1 /*- 2 * Copyright (c) 2003 Networks Associates Technology, Inc. 3 * Copyright (c) 2004-2011 Dag-Erling Smørgrav 4 * All rights reserved. 5 * 6 * This software was developed for the FreeBSD Project by ThinkSec AS and 7 * NAI Labs, the Security Research Division of Network Associates, Inc. 8 * under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the 9 * DARPA CHATS research program. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. The name of the author may not be used to endorse or promote 20 * products derived from this software without specific prior written 21 * permission. 22 * 23 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33 * SUCH DAMAGE. 34 */ 35 36 #include <sys/cdefs.h> 37 __FBSDID("$FreeBSD$"); 38 39 #include <sys/param.h> 40 #include <sys/wait.h> 41 42 #include <errno.h> 43 #include <fcntl.h> 44 #include <paths.h> 45 #include <pwd.h> 46 #include <signal.h> 47 #include <stdio.h> 48 #include <string.h> 49 #include <unistd.h> 50 51 #define PAM_SM_AUTH 52 #define PAM_SM_SESSION 53 54 #include <security/pam_appl.h> 55 #include <security/pam_modules.h> 56 #include <security/openpam.h> 57 58 #include <openssl/evp.h> 59 60 #include "key.h" 61 #include "buffer.h" 62 #include "authfd.h" 63 #include "authfile.h" 64 65 #define ssh_add_identity(auth, key, comment) \ 66 ssh_add_identity_constrained(auth, key, comment, 0, 0) 67 68 extern char **environ; 69 70 struct pam_ssh_key { 71 Key *key; 72 char *comment; 73 }; 74 75 static const char *pam_ssh_prompt = "SSH passphrase: "; 76 static const char *pam_ssh_have_keys = "pam_ssh_have_keys"; 77 78 static const char *pam_ssh_keyfiles[] = { 79 ".ssh/identity", /* SSH1 RSA key */ 80 ".ssh/id_rsa", /* SSH2 RSA key */ 81 ".ssh/id_dsa", /* SSH2 DSA key */ 82 ".ssh/id_ecdsa", /* SSH2 ECDSA key */ 83 NULL 84 }; 85 86 static const char *pam_ssh_agent = "/usr/bin/ssh-agent"; 87 static char *const pam_ssh_agent_argv[] = { "ssh_agent", "-s", NULL }; 88 static char *const pam_ssh_agent_envp[] = { NULL }; 89 90 /* 91 * Attempts to load a private key from the specified file in the specified 92 * directory, using the specified passphrase. If successful, returns a 93 * struct pam_ssh_key containing the key and its comment. 94 */ 95 static struct pam_ssh_key * 96 pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase, 97 int nullok) 98 { 99 struct pam_ssh_key *psk; 100 char fn[PATH_MAX]; 101 char *comment; 102 Key *key; 103 104 if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn)) 105 return (NULL); 106 comment = NULL; 107 /* 108 * If the key is unencrypted, OpenSSL ignores the passphrase, so 109 * it will seem like the user typed in the right one. This allows 110 * a user to circumvent nullok by providing a dummy passphrase. 111 * Verify that the key really *is* encrypted by trying to load it 112 * with an empty passphrase, and if the key is not encrypted, 113 * accept only an empty passphrase. 114 */ 115 key = key_load_private(fn, "", &comment); 116 if (key != NULL && !(*passphrase == '\0' && nullok)) { 117 key_free(key); 118 return (NULL); 119 } 120 if (key == NULL) 121 key = key_load_private(fn, passphrase, &comment); 122 if (key == NULL) { 123 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s", fn); 124 return (NULL); 125 } 126 127 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s", comment, fn); 128 if ((psk = malloc(sizeof(*psk))) == NULL) { 129 key_free(key); 130 free(comment); 131 return (NULL); 132 } 133 psk->key = key; 134 psk->comment = comment; 135 return (psk); 136 } 137 138 /* 139 * Wipes a private key and frees the associated resources. 140 */ 141 static void 142 pam_ssh_free_key(pam_handle_t *pamh __unused, 143 void *data, int pam_err __unused) 144 { 145 struct pam_ssh_key *psk; 146 147 psk = data; 148 key_free(psk->key); 149 free(psk->comment); 150 free(psk); 151 } 152 153 PAM_EXTERN int 154 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 155 int argc __unused, const char *argv[] __unused) 156 { 157 const char **kfn, *passphrase, *user; 158 const void *item; 159 struct passwd *pwd; 160 struct pam_ssh_key *psk; 161 int nkeys, nullok, pam_err, pass; 162 163 nullok = (openpam_get_option(pamh, "nullok") != NULL); 164 165 /* PEM is not loaded by default */ 166 OpenSSL_add_all_algorithms(); 167 168 /* get user name and home directory */ 169 pam_err = pam_get_user(pamh, &user, NULL); 170 if (pam_err != PAM_SUCCESS) 171 return (pam_err); 172 pwd = getpwnam(user); 173 if (pwd == NULL) 174 return (PAM_USER_UNKNOWN); 175 if (pwd->pw_dir == NULL) 176 return (PAM_AUTH_ERR); 177 178 nkeys = 0; 179 pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS && 180 item != NULL); 181 load_keys: 182 /* get passphrase */ 183 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 184 &passphrase, pam_ssh_prompt); 185 if (pam_err != PAM_SUCCESS) 186 return (pam_err); 187 188 /* switch to user credentials */ 189 pam_err = openpam_borrow_cred(pamh, pwd); 190 if (pam_err != PAM_SUCCESS) 191 return (pam_err); 192 193 /* try to load keys from all keyfiles we know of */ 194 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 195 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase, nullok); 196 if (psk != NULL) { 197 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 198 ++nkeys; 199 } 200 } 201 202 /* switch back to arbitrator credentials */ 203 openpam_restore_cred(pamh); 204 205 /* 206 * If we tried an old token and didn't get anything, and 207 * try_first_pass was specified, try again after prompting the 208 * user for a new passphrase. 209 */ 210 if (nkeys == 0 && pass == 1 && 211 openpam_get_option(pamh, "try_first_pass") != NULL) { 212 pam_set_item(pamh, PAM_AUTHTOK, NULL); 213 pass = 0; 214 goto load_keys; 215 } 216 217 /* no keys? */ 218 if (nkeys == 0) 219 return (PAM_AUTH_ERR); 220 221 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 222 return (PAM_SUCCESS); 223 } 224 225 PAM_EXTERN int 226 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 227 int argc __unused, const char *argv[] __unused) 228 { 229 230 return (PAM_SUCCESS); 231 } 232 233 /* 234 * Parses a line from ssh-agent's output. 235 */ 236 static void 237 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 238 { 239 char *line, *p, *key, *val; 240 size_t len; 241 242 while ((line = fgetln(f, &len)) != NULL) { 243 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 244 continue; 245 246 /* find equal sign at end of key */ 247 for (p = key = line; p < line + len; ++p) 248 if (*p == '=') 249 break; 250 if (p == line + len || *p != '=') 251 continue; 252 *p = '\0'; 253 254 /* find semicolon at end of value */ 255 for (val = ++p; p < line + len; ++p) 256 if (*p == ';') 257 break; 258 if (p == line + len || *p != ';') 259 continue; 260 *p = '\0'; 261 262 /* store key-value pair in environment */ 263 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 264 pam_setenv(pamh, key, val, 1); 265 } 266 } 267 268 /* 269 * Starts an ssh agent and stores the environment variables derived from 270 * its output. 271 */ 272 static int 273 pam_ssh_start_agent(pam_handle_t *pamh) 274 { 275 int agent_pipe[2]; 276 pid_t pid; 277 FILE *f; 278 279 /* get a pipe which we will use to read the agent's output */ 280 if (pipe(agent_pipe) == -1) 281 return (PAM_SYSTEM_ERR); 282 283 /* start the agent */ 284 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 285 pid = fork(); 286 if (pid == (pid_t)-1) { 287 /* failed */ 288 close(agent_pipe[0]); 289 close(agent_pipe[1]); 290 return (PAM_SYSTEM_ERR); 291 } 292 if (pid == 0) { 293 int fd; 294 295 /* child: drop privs, close fds and start agent */ 296 setgid(getegid()); 297 setuid(geteuid()); 298 close(STDIN_FILENO); 299 open(_PATH_DEVNULL, O_RDONLY); 300 dup2(agent_pipe[1], STDOUT_FILENO); 301 dup2(agent_pipe[1], STDERR_FILENO); 302 for (fd = 3; fd < getdtablesize(); ++fd) 303 close(fd); 304 execve(pam_ssh_agent, pam_ssh_agent_argv, pam_ssh_agent_envp); 305 _exit(127); 306 } 307 308 /* parent */ 309 close(agent_pipe[1]); 310 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 311 return (PAM_SYSTEM_ERR); 312 pam_ssh_process_agent_output(pamh, f); 313 fclose(f); 314 315 return (PAM_SUCCESS); 316 } 317 318 /* 319 * Adds previously stored keys to a running agent. 320 */ 321 static int 322 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 323 { 324 const struct pam_ssh_key *psk; 325 const char **kfn; 326 const void *item; 327 char **envlist, **env; 328 int fd, pam_err; 329 330 /* switch to PAM environment */ 331 envlist = environ; 332 if ((environ = pam_getenvlist(pamh)) == NULL) { 333 environ = envlist; 334 return (PAM_SYSTEM_ERR); 335 } 336 337 /* get a connection to the agent */ 338 if (ssh_get_authentication_socket(&fd) != 0) { 339 openpam_log(PAM_LOG_DEBUG, "failed to connect to the agent"); 340 pam_err = PAM_SYSTEM_ERR; 341 goto end; 342 } 343 344 /* look for keys to add to it */ 345 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 346 pam_err = pam_get_data(pamh, *kfn, &item); 347 if (pam_err == PAM_SUCCESS && item != NULL) { 348 psk = item; 349 if (ssh_add_identity(fd, psk->key, psk->comment) == 0) 350 openpam_log(PAM_LOG_DEBUG, 351 "added %s to ssh agent", psk->comment); 352 else 353 openpam_log(PAM_LOG_DEBUG, "failed " 354 "to add %s to ssh agent", psk->comment); 355 /* we won't need the key again, so wipe it */ 356 pam_set_data(pamh, *kfn, NULL, NULL); 357 } 358 } 359 pam_err = PAM_SUCCESS; 360 361 /* disconnect from agent */ 362 ssh_close_authentication_socket(fd); 363 364 end: 365 /* switch back to original environment */ 366 for (env = environ; *env != NULL; ++env) 367 free(*env); 368 free(environ); 369 environ = envlist; 370 371 return (pam_err); 372 } 373 374 PAM_EXTERN int 375 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 376 int argc __unused, const char *argv[] __unused) 377 { 378 struct passwd *pwd; 379 const char *user; 380 const void *data; 381 int pam_err; 382 383 /* no keys, no work */ 384 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 385 openpam_get_option(pamh, "want_agent") == NULL) 386 return (PAM_SUCCESS); 387 388 /* switch to user credentials */ 389 pam_err = pam_get_user(pamh, &user, NULL); 390 if (pam_err != PAM_SUCCESS) 391 return (pam_err); 392 pwd = getpwnam(user); 393 if (pwd == NULL) 394 return (PAM_USER_UNKNOWN); 395 pam_err = openpam_borrow_cred(pamh, pwd); 396 if (pam_err != PAM_SUCCESS) 397 return (pam_err); 398 399 /* start the agent */ 400 pam_err = pam_ssh_start_agent(pamh); 401 if (pam_err != PAM_SUCCESS) { 402 openpam_restore_cred(pamh); 403 return (pam_err); 404 } 405 406 /* we have an agent, see if we can add any keys to it */ 407 pam_err = pam_ssh_add_keys_to_agent(pamh); 408 if (pam_err != PAM_SUCCESS) { 409 /* XXX ignore failures */ 410 } 411 412 openpam_restore_cred(pamh); 413 return (PAM_SUCCESS); 414 } 415 416 PAM_EXTERN int 417 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 418 int argc __unused, const char *argv[] __unused) 419 { 420 const char *ssh_agent_pid; 421 char *end; 422 int status; 423 pid_t pid; 424 425 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 426 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 427 return (PAM_SUCCESS); 428 } 429 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 430 if (*ssh_agent_pid == '\0' || *end != '\0') { 431 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 432 return (PAM_SESSION_ERR); 433 } 434 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 435 if (kill(pid, SIGTERM) == -1 || 436 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 437 return (PAM_SYSTEM_ERR); 438 return (PAM_SUCCESS); 439 } 440 441 PAM_MODULE_ENTRY("pam_ssh"); 442