1 /* $OpenBSD: auth2-pubkey.c,v 1.120 2024/05/17 00:30:23 djm Exp $ */
2 /*
3 * Copyright (c) 2000 Markus Friedl. All rights reserved.
4 * Copyright (c) 2010 Damien Miller. All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27 #include "includes.h"
28
29 #include <sys/types.h>
30
31 #include <stdlib.h>
32 #include <errno.h>
33 #ifdef HAVE_PATHS_H
34 # include <paths.h>
35 #endif
36 #include <pwd.h>
37 #include <signal.h>
38 #include <stdio.h>
39 #include <stdarg.h>
40 #include <string.h>
41 #include <time.h>
42 #include <unistd.h>
43 #include <limits.h>
44
45 #include "xmalloc.h"
46 #include "ssh.h"
47 #include "ssh2.h"
48 #include "packet.h"
49 #include "kex.h"
50 #include "sshbuf.h"
51 #include "log.h"
52 #include "misc.h"
53 #include "servconf.h"
54 #include "compat.h"
55 #include "sshkey.h"
56 #include "hostfile.h"
57 #include "auth.h"
58 #include "pathnames.h"
59 #include "uidswap.h"
60 #include "auth-options.h"
61 #include "canohost.h"
62 #ifdef GSSAPI
63 #include "ssh-gss.h"
64 #endif
65 #include "monitor_wrap.h"
66 #include "authfile.h"
67 #include "match.h"
68 #include "ssherr.h"
69 #include "channels.h" /* XXX for session.h */
70 #include "session.h" /* XXX for child_set_env(); refactor? */
71 #include "sk-api.h"
72
73 /* import */
74 extern ServerOptions options;
75 extern struct authmethod_cfg methodcfg_pubkey;
76
77 static char *
format_key(const struct sshkey * key)78 format_key(const struct sshkey *key)
79 {
80 char *ret, *fp = sshkey_fingerprint(key,
81 options.fingerprint_hash, SSH_FP_DEFAULT);
82
83 xasprintf(&ret, "%s %s", sshkey_type(key), fp);
84 free(fp);
85 return ret;
86 }
87
88 static int
userauth_pubkey(struct ssh * ssh,const char * method)89 userauth_pubkey(struct ssh *ssh, const char *method)
90 {
91 Authctxt *authctxt = ssh->authctxt;
92 struct passwd *pw = authctxt->pw;
93 struct sshbuf *b = NULL;
94 struct sshkey *key = NULL, *hostkey = NULL;
95 char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL;
96 u_char *pkblob = NULL, *sig = NULL, have_sig;
97 size_t blen, slen;
98 int hostbound, r, pktype;
99 int req_presence = 0, req_verify = 0, authenticated = 0;
100 struct sshauthopt *authopts = NULL;
101 struct sshkey_sig_details *sig_details = NULL;
102
103 hostbound = strcmp(method, "publickey-hostbound-v00@openssh.com") == 0;
104
105 if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 ||
106 (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 ||
107 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0)
108 fatal_fr(r, "parse %s packet", method);
109
110 /* hostbound auth includes the hostkey offered at initial KEX */
111 if (hostbound) {
112 if ((r = sshpkt_getb_froms(ssh, &b)) != 0 ||
113 (r = sshkey_fromb(b, &hostkey)) != 0)
114 fatal_fr(r, "parse %s hostkey", method);
115 if (ssh->kex->initial_hostkey == NULL)
116 fatal_f("internal error: initial hostkey not recorded");
117 if (!sshkey_equal(hostkey, ssh->kex->initial_hostkey))
118 fatal_f("%s packet contained wrong host key", method);
119 sshbuf_free(b);
120 b = NULL;
121 }
122
123 if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) {
124 char *keystring;
125 struct sshbuf *pkbuf;
126
127 if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL)
128 fatal_f("sshbuf_from failed");
129 if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL)
130 fatal_f("sshbuf_dtob64 failed");
131 debug2_f("%s user %s %s public key %s %s",
132 authctxt->valid ? "valid" : "invalid", authctxt->user,
133 have_sig ? "attempting" : "querying", pkalg, keystring);
134 sshbuf_free(pkbuf);
135 free(keystring);
136 }
137
138 pktype = sshkey_type_from_name(pkalg);
139 if (pktype == KEY_UNSPEC) {
140 /* this is perfectly legal */
141 verbose_f("unsupported public key algorithm: %s", pkalg);
142 goto done;
143 }
144 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
145 error_fr(r, "parse key");
146 goto done;
147 }
148 if (key == NULL) {
149 error_f("cannot decode key: %s", pkalg);
150 goto done;
151 }
152 if (key->type != pktype) {
153 error_f("type mismatch for decoded key "
154 "(received %d, expected %d)", key->type, pktype);
155 goto done;
156 }
157 if (auth2_key_already_used(authctxt, key)) {
158 logit("refusing previously-used %s key", sshkey_type(key));
159 goto done;
160 }
161 if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) {
162 logit_f("signature algorithm %s not in "
163 "PubkeyAcceptedAlgorithms", pkalg);
164 goto done;
165 }
166 if ((r = sshkey_check_cert_sigtype(key,
167 options.ca_sign_algorithms)) != 0) {
168 logit_fr(r, "certificate signature algorithm %s",
169 (key->cert == NULL || key->cert->signature_type == NULL) ?
170 "(null)" : key->cert->signature_type);
171 goto done;
172 }
173 if ((r = sshkey_check_rsa_length(key,
174 options.required_rsa_size)) != 0) {
175 logit_r(r, "refusing %s key", sshkey_type(key));
176 goto done;
177 }
178 key_s = format_key(key);
179 if (sshkey_is_cert(key))
180 ca_s = format_key(key->cert->signature_key);
181
182 if (have_sig) {
183 debug3_f("%s have %s signature for %s%s%s",
184 method, pkalg, key_s,
185 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
186 if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 ||
187 (r = sshpkt_get_end(ssh)) != 0)
188 fatal_fr(r, "parse signature packet");
189 if ((b = sshbuf_new()) == NULL)
190 fatal_f("sshbuf_new failed");
191 if (ssh->compat & SSH_OLD_SESSIONID) {
192 if ((r = sshbuf_putb(b, ssh->kex->session_id)) != 0)
193 fatal_fr(r, "put old session id");
194 } else {
195 if ((r = sshbuf_put_stringb(b,
196 ssh->kex->session_id)) != 0)
197 fatal_fr(r, "put session id");
198 }
199 if (!authctxt->valid || authctxt->user == NULL) {
200 debug2_f("disabled because of invalid user");
201 goto done;
202 }
203 /* reconstruct packet */
204 xasprintf(&userstyle, "%s%s%s", authctxt->user,
205 authctxt->style ? ":" : "",
206 authctxt->style ? authctxt->style : "");
207 if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
208 (r = sshbuf_put_cstring(b, userstyle)) != 0 ||
209 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
210 (r = sshbuf_put_cstring(b, method)) != 0 ||
211 (r = sshbuf_put_u8(b, have_sig)) != 0 ||
212 (r = sshbuf_put_cstring(b, pkalg)) != 0 ||
213 (r = sshbuf_put_string(b, pkblob, blen)) != 0)
214 fatal_fr(r, "reconstruct %s packet", method);
215 if (hostbound &&
216 (r = sshkey_puts(ssh->kex->initial_hostkey, b)) != 0)
217 fatal_fr(r, "reconstruct %s packet", method);
218 #ifdef DEBUG_PK
219 sshbuf_dump(b, stderr);
220 #endif
221 /* test for correct signature */
222 authenticated = 0;
223 if (mm_user_key_allowed(ssh, pw, key, 1, &authopts) &&
224 mm_sshkey_verify(key, sig, slen,
225 sshbuf_ptr(b), sshbuf_len(b),
226 (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL,
227 ssh->compat, &sig_details) == 0) {
228 authenticated = 1;
229 }
230 if (authenticated == 1 && sig_details != NULL) {
231 auth2_record_info(authctxt, "signature count = %u",
232 sig_details->sk_counter);
233 debug_f("sk_counter = %u, sk_flags = 0x%02x",
234 sig_details->sk_counter, sig_details->sk_flags);
235 req_presence = (options.pubkey_auth_options &
236 PUBKEYAUTH_TOUCH_REQUIRED) ||
237 !authopts->no_require_user_presence;
238 if (req_presence && (sig_details->sk_flags &
239 SSH_SK_USER_PRESENCE_REQD) == 0) {
240 error("public key %s signature for %s%s from "
241 "%.128s port %d rejected: user presence "
242 "(authenticator touch) requirement "
243 "not met ", key_s,
244 authctxt->valid ? "" : "invalid user ",
245 authctxt->user, ssh_remote_ipaddr(ssh),
246 ssh_remote_port(ssh));
247 authenticated = 0;
248 goto done;
249 }
250 req_verify = (options.pubkey_auth_options &
251 PUBKEYAUTH_VERIFY_REQUIRED) ||
252 authopts->require_verify;
253 if (req_verify && (sig_details->sk_flags &
254 SSH_SK_USER_VERIFICATION_REQD) == 0) {
255 error("public key %s signature for %s%s from "
256 "%.128s port %d rejected: user "
257 "verification requirement not met ", key_s,
258 authctxt->valid ? "" : "invalid user ",
259 authctxt->user, ssh_remote_ipaddr(ssh),
260 ssh_remote_port(ssh));
261 authenticated = 0;
262 goto done;
263 }
264 }
265 auth2_record_key(authctxt, authenticated, key);
266 } else {
267 debug_f("%s test pkalg %s pkblob %s%s%s", method, pkalg, key_s,
268 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
269
270 if ((r = sshpkt_get_end(ssh)) != 0)
271 fatal_fr(r, "parse packet");
272
273 if (!authctxt->valid || authctxt->user == NULL) {
274 debug2_f("disabled because of invalid user");
275 goto done;
276 }
277 /* XXX fake reply and always send PK_OK ? */
278 /*
279 * XXX this allows testing whether a user is allowed
280 * to login: if you happen to have a valid pubkey this
281 * message is sent. the message is NEVER sent at all
282 * if a user is not allowed to login. is this an
283 * issue? -markus
284 */
285 if (mm_user_key_allowed(ssh, pw, key, 0, NULL)) {
286 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK))
287 != 0 ||
288 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 ||
289 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 ||
290 (r = sshpkt_send(ssh)) != 0 ||
291 (r = ssh_packet_write_wait(ssh)) != 0)
292 fatal_fr(r, "send packet");
293 authctxt->postponed = 1;
294 }
295 }
296 done:
297 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) {
298 debug_f("key options inconsistent with existing");
299 authenticated = 0;
300 }
301 debug2_f("authenticated %d pkalg %s", authenticated, pkalg);
302
303 sshbuf_free(b);
304 sshauthopt_free(authopts);
305 sshkey_free(key);
306 sshkey_free(hostkey);
307 free(userstyle);
308 free(pkalg);
309 free(pkblob);
310 free(key_s);
311 free(ca_s);
312 free(sig);
313 sshkey_sig_details_free(sig_details);
314 return authenticated;
315 }
316
317 static int
match_principals_file(struct passwd * pw,char * file,struct sshkey_cert * cert,struct sshauthopt ** authoptsp)318 match_principals_file(struct passwd *pw, char *file,
319 struct sshkey_cert *cert, struct sshauthopt **authoptsp)
320 {
321 FILE *f;
322 int success;
323
324 if (authoptsp != NULL)
325 *authoptsp = NULL;
326
327 temporarily_use_uid(pw);
328 debug("trying authorized principals file %s", file);
329 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
330 restore_uid();
331 return 0;
332 }
333 success = auth_process_principals(f, file, cert, authoptsp);
334 fclose(f);
335 restore_uid();
336 return success;
337 }
338
339 /*
340 * Checks whether principal is allowed in output of command.
341 * returns 1 if the principal is allowed or 0 otherwise.
342 */
343 static int
match_principals_command(struct passwd * user_pw,const struct sshkey * key,const char * conn_id,const char * rdomain,struct sshauthopt ** authoptsp)344 match_principals_command(struct passwd *user_pw, const struct sshkey *key,
345 const char *conn_id, const char *rdomain, struct sshauthopt **authoptsp)
346 {
347 struct passwd *runas_pw = NULL;
348 const struct sshkey_cert *cert = key->cert;
349 FILE *f = NULL;
350 int r, ok, found_principal = 0;
351 int i, ac = 0, uid_swapped = 0;
352 pid_t pid;
353 char *tmp, *username = NULL, *command = NULL, **av = NULL;
354 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL;
355 char serial_s[32], uidstr[32];
356 void (*osigchld)(int);
357
358 if (authoptsp != NULL)
359 *authoptsp = NULL;
360 if (options.authorized_principals_command == NULL)
361 return 0;
362 if (options.authorized_principals_command_user == NULL) {
363 error("No user for AuthorizedPrincipalsCommand specified, "
364 "skipping");
365 return 0;
366 }
367
368 /*
369 * NB. all returns later this function should go via "out" to
370 * ensure the original SIGCHLD handler is restored properly.
371 */
372 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
373
374 /* Prepare and verify the user for the command */
375 username = percent_expand(options.authorized_principals_command_user,
376 "u", user_pw->pw_name, (char *)NULL);
377 runas_pw = getpwnam(username);
378 if (runas_pw == NULL) {
379 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
380 username, strerror(errno));
381 goto out;
382 }
383
384 /* Turn the command into an argument vector */
385 if (argv_split(options.authorized_principals_command,
386 &ac, &av, 0) != 0) {
387 error("AuthorizedPrincipalsCommand \"%s\" contains "
388 "invalid quotes", options.authorized_principals_command);
389 goto out;
390 }
391 if (ac == 0) {
392 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
393 options.authorized_principals_command);
394 goto out;
395 }
396 if ((ca_fp = sshkey_fingerprint(cert->signature_key,
397 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
398 error_f("sshkey_fingerprint failed");
399 goto out;
400 }
401 if ((key_fp = sshkey_fingerprint(key,
402 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
403 error_f("sshkey_fingerprint failed");
404 goto out;
405 }
406 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) {
407 error_fr(r, "sshkey_to_base64 failed");
408 goto out;
409 }
410 if ((r = sshkey_to_base64(key, &keytext)) != 0) {
411 error_fr(r, "sshkey_to_base64 failed");
412 goto out;
413 }
414 snprintf(serial_s, sizeof(serial_s), "%llu",
415 (unsigned long long)cert->serial);
416 snprintf(uidstr, sizeof(uidstr), "%llu",
417 (unsigned long long)user_pw->pw_uid);
418 for (i = 1; i < ac; i++) {
419 tmp = percent_expand(av[i],
420 "C", conn_id,
421 "D", rdomain,
422 "U", uidstr,
423 "u", user_pw->pw_name,
424 "h", user_pw->pw_dir,
425 "t", sshkey_ssh_name(key),
426 "T", sshkey_ssh_name(cert->signature_key),
427 "f", key_fp,
428 "F", ca_fp,
429 "k", keytext,
430 "K", catext,
431 "i", cert->key_id,
432 "s", serial_s,
433 (char *)NULL);
434 if (tmp == NULL)
435 fatal_f("percent_expand failed");
436 free(av[i]);
437 av[i] = tmp;
438 }
439 /* Prepare a printable command for logs, etc. */
440 command = argv_assemble(ac, av);
441
442 if ((pid = subprocess("AuthorizedPrincipalsCommand", command,
443 ac, av, &f,
444 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
445 runas_pw, temporarily_use_uid, restore_uid)) == 0)
446 goto out;
447
448 uid_swapped = 1;
449 temporarily_use_uid(runas_pw);
450
451 ok = auth_process_principals(f, "(command)", cert, authoptsp);
452
453 fclose(f);
454 f = NULL;
455
456 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0)
457 goto out;
458
459 /* Read completed successfully */
460 found_principal = ok;
461 out:
462 if (f != NULL)
463 fclose(f);
464 ssh_signal(SIGCHLD, osigchld);
465 for (i = 0; i < ac; i++)
466 free(av[i]);
467 free(av);
468 if (uid_swapped)
469 restore_uid();
470 free(command);
471 free(username);
472 free(ca_fp);
473 free(key_fp);
474 free(catext);
475 free(keytext);
476 return found_principal;
477 }
478
479 /* Authenticate a certificate key against TrustedUserCAKeys */
480 static int
user_cert_trusted_ca(struct passwd * pw,struct sshkey * key,const char * remote_ip,const char * remote_host,const char * conn_id,const char * rdomain,struct sshauthopt ** authoptsp)481 user_cert_trusted_ca(struct passwd *pw, struct sshkey *key,
482 const char *remote_ip, const char *remote_host,
483 const char *conn_id, const char *rdomain, struct sshauthopt **authoptsp)
484 {
485 char *ca_fp, *principals_file = NULL;
486 const char *reason;
487 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL;
488 struct sshauthopt *final_opts = NULL;
489 int r, ret = 0, found_principal = 0, use_authorized_principals;
490
491 if (authoptsp != NULL)
492 *authoptsp = NULL;
493
494 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL)
495 return 0;
496
497 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
498 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
499 return 0;
500
501 if ((r = sshkey_in_file(key->cert->signature_key,
502 options.trusted_user_ca_keys, 1, 0)) != 0) {
503 debug2_fr(r, "CA %s %s is not listed in %s",
504 sshkey_type(key->cert->signature_key), ca_fp,
505 options.trusted_user_ca_keys);
506 goto out;
507 }
508 /*
509 * If AuthorizedPrincipals is in use, then compare the certificate
510 * principals against the names in that file rather than matching
511 * against the username.
512 */
513 if ((principals_file = authorized_principals_file(pw)) != NULL) {
514 if (match_principals_file(pw, principals_file,
515 key->cert, &principals_opts))
516 found_principal = 1;
517 }
518 /* Try querying command if specified */
519 if (!found_principal && match_principals_command(pw, key,
520 conn_id, rdomain, &principals_opts))
521 found_principal = 1;
522 /* If principals file or command is specified, then require a match */
523 use_authorized_principals = principals_file != NULL ||
524 options.authorized_principals_command != NULL;
525 if (!found_principal && use_authorized_principals) {
526 reason = "Certificate does not contain an authorized principal";
527 goto fail_reason;
528 }
529 if (use_authorized_principals && principals_opts == NULL)
530 fatal_f("internal error: missing principals_opts");
531 if (sshkey_cert_check_authority_now(key, 0, 1, 0,
532 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
533 goto fail_reason;
534
535 /* Check authority from options in key and from principals file/cmd */
536 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) {
537 reason = "Invalid certificate options";
538 goto fail_reason;
539 }
540 if (auth_authorise_keyopts(pw, cert_opts, 0,
541 remote_ip, remote_host, "cert") != 0) {
542 reason = "Refused by certificate options";
543 goto fail_reason;
544 }
545 if (principals_opts == NULL) {
546 final_opts = cert_opts;
547 cert_opts = NULL;
548 } else {
549 if (auth_authorise_keyopts(pw, principals_opts, 0,
550 remote_ip, remote_host, "principals") != 0) {
551 reason = "Refused by certificate principals options";
552 goto fail_reason;
553 }
554 if ((final_opts = sshauthopt_merge(principals_opts,
555 cert_opts, &reason)) == NULL) {
556 fail_reason:
557 error("%s", reason);
558 auth_debug_add("%s", reason);
559 goto out;
560 }
561 }
562
563 /* Success */
564 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by "
565 "%s CA %s via %s", key->cert->key_id,
566 (unsigned long long)key->cert->serial,
567 sshkey_type(key->cert->signature_key), ca_fp,
568 options.trusted_user_ca_keys);
569 if (authoptsp != NULL) {
570 *authoptsp = final_opts;
571 final_opts = NULL;
572 }
573 ret = 1;
574 out:
575 sshauthopt_free(principals_opts);
576 sshauthopt_free(cert_opts);
577 sshauthopt_free(final_opts);
578 free(principals_file);
579 free(ca_fp);
580 return ret;
581 }
582
583 /*
584 * Checks whether key is allowed in file.
585 * returns 1 if the key is allowed or 0 otherwise.
586 */
587 static int
user_key_allowed2(struct passwd * pw,struct sshkey * key,char * file,const char * remote_ip,const char * remote_host,struct sshauthopt ** authoptsp)588 user_key_allowed2(struct passwd *pw, struct sshkey *key,
589 char *file, const char *remote_ip, const char *remote_host,
590 struct sshauthopt **authoptsp)
591 {
592 FILE *f;
593 int found_key = 0;
594
595 if (authoptsp != NULL)
596 *authoptsp = NULL;
597
598 /* Temporarily use the user's uid. */
599 temporarily_use_uid(pw);
600
601 debug("trying public key file %s", file);
602 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
603 found_key = auth_check_authkeys_file(pw, f, file,
604 key, remote_ip, remote_host, authoptsp);
605 fclose(f);
606 }
607
608 restore_uid();
609 return found_key;
610 }
611
612 /*
613 * Checks whether key is allowed in output of command.
614 * returns 1 if the key is allowed or 0 otherwise.
615 */
616 static int
user_key_command_allowed2(struct passwd * user_pw,struct sshkey * key,const char * remote_ip,const char * remote_host,const char * conn_id,const char * rdomain,struct sshauthopt ** authoptsp)617 user_key_command_allowed2(struct passwd *user_pw, struct sshkey *key,
618 const char *remote_ip, const char *remote_host,
619 const char *conn_id, const char *rdomain, struct sshauthopt **authoptsp)
620 {
621 struct passwd *runas_pw = NULL;
622 FILE *f = NULL;
623 int r, ok, found_key = 0;
624 int i, uid_swapped = 0, ac = 0;
625 pid_t pid;
626 char *username = NULL, *key_fp = NULL, *keytext = NULL;
627 char uidstr[32], *tmp, *command = NULL, **av = NULL;
628 void (*osigchld)(int);
629
630 if (authoptsp != NULL)
631 *authoptsp = NULL;
632 if (options.authorized_keys_command == NULL)
633 return 0;
634 if (options.authorized_keys_command_user == NULL) {
635 error("No user for AuthorizedKeysCommand specified, skipping");
636 return 0;
637 }
638
639 /*
640 * NB. all returns later this function should go via "out" to
641 * ensure the original SIGCHLD handler is restored properly.
642 */
643 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
644
645 /* Prepare and verify the user for the command */
646 username = percent_expand(options.authorized_keys_command_user,
647 "u", user_pw->pw_name, (char *)NULL);
648 runas_pw = getpwnam(username);
649 if (runas_pw == NULL) {
650 error("AuthorizedKeysCommandUser \"%s\" not found: %s",
651 username, strerror(errno));
652 goto out;
653 }
654
655 /* Prepare AuthorizedKeysCommand */
656 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash,
657 SSH_FP_DEFAULT)) == NULL) {
658 error_f("sshkey_fingerprint failed");
659 goto out;
660 }
661 if ((r = sshkey_to_base64(key, &keytext)) != 0) {
662 error_fr(r, "sshkey_to_base64 failed");
663 goto out;
664 }
665
666 /* Turn the command into an argument vector */
667 if (argv_split(options.authorized_keys_command, &ac, &av, 0) != 0) {
668 error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
669 options.authorized_keys_command);
670 goto out;
671 }
672 if (ac == 0) {
673 error("AuthorizedKeysCommand \"%s\" yielded no arguments",
674 options.authorized_keys_command);
675 goto out;
676 }
677 snprintf(uidstr, sizeof(uidstr), "%llu",
678 (unsigned long long)user_pw->pw_uid);
679 for (i = 1; i < ac; i++) {
680 tmp = percent_expand(av[i],
681 "C", conn_id,
682 "D", rdomain,
683 "U", uidstr,
684 "u", user_pw->pw_name,
685 "h", user_pw->pw_dir,
686 "t", sshkey_ssh_name(key),
687 "f", key_fp,
688 "k", keytext,
689 (char *)NULL);
690 if (tmp == NULL)
691 fatal_f("percent_expand failed");
692 free(av[i]);
693 av[i] = tmp;
694 }
695 /* Prepare a printable command for logs, etc. */
696 command = argv_assemble(ac, av);
697
698 /*
699 * If AuthorizedKeysCommand was run without arguments
700 * then fall back to the old behaviour of passing the
701 * target username as a single argument.
702 */
703 if (ac == 1) {
704 av = xreallocarray(av, ac + 2, sizeof(*av));
705 av[1] = xstrdup(user_pw->pw_name);
706 av[2] = NULL;
707 /* Fix up command too, since it is used in log messages */
708 free(command);
709 xasprintf(&command, "%s %s", av[0], av[1]);
710 }
711
712 if ((pid = subprocess("AuthorizedKeysCommand", command,
713 ac, av, &f,
714 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
715 runas_pw, temporarily_use_uid, restore_uid)) == 0)
716 goto out;
717
718 uid_swapped = 1;
719 temporarily_use_uid(runas_pw);
720
721 ok = auth_check_authkeys_file(user_pw, f,
722 options.authorized_keys_command, key, remote_ip,
723 remote_host, authoptsp);
724
725 fclose(f);
726 f = NULL;
727
728 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0)
729 goto out;
730
731 /* Read completed successfully */
732 found_key = ok;
733 out:
734 if (f != NULL)
735 fclose(f);
736 ssh_signal(SIGCHLD, osigchld);
737 for (i = 0; i < ac; i++)
738 free(av[i]);
739 free(av);
740 if (uid_swapped)
741 restore_uid();
742 free(command);
743 free(username);
744 free(key_fp);
745 free(keytext);
746 return found_key;
747 }
748
749 /*
750 * Check whether key authenticates and authorises the user.
751 */
752 int
user_key_allowed(struct ssh * ssh,struct passwd * pw,struct sshkey * key,int auth_attempt,struct sshauthopt ** authoptsp)753 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
754 int auth_attempt, struct sshauthopt **authoptsp)
755 {
756 u_int success = 0, i;
757 char *file, *conn_id;
758 struct sshauthopt *opts = NULL;
759 const char *rdomain, *remote_ip, *remote_host;
760
761 if (authoptsp != NULL)
762 *authoptsp = NULL;
763
764 if (auth_key_is_revoked(key))
765 return 0;
766 if (sshkey_is_cert(key) &&
767 auth_key_is_revoked(key->cert->signature_key))
768 return 0;
769
770 if ((rdomain = ssh_packet_rdomain_in(ssh)) == NULL)
771 rdomain = "";
772 remote_ip = ssh_remote_ipaddr(ssh);
773 remote_host = auth_get_canonical_hostname(ssh, options.use_dns);
774 xasprintf(&conn_id, "%s %d %s %d",
775 ssh_local_ipaddr(ssh), ssh_local_port(ssh),
776 remote_ip, ssh_remote_port(ssh));
777
778 for (i = 0; !success && i < options.num_authkeys_files; i++) {
779 if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
780 continue;
781 file = expand_authorized_keys(
782 options.authorized_keys_files[i], pw);
783 success = user_key_allowed2(pw, key, file,
784 remote_ip, remote_host, &opts);
785 free(file);
786 if (!success) {
787 sshauthopt_free(opts);
788 opts = NULL;
789 }
790 }
791 if (success)
792 goto out;
793
794 if ((success = user_cert_trusted_ca(pw, key, remote_ip, remote_host,
795 conn_id, rdomain, &opts)) != 0)
796 goto out;
797 sshauthopt_free(opts);
798 opts = NULL;
799
800 if ((success = user_key_command_allowed2(pw, key, remote_ip,
801 remote_host, conn_id, rdomain, &opts)) != 0)
802 goto out;
803 sshauthopt_free(opts);
804 opts = NULL;
805
806 out:
807 free(conn_id);
808 if (success && authoptsp != NULL) {
809 *authoptsp = opts;
810 opts = NULL;
811 }
812 sshauthopt_free(opts);
813 return success;
814 }
815
816 Authmethod method_pubkey = {
817 &methodcfg_pubkey,
818 userauth_pubkey,
819 };
820