1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 2003 Networks Associates Technology, Inc. 5 * Copyright (c) 2004-2011 Dag-Erling Smørgrav 6 * All rights reserved. 7 * 8 * This software was developed for the FreeBSD Project by ThinkSec AS and 9 * NAI Labs, the Security Research Division of Network Associates, Inc. 10 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 11 * DARPA CHATS research program. 12 * 13 * Redistribution and use in source and binary forms, with or without 14 * modification, are permitted provided that the following conditions 15 * are met: 16 * 1. Redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer. 18 * 2. Redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution. 21 * 3. The name of the author may not be used to endorse or promote 22 * products derived from this software without specific prior written 23 * permission. 24 * 25 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 28 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 35 * SUCH DAMAGE. 36 */ 37 38 #include <sys/cdefs.h> 39 __FBSDID("$FreeBSD$"); 40 41 #include <sys/param.h> 42 #include <sys/wait.h> 43 44 #include <errno.h> 45 #include <fcntl.h> 46 #include <paths.h> 47 #include <pwd.h> 48 #include <signal.h> 49 #include <stdio.h> 50 #include <string.h> 51 #include <unistd.h> 52 53 #define PAM_SM_AUTH 54 #define PAM_SM_SESSION 55 56 #include <security/pam_appl.h> 57 #include <security/pam_modules.h> 58 #include <security/openpam.h> 59 60 #include <openssl/evp.h> 61 62 #define __bounded__(x, y, z) 63 #include "authfd.h" 64 #include "authfile.h" 65 #include "sshkey.h" 66 67 #define ssh_add_identity(auth, key, comment) \ 68 ssh_add_identity_constrained(auth, key, comment, 0, 0, 0, NULL) 69 70 extern char **environ; 71 72 struct pam_ssh_key { 73 struct sshkey *key; 74 char *comment; 75 }; 76 77 static const char *pam_ssh_prompt = "SSH passphrase: "; 78 static const char *pam_ssh_have_keys = "pam_ssh_have_keys"; 79 80 static const char *pam_ssh_keyfiles[] = { 81 ".ssh/id_rsa", /* SSH2 RSA key */ 82 ".ssh/id_dsa", /* SSH2 DSA key */ 83 ".ssh/id_ecdsa", /* SSH2 ECDSA key */ 84 ".ssh/id_ed25519", /* SSH2 Ed25519 key */ 85 NULL 86 }; 87 88 static const char *pam_ssh_agent = "/usr/bin/ssh-agent"; 89 static char str_ssh_agent[] = "ssh-agent"; 90 static char str_dash_s[] = "-s"; 91 static char *const pam_ssh_agent_argv[] = { str_ssh_agent, str_dash_s, NULL }; 92 static char *const pam_ssh_agent_envp[] = { NULL }; 93 94 /* 95 * Attempts to load a private key from the specified file in the specified 96 * directory, using the specified passphrase. If successful, returns a 97 * struct pam_ssh_key containing the key and its comment. 98 */ 99 static struct pam_ssh_key * 100 pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase, 101 int nullok) 102 { 103 char fn[PATH_MAX]; 104 struct pam_ssh_key *psk; 105 struct sshkey *key; 106 char *comment; 107 int ret; 108 109 if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn)) 110 return (NULL); 111 /* 112 * If the key is unencrypted, OpenSSL ignores the passphrase, so 113 * it will seem like the user typed in the right one. This allows 114 * a user to circumvent nullok by providing a dummy passphrase. 115 * Verify that the key really *is* encrypted by trying to load it 116 * with an empty passphrase, and if the key is not encrypted, 117 * accept only an empty passphrase. 118 */ 119 ret = sshkey_load_private(fn, "", &key, &comment); 120 if (ret == 0 && !(*passphrase == '\0' && nullok)) { 121 sshkey_free(key); 122 return (NULL); 123 } 124 if (ret != 0) 125 ret = sshkey_load_private(fn, passphrase, &key, &comment); 126 if (ret != 0) { 127 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s", fn); 128 return (NULL); 129 } 130 131 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s", comment, fn); 132 if ((psk = malloc(sizeof(*psk))) == NULL) { 133 sshkey_free(key); 134 free(comment); 135 return (NULL); 136 } 137 psk->key = key; 138 psk->comment = comment; 139 return (psk); 140 } 141 142 /* 143 * Wipes a private key and frees the associated resources. 144 */ 145 static void 146 pam_ssh_free_key(pam_handle_t *pamh __unused, 147 void *data, int pam_err __unused) 148 { 149 struct pam_ssh_key *psk; 150 151 psk = data; 152 sshkey_free(psk->key); 153 free(psk->comment); 154 free(psk); 155 } 156 157 PAM_EXTERN int 158 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 159 int argc __unused, const char *argv[] __unused) 160 { 161 const char **kfn, *passphrase, *user; 162 const void *item; 163 struct passwd *pwd; 164 struct pam_ssh_key *psk; 165 int nkeys, nullok, pam_err, pass; 166 167 nullok = (openpam_get_option(pamh, "nullok") != NULL); 168 169 /* PEM is not loaded by default */ 170 OpenSSL_add_all_algorithms(); 171 172 /* get user name and home directory */ 173 pam_err = pam_get_user(pamh, &user, NULL); 174 if (pam_err != PAM_SUCCESS) 175 return (pam_err); 176 pwd = getpwnam(user); 177 if (pwd == NULL) 178 return (PAM_USER_UNKNOWN); 179 if (pwd->pw_dir == NULL) 180 return (PAM_AUTH_ERR); 181 182 nkeys = 0; 183 pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS && 184 item != NULL); 185 load_keys: 186 /* get passphrase */ 187 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 188 &passphrase, pam_ssh_prompt); 189 if (pam_err != PAM_SUCCESS) 190 return (pam_err); 191 192 /* switch to user credentials */ 193 pam_err = openpam_borrow_cred(pamh, pwd); 194 if (pam_err != PAM_SUCCESS) 195 return (pam_err); 196 197 /* try to load keys from all keyfiles we know of */ 198 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 199 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase, nullok); 200 if (psk != NULL) { 201 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 202 ++nkeys; 203 } 204 } 205 206 /* switch back to arbitrator credentials */ 207 openpam_restore_cred(pamh); 208 209 /* 210 * If we tried an old token and didn't get anything, and 211 * try_first_pass was specified, try again after prompting the 212 * user for a new passphrase. 213 */ 214 if (nkeys == 0 && pass == 1 && 215 openpam_get_option(pamh, "try_first_pass") != NULL) { 216 pam_set_item(pamh, PAM_AUTHTOK, NULL); 217 pass = 0; 218 goto load_keys; 219 } 220 221 /* no keys? */ 222 if (nkeys == 0) 223 return (PAM_AUTH_ERR); 224 225 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 226 return (PAM_SUCCESS); 227 } 228 229 PAM_EXTERN int 230 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 231 int argc __unused, const char *argv[] __unused) 232 { 233 234 return (PAM_SUCCESS); 235 } 236 237 /* 238 * Parses a line from ssh-agent's output. 239 */ 240 static void 241 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 242 { 243 char *line, *p, *key, *val; 244 size_t len; 245 246 while ((line = fgetln(f, &len)) != NULL) { 247 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 248 continue; 249 250 /* find equal sign at end of key */ 251 for (p = key = line; p < line + len; ++p) 252 if (*p == '=') 253 break; 254 if (p == line + len || *p != '=') 255 continue; 256 *p = '\0'; 257 258 /* find semicolon at end of value */ 259 for (val = ++p; p < line + len; ++p) 260 if (*p == ';') 261 break; 262 if (p == line + len || *p != ';') 263 continue; 264 *p = '\0'; 265 266 /* store key-value pair in environment */ 267 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 268 pam_setenv(pamh, key, val, 1); 269 } 270 } 271 272 /* 273 * Starts an ssh agent and stores the environment variables derived from 274 * its output. 275 */ 276 static int 277 pam_ssh_start_agent(pam_handle_t *pamh) 278 { 279 int agent_pipe[2]; 280 pid_t pid; 281 FILE *f; 282 283 /* get a pipe which we will use to read the agent's output */ 284 if (pipe(agent_pipe) == -1) 285 return (PAM_SYSTEM_ERR); 286 287 /* start the agent */ 288 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 289 pid = fork(); 290 if (pid == (pid_t)-1) { 291 /* failed */ 292 close(agent_pipe[0]); 293 close(agent_pipe[1]); 294 return (PAM_SYSTEM_ERR); 295 } 296 if (pid == 0) { 297 int fd; 298 299 /* child: drop privs, close fds and start agent */ 300 setgid(getegid()); 301 setuid(geteuid()); 302 close(STDIN_FILENO); 303 open(_PATH_DEVNULL, O_RDONLY); 304 dup2(agent_pipe[1], STDOUT_FILENO); 305 dup2(agent_pipe[1], STDERR_FILENO); 306 for (fd = 3; fd < getdtablesize(); ++fd) 307 close(fd); 308 execve(pam_ssh_agent, pam_ssh_agent_argv, pam_ssh_agent_envp); 309 _exit(127); 310 } 311 312 /* parent */ 313 close(agent_pipe[1]); 314 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 315 return (PAM_SYSTEM_ERR); 316 pam_ssh_process_agent_output(pamh, f); 317 fclose(f); 318 319 return (PAM_SUCCESS); 320 } 321 322 /* 323 * Adds previously stored keys to a running agent. 324 */ 325 static int 326 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 327 { 328 const struct pam_ssh_key *psk; 329 const char **kfn; 330 const void *item; 331 char **envlist, **env; 332 int fd, pam_err; 333 334 /* switch to PAM environment */ 335 envlist = environ; 336 if ((environ = pam_getenvlist(pamh)) == NULL) { 337 environ = envlist; 338 return (PAM_SYSTEM_ERR); 339 } 340 341 /* get a connection to the agent */ 342 if (ssh_get_authentication_socket(&fd) != 0) { 343 openpam_log(PAM_LOG_DEBUG, "failed to connect to the agent"); 344 pam_err = PAM_SYSTEM_ERR; 345 goto end; 346 } 347 348 /* look for keys to add to it */ 349 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 350 pam_err = pam_get_data(pamh, *kfn, &item); 351 if (pam_err == PAM_SUCCESS && item != NULL) { 352 psk = item; 353 if (ssh_add_identity(fd, psk->key, psk->comment) == 0) 354 openpam_log(PAM_LOG_DEBUG, 355 "added %s to ssh agent", psk->comment); 356 else 357 openpam_log(PAM_LOG_DEBUG, "failed " 358 "to add %s to ssh agent", psk->comment); 359 /* we won't need the key again, so wipe it */ 360 pam_set_data(pamh, *kfn, NULL, NULL); 361 } 362 } 363 pam_err = PAM_SUCCESS; 364 365 /* disconnect from agent */ 366 ssh_close_authentication_socket(fd); 367 368 end: 369 /* switch back to original environment */ 370 for (env = environ; *env != NULL; ++env) 371 free(*env); 372 free(environ); 373 environ = envlist; 374 375 return (pam_err); 376 } 377 378 PAM_EXTERN int 379 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 380 int argc __unused, const char *argv[] __unused) 381 { 382 struct passwd *pwd; 383 const char *user; 384 const void *data; 385 int pam_err; 386 387 /* no keys, no work */ 388 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 389 openpam_get_option(pamh, "want_agent") == NULL) 390 return (PAM_SUCCESS); 391 392 /* switch to user credentials */ 393 pam_err = pam_get_user(pamh, &user, NULL); 394 if (pam_err != PAM_SUCCESS) 395 return (pam_err); 396 pwd = getpwnam(user); 397 if (pwd == NULL) 398 return (PAM_USER_UNKNOWN); 399 pam_err = openpam_borrow_cred(pamh, pwd); 400 if (pam_err != PAM_SUCCESS) 401 return (pam_err); 402 403 /* start the agent */ 404 pam_err = pam_ssh_start_agent(pamh); 405 if (pam_err != PAM_SUCCESS) { 406 openpam_restore_cred(pamh); 407 return (pam_err); 408 } 409 410 /* we have an agent, see if we can add any keys to it */ 411 pam_err = pam_ssh_add_keys_to_agent(pamh); 412 if (pam_err != PAM_SUCCESS) { 413 /* XXX ignore failures */ 414 } 415 416 openpam_restore_cred(pamh); 417 return (PAM_SUCCESS); 418 } 419 420 PAM_EXTERN int 421 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 422 int argc __unused, const char *argv[] __unused) 423 { 424 const char *ssh_agent_pid; 425 char *end; 426 int status; 427 pid_t pid; 428 429 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 430 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 431 return (PAM_SUCCESS); 432 } 433 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 434 if (*ssh_agent_pid == '\0' || *end != '\0') { 435 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 436 return (PAM_SESSION_ERR); 437 } 438 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 439 if (kill(pid, SIGTERM) == -1 || 440 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 441 return (PAM_SYSTEM_ERR); 442 return (PAM_SUCCESS); 443 } 444 445 PAM_MODULE_ENTRY("pam_ssh"); 446