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