_path)) != 0 ||
398 (r = sshbuf_put_cstring(req, device)) != 0 ||
399 (r = sshbuf_put_cstring(req, pin)) != 0) {
400 error_fr(r, "compose");
401 goto out;
402 }
403
404 if ((r = client_converse(req, &resp, SSH_SK_HELPER_LOAD_RESIDENT)) != 0)
405 goto out;
406
407 while (sshbuf_len(resp) != 0) {
408 /* key, comment */
409 if ((r = sshbuf_get_stringb(resp, kbuf)) != 0 ||
410 (r = sshbuf_get_cstring(resp, NULL, NULL)) != 0) {
411 error_fr(r, "parse signature");
412 r = SSH_ERR_INVALID_FORMAT;
413 goto out;
414 }
415 if ((r = sshkey_private_deserialize(kbuf, &key)) != 0) {
416 error_fr(r, "decode key");
417 goto out;
418 }
419 if ((tmp = recallocarray(keys, nkeys, nkeys + 1,
420 sizeof(*keys))) == NULL) {
421 error_f("recallocarray keys failed");
422 goto out;
423 }
424 debug_f("keys[%zu]: %s %s", nkeys, sshkey_type(key),
425 key->sk_application);
426 keys = tmp;
427 keys[nkeys++] = key;
428 key = NULL;
429 }
430
431 /* success */
432 r = 0;
433 *keysp = keys;
434 *nkeysp = nkeys;
435 keys = NULL;
436 nkeys = 0;
437 out:
438 oerrno = errno;
439 for (i = 0; i < nkeys; i++)
440 sshkey_free(keys[i]);
441 free(keys);
442 sshkey_free(key);
443 sshbuf_free(kbuf);
444 sshbuf_free(req);
445 sshbuf_free(resp);
446 errno = oerrno;
447 return r;
448 }
449