lib/pam_module/pam_ssh/pam_ssh.c

   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  * $FreeBSD: src/lib/libpam/modules/pam_ssh/pam_ssh.c,v 1.45 2007/12/21 12:00:15 des Exp $
  35  * $DragonFly: src/lib/pam_module/pam_ssh/pam_ssh.c,v 1.2 2006/09/29 06:35:03 corecode 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 "buffer.h"
  62 #include "authfd.h"
  63 #include "authfile.h"
  64
  65 extern char **environ;
  66
  67 struct pam_ssh_key {
  68         Key     *key;
  69         char    *comment;
  70 };
  71
  72 static const char *pam_ssh_prompt = "SSH passphrase: ";
  73 static const char *pam_ssh_have_keys = "pam_ssh_have_keys";
  74
  75 static const char *pam_ssh_keyfiles[] = {
  76         ".ssh/identity",        /* SSH1 RSA key */
  77         ".ssh/id_rsa",          /* SSH2 RSA key */
  78         ".ssh/id_dsa",          /* SSH2 DSA key */
  79         NULL
  80 };
  81
  82 static const char *pam_ssh_agent = "/usr/bin/ssh-agent";
  83 static const char *pam_ssh_agent_argv[] = { "ssh_agent", "-s", NULL };
  84 static char *const pam_ssh_agent_envp[] = { NULL };
  85
  86 /*
  87  * Attempts to load a private key from the specified file in the specified
  88  * directory, using the specified passphrase.  If successful, returns a
  89  * struct pam_ssh_key containing the key and its comment.
  90  */
  91 static struct pam_ssh_key *
  92 pam_ssh_load_key(const char *dir, const char *kfn, const char *passphrase)
  93 {
  94         struct pam_ssh_key *psk;
  95         char fn[PATH_MAX];
  96         char *comment;
  97         Key *key;
  98
  99         if (snprintf(fn, sizeof(fn), "%s/%s", dir, kfn) > (int)sizeof(fn))
 100                 return (NULL);
 101         comment = NULL;
 102         key = key_load_private(fn, passphrase, &comment);
 103         if (key == NULL) {
 104                 openpam_log(PAM_LOG_DEBUG, "failed to load key from %s\n", fn);
 105                 return (NULL);
 106         }
 107
 108         openpam_log(PAM_LOG_DEBUG, "loaded '%s' from %s\n", comment, fn);
 109         if ((psk = malloc(sizeof(*psk))) == NULL) {
 110                 key_free(key);
 111                 free(comment);
 112                 return (NULL);
 113         }
 114         psk->key = key;
 115         psk->comment = comment;
 116         return (psk);
 117 }
 118
 119 /*
 120  * Wipes a private key and frees the associated resources.
 121  */
 122 static void
 123 pam_ssh_free_key(pam_handle_t *pamh __unused,
 124     void *data, int pam_err __unused)
 125 {
 126         struct pam_ssh_key *psk;
 127
 128         psk = data;
 129         key_free(psk->key);
 130         free(psk->comment);
 131         free(psk);
 132 }
 133
 134 PAM_EXTERN int
 135 pam_sm_authenticate(pam_handle_t *pamh, int flags __unused,
 136     int argc __unused, const char *argv[] __unused)
 137 {
 138         const char **kfn, *passphrase, *user;
 139         const void *item;
 140         struct passwd *pwd;
 141         struct pam_ssh_key *psk;
 142         int nkeys, nullok, pam_err, pass;
 143
 144         nullok = (openpam_get_option(pamh, "nullok") != NULL);
 145
 146         /* PEM is not loaded by default */
 147         OpenSSL_add_all_algorithms();
 148
 149         /* get user name and home directory */
 150         pam_err = pam_get_user(pamh, &user, NULL);
 151         if (pam_err != PAM_SUCCESS)
 152                 return (pam_err);
 153         pwd = getpwnam(user);
 154         if (pwd == NULL)
 155                 return (PAM_USER_UNKNOWN);
 156         if (pwd->pw_dir == NULL)
 157                 return (PAM_AUTH_ERR);
 158
 159         nkeys = 0;
 160         pass = (pam_get_item(pamh, PAM_AUTHTOK, &item) == PAM_SUCCESS &&
 161             item != NULL);
 162  load_keys:
 163         /* get passphrase */
 164         pam_err = pam_get_authtok(pamh, PAM_AUTHTOK,
 165             &passphrase, pam_ssh_prompt);
 166         if (pam_err != PAM_SUCCESS)
 167                 return (pam_err);
 168
 169         if (*passphrase == '\0' && !nullok)
 170                 goto skip_keys;
 171
 172         /* switch to user credentials */
 173         pam_err = openpam_borrow_cred(pamh, pwd);
 174         if (pam_err != PAM_SUCCESS)
 175                 return (pam_err);
 176
 177         /* try to load keys from all keyfiles we know of */
 178         for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
 179                 psk = pam_ssh_load_key(pwd->pw_dir, *kfn, passphrase);
 180                 if (psk != NULL) {
 181                         pam_set_data(pamh, *kfn, psk, pam_ssh_free_key);
 182                         ++nkeys;
 183                 }
 184         }
 185
 186         /* switch back to arbitrator credentials */
 187         openpam_restore_cred(pamh);
 188
 189  skip_keys:
 190         /*
 191          * If we tried an old token and didn't get anything, and
 192          * try_first_pass was specified, try again after prompting the
 193          * user for a new passphrase.
 194          */
 195         if (nkeys == 0 && pass == 1 &&
 196             openpam_get_option(pamh, "try_first_pass") != NULL) {
 197                 pam_set_item(pamh, PAM_AUTHTOK, NULL);
 198                 pass = 0;
 199                 goto load_keys;
 200         }
 201
 202         /* no keys? */
 203         if (nkeys == 0)
 204                 return (PAM_AUTH_ERR);
 205
 206         pam_set_data(pamh, pam_ssh_have_keys, NULL, NULL);
 207         return (PAM_SUCCESS);
 208 }
 209
 210 PAM_EXTERN int
 211 pam_sm_setcred(pam_handle_t *pamh __unused, int flags __unused,
 212     int argc __unused, const char *argv[] __unused)
 213 {
 214
 215         return (PAM_SUCCESS);
 216 }
 217
 218 /*
 219  * Parses a line from ssh-agent's output.
 220  */
 221 static void
 222 pam_ssh_process_agent_output(pam_handle_t *pamh, FILE *f)
 223 {
 224         char *line, *p, *key, *val;
 225         size_t len;
 226
 227         while ((line = fgetln(f, &len)) != NULL) {
 228                 if (len < 4 || strncmp(line, "SSH_", 4) != 0)
 229                         continue;
 230
 231                 /* find equal sign at end of key */
 232                 for (p = key = line; p < line + len; ++p)
 233                         if (*p == '=')
 234                                 break;
 235                 if (p == line + len || *p != '=')
 236                         continue;
 237                 *p = '\0';
 238
 239                 /* find semicolon at end of value */
 240                 for (val = ++p; p < line + len; ++p)
 241                         if (*p == ';')
 242                                 break;
 243                 if (p == line + len || *p != ';')
 244                         continue;
 245                 *p = '\0';
 246
 247                 /* store key-value pair in environment */
 248                 openpam_log(PAM_LOG_DEBUG, "got %s: %s", key, val);
 249                 pam_setenv(pamh, key, val, 1);
 250         }
 251 }
 252
 253 /*
 254  * Starts an ssh agent and stores the environment variables derived from
 255  * its output.
 256  */
 257 static int
 258 pam_ssh_start_agent(pam_handle_t *pamh)
 259 {
 260         int agent_pipe[2];
 261         pid_t pid;
 262         FILE *f;
 263
 264         /* get a pipe which we will use to read the agent's output */
 265         if (pipe(agent_pipe) == -1)
 266                 return (PAM_SYSTEM_ERR);
 267
 268         /* start the agent */
 269         openpam_log(PAM_LOG_DEBUG, "starting an ssh agent");
 270         pid = fork();
 271         if (pid == (pid_t)-1) {
 272                 /* failed */
 273                 close(agent_pipe[0]);
 274                 close(agent_pipe[1]);
 275                 return (PAM_SYSTEM_ERR);
 276         }
 277         if (pid == 0) {
 278                 int fd;
 279
 280                 /* child: drop privs, close fds and start agent */
 281                 setgid(getegid());
 282                 setuid(geteuid());
 283                 close(STDIN_FILENO);
 284                 open(_PATH_DEVNULL, O_RDONLY);
 285                 dup2(agent_pipe[1], STDOUT_FILENO);
 286                 dup2(agent_pipe[1], STDERR_FILENO);
 287                 for (fd = 3; fd < getdtablesize(); ++fd)
 288                         close(fd);
 289                 execve(pam_ssh_agent,
 290                     __DECONST(char * const *, pam_ssh_agent_argv),
 291                     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         char **envlist, **env;
 315         int pam_err;
 316
 317         /* switch to PAM environment */
 318         envlist = environ;
 319         if ((environ = pam_getenvlist(pamh)) == NULL) {
 320                 environ = envlist;
 321                 return (PAM_SYSTEM_ERR);
 322         }
 323
 324         /* get a connection to the agent */
 325         if ((ac = ssh_get_authentication_connection()) == NULL) {
 326                 pam_err = PAM_SYSTEM_ERR;
 327                 goto end;
 328         }
 329
 330         /* look for keys to add to it */
 331         for (kfn = pam_ssh_keyfiles; *kfn != NULL; ++kfn) {
 332                 const void *vp;
 333                 pam_err = pam_get_data(pamh, *kfn, &vp);
 334                 psk = vp;
 335                 if (pam_err == PAM_SUCCESS && psk != NULL) {
 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");