| 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 | * $FreeBSD: src/lib/libpam/modules/pam_ssh/pam_ssh.c,v 1.49 2011/11/20 15:18:49 des Exp $ |
| 36 | */ |
| 37 | |
| 38 | #include <sys/param.h> |
| 39 | #include <sys/wait.h> |
| 40 | |
| 41 | #include <errno.h> |
| 42 | #include <fcntl.h> |
| 43 | #include <paths.h> |
| 44 | #include <pwd.h> |
| 45 | #include <signal.h> |
| 46 | #include <stdio.h> |
| 47 | #include <string.h> |
| 48 | #include <unistd.h> |
| 49 | |
| 50 | #define PAM_SM_AUTH |
| 51 | #define PAM_SM_SESSION |
| 52 | |
| 53 | #include <security/pam_appl.h> |
| 54 | #include <security/pam_modules.h> |
| 55 | #include <security/openpam.h> |
| 56 | |
| 57 | #include <openssl/evp.h> |
| 58 | |
| 59 | #include "buffer.h" |
| 60 | #include "key.h" |
| 61 | #include "authfd.h" |
| 62 | #include "authfile.h" |
| 63 | |
| 64 | #define ssh_add_identity(auth, key, comment) \ |
| 65 | ssh_add_identity_constrained(auth, key, comment, 0, 0) |
| 66 | |
| 67 | extern char **environ; |
| 68 | |
| 69 | struct pam_ssh_key { |
| 70 | Key *key; |
| 71 | char *comment; |
| 72 | }; |
| 73 | |
| 74 | static const char *pam_ssh_prompt = "SSH passphrase: "; |
| 75 | static const char *pam_ssh_have_keys = "pam_ssh_have_keys"; |
| 76 | |
| 77 | static const char *pam_ssh_keyfiles[] = { |
| 78 | ".ssh/identity", /* SSH1 RSA key */ |
| 79 | ".ssh/id_rsa", /* SSH2 RSA key */ |
| 80 | ".ssh/id_dsa", /* SSH2 DSA key */ |
| 81 | ".ssh/id_ecdsa", /* SSH2 ECDSA key */ |
| 82 | NULL |
| 83 | }; |
| 84 | |
| 85 | static const char *pam_ssh_agent = "/usr/bin/ssh-agent"; |
| 86 | static const char *pam_ssh_agent_argv[] = { "ssh_agent", "-s", NULL }; |
| 87 | static char *const pam_ssh_agent_envp[] = { NULL }; |
| 88 | |
| 89 | /* |
| 90 | * Attempts to load a private key from the specified file in the specified |
| 91 | * directory, using the specified passphrase. If successful, returns a |
| 92 | * struct pam_ssh_key containing the key and its comment. |
| 93 | */ |
| 94 | static struct pam_ssh_key * |
| 95 | pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase, |
| 96 | int nullok) |
| 97 | { |
| 98 | struct pam_ssh_key *psk; |
| 99 | char fn[PATH_MAX]; |
| 100 | char *comment; |
| 101 | Key *key; |
| 102 | |
| 103 | if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn)) |
| 104 | return (NULL); |
| 105 | comment = NULL; |
| 106 | /* |
| 107 | * If the key is unencrypted, OpenSSL ignores the passphrase, so |
| 108 | * it will seem like the user typed in the right one. This allows |
| 109 | * a user to circumvent nullok by providing a dummy passphrase. |
| 110 | * Verify that the key really *is* encrypted by trying to load it |
| 111 | * with an empty passphrase, and if the key is not encrypted, |
| 112 | * accept only an empty passphrase. |
| 113 | */ |
| 114 | key = key_load_private(fn, NULL, &comment); |
| 115 | if (key != NULL && !(*passphrase == '\0' && nullok)) { |
| 116 | key_free(key); |
| 117 | return (NULL); |
| 118 | } |
| 119 | if (key == NULL) |
| 120 | key = key_load_private(fn, passphrase, &comment); |
| 121 | if (key == NULL) { |
| 122 | openpam_log(PAM_LOG_DEBUG, "failed to load key from %s", fn); |
| 123 | return (NULL); |
| 124 | } |
| 125 | |
| 126 | openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s", comment, fn); |
| 127 | if ((psk = malloc(sizeof(*psk))) == NULL) { |
| 128 | key_free(key); |
| 129 | free(comment); |
| 130 | return (NULL); |
| 131 | } |
| 132 | psk->key = key; |
| 133 | psk->comment = comment; |
| 134 | return (psk); |
| 135 | } |
| 136 | |
| 137 | /* |
| 138 | * Wipes a private key and frees the associated resources. |
| 139 | */ |
| 140 | static void |
| 141 | pam_ssh_free_key(pam_handle_t *pamh __unused, |
| 142 | void *data, int pam_err __unused) |
| 143 | { |
| 144 | struct pam_ssh_key *psk; |
| 145 | |
| 146 | psk = data; |
| 147 | key_free(psk->key); |
| 148 | free(psk->comment); |
| 149 | free(psk); |
| 150 | } |
| 151 | |
| 152 | PAM_EXTERN int |
| 153 | pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, |
| 154 | int argc __unused, const char *argv[] __unused) |
| 155 | { |
| 156 | const char **kfn, *passphrase, *user; |
| 157 | const void *item; |
| 158 | struct passwd *pwd; |
| 159 | struct pam_ssh_key *psk; |
| 160 | int nkeys, nullok, pam_err, pass; |
| 161 | |
| 162 | nullok = (openpam_get_option(pamh, "nullok") != NULL); |
| 163 | |
| 164 | /* PEM is not loaded by default */ |
| 165 | OpenSSL_add_all_algorithms(); |
| 166 | |
| 167 | /* get user name and home directory */ |
| 168 | pam_err = pam_get_user(pamh, &user, NULL); |
| 169 | if (pam_err != PAM_SUCCESS) |
| 170 | return (pam_err); |
| 171 | pwd = getpwnam(user); |
| 172 | if (pwd == NULL) |
| 173 | return (PAM_USER_UNKNOWN); |
| 174 | if (pwd->pw_dir == NULL) |
| 175 | return (PAM_AUTH_ERR); |
| 176 | |
| 177 | nkeys = 0; |
| 178 | pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS && |
| 179 | item != NULL); |
| 180 | load_keys: |
| 181 | /* get passphrase */ |
| 182 | pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, |
| 183 | &passphrase, pam_ssh_prompt); |
| 184 | if (pam_err != PAM_SUCCESS) |
| 185 | return (pam_err); |
| 186 | |
| 187 | /* switch to user credentials */ |
| 188 | pam_err = openpam_borrow_cred(pamh, pwd); |
| 189 | if (pam_err != PAM_SUCCESS) |
| 190 | return (pam_err); |
| 191 | |
| 192 | /* try to load keys from all keyfiles we know of */ |
| 193 | for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { |
| 194 | psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase, nullok); |
| 195 | if (psk != NULL) { |
| 196 | pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); |
| 197 | ++nkeys; |
| 198 | } |
| 199 | } |
| 200 | |
| 201 | /* switch back to arbitrator credentials */ |
| 202 | openpam_restore_cred(pamh); |
| 203 | |
| 204 | /* |
| 205 | * If we tried an old token and didn't get anything, and |
| 206 | * try_first_pass was specified, try again after prompting the |
| 207 | * user for a new passphrase. |
| 208 | */ |
| 209 | if (nkeys == 0 && pass == 1 && |
| 210 | openpam_get_option(pamh, "try_first_pass") != NULL) { |
| 211 | pam_set_item(pamh, PAM_AUTHTOK, NULL); |
| 212 | pass = 0; |
| 213 | goto load_keys; |
| 214 | } |
| 215 | |
| 216 | /* no keys? */ |
| 217 | if (nkeys == 0) |
| 218 | return (PAM_AUTH_ERR); |
| 219 | |
| 220 | pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); |
| 221 | return (PAM_SUCCESS); |
| 222 | } |
| 223 | |
| 224 | PAM_EXTERN int |
| 225 | pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, |
| 226 | int argc __unused, const char *argv[] __unused) |
| 227 | { |
| 228 | |
| 229 | return (PAM_SUCCESS); |
| 230 | } |
| 231 | |
| 232 | /* |
| 233 | * Parses a line from ssh-agent's output. |
| 234 | */ |
| 235 | static void |
| 236 | pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) |
| 237 | { |
| 238 | char *line, *p, *key, *val; |
| 239 | size_t len; |
| 240 | |
| 241 | while ((line = fgetln(f, &len)) != NULL) { |
| 242 | if (len < 4 || strncmp(line, "SSH_", 4) != 0) |
| 243 | continue; |
| 244 | |
| 245 | /* find equal sign at end of key */ |
| 246 | for (p = key = line; p < line + len; ++p) |
| 247 | if (*p == '=') |
| 248 | break; |
| 249 | if (p == line + len || *p != '=') |
| 250 | continue; |
| 251 | *p = '\0'; |
| 252 | |
| 253 | /* find semicolon at end of value */ |
| 254 | for (val = ++p; p < line + len; ++p) |
| 255 | if (*p == ';') |
| 256 | break; |
| 257 | if (p == line + len || *p != ';') |
| 258 | continue; |
| 259 | *p = '\0'; |
| 260 | |
| 261 | /* store key-value pair in environment */ |
| 262 | openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); |
| 263 | pam_setenv(pamh, key, val, 1); |
| 264 | } |
| 265 | } |
| 266 | |
| 267 | /* |
| 268 | * Starts an ssh agent and stores the environment variables derived from |
| 269 | * its output. |
| 270 | */ |
| 271 | static int |
| 272 | pam_ssh_start_agent(pam_handle_t *pamh) |
| 273 | { |
| 274 | int agent_pipe[2]; |
| 275 | pid_t pid; |
| 276 | FILE *f; |
| 277 | |
| 278 | /* get a pipe which we will use to read the agent's output */ |
| 279 | if (pipe(agent_pipe) == -1) |
| 280 | return (PAM_SYSTEM_ERR); |
| 281 | |
| 282 | /* start the agent */ |
| 283 | openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); |
| 284 | pid = fork(); |
| 285 | if (pid == (pid_t)-1) { |
| 286 | /* failed */ |
| 287 | close(agent_pipe[0]); |
| 288 | close(agent_pipe[1]); |
| 289 | return (PAM_SYSTEM_ERR); |
| 290 | } |
| 291 | if (pid == 0) { |
| 292 | int fd; |
| 293 | |
| 294 | /* child: drop privs, close fds and start agent */ |
| 295 | setgid(getegid()); |
| 296 | setuid(geteuid()); |
| 297 | close(STDIN_FILENO); |
| 298 | open(_PATH_DEVNULL, O_RDONLY); |
| 299 | dup2(agent_pipe[1], STDOUT_FILENO); |
| 300 | dup2(agent_pipe[1], STDERR_FILENO); |
| 301 | for (fd = 3; fd < getdtablesize(); ++fd) |
| 302 | close(fd); |
| 303 | execve(pam_ssh_agent, |
| 304 | __DECONST(char * const *, pam_ssh_agent_argv), |
| 305 | pam_ssh_agent_envp); |
| 306 | _exit(127); |
| 307 | } |
| 308 | |
| 309 | /* parent */ |
| 310 | close(agent_pipe[1]); |
| 311 | if ((f = fdopen(agent_pipe[0], "r")) == NULL) |
| 312 | return (PAM_SYSTEM_ERR); |
| 313 | pam_ssh_process_agent_output(pamh, f); |
| 314 | fclose(f); |
| 315 | |
| 316 | return (PAM_SUCCESS); |
| 317 | } |
| 318 | |
| 319 | /* |
| 320 | * Adds previously stored keys to a running agent. |
| 321 | */ |
| 322 | static int |
| 323 | pam_ssh_add_keys_to_agent(pam_handle_t *pamh) |
| 324 | { |
| 325 | AuthenticationConnection *ac; |
| 326 | const struct pam_ssh_key *psk; |
| 327 | const char **kfn; |
| 328 | const void *item; |
| 329 | char **envlist, **env; |
| 330 | int pam_err; |
| 331 | |
| 332 | /* switch to PAM environment */ |
| 333 | envlist = environ; |
| 334 | if ((environ = pam_getenvlist(pamh)) == NULL) { |
| 335 | environ = envlist; |
| 336 | return (PAM_SYSTEM_ERR); |
| 337 | } |
| 338 | |
| 339 | /* get a connection to the agent */ |
| 340 | if ((ac = ssh_get_authentication_connection()) == NULL) { |
| 341 | openpam_log(PAM_LOG_DEBUG, "failed to connect to the agent"); |
| 342 | pam_err = PAM_SYSTEM_ERR; |
| 343 | goto end; |
| 344 | } |
| 345 | |
| 346 | /* look for keys to add to it */ |
| 347 | for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { |
| 348 | pam_err = pam_get_data(pamh, *kfn, &item); |
| 349 | if (pam_err == PAM_SUCCESS && item != NULL) { |
| 350 | psk = item; |
| 351 | if (ssh_add_identity(ac, psk->key, psk->comment)) |
| 352 | openpam_log(PAM_LOG_DEBUG, |
| 353 | "added %s to ssh agent", psk->comment); |
| 354 | else |
| 355 | openpam_log(PAM_LOG_DEBUG, "failed " |
| 356 | "to add %s to ssh agent", psk->comment); |
| 357 | /* we won't need the key again, so wipe it */ |
| 358 | pam_set_data(pamh, *kfn, NULL, NULL); |
| 359 | } |
| 360 | } |
| 361 | pam_err = PAM_SUCCESS; |
| 362 | end: |
| 363 | /* disconnect from agent */ |
| 364 | if (ac != NULL) |
| 365 | ssh_close_authentication_connection(ac); |
| 366 | |
| 367 | /* switch back to original environment */ |
| 368 | for (env = environ; *env != NULL; ++env) |
| 369 | free(*env); |
| 370 | free(environ); |
| 371 | environ = envlist; |
| 372 | |
| 373 | return (pam_err); |
| 374 | } |
| 375 | |
| 376 | PAM_EXTERN int |
| 377 | pam_sm_open_session(pam_handle_t *pamh, int flags __unused, |
| 378 | int argc __unused, const char *argv[] __unused) |
| 379 | { |
| 380 | struct passwd *pwd; |
| 381 | const char *user; |
| 382 | const void *data; |
| 383 | int pam_err; |
| 384 | |
| 385 | /* no keys, no work */ |
| 386 | if (pam_get_data(pamh, pam_ssh_have_keys, &data) != PAM_SUCCESS && |
| 387 | openpam_get_option(pamh, "want_agent") == NULL) |
| 388 | return (PAM_SUCCESS); |
| 389 | |
| 390 | /* switch to user credentials */ |
| 391 | pam_err = pam_get_user(pamh, &user, NULL); |
| 392 | if (pam_err != PAM_SUCCESS) |
| 393 | return (pam_err); |
| 394 | pwd = getpwnam(user); |
| 395 | if (pwd == NULL) |
| 396 | return (PAM_USER_UNKNOWN); |
| 397 | pam_err = openpam_borrow_cred(pamh, pwd); |
| 398 | if (pam_err != PAM_SUCCESS) |
| 399 | return (pam_err); |
| 400 | |
| 401 | /* start the agent */ |
| 402 | pam_err = pam_ssh_start_agent(pamh); |
| 403 | if (pam_err != PAM_SUCCESS) { |
| 404 | openpam_restore_cred(pamh); |
| 405 | return (pam_err); |
| 406 | } |
| 407 | |
| 408 | /* we have an agent, see if we can add any keys to it */ |
| 409 | pam_err = pam_ssh_add_keys_to_agent(pamh); |
| 410 | if (pam_err != PAM_SUCCESS) { |
| 411 | /* XXX ignore failures */ |
| 412 | } |
| 413 | |
| 414 | openpam_restore_cred(pamh); |
| 415 | return (PAM_SUCCESS); |
| 416 | } |
| 417 | |
| 418 | PAM_EXTERN int |
| 419 | pam_sm_close_session(pam_handle_t *pamh, int flags __unused, |
| 420 | int argc __unused, const char *argv[] __unused) |
| 421 | { |
| 422 | const char *ssh_agent_pid; |
| 423 | char *end; |
| 424 | int status; |
| 425 | pid_t pid; |
| 426 | |
| 427 | if ((ssh_agent_pid = pam_getenv(pamh, "SSH_AGENT_PID")) == NULL) { |
| 428 | openpam_log(PAM_LOG_DEBUG, "no ssh agent"); |
| 429 | return (PAM_SUCCESS); |
| 430 | } |
| 431 | pid = (pid_t)strtol(ssh_agent_pid, &end, 10); |
| 432 | if (*ssh_agent_pid == '\0' || *end != '\0') { |
| 433 | openpam_log(PAM_LOG_DEBUG, "invalid ssh agent pid"); |
| 434 | return (PAM_SESSION_ERR); |
| 435 | } |
| 436 | openpam_log(PAM_LOG_DEBUG, "killing ssh agent %d", (int)pid); |
| 437 | if (kill(pid, SIGTERM) == -1 || |
| 438 | (waitpid(pid, &status, 0) == -1 && errno != ECHILD)) |
| 439 | return (PAM_SYSTEM_ERR); |
| 440 | return (PAM_SUCCESS); |
| 441 | } |
| 442 | |
| 443 | PAM_MODULE_ENTRY("pam_ssh"); |