1 /* $OpenBSD: auth2-pubkey.c,v 1.118 2023/02/17 04:22:50 dtucker Exp $ */
3 * Copyright (c) 2000 Markus Friedl. All rights reserved.
4 * Copyright (c) 2010 Damien Miller. All rights reserved.
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
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.
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.
29 #include <sys/types.h>
58 #include "pathnames.h"
60 #include "auth-options.h"
65 #include "monitor_wrap.h"
69 #include "channels.h" /* XXX for session.h */
70 #include "session.h" /* XXX for child_set_env(); refactor? */
74 extern ServerOptions options;
77 format_key(const struct sshkey *key)
79 char *ret, *fp = sshkey_fingerprint(key,
80 options.fingerprint_hash, SSH_FP_DEFAULT);
82 xasprintf(&ret, "%s %s", sshkey_type(key), fp);
88 userauth_pubkey(struct ssh *ssh, const char *method)
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;
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;
102 hostbound = strcmp(method, "publickey-hostbound-v00@openssh.com") == 0;
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);
109 /* hostbound auth includes the hostkey offered at initial KEX */
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);
122 if (log_level_get() >= SYSLOG_LEVEL_DEBUG2) {
124 struct sshbuf *pkbuf;
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);
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);
143 if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) {
144 error_fr(r, "parse key");
148 error_f("cannot decode key: %s", pkalg);
151 if (key->type != pktype) {
152 error_f("type mismatch for decoded key "
153 "(received %d, expected %d)", key->type, pktype);
156 if (auth2_key_already_used(authctxt, key)) {
157 logit("refusing previously-used %s key", sshkey_type(key));
160 if (match_pattern_list(pkalg, options.pubkey_accepted_algos, 0) != 1) {
161 logit_f("signature algorithm %s not in "
162 "PubkeyAcceptedAlgorithms", pkalg);
165 if ((r = sshkey_check_cert_sigtype(key,
166 options.ca_sign_algorithms)) != 0) {
167 logit_fr(r, "certificate signature algorithm %s",
168 (key->cert == NULL || key->cert->signature_type == NULL) ?
169 "(null)" : key->cert->signature_type);
172 if ((r = sshkey_check_rsa_length(key,
173 options.required_rsa_size)) != 0) {
174 logit_r(r, "refusing %s key", sshkey_type(key));
177 key_s = format_key(key);
178 if (sshkey_is_cert(key))
179 ca_s = format_key(key->cert->signature_key);
182 debug3_f("%s have %s signature for %s%s%s",
183 method, pkalg, key_s,
184 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
185 if ((r = sshpkt_get_string(ssh, &sig, &slen)) != 0 ||
186 (r = sshpkt_get_end(ssh)) != 0)
187 fatal_fr(r, "parse signature packet");
188 if ((b = sshbuf_new()) == NULL)
189 fatal_f("sshbuf_new failed");
190 if (ssh->compat & SSH_OLD_SESSIONID) {
191 if ((r = sshbuf_putb(b, ssh->kex->session_id)) != 0)
192 fatal_fr(r, "put old session id");
194 if ((r = sshbuf_put_stringb(b,
195 ssh->kex->session_id)) != 0)
196 fatal_fr(r, "put session id");
198 if (!authctxt->valid || authctxt->user == NULL) {
199 debug2_f("disabled because of invalid user");
202 /* reconstruct packet */
203 xasprintf(&userstyle, "%s%s%s", authctxt->user,
204 authctxt->style ? ":" : "",
205 authctxt->style ? authctxt->style : "");
206 if ((r = sshbuf_put_u8(b, SSH2_MSG_USERAUTH_REQUEST)) != 0 ||
207 (r = sshbuf_put_cstring(b, userstyle)) != 0 ||
208 (r = sshbuf_put_cstring(b, authctxt->service)) != 0 ||
209 (r = sshbuf_put_cstring(b, method)) != 0 ||
210 (r = sshbuf_put_u8(b, have_sig)) != 0 ||
211 (r = sshbuf_put_cstring(b, pkalg)) != 0 ||
212 (r = sshbuf_put_string(b, pkblob, blen)) != 0)
213 fatal_fr(r, "reconstruct %s packet", method);
215 (r = sshkey_puts(ssh->kex->initial_hostkey, b)) != 0)
216 fatal_fr(r, "reconstruct %s packet", method);
218 sshbuf_dump(b, stderr);
220 /* test for correct signature */
222 if (PRIVSEP(user_key_allowed(ssh, pw, key, 1, &authopts)) &&
223 PRIVSEP(sshkey_verify(key, sig, slen,
224 sshbuf_ptr(b), sshbuf_len(b),
225 (ssh->compat & SSH_BUG_SIGTYPE) == 0 ? pkalg : NULL,
226 ssh->compat, &sig_details)) == 0) {
229 if (authenticated == 1 && sig_details != NULL) {
230 auth2_record_info(authctxt, "signature count = %u",
231 sig_details->sk_counter);
232 debug_f("sk_counter = %u, sk_flags = 0x%02x",
233 sig_details->sk_counter, sig_details->sk_flags);
234 req_presence = (options.pubkey_auth_options &
235 PUBKEYAUTH_TOUCH_REQUIRED) ||
236 !authopts->no_require_user_presence;
237 if (req_presence && (sig_details->sk_flags &
238 SSH_SK_USER_PRESENCE_REQD) == 0) {
239 error("public key %s signature for %s%s from "
240 "%.128s port %d rejected: user presence "
241 "(authenticator touch) requirement "
243 authctxt->valid ? "" : "invalid user ",
244 authctxt->user, ssh_remote_ipaddr(ssh),
245 ssh_remote_port(ssh));
249 req_verify = (options.pubkey_auth_options &
250 PUBKEYAUTH_VERIFY_REQUIRED) ||
251 authopts->require_verify;
252 if (req_verify && (sig_details->sk_flags &
253 SSH_SK_USER_VERIFICATION_REQD) == 0) {
254 error("public key %s signature for %s%s from "
255 "%.128s port %d rejected: user "
256 "verification requirement not met ", key_s,
257 authctxt->valid ? "" : "invalid user ",
258 authctxt->user, ssh_remote_ipaddr(ssh),
259 ssh_remote_port(ssh));
264 auth2_record_key(authctxt, authenticated, key);
266 debug_f("%s test pkalg %s pkblob %s%s%s", method, pkalg, key_s,
267 ca_s == NULL ? "" : " CA ", ca_s == NULL ? "" : ca_s);
269 if ((r = sshpkt_get_end(ssh)) != 0)
270 fatal_fr(r, "parse packet");
272 if (!authctxt->valid || authctxt->user == NULL) {
273 debug2_f("disabled because of invalid user");
276 /* XXX fake reply and always send PK_OK ? */
278 * XXX this allows testing whether a user is allowed
279 * to login: if you happen to have a valid pubkey this
280 * message is sent. the message is NEVER sent at all
281 * if a user is not allowed to login. is this an
284 if (PRIVSEP(user_key_allowed(ssh, pw, key, 0, NULL))) {
285 if ((r = sshpkt_start(ssh, SSH2_MSG_USERAUTH_PK_OK))
287 (r = sshpkt_put_cstring(ssh, pkalg)) != 0 ||
288 (r = sshpkt_put_string(ssh, pkblob, blen)) != 0 ||
289 (r = sshpkt_send(ssh)) != 0 ||
290 (r = ssh_packet_write_wait(ssh)) != 0)
291 fatal_fr(r, "send packet");
292 authctxt->postponed = 1;
296 if (authenticated == 1 && auth_activate_options(ssh, authopts) != 0) {
297 debug_f("key options inconsistent with existing");
300 debug2_f("authenticated %d pkalg %s", authenticated, pkalg);
303 sshauthopt_free(authopts);
305 sshkey_free(hostkey);
312 sshkey_sig_details_free(sig_details);
313 return authenticated;
317 match_principals_file(struct passwd *pw, char *file,
318 struct sshkey_cert *cert, struct sshauthopt **authoptsp)
323 if (authoptsp != NULL)
326 temporarily_use_uid(pw);
327 debug("trying authorized principals file %s", file);
328 if ((f = auth_openprincipals(file, pw, options.strict_modes)) == NULL) {
332 success = auth_process_principals(f, file, cert, authoptsp);
339 * Checks whether principal is allowed in output of command.
340 * returns 1 if the principal is allowed or 0 otherwise.
343 match_principals_command(struct passwd *user_pw,
344 const struct sshkey *key, struct sshauthopt **authoptsp)
346 struct passwd *runas_pw = NULL;
347 const struct sshkey_cert *cert = key->cert;
349 int r, ok, found_principal = 0;
350 int i, ac = 0, uid_swapped = 0;
352 char *tmp, *username = NULL, *command = NULL, **av = NULL;
353 char *ca_fp = NULL, *key_fp = NULL, *catext = NULL, *keytext = NULL;
354 char serial_s[32], uidstr[32];
355 void (*osigchld)(int);
357 if (authoptsp != NULL)
359 if (options.authorized_principals_command == NULL)
361 if (options.authorized_principals_command_user == NULL) {
362 error("No user for AuthorizedPrincipalsCommand specified, "
368 * NB. all returns later this function should go via "out" to
369 * ensure the original SIGCHLD handler is restored properly.
371 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
373 /* Prepare and verify the user for the command */
374 username = percent_expand(options.authorized_principals_command_user,
375 "u", user_pw->pw_name, (char *)NULL);
376 runas_pw = getpwnam(username);
377 if (runas_pw == NULL) {
378 error("AuthorizedPrincipalsCommandUser \"%s\" not found: %s",
379 username, strerror(errno));
383 /* Turn the command into an argument vector */
384 if (argv_split(options.authorized_principals_command,
386 error("AuthorizedPrincipalsCommand \"%s\" contains "
387 "invalid quotes", options.authorized_principals_command);
391 error("AuthorizedPrincipalsCommand \"%s\" yielded no arguments",
392 options.authorized_principals_command);
395 if ((ca_fp = sshkey_fingerprint(cert->signature_key,
396 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
397 error_f("sshkey_fingerprint failed");
400 if ((key_fp = sshkey_fingerprint(key,
401 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL) {
402 error_f("sshkey_fingerprint failed");
405 if ((r = sshkey_to_base64(cert->signature_key, &catext)) != 0) {
406 error_fr(r, "sshkey_to_base64 failed");
409 if ((r = sshkey_to_base64(key, &keytext)) != 0) {
410 error_fr(r, "sshkey_to_base64 failed");
413 snprintf(serial_s, sizeof(serial_s), "%llu",
414 (unsigned long long)cert->serial);
415 snprintf(uidstr, sizeof(uidstr), "%llu",
416 (unsigned long long)user_pw->pw_uid);
417 for (i = 1; i < ac; i++) {
418 tmp = percent_expand(av[i],
420 "u", user_pw->pw_name,
421 "h", user_pw->pw_dir,
422 "t", sshkey_ssh_name(key),
423 "T", sshkey_ssh_name(cert->signature_key),
432 fatal_f("percent_expand failed");
436 /* Prepare a printable command for logs, etc. */
437 command = argv_assemble(ac, av);
439 if ((pid = subprocess("AuthorizedPrincipalsCommand", command,
441 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
442 runas_pw, temporarily_use_uid, restore_uid)) == 0)
446 temporarily_use_uid(runas_pw);
448 ok = auth_process_principals(f, "(command)", cert, authoptsp);
453 if (exited_cleanly(pid, "AuthorizedPrincipalsCommand", command, 0) != 0)
456 /* Read completed successfully */
457 found_principal = ok;
461 ssh_signal(SIGCHLD, osigchld);
462 for (i = 0; i < ac; i++)
473 return found_principal;
476 /* Authenticate a certificate key against TrustedUserCAKeys */
478 user_cert_trusted_ca(struct passwd *pw, struct sshkey *key,
479 const char *remote_ip, const char *remote_host,
480 struct sshauthopt **authoptsp)
482 char *ca_fp, *principals_file = NULL;
484 struct sshauthopt *principals_opts = NULL, *cert_opts = NULL;
485 struct sshauthopt *final_opts = NULL;
486 int r, ret = 0, found_principal = 0, use_authorized_principals;
488 if (authoptsp != NULL)
491 if (!sshkey_is_cert(key) || options.trusted_user_ca_keys == NULL)
494 if ((ca_fp = sshkey_fingerprint(key->cert->signature_key,
495 options.fingerprint_hash, SSH_FP_DEFAULT)) == NULL)
498 if ((r = sshkey_in_file(key->cert->signature_key,
499 options.trusted_user_ca_keys, 1, 0)) != 0) {
500 debug2_fr(r, "CA %s %s is not listed in %s",
501 sshkey_type(key->cert->signature_key), ca_fp,
502 options.trusted_user_ca_keys);
506 * If AuthorizedPrincipals is in use, then compare the certificate
507 * principals against the names in that file rather than matching
508 * against the username.
510 if ((principals_file = authorized_principals_file(pw)) != NULL) {
511 if (match_principals_file(pw, principals_file,
512 key->cert, &principals_opts))
515 /* Try querying command if specified */
516 if (!found_principal && match_principals_command(pw, key,
519 /* If principals file or command is specified, then require a match */
520 use_authorized_principals = principals_file != NULL ||
521 options.authorized_principals_command != NULL;
522 if (!found_principal && use_authorized_principals) {
523 reason = "Certificate does not contain an authorized principal";
526 if (use_authorized_principals && principals_opts == NULL)
527 fatal_f("internal error: missing principals_opts");
528 if (sshkey_cert_check_authority_now(key, 0, 1, 0,
529 use_authorized_principals ? NULL : pw->pw_name, &reason) != 0)
532 /* Check authority from options in key and from principals file/cmd */
533 if ((cert_opts = sshauthopt_from_cert(key)) == NULL) {
534 reason = "Invalid certificate options";
537 if (auth_authorise_keyopts(pw, cert_opts, 0,
538 remote_ip, remote_host, "cert") != 0) {
539 reason = "Refused by certificate options";
542 if (principals_opts == NULL) {
543 final_opts = cert_opts;
546 if (auth_authorise_keyopts(pw, principals_opts, 0,
547 remote_ip, remote_host, "principals") != 0) {
548 reason = "Refused by certificate principals options";
551 if ((final_opts = sshauthopt_merge(principals_opts,
552 cert_opts, &reason)) == NULL) {
555 auth_debug_add("%s", reason);
561 verbose("Accepted certificate ID \"%s\" (serial %llu) signed by "
562 "%s CA %s via %s", key->cert->key_id,
563 (unsigned long long)key->cert->serial,
564 sshkey_type(key->cert->signature_key), ca_fp,
565 options.trusted_user_ca_keys);
566 if (authoptsp != NULL) {
567 *authoptsp = final_opts;
572 sshauthopt_free(principals_opts);
573 sshauthopt_free(cert_opts);
574 sshauthopt_free(final_opts);
575 free(principals_file);
581 * Checks whether key is allowed in file.
582 * returns 1 if the key is allowed or 0 otherwise.
585 user_key_allowed2(struct passwd *pw, struct sshkey *key,
586 char *file, const char *remote_ip, const char *remote_host,
587 struct sshauthopt **authoptsp)
592 if (authoptsp != NULL)
595 /* Temporarily use the user's uid. */
596 temporarily_use_uid(pw);
598 debug("trying public key file %s", file);
599 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
600 found_key = auth_check_authkeys_file(pw, f, file,
601 key, remote_ip, remote_host, authoptsp);
610 * Checks whether key is allowed in output of command.
611 * returns 1 if the key is allowed or 0 otherwise.
614 user_key_command_allowed2(struct passwd *user_pw, struct sshkey *key,
615 const char *remote_ip, const char *remote_host,
616 struct sshauthopt **authoptsp)
618 struct passwd *runas_pw = NULL;
620 int r, ok, found_key = 0;
621 int i, uid_swapped = 0, ac = 0;
623 char *username = NULL, *key_fp = NULL, *keytext = NULL;
624 char uidstr[32], *tmp, *command = NULL, **av = NULL;
625 void (*osigchld)(int);
627 if (authoptsp != NULL)
629 if (options.authorized_keys_command == NULL)
631 if (options.authorized_keys_command_user == NULL) {
632 error("No user for AuthorizedKeysCommand specified, skipping");
637 * NB. all returns later this function should go via "out" to
638 * ensure the original SIGCHLD handler is restored properly.
640 osigchld = ssh_signal(SIGCHLD, SIG_DFL);
642 /* Prepare and verify the user for the command */
643 username = percent_expand(options.authorized_keys_command_user,
644 "u", user_pw->pw_name, (char *)NULL);
645 runas_pw = getpwnam(username);
646 if (runas_pw == NULL) {
647 error("AuthorizedKeysCommandUser \"%s\" not found: %s",
648 username, strerror(errno));
652 /* Prepare AuthorizedKeysCommand */
653 if ((key_fp = sshkey_fingerprint(key, options.fingerprint_hash,
654 SSH_FP_DEFAULT)) == NULL) {
655 error_f("sshkey_fingerprint failed");
658 if ((r = sshkey_to_base64(key, &keytext)) != 0) {
659 error_fr(r, "sshkey_to_base64 failed");
663 /* Turn the command into an argument vector */
664 if (argv_split(options.authorized_keys_command, &ac, &av, 0) != 0) {
665 error("AuthorizedKeysCommand \"%s\" contains invalid quotes",
666 options.authorized_keys_command);
670 error("AuthorizedKeysCommand \"%s\" yielded no arguments",
671 options.authorized_keys_command);
674 snprintf(uidstr, sizeof(uidstr), "%llu",
675 (unsigned long long)user_pw->pw_uid);
676 for (i = 1; i < ac; i++) {
677 tmp = percent_expand(av[i],
679 "u", user_pw->pw_name,
680 "h", user_pw->pw_dir,
681 "t", sshkey_ssh_name(key),
686 fatal_f("percent_expand failed");
690 /* Prepare a printable command for logs, etc. */
691 command = argv_assemble(ac, av);
694 * If AuthorizedKeysCommand was run without arguments
695 * then fall back to the old behaviour of passing the
696 * target username as a single argument.
699 av = xreallocarray(av, ac + 2, sizeof(*av));
700 av[1] = xstrdup(user_pw->pw_name);
702 /* Fix up command too, since it is used in log messages */
704 xasprintf(&command, "%s %s", av[0], av[1]);
707 if ((pid = subprocess("AuthorizedKeysCommand", command,
709 SSH_SUBPROCESS_STDOUT_CAPTURE|SSH_SUBPROCESS_STDERR_DISCARD,
710 runas_pw, temporarily_use_uid, restore_uid)) == 0)
714 temporarily_use_uid(runas_pw);
716 ok = auth_check_authkeys_file(user_pw, f,
717 options.authorized_keys_command, key, remote_ip,
718 remote_host, authoptsp);
723 if (exited_cleanly(pid, "AuthorizedKeysCommand", command, 0) != 0)
726 /* Read completed successfully */
731 ssh_signal(SIGCHLD, osigchld);
732 for (i = 0; i < ac; i++)
745 * Check whether key authenticates and authorises the user.
748 user_key_allowed(struct ssh *ssh, struct passwd *pw, struct sshkey *key,
749 int auth_attempt, struct sshauthopt **authoptsp)
751 u_int success = 0, i;
753 struct sshauthopt *opts = NULL;
754 const char *remote_ip = ssh_remote_ipaddr(ssh);
755 const char *remote_host = auth_get_canonical_hostname(ssh,
758 if (authoptsp != NULL)
761 if (auth_key_is_revoked(key))
763 if (sshkey_is_cert(key) &&
764 auth_key_is_revoked(key->cert->signature_key))
767 for (i = 0; !success && i < options.num_authkeys_files; i++) {
768 if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
770 file = expand_authorized_keys(
771 options.authorized_keys_files[i], pw);
772 success = user_key_allowed2(pw, key, file,
773 remote_ip, remote_host, &opts);
776 sshauthopt_free(opts);
783 if ((success = user_cert_trusted_ca(pw, key, remote_ip, remote_host,
786 sshauthopt_free(opts);
789 if ((success = user_key_command_allowed2(pw, key, remote_ip,
790 remote_host, &opts)) != 0)
792 sshauthopt_free(opts);
796 if (success && authoptsp != NULL) {
800 sshauthopt_free(opts);
804 Authmethod method_pubkey = {
806 "publickey-hostbound-v00@openssh.com",
808 &options.pubkey_authentication