1 /* $NetBSD: pam_ssh.c,v 1.30 2022/06/15 08:31:34 hannken Exp $ */ 2 3 /*- 4 * Copyright (c) 2003 Networks Associates Technology, Inc. 5 * All rights reserved. 6 * 7 * This software was developed for the FreeBSD Project by ThinkSec AS and 8 * NAI Labs, the Security Research Division of Network Associates, Inc. 9 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 10 * DARPA CHATS research program. 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. The name of the author may not be used to endorse or promote 21 * products derived from this software without specific prior written 22 * permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34 * SUCH DAMAGE. 35 */ 36 37 #include <sys/cdefs.h> 38 #ifdef __FreeBSD__ 39 __FBSDID("$FreeBSD: src/lib/libpam/modules/pam_ssh/pam_ssh.c,v 1.40 2004/02/10 10:13:21 des Exp $"); 40 #else 41 __RCSID("$NetBSD: pam_ssh.c,v 1.30 2022/06/15 08:31:34 hannken Exp $"); 42 #endif 43 44 #include <sys/param.h> 45 #include <sys/wait.h> 46 47 #include <errno.h> 48 #include <fcntl.h> 49 #include <paths.h> 50 #include <pwd.h> 51 #include <signal.h> 52 #include <stdio.h> 53 #include <string.h> 54 #include <unistd.h> 55 56 #define PAM_SM_AUTH 57 #define PAM_SM_SESSION 58 59 #include <security/pam_appl.h> 60 #include <security/pam_modules.h> 61 #include <security/openpam.h> 62 63 #include <openssl/evp.h> 64 65 #include "sshkey.h" 66 #include "sshbuf.h" 67 #include "authfd.h" 68 #include "authfile.h" 69 70 #define ssh_add_identity(auth, key, comment) \ 71 ssh_add_identity_constrained(auth, key, comment, 0, 0, 0, NULL, NULL, 00) 72 73 extern char **environ; 74 75 struct pam_ssh_key { 76 struct sshkey *key; 77 char *comment; 78 }; 79 80 static const char *pam_ssh_prompt = "SSH passphrase: "; 81 static const char *pam_ssh_have_keys = "pam_ssh_have_keys"; 82 83 static const char *pam_ssh_keyfiles[] = { 84 ".ssh/identity", /* SSH1 RSA key */ 85 ".ssh/id_rsa", /* SSH2 RSA key */ 86 ".ssh/id_dsa", /* SSH2 DSA key */ 87 ".ssh/id_ecdsa", /* SSH2 ECDSA key */ 88 NULL 89 }; 90 91 static const char *pam_ssh_agent = "/usr/bin/ssh-agent"; 92 static const char *const pam_ssh_agent_argv[] = { "ssh_agent", "-s", NULL }; 93 static const char *const pam_ssh_agent_envp[] = { NULL }; 94 95 /* 96 * Attempts to load a private key from the specified file in the specified 97 * directory, using the specified passphrase. If successful, returns a 98 * struct pam_ssh_key containing the key and its comment. 99 */ 100 static struct pam_ssh_key * 101 pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase, 102 int nullok) 103 { 104 struct pam_ssh_key *psk; 105 char fn[PATH_MAX]; 106 int r; 107 char *comment; 108 struct sshkey *key; 109 110 if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn)) 111 return (NULL); 112 comment = NULL; 113 /* 114 * If the key is unencrypted, OpenSSL ignores the passphrase, so 115 * it will seem like the user typed in the right one. This allows 116 * a user to circumvent nullok by providing a dummy passphrase. 117 * Verify that the key really *is* encrypted by trying to load it 118 * with an empty passphrase, and if the key is not encrypted, 119 * accept only an empty passphrase. 120 */ 121 r = sshkey_load_private(fn, "", &key, &comment); 122 if (r == 0 && !(*passphrase == '\0' && nullok)) { 123 openpam_log(PAM_LOG_DEBUG, "rejected unencrypted key from %s", fn); 124 sshkey_free(key); 125 free(comment); 126 return (NULL); 127 } 128 if (r) 129 r = sshkey_load_private(fn, passphrase, &key, &comment); 130 if (r) { 131 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s", fn); 132 if (comment != NULL) 133 free(comment); 134 return (NULL); 135 } 136 137 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s", comment, fn); 138 if ((psk = malloc(sizeof(*psk))) == NULL) { 139 sshkey_free(key); 140 free(comment); 141 return (NULL); 142 } 143 psk->key = key; 144 psk->comment = comment; 145 return (psk); 146 } 147 148 /* 149 * Wipes a private key and frees the associated resources. 150 */ 151 static void 152 pam_ssh_free_key(pam_handle_t *pamh __unused, 153 void *data, int pam_err __unused) 154 { 155 struct pam_ssh_key *psk; 156 157 psk = data; 158 sshkey_free(psk->key); 159 free(psk->comment); 160 free(psk); 161 } 162 163 PAM_EXTERN int 164 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 165 int argc __unused, const char *argv[] __unused) 166 { 167 const char **kfn, *passphrase, *user; 168 const void *item; 169 struct passwd *pwd, pwres; 170 struct pam_ssh_key *psk; 171 int nkeys, nullok, pam_err, pass; 172 char pwbuf[1024]; 173 174 nullok = (openpam_get_option(pamh, "nullok") != NULL); 175 176 /* PEM is not loaded by default */ 177 OpenSSL_add_all_algorithms(); 178 179 /* get user name and home directory */ 180 pam_err = pam_get_user(pamh, &user, NULL); 181 if (pam_err != PAM_SUCCESS) 182 return (pam_err); 183 if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 || 184 pwd == NULL) 185 return (PAM_USER_UNKNOWN); 186 if (pwd->pw_dir == NULL) 187 return (PAM_AUTH_ERR); 188 189 nkeys = 0; 190 pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS && 191 item != NULL); 192 load_keys: 193 /* get passphrase */ 194 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 195 &passphrase, pam_ssh_prompt); 196 if (pam_err != PAM_SUCCESS) 197 return (pam_err); 198 199 /* switch to user credentials */ 200 pam_err = openpam_borrow_cred(pamh, pwd); 201 if (pam_err != PAM_SUCCESS) 202 return (pam_err); 203 204 /* try to load keys from all keyfiles we know of */ 205 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 206 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase, nullok); 207 if (psk != NULL) { 208 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 209 ++nkeys; 210 } 211 } 212 213 /* switch back to arbitrator credentials */ 214 openpam_restore_cred(pamh); 215 216 /* 217 * If we tried an old token and didn't get anything, and 218 * try_first_pass was specified, try again after prompting the 219 * user for a new passphrase. 220 */ 221 if (nkeys == 0 && pass == 1 && 222 openpam_get_option(pamh, "try_first_pass") != NULL) { 223 pam_set_item(pamh, PAM_AUTHTOK, NULL); 224 pass = 0; 225 goto load_keys; 226 } 227 228 /* no keys? */ 229 if (nkeys == 0) 230 return (PAM_AUTH_ERR); 231 232 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 233 return (PAM_SUCCESS); 234 } 235 236 PAM_EXTERN int 237 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 238 int argc __unused, const char *argv[] __unused) 239 { 240 241 return (PAM_SUCCESS); 242 } 243 244 /* 245 * Parses a line from ssh-agent's output. 246 */ 247 static void 248 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 249 { 250 char *line, *p, *key, *val; 251 size_t len; 252 253 while ((line = fgetln(f, &len)) != NULL) { 254 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 255 continue; 256 257 /* find equal sign at end of key */ 258 for (p = key = line; p < line + len; ++p) 259 if (*p == '=') 260 break; 261 if (p == line + len || *p != '=') 262 continue; 263 *p = '\0'; 264 265 /* find semicolon at end of value */ 266 for (val = ++p; p < line + len; ++p) 267 if (*p == ';') 268 break; 269 if (p == line + len || *p != ';') 270 continue; 271 *p = '\0'; 272 273 /* store key-value pair in environment */ 274 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 275 pam_setenv(pamh, key, val, 1); 276 } 277 } 278 279 /* 280 * Starts an ssh agent and stores the environment variables derived from 281 * its output. 282 */ 283 static int 284 pam_ssh_start_agent(pam_handle_t *pamh, struct passwd *pwd) 285 { 286 int agent_pipe[2]; 287 pid_t pid; 288 FILE *f; 289 290 /* get a pipe which we will use to read the agent's output */ 291 if (pipe(agent_pipe) == -1) 292 return (PAM_SYSTEM_ERR); 293 294 /* start the agent */ 295 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 296 pid = fork(); 297 if (pid == (pid_t)-1) { 298 /* failed */ 299 close(agent_pipe[0]); 300 close(agent_pipe[1]); 301 return (PAM_SYSTEM_ERR); 302 } 303 if (pid == 0) { 304 #ifndef F_CLOSEM 305 int fd; 306 #endif 307 /* child: drop privs, close fds and start agent */ 308 if (setgid(pwd->pw_gid) == -1) { 309 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setgid %d (%s)", 310 __func__, (int)pwd->pw_gid, strerror(errno)); 311 goto done; 312 } 313 if (initgroups(pwd->pw_name, pwd->pw_gid) == -1) { 314 openpam_log(PAM_LOG_DEBUG, 315 "%s: Cannot initgroups for %s (%s)", 316 __func__, pwd->pw_name, strerror(errno)); 317 goto done; 318 } 319 if (setuid(pwd->pw_uid) == -1) { 320 openpam_log(PAM_LOG_DEBUG, "%s: Cannot setuid %d (%s)", 321 __func__, (int)pwd->pw_uid, strerror(errno)); 322 goto done; 323 } 324 (void)close(STDIN_FILENO); 325 (void)open(_PATH_DEVNULL, O_RDONLY); 326 (void)dup2(agent_pipe[1], STDOUT_FILENO); 327 (void)dup2(agent_pipe[1], STDERR_FILENO); 328 #ifdef F_CLOSEM 329 (void)fcntl(3, F_CLOSEM, 0); 330 #else 331 for (fd = 3; fd < getdtablesize(); ++fd) 332 (void)close(fd); 333 #endif 334 (void)execve(pam_ssh_agent, 335 (char **)__UNCONST(pam_ssh_agent_argv), 336 (char **)__UNCONST(pam_ssh_agent_envp)); 337 done: 338 _exit(127); 339 } 340 341 /* parent */ 342 close(agent_pipe[1]); 343 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 344 return (PAM_SYSTEM_ERR); 345 pam_ssh_process_agent_output(pamh, f); 346 fclose(f); 347 348 return (PAM_SUCCESS); 349 } 350 351 /* 352 * Adds previously stored keys to a running agent. 353 */ 354 static int 355 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 356 { 357 const struct pam_ssh_key *psk; 358 const char **kfn; 359 char **envlist, **env; 360 int pam_err; 361 int agent_fd; 362 363 /* switch to PAM environment */ 364 envlist = environ; 365 if ((environ = pam_getenvlist(pamh)) == NULL) { 366 openpam_log(PAM_LOG_DEBUG, "%s: cannot get envlist", 367 __func__); 368 environ = envlist; 369 return (PAM_SYSTEM_ERR); 370 } 371 372 /* get a connection to the agent */ 373 if (ssh_get_authentication_socket(&agent_fd) != 0) { 374 openpam_log(PAM_LOG_DEBUG, 375 "%s: cannot get authentication connection", 376 __func__); 377 pam_err = PAM_SYSTEM_ERR; 378 agent_fd = -1; 379 goto end; 380 } 381 382 /* look for keys to add to it */ 383 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 384 const void *vp; 385 pam_err = pam_get_data(pamh, *kfn, &vp); 386 psk = vp; 387 if (pam_err == PAM_SUCCESS && psk != NULL) { 388 if (ssh_add_identity(agent_fd, psk->key, psk->comment)) 389 openpam_log(PAM_LOG_DEBUG, 390 "added %s to ssh agent", psk->comment); 391 else 392 openpam_log(PAM_LOG_DEBUG, "failed " 393 "to add %s to ssh agent", psk->comment); 394 /* we won't need the key again, so wipe it */ 395 pam_set_data(pamh, *kfn, NULL, NULL); 396 } 397 } 398 pam_err = PAM_SUCCESS; 399 end: 400 /* disconnect from agent */ 401 if (agent_fd != -1) 402 ssh_close_authentication_socket(agent_fd); 403 404 /* switch back to original environment */ 405 for (env = environ; *env != NULL; ++env) 406 free(*env); 407 free(environ); 408 environ = envlist; 409 410 return (pam_err); 411 } 412 413 PAM_EXTERN int 414 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 415 int argc __unused, const char *argv[] __unused) 416 { 417 struct passwd *pwd, pwres; 418 const char *user; 419 const void *data; 420 int pam_err = PAM_SUCCESS; 421 char pwbuf[1024]; 422 423 /* no keys, no work */ 424 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 425 openpam_get_option(pamh, "want_agent") == NULL) 426 return (PAM_SUCCESS); 427 428 /* switch to user credentials */ 429 pam_err = pam_get_user(pamh, &user, NULL); 430 if (pam_err != PAM_SUCCESS) 431 return (pam_err); 432 if (getpwnam_r(user, &pwres, pwbuf, sizeof(pwbuf), &pwd) != 0 || 433 pwd == NULL) 434 return (PAM_USER_UNKNOWN); 435 436 /* start the agent */ 437 pam_err = pam_ssh_start_agent(pamh, pwd); 438 if (pam_err != PAM_SUCCESS) 439 return pam_err; 440 441 pam_err = openpam_borrow_cred(pamh, pwd); 442 if (pam_err != PAM_SUCCESS) 443 return pam_err; 444 445 /* we have an agent, see if we can add any keys to it */ 446 pam_err = pam_ssh_add_keys_to_agent(pamh); 447 if (pam_err != PAM_SUCCESS) { 448 /* XXX ignore failures */ 449 openpam_log(PAM_LOG_DEBUG, "failed adding keys to ssh agent"); 450 pam_err = PAM_SUCCESS; 451 } 452 453 openpam_restore_cred(pamh); 454 return pam_err; 455 } 456 457 PAM_EXTERN int 458 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 459 int argc __unused, const char *argv[] __unused) 460 { 461 const char *ssh_agent_pid; 462 char *end; 463 int status; 464 pid_t pid; 465 466 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 467 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 468 return (PAM_SUCCESS); 469 } 470 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 471 if (*ssh_agent_pid == '\0' || *end != '\0') { 472 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 473 return (PAM_SESSION_ERR); 474 } 475 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 476 if (kill(pid, SIGTERM) == -1 || 477 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 478 return (PAM_SYSTEM_ERR); 479 return (PAM_SUCCESS); 480 } 481 482 PAM_MODULE_ENTRY("pam_ssh"); 483
Indexes created Sat Sep 20 22:09:52 GMT 2025