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