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 #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 "authfd.h" 62 #include "authfile.h" 63 #include "sshkey.h" 64 65 #define ssh_add_identity(auth, key, comment) \ 66 ssh_add_identity_constrained(auth, key, comment, 0, 0, 0, NULL, NULL, 0) 67 68 extern char **environ; 69 70 struct pam_ssh_key { 71 struct sshkey *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/id_rsa", /* SSH2 RSA key */ 80 ".ssh/id_dsa", /* SSH2 DSA key */ 81 ".ssh/id_ecdsa", /* SSH2 ECDSA key */ 82 ".ssh/id_ed25519", /* SSH2 Ed25519 key */ 83 NULL 84 }; 85 86 static const char *pam_ssh_agent = "/usr/bin/ssh-agent"; 87 static char str_ssh_agent[] = "ssh-agent"; 88 static char str_dash_s[] = "-s"; 89 static char *const pam_ssh_agent_argv[] = { str_ssh_agent, str_dash_s, NULL }; 90 static char *const pam_ssh_agent_envp[] = { NULL }; 91 92 /* 93 * Attempts to load a private key from the specified file in the specified 94 * directory, using the specified passphrase. If successful, returns a 95 * struct pam_ssh_key containing the key and its comment. 96 */ 97 static struct pam_ssh_key * 98 pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase, 99 int nullok) 100 { 101 char fn[PATH_MAX]; 102 struct pam_ssh_key *psk; 103 struct sshkey *key; 104 char *comment; 105 int ret; 106 107 if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn)) 108 return (NULL); 109 /* 110 * If the key is unencrypted, OpenSSL ignores the passphrase, so 111 * it will seem like the user typed in the right one. This allows 112 * a user to circumvent nullok by providing a dummy passphrase. 113 * Verify that the key really *is* encrypted by trying to load it 114 * with an empty passphrase, and if the key is not encrypted, 115 * accept only an empty passphrase. 116 */ 117 ret = sshkey_load_private(fn, "", &key, &comment); 118 if (ret == 0 && !(*passphrase == '\0' && nullok)) { 119 sshkey_free(key); 120 return (NULL); 121 } 122 if (ret != 0) 123 ret = sshkey_load_private(fn, passphrase, &key, &comment); 124 if (ret != 0) { 125 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s", fn); 126 return (NULL); 127 } 128 129 openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s", comment, fn); 130 if ((psk = malloc(sizeof(*psk))) == NULL) { 131 sshkey_free(key); 132 free(comment); 133 return (NULL); 134 } 135 psk->key = key; 136 psk->comment = comment; 137 return (psk); 138 } 139 140 /* 141 * Wipes a private key and frees the associated resources. 142 */ 143 static void 144 pam_ssh_free_key(pam_handle_t *pamh __unused, 145 void *data, int pam_err __unused) 146 { 147 struct pam_ssh_key *psk; 148 149 psk = data; 150 sshkey_free(psk->key); 151 free(psk->comment); 152 free(psk); 153 } 154 155 PAM_EXTERN int 156 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused, 157 int argc __unused, const char *argv[] __unused) 158 { 159 const char **kfn, *passphrase, *user; 160 const void *item; 161 struct passwd *pwd; 162 struct pam_ssh_key *psk; 163 int nkeys, nullok, pam_err, pass; 164 165 nullok = (openpam_get_option(pamh, "nullok") != NULL); 166 167 /* PEM is not loaded by default */ 168 OpenSSL_add_all_algorithms(); 169 170 /* get user name and home directory */ 171 pam_err = pam_get_user(pamh, &user, NULL); 172 if (pam_err != PAM_SUCCESS) 173 return (pam_err); 174 pwd = getpwnam(user); 175 if (pwd == NULL) 176 return (PAM_USER_UNKNOWN); 177 if (pwd->pw_dir == NULL) 178 return (PAM_AUTH_ERR); 179 180 nkeys = 0; 181 pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS && 182 item != NULL); 183 load_keys: 184 /* get passphrase */ 185 pam_err = pam_get_authtok(pamh, PAM_AUTHTOK, 186 &passphrase, pam_ssh_prompt); 187 if (pam_err != PAM_SUCCESS) 188 return (pam_err); 189 190 /* switch to user credentials */ 191 pam_err = openpam_borrow_cred(pamh, pwd); 192 if (pam_err != PAM_SUCCESS) 193 return (pam_err); 194 195 /* try to load keys from all keyfiles we know of */ 196 for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) { 197 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase, nullok); 198 if (psk != NULL) { 199 pam_set_data(pamh, *kfn, psk, pam_ssh_free_key); 200 ++nkeys; 201 } 202 } 203 204 /* switch back to arbitrator credentials */ 205 openpam_restore_cred(pamh); 206 207 /* 208 * If we tried an old token and didn't get anything, and 209 * try_first_pass was specified, try again after prompting the 210 * user for a new passphrase. 211 */ 212 if (nkeys == 0 && pass == 1 && 213 openpam_get_option(pamh, "try_first_pass") != NULL) { 214 pam_set_item(pamh, PAM_AUTHTOK, NULL); 215 pass = 0; 216 goto load_keys; 217 } 218 219 /* no keys? */ 220 if (nkeys == 0) 221 return (PAM_AUTH_ERR); 222 223 pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL); 224 return (PAM_SUCCESS); 225 } 226 227 PAM_EXTERN int 228 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused, 229 int argc __unused, const char *argv[] __unused) 230 { 231 232 return (PAM_SUCCESS); 233 } 234 235 /* 236 * Parses a line from ssh-agent's output. 237 */ 238 static void 239 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f) 240 { 241 char *line, *p, *key, *val; 242 size_t len; 243 244 while ((line = fgetln(f, &len)) != NULL) { 245 if (len < 4 || strncmp(line, "SSH_", 4) != 0) 246 continue; 247 248 /* find equal sign at end of key */ 249 for (p = key = line; p < line + len; ++p) 250 if (*p == '=') 251 break; 252 if (p == line + len || *p != '=') 253 continue; 254 *p = '\0'; 255 256 /* find semicolon at end of value */ 257 for (val = ++p; p < line + len; ++p) 258 if (*p == ';') 259 break; 260 if (p == line + len || *p != ';') 261 continue; 262 *p = '\0'; 263 264 /* store key-value pair in environment */ 265 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val); 266 pam_setenv(pamh, key, val, 1); 267 } 268 } 269 270 /* 271 * Starts an ssh agent and stores the environment variables derived from 272 * its output. 273 */ 274 static int 275 pam_ssh_start_agent(pam_handle_t *pamh) 276 { 277 int agent_pipe[2]; 278 pid_t pid; 279 FILE *f; 280 281 /* get a pipe which we will use to read the agent's output */ 282 if (pipe(agent_pipe) == -1) 283 return (PAM_SYSTEM_ERR); 284 285 /* start the agent */ 286 openpam_log(PAM_LOG_DEBUG, "starting an ssh agent"); 287 pid = fork(); 288 if (pid == (pid_t)-1) { 289 /* failed */ 290 close(agent_pipe[0]); 291 close(agent_pipe[1]); 292 return (PAM_SYSTEM_ERR); 293 } 294 if (pid == 0) { 295 int fd; 296 297 /* child: drop privs, close fds and start agent */ 298 setgid(getegid()); 299 setuid(geteuid()); 300 close(STDIN_FILENO); 301 open(_PATH_DEVNULL, O_RDONLY); 302 dup2(agent_pipe[1], STDOUT_FILENO); 303 dup2(agent_pipe[1], STDERR_FILENO); 304 for (fd = 3; fd < getdtablesize(); ++fd) 305 close(fd); 306 execve(pam_ssh_agent, pam_ssh_agent_argv, pam_ssh_agent_envp); 307 _exit(127); 308 } 309 310 /* parent */ 311 close(agent_pipe[1]); 312 if ((f = fdopen(agent_pipe[0], "r")) == NULL) 313 return (PAM_SYSTEM_ERR); 314 pam_ssh_process_agent_output(pamh, f); 315 fclose(f); 316 317 return (PAM_SUCCESS); 318 } 319 320 /* 321 * Adds previously stored keys to a running agent. 322 */ 323 static int 324 pam_ssh_add_keys_to_agent(pam_handle_t *pamh) 325 { 326 const struct pam_ssh_key *psk; 327 const char **kfn; 328 const void *item; 329 char **envlist, **env; 330 int fd, 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 (ssh_get_authentication_socket(&fd) != 0) { 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(fd, psk->key, psk->comment) == 0) 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; 362 363 /* disconnect from agent */ 364 ssh_close_authentication_socket(fd); 365 366 end: 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"); 444