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 #define __bounded__(x, y, z) 61 #include "key.h" 62 #include "buffer.h" 63 #include "authfd.h" 64 #include "authfile.h" 65 66 #define ssh_add_identity(auth, key, comment) \ 67 ssh_add_identity_constrained(auth, key, comment, 0, 0) 68 69 extern char **environ; 70 71 struct pam_ssh_key { 72 Key *key; 73 char *comment; 74 }; 75 76 static const char *pam_ssh_prompt = "SSH passphrase: "; 77 static const char *pam_ssh_have_keys = "pam_ssh_have_keys"; 78 79 static const char *pam_ssh_keyfiles[] = { 80 ".ssh/id_rsa", /* SSH2 RSA key */ 81 ".ssh/id_dsa", /* SSH2 DSA key */ 82 ".ssh/id_ecdsa", /* SSH2 ECDSA key */ 83 ".ssh/id_ed25519", /* SSH2 Ed25519 key */ 84 NULL 85 }; 86 87 static const char *pam_ssh_agent = "/usr/bin/ssh-agent"; 88 static char str_ssh_agent[] = "ssh-agent"; 89 static char str_dash_s[] = "-s"; 90 static char *const pam_ssh_agent_argv[] = { str_ssh_agent, str_dash_s, NULL }; 91 static char *const pam_ssh_agent_envp[] = { NULL }; 92 93 /* 94 * Attempts to load a private key from the specified file in the specified 95 * directory, using the specified passphrase. If successful, returns a 96 * struct pam_ssh_key containing the key and its comment. 97 */ 98 static struct pam_ssh_key * 99 pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase, 100 int nullok) 101 { 102 struct pam_ssh_key *psk; 103 char fn[PATH_MAX]; 104 char *comment; 105 Key *key; 106 107 if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn)) 108 return (NULL); 109 comment = NULL; 110 /* 111 * If the key is unencrypted, OpenSSL ignores the passphrase, so 112 * it will seem like the user typed in the right one. This allows 113 * a user to circumvent nullok by providing a dummy passphrase. 114 * Verify that the key really *is* encrypted by trying to load it 115 * with an empty passphrase, and if the key is not encrypted, 116 * accept only an empty passphrase. 117 */ 118 key = key_load_private(fn, "", &comment); 119 if (key != NULL && !(*passphrase == '\0' && nullok)) { 120 key_free(key); 121 return (NULL); 122 } 123 if (key == NULL) 124 key = key_load_private(fn, passphrase, &comment); 125 if (key == NULL) { 126 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s", fn); 127 return (NULL); 128 } 129 130 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s", comment, fn); 131 if ((psk = malloc(sizeof(*psk))) == NULL) { 132 key_free(key); 133 free(comment); 134 return (NULL); 135 } 136 psk->key = key; 137 psk->comment = comment; 138 return (psk); 139 } 140 141 /* 142 * Wipes a private key and frees the associated resources. 143 */ 144 static void 145 pam_ssh_free_key(pam_handle_t *pamh __unused, 146 void *data, int pam_err __unused) 147 { 148 struct pam_ssh_key *psk; 149 150 psk = data; 151 key_free(psk->key); 152 free(psk->comment); 153 free(psk); 154 } 155 156 PAM_EXTERN int 157 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 158 int argc __unused, const char *argv[] __unused) 159 { 160 const char **kfn, *passphrase, *user; 161 const void *item; 162 struct passwd *pwd; 163 struct pam_ssh_key *psk; 164 int nkeys, nullok, pam_err, pass; 165 166 nullok = (openpam_get_option(pamh, "nullok") != NULL); 167 168 /* PEM is not loaded by default */ 169 OpenSSL_add_all_algorithms(); 170 171 /* get user name and home directory */ 172 pam_err = pam_get_user(pamh, &user, NULL); 173 if (pam_err != PAM_SUCCESS) 174 return (pam_err); 175 pwd = getpwnam(user); 176 if (pwd == NULL) 177 return (PAM_USER_UNKNOWN); 178 if (pwd->pw_dir == NULL) 179 return (PAM_AUTH_ERR); 180 181 nkeys = 0; 182 pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS && 183 item != NULL); 184 load_keys: 185 /* get passphrase */ 186 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 187 &passphrase, pam_ssh_prompt); 188 if (pam_err != PAM_SUCCESS) 189 return (pam_err); 190 191 /* switch to user credentials */ 192 pam_err = openpam_borrow_cred(pamh, pwd); 193 if (pam_err != PAM_SUCCESS) 194 return (pam_err); 195 196 /* try to load keys from all keyfiles we know of */ 197 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 198 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase, nullok); 199 if (psk != NULL) { 200 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 201 ++nkeys; 202 } 203 } 204 205 /* switch back to arbitrator credentials */ 206 openpam_restore_cred(pamh); 207 208 /* 209 * If we tried an old token and didn't get anything, and 210 * try_first_pass was specified, try again after prompting the 211 * user for a new passphrase. 212 */ 213 if (nkeys == 0 && pass == 1 && 214 openpam_get_option(pamh, "try_first_pass") != NULL) { 215 pam_set_item(pamh, PAM_AUTHTOK, NULL); 216 pass = 0; 217 goto load_keys; 218 } 219 220 /* no keys? */ 221 if (nkeys == 0) 222 return (PAM_AUTH_ERR); 223 224 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 225 return (PAM_SUCCESS); 226 } 227 228 PAM_EXTERN int 229 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 230 int argc __unused, const char *argv[] __unused) 231 { 232 233 return (PAM_SUCCESS); 234 } 235 236 /* 237 * Parses a line from ssh-agent's output. 238 */ 239 static void 240 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 241 { 242 char *line, *p, *key, *val; 243 size_t len; 244 245 while ((line = fgetln(f, &len)) != NULL) { 246 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 247 continue; 248 249 /* find equal sign at end of key */ 250 for (p = key = line; p < line + len; ++p) 251 if (*p == '=') 252 break; 253 if (p == line + len || *p != '=') 254 continue; 255 *p = '\0'; 256 257 /* find semicolon at end of value */ 258 for (val = ++p; p < line + len; ++p) 259 if (*p == ';') 260 break; 261 if (p == line + len || *p != ';') 262 continue; 263 *p = '\0'; 264 265 /* store key-value pair in environment */ 266 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 267 pam_setenv(pamh, key, val, 1); 268 } 269 } 270 271 /* 272 * Starts an ssh agent and stores the environment variables derived from 273 * its output. 274 */ 275 static int 276 pam_ssh_start_agent(pam_handle_t *pamh) 277 { 278 int agent_pipe[2]; 279 pid_t pid; 280 FILE *f; 281 282 /* get a pipe which we will use to read the agent's output */ 283 if (pipe(agent_pipe) == -1) 284 return (PAM_SYSTEM_ERR); 285 286 /* start the agent */ 287 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 288 pid = fork(); 289 if (pid == (pid_t)-1) { 290 /* failed */ 291 close(agent_pipe[0]); 292 close(agent_pipe[1]); 293 return (PAM_SYSTEM_ERR); 294 } 295 if (pid == 0) { 296 int fd; 297 298 /* child: drop privs, close fds and start agent */ 299 setgid(getegid()); 300 setuid(geteuid()); 301 close(STDIN_FILENO); 302 open(_PATH_DEVNULL, O_RDONLY); 303 dup2(agent_pipe[1], STDOUT_FILENO); 304 dup2(agent_pipe[1], STDERR_FILENO); 305 for (fd = 3; fd < getdtablesize(); ++fd) 306 close(fd); 307 execve(pam_ssh_agent, pam_ssh_agent_argv, pam_ssh_agent_envp); 308 _exit(127); 309 } 310 311 /* parent */ 312 close(agent_pipe[1]); 313 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 314 return (PAM_SYSTEM_ERR); 315 pam_ssh_process_agent_output(pamh, f); 316 fclose(f); 317 318 return (PAM_SUCCESS); 319 } 320 321 /* 322 * Adds previously stored keys to a running agent. 323 */ 324 static int 325 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 326 { 327 const struct pam_ssh_key *psk; 328 const char **kfn; 329 const void *item; 330 char **envlist, **env; 331 int fd, pam_err; 332 333 /* switch to PAM environment */ 334 envlist = environ; 335 if ((environ = pam_getenvlist(pamh)) == NULL) { 336 environ = envlist; 337 return (PAM_SYSTEM_ERR); 338 } 339 340 /* get a connection to the agent */ 341 if (ssh_get_authentication_socket(&fd) != 0) { 342 openpam_log(PAM_LOG_DEBUG, "failed to connect to the agent"); 343 pam_err = PAM_SYSTEM_ERR; 344 goto end; 345 } 346 347 /* look for keys to add to it */ 348 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 349 pam_err = pam_get_data(pamh, *kfn, &item); 350 if (pam_err == PAM_SUCCESS && item != NULL) { 351 psk = item; 352 if (ssh_add_identity(fd, psk->key, psk->comment) == 0) 353 openpam_log(PAM_LOG_DEBUG, 354 "added %s to ssh agent", psk->comment); 355 else 356 openpam_log(PAM_LOG_DEBUG, "failed " 357 "to add %s to ssh agent", psk->comment); 358 /* we won't need the key again, so wipe it */ 359 pam_set_data(pamh, *kfn, NULL, NULL); 360 } 361 } 362 pam_err = PAM_SUCCESS; 363 364 /* disconnect from agent */ 365 ssh_close_authentication_socket(fd); 366 367 end: 368 /* switch back to original environment */ 369 for (env = environ; *env != NULL; ++env) 370 free(*env); 371 free(environ); 372 environ = envlist; 373 374 return (pam_err); 375 } 376 377 PAM_EXTERN int 378 pam_sm_open_session(pam_handle_t *pamh, int flags __unused, 379 int argc __unused, const char *argv[] __unused) 380 { 381 struct passwd *pwd; 382 const char *user; 383 const void *data; 384 int pam_err; 385 386 /* no keys, no work */ 387 if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && 388 openpam_get_option(pamh, "want_agent") == NULL) 389 return (PAM_SUCCESS); 390 391 /* switch to user credentials */ 392 pam_err = pam_get_user(pamh, &user, NULL); 393 if (pam_err != PAM_SUCCESS) 394 return (pam_err); 395 pwd = getpwnam(user); 396 if (pwd == NULL) 397 return (PAM_USER_UNKNOWN); 398 pam_err = openpam_borrow_cred(pamh, pwd); 399 if (pam_err != PAM_SUCCESS) 400 return (pam_err); 401 402 /* start the agent */ 403 pam_err = pam_ssh_start_agent(pamh); 404 if (pam_err != PAM_SUCCESS) { 405 openpam_restore_cred(pamh); 406 return (pam_err); 407 } 408 409 /* we have an agent, see if we can add any keys to it */ 410 pam_err = pam_ssh_add_keys_to_agent(pamh); 411 if (pam_err != PAM_SUCCESS) { 412 /* XXX ignore failures */ 413 } 414 415 openpam_restore_cred(pamh); 416 return (PAM_SUCCESS); 417 } 418 419 PAM_EXTERN int 420 pam_sm_close_session(pam_handle_t *pamh, int flags __unused, 421 int argc __unused, const char *argv[] __unused) 422 { 423 const char *ssh_agent_pid; 424 char *end; 425 int status; 426 pid_t pid; 427 428 if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { 429 openpam_log(PAM_LOG_DEBUG, "no ssh agent"); 430 return (PAM_SUCCESS); 431 } 432 pid = (pid_t)strtol(ssh_agent_pid, &end, 10); 433 if (*ssh_agent_pid == '\0' || *end != '\0') { 434 openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); 435 return (PAM_SESSION_ERR); 436 } 437 openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); 438 if (kill(pid, SIGTERM) == -1 || 439 (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) 440 return (PAM_SYSTEM_ERR); 441 return (PAM_SUCCESS); 442 } 443 444 PAM_MODULE_ENTRY("pam_ssh"); 445