1/* $NetBSD: authfd.c,v 1.18 2019/04/20 17:16:40 christos Exp $ */
2/* $OpenBSD: authfd.c,v 1.113 2018/12/27 23:02:11 djm Exp $ */
3/*
4 * Author: Tatu Ylonen <ylo@cs.hut.fi>
5 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
6 * All rights reserved
7 * Functions for connecting the local authentication agent.
8 *
9 * As far as I am concerned, the code I have written for this software
10 * can be used freely for any purpose. Any derived versions of this
11 * software must be clearly marked as such, and if the derived work is
12 * incompatible with the protocol description in the RFC file, it must be
13 * called by a name other than "ssh" or "Secure Shell".
14 *
15 * SSH2 implementation,
16 * Copyright (c) 2000 Markus Friedl. All rights reserved.
17 *
18 * Redistribution and use in source and binary forms, with or without
19 * modification, are permitted provided that the following conditions
20 * are met:
21 * 1. Redistributions of source code must retain the above copyright
22 * notice, this list of conditions and the following disclaimer.
23 * 2. Redistributions in binary form must reproduce the above copyright
24 * notice, this list of conditions and the following disclaimer in the
25 * documentation and/or other materials provided with the distribution.
26 *
27 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
28 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
29 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
30 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
31 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
32 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
33 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
34 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
35 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
36 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
37 */
38
39#include "includes.h"
40__RCSID("$NetBSD: authfd.c,v 1.18 2019/04/20 17:16:40 christos Exp $");
41#include <sys/types.h>
42#include <sys/un.h>
43#include <sys/socket.h>
44
45#include <fcntl.h>
46#include <stdlib.h>
47#include <signal.h>
48#include <string.h>
49#include <unistd.h>
50#include <errno.h>
51
52#include "xmalloc.h"
53#include "ssh.h"
54#include "sshbuf.h"
55#include "sshkey.h"
56#include "authfd.h"
57#include "cipher.h"
58#include "compat.h"
59#include "log.h"
60#include "atomicio.h"
61#include "misc.h"
62#include "ssherr.h"
63
64#define MAX_AGENT_IDENTITIES 2048 /* Max keys in agent reply */
65#define MAX_AGENT_REPLY_LEN (256 * 1024) /* Max bytes in agent reply */
66
67/* macro to check for "agent failure" message */
68#define agent_failed(x) \
69 ((x == SSH_AGENT_FAILURE) || \
70 (x == SSH_COM_AGENT2_FAILURE) || \
71 (x == SSH2_AGENT_FAILURE))
72
73/* Convert success/failure response from agent to a err.h status */
74static int
75decode_reply(u_char type)
76{
77 if (agent_failed(type))
78 return SSH_ERR_AGENT_FAILURE;
79 else if (type == SSH_AGENT_SUCCESS)
80 return 0;
81 else
82 return SSH_ERR_INVALID_FORMAT;
83}
84
85/* Returns the number of the authentication fd, or -1 if there is none. */
86int
87ssh_get_authentication_socket(int *fdp)
88{
89 const char *authsocket;
90 int sock, oerrno;
91 struct sockaddr_un sunaddr;
92
93 if (fdp != NULL)
94 *fdp = -1;
95
96 authsocket = getenv(SSH_AUTHSOCKET_ENV_NAME);
97 if (authsocket == NULL || *authsocket == '\0')
98 return SSH_ERR_AGENT_NOT_PRESENT;
99
100 memset(&sunaddr, 0, sizeof(sunaddr));
101 sunaddr.sun_family = AF_UNIX;
102 strlcpy(sunaddr.sun_path, authsocket, sizeof(sunaddr.sun_path));
103
104 if ((sock = socket(AF_UNIX, SOCK_STREAM, 0)) < 0)
105 return SSH_ERR_SYSTEM_ERROR;
106
107 /* close on exec */
108 if (fcntl(sock, F_SETFD, FD_CLOEXEC) == -1 ||
109 connect(sock, (struct sockaddr *)&sunaddr, sizeof(sunaddr)) < 0) {
110 oerrno = errno;
111 close(sock);
112 errno = oerrno;
113 return SSH_ERR_SYSTEM_ERROR;
114 }
115 if (fdp != NULL)
116 *fdp = sock;
117 else
118 close(sock);
119 return 0;
120}
121
122/* Communicate with agent: send request and read reply */
123static int
124ssh_request_reply(int sock, struct sshbuf *request, struct sshbuf *reply)
125{
126 int r;
127 size_t l, len;
128 char buf[1024];
129
130 /* Get the length of the message, and format it in the buffer. */
131 len = sshbuf_len(request);
132 POKE_U32(buf, len);
133
134 /* Send the length and then the packet to the agent. */
135 if (atomicio(vwrite, sock, buf, 4) != 4 ||
136 atomicio(vwrite, sock, sshbuf_mutable_ptr(request),
137 sshbuf_len(request)) != sshbuf_len(request))
138 return SSH_ERR_AGENT_COMMUNICATION;
139 /*
140 * Wait for response from the agent. First read the length of the
141 * response packet.
142 */
143 if (atomicio(read, sock, buf, 4) != 4)
144 return SSH_ERR_AGENT_COMMUNICATION;
145
146 /* Extract the length, and check it for sanity. */
147 len = PEEK_U32(buf);
148 if (len > MAX_AGENT_REPLY_LEN)
149 return SSH_ERR_INVALID_FORMAT;
150
151 /* Read the rest of the response in to the buffer. */
152 sshbuf_reset(reply);
153 while (len > 0) {
154 l = len;
155 if (l > sizeof(buf))
156 l = sizeof(buf);
157 if (atomicio(read, sock, buf, l) != l)
158 return SSH_ERR_AGENT_COMMUNICATION;
159 if ((r = sshbuf_put(reply, buf, l)) != 0)
160 return r;
161 len -= l;
162 }
163 return 0;
164}
165
166/*
167 * Closes the agent socket if it should be closed (depends on how it was
168 * obtained). The argument must have been returned by
169 * ssh_get_authentication_socket().
170 */
171void
172ssh_close_authentication_socket(int sock)
173{
174 if (getenv(SSH_AUTHSOCKET_ENV_NAME))
175 close(sock);
176}
177
178/* Lock/unlock agent */
179int
180ssh_lock_agent(int sock, int lock, const char *password)
181{
182 int r;
183 u_char type = lock ? SSH_AGENTC_LOCK : SSH_AGENTC_UNLOCK;
184 struct sshbuf *msg;
185
186 if ((msg = sshbuf_new()) == NULL)
187 return SSH_ERR_ALLOC_FAIL;
188 if ((r = sshbuf_put_u8(msg, type)) != 0 ||
189 (r = sshbuf_put_cstring(msg, password)) != 0)
190 goto out;
191 if ((r = ssh_request_reply(sock, msg, msg)) != 0)
192 goto out;
193 if ((r = sshbuf_get_u8(msg, &type)) != 0)
194 goto out;
195 r = decode_reply(type);
196 out:
197 sshbuf_free(msg);
198 return r;
199}
200
201
202static int
203deserialise_identity2(struct sshbuf *ids, struct sshkey **keyp, char **commentp)
204{
205 int r;
206 char *comment = NULL;
207 const u_char *blob;
208 size_t blen;
209
210 if ((r = sshbuf_get_string_direct(ids, &blob, &blen)) != 0 ||
211 (r = sshbuf_get_cstring(ids, &comment, NULL)) != 0)
212 goto out;
213 if ((r = sshkey_from_blob(blob, blen, keyp)) != 0)
214 goto out;
215 if (commentp != NULL) {
216 *commentp = comment;
217 comment = NULL;
218 }
219 r = 0;
220 out:
221 free(comment);
222 return r;
223}
224
225/*
226 * Fetch list of identities held by the agent.
227 */
228int
229ssh_fetch_identitylist(int sock, struct ssh_identitylist **idlp)
230{
231 u_char type;
232 u_int32_t num, i;
233 struct sshbuf *msg;
234 struct ssh_identitylist *idl = NULL;
235 int r;
236
237 /*
238 * Send a message to the agent requesting for a list of the
239 * identities it can represent.
240 */
241 if ((msg = sshbuf_new()) == NULL)
242 return SSH_ERR_ALLOC_FAIL;
243 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_REQUEST_IDENTITIES)) != 0)
244 goto out;
245
246 if ((r = ssh_request_reply(sock, msg, msg)) != 0)
247 goto out;
248
249 /* Get message type, and verify that we got a proper answer. */
250 if ((r = sshbuf_get_u8(msg, &type)) != 0)
251 goto out;
252 if (agent_failed(type)) {
253 r = SSH_ERR_AGENT_FAILURE;
254 goto out;
255 } else if (type != SSH2_AGENT_IDENTITIES_ANSWER) {
256 r = SSH_ERR_INVALID_FORMAT;
257 goto out;
258 }
259
260 /* Get the number of entries in the response and check it for sanity. */
261 if ((r = sshbuf_get_u32(msg, &num)) != 0)
262 goto out;
263 if (num > MAX_AGENT_IDENTITIES) {
264 r = SSH_ERR_INVALID_FORMAT;
265 goto out;
266 }
267 if (num == 0) {
268 r = SSH_ERR_AGENT_NO_IDENTITIES;
269 goto out;
270 }
271
272 /* Deserialise the response into a list of keys/comments */
273 if ((idl = calloc(1, sizeof(*idl))) == NULL ||
274 (idl->keys = calloc(num, sizeof(*idl->keys))) == NULL ||
275 (idl->comments = calloc(num, sizeof(*idl->comments))) == NULL) {
276 r = SSH_ERR_ALLOC_FAIL;
277 goto out;
278 }
279 for (i = 0; i < num;) {
280 if ((r = deserialise_identity2(msg, &(idl->keys[i]),
281 &(idl->comments[i]))) != 0) {
282 if (r == SSH_ERR_KEY_TYPE_UNKNOWN) {
283 /* Gracefully skip unknown key types */
284 num--;
285 continue;
286 } else
287 goto out;
288 }
289 i++;
290 }
291 idl->nkeys = num;
292 *idlp = idl;
293 idl = NULL;
294 r = 0;
295 out:
296 sshbuf_free(msg);
297 if (idl != NULL)
298 ssh_free_identitylist(idl);
299 return r;
300}
301
302void
303ssh_free_identitylist(struct ssh_identitylist *idl)
304{
305 size_t i;
306
307 if (idl == NULL)
308 return;
309 for (i = 0; i < idl->nkeys; i++) {
310 if (idl->keys != NULL)
311 sshkey_free(idl->keys[i]);
312 if (idl->comments != NULL)
313 free(idl->comments[i]);
314 }
315 free(idl);
316}
317
318/*
319 * Sends a challenge (typically from a server via ssh(1)) to the agent,
320 * and waits for a response from the agent.
321 * Returns true (non-zero) if the agent gave the correct answer, zero
322 * otherwise.
323 */
324
325
326/* encode signature algorithm in flag bits, so we can keep the msg format */
327static u_int
328agent_encode_alg(const struct sshkey *key, const char *alg)
329{
330 if (alg != NULL && sshkey_type_plain(key->type) == KEY_RSA) {
331 if (strcmp(alg, "rsa-sha2-256") == 0 ||
332 strcmp(alg, "rsa-sha2-256-cert-v01@openssh.com") == 0)
333 return SSH_AGENT_RSA_SHA2_256;
334 if (strcmp(alg, "rsa-sha2-512") == 0 ||
335 strcmp(alg, "rsa-sha2-512-cert-v01@openssh.com") == 0)
336 return SSH_AGENT_RSA_SHA2_512;
337 }
338 return 0;
339}
340
341/* ask agent to sign data, returns err.h code on error, 0 on success */
342int
343ssh_agent_sign(int sock, const struct sshkey *key,
344 u_char **sigp, size_t *lenp,
345 const u_char *data, size_t datalen, const char *alg, u_int compat)
346{
347 struct sshbuf *msg;
348 u_char *sig = NULL, type = 0;
349 size_t len = 0;
350 u_int flags = 0;
351 int r = SSH_ERR_INTERNAL_ERROR;
352
353 *sigp = NULL;
354 *lenp = 0;
355
356 if (datalen > SSH_KEY_MAX_SIGN_DATA_SIZE)
357 return SSH_ERR_INVALID_ARGUMENT;
358 if ((msg = sshbuf_new()) == NULL)
359 return SSH_ERR_ALLOC_FAIL;
360 flags |= agent_encode_alg(key, alg);
361 if ((r = sshbuf_put_u8(msg, SSH2_AGENTC_SIGN_REQUEST)) != 0 ||
362 (r = sshkey_puts(key, msg)) != 0 ||
363 (r = sshbuf_put_string(msg, data, datalen)) != 0 ||
364 (r = sshbuf_put_u32(msg, flags)) != 0)
365 goto out;
366 if ((r = ssh_request_reply(sock, msg, msg)) != 0)
367 goto out;
368 if ((r = sshbuf_get_u8(msg, &type)) != 0)
369 goto out;
370 if (agent_failed(type)) {
371 r = SSH_ERR_AGENT_FAILURE;
372 goto out;
373 } else if (type != SSH2_AGENT_SIGN_RESPONSE) {
374 r = SSH_ERR_INVALID_FORMAT;
375 goto out;
376 }
377 if ((r = sshbuf_get_string(msg, &sig, &len)) != 0)
378 goto out;
379 /* Check what we actually got back from the agent. */
380 if ((r = sshkey_check_sigtype(sig, len, alg)) != 0)
381 goto out;
382 /* success */
383 *sigp = sig;
384 *lenp = len;
385 sig = NULL;
386 len = 0;
387 r = 0;
388 out:
389 freezero(sig, len);
390 sshbuf_free(msg);
391 return r;
392}
393
394/* Encode key for a message to the agent. */
395
396
397static int
398encode_constraints(struct sshbuf *m, u_int life, u_int confirm, u_int maxsign)
399{
400 int r;
401
402 if (life != 0) {
403 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_LIFETIME)) != 0 ||
404 (r = sshbuf_put_u32(m, life)) != 0)
405 goto out;
406 }
407 if (confirm != 0) {
408 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_CONFIRM)) != 0)
409 goto out;
410 }
411 if (maxsign != 0) {
412 if ((r = sshbuf_put_u8(m, SSH_AGENT_CONSTRAIN_MAXSIGN)) != 0 ||
413 (r = sshbuf_put_u32(m, maxsign)) != 0)
414 goto out;
415 }
416 r = 0;
417 out:
418 return r;
419}
420
421/*
422 * Adds an identity to the authentication server.
423 * This call is intended only for use by ssh-add(1) and like applications.
424 */
425int
426ssh_add_identity_constrained(int sock, const struct sshkey *key,
427 const char *comment, u_int life, u_int confirm, u_int maxsign)
428{
429 struct sshbuf *msg;
430 int r, constrained = (life || confirm || maxsign);
431 u_char type;
432
433 if ((msg = sshbuf_new()) == NULL)
434 return SSH_ERR_ALLOC_FAIL;
435
436 switch (key->type) {
437#ifdef WITH_OPENSSL
438 case KEY_RSA:
439 case KEY_RSA_CERT:
440 case KEY_DSA:
441 case KEY_DSA_CERT:
442 case KEY_ECDSA:
443 case KEY_ECDSA_CERT:
444#endif
445 case KEY_ED25519:
446 case KEY_ED25519_CERT:
447 case KEY_XMSS:
448 case KEY_XMSS_CERT:
449 type = constrained ?
450 SSH2_AGENTC_ADD_ID_CONSTRAINED :
451 SSH2_AGENTC_ADD_IDENTITY;
452 if ((r = sshbuf_put_u8(msg, type)) != 0 ||
453 (r = sshkey_private_serialize_maxsign(key, msg, maxsign,
454 NULL)) != 0 ||
455 (r = sshbuf_put_cstring(msg, comment)) != 0)
456 goto out;
457 break;
458 default:
459 r = SSH_ERR_INVALID_ARGUMENT;
460 goto out;
461 }
462 if (constrained &&
463 (r = encode_constraints(msg, life, confirm, maxsign)) != 0)
464 goto out;
465 if ((r = ssh_request_reply(sock, msg, msg)) != 0)
466 goto out;
467 if ((r = sshbuf_get_u8(msg, &type)) != 0)
468 goto out;
469 r = decode_reply(type);
470 out:
471 sshbuf_free(msg);
472 return r;
473}
474
475/*
476 * Removes an identity from the authentication server.
477 * This call is intended only for use by ssh-add(1) and like applications.
478 */
479int
480ssh_remove_identity(int sock, struct sshkey *key)
481{
482 struct sshbuf *msg;
483 int r;
484 u_char type, *blob = NULL;
485 size_t blen;
486
487 if ((msg = sshbuf_new()) == NULL)
488 return SSH_ERR_ALLOC_FAIL;
489
490 if (key->type != KEY_UNSPEC) {
491 if ((r = sshkey_to_blob(key, &blob, &blen)) != 0)
492 goto out;
493 if ((r = sshbuf_put_u8(msg,
494 SSH2_AGENTC_REMOVE_IDENTITY)) != 0 ||
495 (r = sshbuf_put_string(msg, blob, blen)) != 0)
496 goto out;
497 } else {
498 r = SSH_ERR_INVALID_ARGUMENT;
499 goto out;
500 }
501 if ((r = ssh_request_reply(sock, msg, msg)) != 0)
502 goto out;
503 if ((r = sshbuf_get_u8(msg, &type)) != 0)
504 goto out;
505 r = decode_reply(type);
506 out:
507 if (blob != NULL) {
508 explicit_bzero(blob, blen);
509 free(blob);
510 }
511 sshbuf_free(msg);
512 return r;
513}
514
515/*
516 * Add/remove an token-based identity from the authentication server.
517 * This call is intended only for use by ssh-add(1) and like applications.
518 */
519int
520ssh_update_card(int sock, int add, const char *reader_id, const char *pin,
521 u_int life, u_int confirm)
522{
523 struct sshbuf *msg;
524 int r, constrained = (life || confirm);
525 u_char type;
526
527 if (add) {
528 type = constrained ?
529 SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED :
530 SSH_AGENTC_ADD_SMARTCARD_KEY;
531 } else
532 type = SSH_AGENTC_REMOVE_SMARTCARD_KEY;
533
534 if ((msg = sshbuf_new()) == NULL)
535 return SSH_ERR_ALLOC_FAIL;
536 if ((r = sshbuf_put_u8(msg, type)) != 0 ||
537 (r = sshbuf_put_cstring(msg, reader_id)) != 0 ||
538 (r = sshbuf_put_cstring(msg, pin)) != 0)
539 goto out;
540 if (constrained &&
541 (r = encode_constraints(msg, life, confirm, 0)) != 0)
542 goto out;
543 if ((r = ssh_request_reply(sock, msg, msg)) != 0)
544 goto out;
545 if ((r = sshbuf_get_u8(msg, &type)) != 0)
546 goto out;
547 r = decode_reply(type);
548 out:
549 sshbuf_free(msg);
550 return r;
551}
552
553/*
554 * Removes all identities from the agent.
555 * This call is intended only for use by ssh-add(1) and like applications.
556 *
557 * This supports the SSH protocol 1 message to because, when clearing all
558 * keys from an agent, we generally want to clear both protocol v1 and v2
559 * keys.
560 */
561int
562ssh_remove_all_identities(int sock, int version)
563{
564 struct sshbuf *msg;
565 u_char type = (version == 1) ?
566 SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES :
567 SSH2_AGENTC_REMOVE_ALL_IDENTITIES;
568 int r;
569
570 if ((msg = sshbuf_new()) == NULL)
571 return SSH_ERR_ALLOC_FAIL;
572 if ((r = sshbuf_put_u8(msg, type)) != 0)
573 goto out;
574 if ((r = ssh_request_reply(sock, msg, msg)) != 0)
575 goto out;
576 if ((r = sshbuf_get_u8(msg, &type)) != 0)
577 goto out;
578 r = decode_reply(type);
579 out:
580 sshbuf_free(msg);
581 return r;
582}
583