1 /* $OpenBSD: auth2-pubkey.c,v 1.117 2022/09/17 10:34:29 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
76 static char *
format_key(const struct sshkey * key)77 format_key(const struct sshkey *key)
78 {
79 char *ret, *fp = sshkey_fingerprint(key,
80 options.fingerprint_hash, SSH_FP_DEFAULT);
81
82 xasprintf(&ret, "%s %s", sshkey_type(key), fp);
83 free(fp);
84 return ret;
85 }
86
87 static int
userauth_pubkey(struct ssh * ssh,const char * method)88 userauth_pubkey(struct ssh *ssh, const char *method)
89 {
90 Authctxt *authctxt = ssh->authctxt;
91 struct passwd *pw = authctxt->pw;
92 struct sshbuf *b = NULL;
93 struct sshkey *key = NULL, *hostkey = NULL;
94 char *pkalg = NULL, *userstyle = NULL, *key_s = NULL, *ca_s = NULL;
95 u_char *pkblob = NULL, *sig = NULL, have_sig;
96 size_t blen, slen;
97 int hostbound, r, pktype;
98 int req_presence = 0, req_verify = 0, authenticated = 0;
99 struct sshauthopt *authopts = NULL;
100 struct sshkey_sig_details *sig_details = NULL;
101
102 hostbound = strcmp(method, "publickey-hostbound-v00@openssh.com") == 0;
103
104 if ((r = sshpkt_get_u8(ssh, &have_sig)) != 0 ||
105 (r = sshpkt_get_cstring(ssh, &pkalg, NULL)) != 0 ||
106 (r = sshpkt_get_string(ssh, &pkblob, &blen)) != 0)
107 fatal_fr(r, "parse %s packet", method);
108
109 /* hostbound auth includes the hostkey offered at initial KEX */
110 if (hostbound) {
111 if ((r = sshpkt_getb_froms(ssh, &b)) != 0 ||
112 (r = sshkey_fromb(b, &hostkey)) != 0)
113 fatal_fr(r, "parse %s hostkey", method);
114 if (ssh->kex->initial_hostkey == NULL)
115 fatal_f("internal error: initial hostkey not recorded");
116 if (!sshkey_equal(hostkey, ssh->kex->initial_hostkey))
117 fatal_f("%s packet contained wrong host key", method);
118 sshbuf_free(b);
119 b = NULL;
120 }
121
122 if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) {
123 char *keystring;
124 struct sshbuf *pkbuf;
125
126 if ((pkbuf = sshbuf_from(pkblob, blen)) == NULL)
127 fatal_f("sshbuf_from failed");
128 if ((keystring = sshbuf_dtob64_string(pkbuf, 0)) == NULL)
129 fatal_f("sshbuf_dtob64 failed");
130 debug2_f("%s user %s %s public key %s %s",
131 authctxt->valid ? "valid" : "invalid", authctxt->user,
132 have_sig ? "attempting" : "querying", pkalg, keystring);
133 sshbuf_free(pkbuf);
134 free(keystring);
135 }
136
137 pktype = sshkey_type_from_name(pkalg);
138 if (pktype == KEY_UNSPEC) {
139 /* this is perfectly legal */
140 verbose_f("unsupported public key algorithm: %s", pkalg);
141 goto done;
142 }
143 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
144 error_fr(r, "parse key");
145 goto done;
146 }
147 if (key == NULL) {
148 error_f("cannot decode key: %s", pkalg);
149 goto done;
150 }
151 if (key->type != pktype) {
152 error_f("type mismatch for decoded key "
153 "(received %d, expected %d)", key->type, pktype);
154 goto done;
155 }
156 if (sshkey_type_plain(key->type) == KEY_RSA &&
157 (ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
158 logit("Refusing RSA key because client uses unsafe "
159 "signature scheme");
160 goto done;
161 }
162 if (auth2_key_already_used(authctxt, key)) {
163 logit("refusing previously-used %s key", sshkey_type(key));
164 goto done;
165 }
166 if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) {
167 logit_f("signature algorithm %s not in "
168 "PubkeyAcceptedAlgorithms", pkalg);
169 goto done;
170 }
171 if ((r = sshkey_check_cert_sigtype(key,
172 options.ca_sign_algorithms)) != 0) {
173 logit_fr(r, "certificate signature algorithm %s",
174 (key->cert == NULL || key->cert->signature_type == NULL) ?
175 "(null)" : key->cert->signature_type);
176 goto done;
177 }
178 if ((r = sshkey_check_rsa_length(key,
179 options.required_rsa_size)) != 0) {
180 logit_r(r, "refusing %s key", sshkey_type(key));
181 goto done;
182 }
183 key_s = format_key(key);
184 if (sshkey_is_cert(key))
185 ca_s = format_key(key->cert->signature_key);
186
187 if (have_sig) {
188 debug3_f("%s have %s signature for %s%s%s",
189 method, pkalg, key_s,
190 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
191 if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 ||
192 (r = sshpkt_get_end(ssh)) != 0)
193 fatal_fr(r, "parse signature packet");
194 if ((b = sshbuf_new()) == NULL)
195 fatal_f("sshbuf_new failed");
196 if (ssh->compat & SSH_OLD_SESSIONID) {
197 if ((r = sshbuf_putb(b, ssh->kex->session_id)) != 0)
198 fatal_fr(r, "put old session id");
199 } else {
200 if ((r = sshbuf_put_stringb(b,
201 ssh->kex->session_id)) != 0)
202 fatal_fr(r, "put session id");
203 }
204 if (!authctxt->valid || authctxt->user == NULL) {
205 debug2_f("disabled because of invalid user");
206 goto done;
207 }
208 /* reconstruct packet */
209 xasprintf(&userstyle, "%s%s%s", authctxt->user,
210 authctxt->style ? ":" : "",
211 authctxt->style ? authctxt->style : "");
212 if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
213 (r = sshbuf_put_cstring(b, userstyle)) != 0 ||
214 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
215 (r = sshbuf_put_cstring(b, method)) != 0 ||
216 (r = sshbuf_put_u8(b, have_sig)) != 0 ||
217 (r = sshbuf_put_cstring(b, pkalg)) != 0 ||
218 (r = sshbuf_put_string(b, pkblob, blen)) != 0)
219 fatal_fr(r, "reconstruct %s packet", method);
220 if (hostbound &&
221 (r = sshkey_puts(ssh->kex->initial_hostkey, b)) != 0)
222 fatal_fr(r, "reconstruct %s packet", method);
223 #ifdef DEBUG_PK
224 sshbuf_dump(b, stderr);
225 #endif
226 /* test for correct signature */
227 authenticated = 0;
228 if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) &&
229 PRIVSEP(sshkey_verify(key, sig, slen,
230 sshbuf_ptr(b), sshbuf_len(b),
231 (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL,
232 ssh->compat, &sig_details)) == 0) {
233 authenticated = 1;
234 }
235 if (authenticated == 1 && sig_details != NULL) {
236 auth2_record_info(authctxt, "signature count = %u",
237 sig_details->sk_counter);
238 debug_f("sk_counter = %u, sk_flags = 0x%02x",
239 sig_details->sk_counter, sig_details->sk_flags);
240 req_presence = (options.pubkey_auth_options &
241 PUBKEYAUTH_TOUCH_REQUIRED) ||
242 !authopts->no_require_user_presence;
243 if (req_presence && (sig_details->sk_flags &
244 SSH_SK_USER_PRESENCE_REQD) == 0) {
245 error("public key %s signature for %s%s from "
246 "%.128s port %d rejected: user presence "
247 "(authenticator touch) requirement "
248 "not met ", key_s,
249 authctxt->valid ? "" : "invalid user ",
250 authctxt->user, ssh_remote_ipaddr(ssh),
251 ssh_remote_port(ssh));
252 authenticated = 0;
253 goto done;
254 }
255 req_verify = (options.pubkey_auth_options &
256 PUBKEYAUTH_VERIFY_REQUIRED) ||
257 authopts->require_verify;
258 if (req_verify && (sig_details->sk_flags &
259 SSH_SK_USER_VERIFICATION_REQD) == 0) {
260 error("public key %s signature for %s%s from "
261 "%.128s port %d rejected: user "
262 "verification requirement not met ", key_s,
263 authctxt->valid ? "" : "invalid user ",
264 authctxt->user, ssh_remote_ipaddr(ssh),
265 ssh_remote_port(ssh));
266 authenticated = 0;
267 goto done;
268 }
269 }
270 auth2_record_key(authctxt, authenticated, key);
271 } else {
272 debug_f("%s test pkalg %s pkblob %s%s%s", method, pkalg, key_s,
273 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
274
275 if ((r = sshpkt_get_end(ssh)) != 0)
276 fatal_fr(r, "parse packet");
277
278 if (!authctxt->valid || authctxt->user == NULL) {
279 debug2_f("disabled because of invalid user");
280 goto done;
281 }
282 /* XXX fake reply and always send PK_OK ? */
283 /*
284 * XXX this allows testing whether a user is allowed
285 * to login: if you happen to have a valid pubkey this
286 * message is sent. the message is NEVER sent at all
287 * if a user is not allowed to login. is this an
288 * issue? -markus
289 */
290 if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) {
291 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK))
292 != 0 ||
293 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 ||
294 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 ||
295 (r = sshpkt_send(ssh)) != 0 ||
296 (r = ssh_packet_write_wait(ssh)) != 0)
297 fatal_fr(r, "send packet");
298 authctxt->postponed = 1;
299 }
300 }
301 done:
302 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) {
303 debug_f("key options inconsistent with existing");
304 authenticated = 0;
305 }
306 debug2_f("authenticated %d pkalg %s", authenticated, pkalg);
307
308 sshbuf_free(b);
309 sshauthopt_free(authopts);
310 sshkey_free(key);
311 sshkey_free(hostkey);
312 free(userstyle);
313 free(pkalg);
314 free(pkblob);
315 free(key_s);
316 free(ca_s);
317 free(sig);
318 sshkey_sig_details_free(sig_details);
319 return authenticated;
320 }
321
322 static int
match_principals_file(struct passwd * pw,char * file,struct sshkey_cert * cert,struct sshauthopt ** authoptsp)323 match_principals_file(struct passwd *pw, char *file,
324 struct sshkey_cert *cert, struct sshauthopt **authoptsp)
325 {
326 FILE *f;
327 int success;
328
329 if (authoptsp != NULL)
330 *authoptsp = NULL;
331
332 temporarily_use_uid(pw);
333 debug("trying authorized principals file %s", file);
334 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
335 restore_uid();
336 return 0;
337 }
338 success = auth_process_principals(f, file, cert, authoptsp);
339 fclose(f);
340 restore_uid();
341 return success;
342 }
343
344 /*
345 * Checks whether principal is allowed in output of command.
346 * returns 1 if the principal is allowed or 0 otherwise.
347 */
348 static int
match_principals_command(struct passwd * user_pw,const struct sshkey * key,struct sshauthopt ** authoptsp)349 match_principals_command(struct passwd *user_pw,
350 const struct sshkey *key, struct sshauthopt **authoptsp)
351 {
352 struct passwd *runas_pw = NULL;
353 const struct sshkey_cert *cert = key->cert;
354 FILE *f = NULL;
355 int r, ok, found_principal = 0;
356 int i, ac = 0, uid_swapped = 0;
357 pid_t pid;
358 char *tmp, *username = NULL, *command = NULL, **av = NULL;
359 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL;
360 char serial_s[32], uidstr[32];
361 void (*osigchld)(int);
362
363 if (authoptsp != NULL)
364 *authoptsp = NULL;
365 if (options.authorized_principals_command == NULL)
366 return 0;
367 if (options.authorized_principals_command_user == NULL) {
368 error("No user for AuthorizedPrincipalsCommand specified, "
369 "skipping");
370 return 0;
371 }
372
373 /*
374 * NB. all returns later this function should go via "out" to
375 * ensure the original SIGCHLD handler is restored properly.
376 */
377 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
378
379 /* Prepare and verify the user for the command */
380 username = percent_expand(options.authorized_principals_command_user,
381 "u", user_pw->pw_name, (char *)NULL);
382 runas_pw = getpwnam(username);
383 if (runas_pw == NULL) {
384 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
385 username, strerror(errno));
386 goto out;
387 }
388
389 /* Turn the command into an argument vector */
390 if (argv_split(options.authorized_principals_command,
391 &ac, &av, 0) != 0) {
392 error("AuthorizedPrincipalsCommand \"%s\" contains "
393 "invalid quotes", options.authorized_principals_command);
394 goto out;
395 }
396 if (ac == 0) {
397 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
398 options.authorized_principals_command);
399 goto out;
400 }
401 if ((ca_fp = sshkey_fingerprint(cert->signature_key,
402 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
403 error_f("sshkey_fingerprint failed");
404 goto out;
405 }
406 if ((key_fp = sshkey_fingerprint(key,
407 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
408 error_f("sshkey_fingerprint failed");
409 goto out;
410 }
411 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) {
412 error_fr(r, "sshkey_to_base64 failed");
413 goto out;
414 }
415 if ((r = sshkey_to_base64(key, &keytext)) != 0) {
416 error_fr(r, "sshkey_to_base64 failed");
417 goto out;
418 }
419 snprintf(serial_s, sizeof(serial_s), "%llu",
420 (unsigned long long)cert->serial);
421 snprintf(uidstr, sizeof(uidstr), "%llu",
422 (unsigned long long)user_pw->pw_uid);
423 for (i = 1; i < ac; i++) {
424 tmp = percent_expand(av[i],
425 "U", uidstr,
426 "u", user_pw->pw_name,
427 "h", user_pw->pw_dir,
428 "t", sshkey_ssh_name(key),
429 "T", sshkey_ssh_name(cert->signature_key),
430 "f", key_fp,
431 "F", ca_fp,
432 "k", keytext,
433 "K", catext,
434 "i", cert->key_id,
435 "s", serial_s,
436 (char *)NULL);
437 if (tmp == NULL)
438 fatal_f("percent_expand failed");
439 free(av[i]);
440 av[i] = tmp;
441 }
442 /* Prepare a printable command for logs, etc. */
443 command = argv_assemble(ac, av);
444
445 if ((pid = subprocess("AuthorizedPrincipalsCommand", command,
446 ac, av, &f,
447 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
448 runas_pw, temporarily_use_uid, restore_uid)) == 0)
449 goto out;
450
451 uid_swapped = 1;
452 temporarily_use_uid(runas_pw);
453
454 ok = auth_process_principals(f, "(command)", cert, authoptsp);
455
456 fclose(f);
457 f = NULL;
458
459 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0)
460 goto out;
461
462 /* Read completed successfully */
463 found_principal = ok;
464 out:
465 if (f != NULL)
466 fclose(f);
467 ssh_signal(SIGCHLD, osigchld);
468 for (i = 0; i < ac; i++)
469 free(av[i]);
470 free(av);
471 if (uid_swapped)
472 restore_uid();
473 free(command);
474 free(username);
475 free(ca_fp);
476 free(key_fp);
477 free(catext);
478 free(keytext);
479 return found_principal;
480 }
481
482 /* Authenticate a certificate key against TrustedUserCAKeys */
483 static int
user_cert_trusted_ca(struct passwd * pw,struct sshkey * key,const char * remote_ip,const char * remote_host,struct sshauthopt ** authoptsp)484 user_cert_trusted_ca(struct passwd *pw, struct sshkey *key,
485 const char *remote_ip, const char *remote_host,
486 struct sshauthopt **authoptsp)
487 {
488 char *ca_fp, *principals_file = NULL;
489 const char *reason;
490 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL;
491 struct sshauthopt *final_opts = NULL;
492 int r, ret = 0, found_principal = 0, use_authorized_principals;
493
494 if (authoptsp != NULL)
495 *authoptsp = NULL;
496
497 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL)
498 return 0;
499
500 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
501 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
502 return 0;
503
504 if ((r = sshkey_in_file(key->cert->signature_key,
505 options.trusted_user_ca_keys, 1, 0)) != 0) {
506 debug2_fr(r, "CA %s %s is not listed in %s",
507 sshkey_type(key->cert->signature_key), ca_fp,
508 options.trusted_user_ca_keys);
509 goto out;
510 }
511 /*
512 * If AuthorizedPrincipals is in use, then compare the certificate
513 * principals against the names in that file rather than matching
514 * against the username.
515 */
516 if ((principals_file = authorized_principals_file(pw)) != NULL) {
517 if (match_principals_file(pw, principals_file,
518 key->cert, &principals_opts))
519 found_principal = 1;
520 }
521 /* Try querying command if specified */
522 if (!found_principal && match_principals_command(pw, key,
523 &principals_opts))
524 found_principal = 1;
525 /* If principals file or command is specified, then require a match */
526 use_authorized_principals = principals_file != NULL ||
527 options.authorized_principals_command != NULL;
528 if (!found_principal && use_authorized_principals) {
529 reason = "Certificate does not contain an authorized principal";
530 goto fail_reason;
531 }
532 if (use_authorized_principals && principals_opts == NULL)
533 fatal_f("internal error: missing principals_opts");
534 if (sshkey_cert_check_authority_now(key, 0, 1, 0,
535 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
536 goto fail_reason;
537
538 /* Check authority from options in key and from principals file/cmd */
539 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) {
540 reason = "Invalid certificate options";
541 goto fail_reason;
542 }
543 if (auth_authorise_keyopts(pw, cert_opts, 0,
544 remote_ip, remote_host, "cert") != 0) {
545 reason = "Refused by certificate options";
546 goto fail_reason;
547 }
548 if (principals_opts == NULL) {
549 final_opts = cert_opts;
550 cert_opts = NULL;
551 } else {
552 if (auth_authorise_keyopts(pw, principals_opts, 0,
553 remote_ip, remote_host, "principals") != 0) {
554 reason = "Refused by certificate principals options";
555 goto fail_reason;
556 }
557 if ((final_opts = sshauthopt_merge(principals_opts,
558 cert_opts, &reason)) == NULL) {
559 fail_reason:
560 error("%s", reason);
561 auth_debug_add("%s", reason);
562 goto out;
563 }
564 }
565
566 /* Success */
567 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by "
568 "%s CA %s via %s", key->cert->key_id,
569 (unsigned long long)key->cert->serial,
570 sshkey_type(key->cert->signature_key), ca_fp,
571 options.trusted_user_ca_keys);
572 if (authoptsp != NULL) {
573 *authoptsp = final_opts;
574 final_opts = NULL;
575 }
576 ret = 1;
577 out:
578 sshauthopt_free(principals_opts);
579 sshauthopt_free(cert_opts);
580 sshauthopt_free(final_opts);
581 free(principals_file);
582 free(ca_fp);
583 return ret;
584 }
585
586 /*
587 * Checks whether key is allowed in file.
588 * returns 1 if the key is allowed or 0 otherwise.
589 */
590 static int
user_key_allowed2(struct passwd * pw,struct sshkey * key,char * file,const char * remote_ip,const char * remote_host,struct sshauthopt ** authoptsp)591 user_key_allowed2(struct passwd *pw, struct sshkey *key,
592 char *file, const char *remote_ip, const char *remote_host,
593 struct sshauthopt **authoptsp)
594 {
595 FILE *f;
596 int found_key = 0;
597
598 if (authoptsp != NULL)
599 *authoptsp = NULL;
600
601 /* Temporarily use the user's uid. */
602 temporarily_use_uid(pw);
603
604 debug("trying public key file %s", file);
605 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
606 found_key = auth_check_authkeys_file(pw, f, file,
607 key, remote_ip, remote_host, authoptsp);
608 fclose(f);
609 }
610
611 restore_uid();
612 return found_key;
613 }
614
615 /*
616 * Checks whether key is allowed in output of command.
617 * returns 1 if the key is allowed or 0 otherwise.
618 */
619 static int
user_key_command_allowed2(struct passwd * user_pw,struct sshkey * key,const char * remote_ip,const char * remote_host,struct sshauthopt ** authoptsp)620 user_key_command_allowed2(struct passwd *user_pw, struct sshkey *key,
621 const char *remote_ip, const char *remote_host,
622 struct sshauthopt **authoptsp)
623 {
624 struct passwd *runas_pw = NULL;
625 FILE *f = NULL;
626 int r, ok, found_key = 0;
627 int i, uid_swapped = 0, ac = 0;
628 pid_t pid;
629 char *username = NULL, *key_fp = NULL, *keytext = NULL;
630 char uidstr[32], *tmp, *command = NULL, **av = NULL;
631 void (*osigchld)(int);
632
633 if (authoptsp != NULL)
634 *authoptsp = NULL;
635 if (options.authorized_keys_command == NULL)
636 return 0;
637 if (options.authorized_keys_command_user == NULL) {
638 error("No user for AuthorizedKeysCommand specified, skipping");
639 return 0;
640 }
641
642 /*
643 * NB. all returns later this function should go via "out" to
644 * ensure the original SIGCHLD handler is restored properly.
645 */
646 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
647
648 /* Prepare and verify the user for the command */
649 username = percent_expand(options.authorized_keys_command_user,
650 "u", user_pw->pw_name, (char *)NULL);
651 runas_pw = getpwnam(username);
652 if (runas_pw == NULL) {
653 error("AuthorizedKeysCommandUser \"%s\" not found: %s",
654 username, strerror(errno));
655 goto out;
656 }
657
658 /* Prepare AuthorizedKeysCommand */
659 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash,
660 SSH_FP_DEFAULT)) == NULL) {
661 error_f("sshkey_fingerprint failed");
662 goto out;
663 }
664 if ((r = sshkey_to_base64(key, &keytext)) != 0) {
665 error_fr(r, "sshkey_to_base64 failed");
666 goto out;
667 }
668
669 /* Turn the command into an argument vector */
670 if (argv_split(options.authorized_keys_command, &ac, &av, 0) != 0) {
671 error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
672 options.authorized_keys_command);
673 goto out;
674 }
675 if (ac == 0) {
676 error("AuthorizedKeysCommand \"%s\" yielded no arguments",
677 options.authorized_keys_command);
678 goto out;
679 }
680 snprintf(uidstr, sizeof(uidstr), "%llu",
681 (unsigned long long)user_pw->pw_uid);
682 for (i = 1; i < ac; i++) {
683 tmp = percent_expand(av[i],
684 "U", uidstr,
685 "u", user_pw->pw_name,
686 "h", user_pw->pw_dir,
687 "t", sshkey_ssh_name(key),
688 "f", key_fp,
689 "k", keytext,
690 (char *)NULL);
691 if (tmp == NULL)
692 fatal_f("percent_expand failed");
693 free(av[i]);
694 av[i] = tmp;
695 }
696 /* Prepare a printable command for logs, etc. */
697 command = argv_assemble(ac, av);
698
699 /*
700 * If AuthorizedKeysCommand was run without arguments
701 * then fall back to the old behaviour of passing the
702 * target username as a single argument.
703 */
704 if (ac == 1) {
705 av = xreallocarray(av, ac + 2, sizeof(*av));
706 av[1] = xstrdup(user_pw->pw_name);
707 av[2] = NULL;
708 /* Fix up command too, since it is used in log messages */
709 free(command);
710 xasprintf(&command, "%s %s", av[0], av[1]);
711 }
712
713 if ((pid = subprocess("AuthorizedKeysCommand", command,
714 ac, av, &f,
715 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
716 runas_pw, temporarily_use_uid, restore_uid)) == 0)
717 goto out;
718
719 uid_swapped = 1;
720 temporarily_use_uid(runas_pw);
721
722 ok = auth_check_authkeys_file(user_pw, f,
723 options.authorized_keys_command, key, remote_ip,
724 remote_host, authoptsp);
725
726 fclose(f);
727 f = NULL;
728
729 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0)
730 goto out;
731
732 /* Read completed successfully */
733 found_key = ok;
734 out:
735 if (f != NULL)
736 fclose(f);
737 ssh_signal(SIGCHLD, osigchld);
738 for (i = 0; i < ac; i++)
739 free(av[i]);
740 free(av);
741 if (uid_swapped)
742 restore_uid();
743 free(command);
744 free(username);
745 free(key_fp);
746 free(keytext);
747 return found_key;
748 }
749
750 /*
751 * Check whether key authenticates and authorises the user.
752 */
753 int
user_key_allowed(struct ssh * ssh,struct passwd * pw,struct sshkey * key,int auth_attempt,struct sshauthopt ** authoptsp)754 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
755 int auth_attempt, struct sshauthopt **authoptsp)
756 {
757 u_int success = 0, i;
758 char *file;
759 struct sshauthopt *opts = NULL;
760 const char *remote_ip = ssh_remote_ipaddr(ssh);
761 const char *remote_host = auth_get_canonical_hostname(ssh,
762 options.use_dns);
763
764 if (authoptsp != NULL)
765 *authoptsp = NULL;
766
767 if (auth_key_is_revoked(key))
768 return 0;
769 if (sshkey_is_cert(key) &&
770 auth_key_is_revoked(key->cert->signature_key))
771 return 0;
772
773 for (i = 0; !success && i < options.num_authkeys_files; i++) {
774 if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
775 continue;
776 file = expand_authorized_keys(
777 options.authorized_keys_files[i], pw);
778 success = user_key_allowed2(pw, key, file,
779 remote_ip, remote_host, &opts);
780 free(file);
781 if (!success) {
782 sshauthopt_free(opts);
783 opts = NULL;
784 }
785 }
786 if (success)
787 goto out;
788
789 if ((success = user_cert_trusted_ca(pw, key, remote_ip, remote_host,
790 &opts)) != 0)
791 goto out;
792 sshauthopt_free(opts);
793 opts = NULL;
794
795 if ((success = user_key_command_allowed2(pw, key, remote_ip,
796 remote_host, &opts)) != 0)
797 goto out;
798 sshauthopt_free(opts);
799 opts = NULL;
800
801 out:
802 if (success && authoptsp != NULL) {
803 *authoptsp = opts;
804 opts = NULL;
805 }
806 sshauthopt_free(opts);
807 return success;
808 }
809
810 Authmethod method_pubkey = {
811 "publickey",
812 "publickey-hostbound-v00@openssh.com",
813 userauth_pubkey,
814 &options.pubkey_authentication
815 };
816