src/pam-module.c

   1 /*-*- Mode: C; c-basic-offset: 8 -*-*/
   2
   3 /***
   4   This file is part of systemd.
   5
   6   Copyright 2010 Lennart Poettering
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU General Public License as published by
  10   the Free Software Foundation; either version 2 of the License, or
  11   (at your option) any later version.
  12
  13   systemd is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include <errno.h>
  23 #include <fcntl.h>
  24 #include <sys/file.h>
  25 #include <pwd.h>
  26 #include <endian.h>
  27
  28 #include <security/pam_modules.h>
  29 #include <security/_pam_macros.h>
  30 #include <security/pam_modutil.h>
  31 #include <security/pam_ext.h>
  32 #include <security/pam_misc.h>
  33
  34 #include "util.h"
  35 #include "cgroup-util.h"
  36 #include "macro.h"
  37 #include "sd-daemon.h"
  38
  39 static int parse_argv(pam_handle_t *handle,
  40                       int argc, const char **argv,
  41                       bool *create_session,
  42                       bool *kill_session,
  43                       bool *kill_user) {
  44
  45         unsigned i;
  46
  47         assert(argc >= 0);
  48         assert(argc == 0 || argv);
  49
  50         for (i = 0; i < (unsigned) argc; i++) {
  51                 int k;
  52
  53                 if (startswith(argv[i], "create-session=")) {
  54                         if ((k = parse_boolean(argv[i] + 15)) < 0) {
  55                                 pam_syslog(handle, LOG_ERR, "Failed to parse create-session= argument.");
  56                                 return k;
  57                         }
  58
  59                         if (create_session)
  60                                 *create_session = k;
  61                 } else if (startswith(argv[i], "kill-session=")) {
  62                         if ((k = parse_boolean(argv[i] + 13)) < 0) {
  63                                 pam_syslog(handle, LOG_ERR, "Failed to parse kill-session= argument.");
  64                                 return k;
  65                         }
  66
  67                         if (kill_session)
  68                                 *kill_session = k;
  69
  70                 } else if (startswith(argv[i], "kill-user=")) {
  71                         if ((k = parse_boolean(argv[i] + 10)) < 0) {
  72                                 pam_syslog(handle, LOG_ERR, "Failed to parse kill-user= argument.");
  73                                 return k;
  74                         }
  75
  76                         if (kill_user)
  77                                 *kill_user = k;
  78                 } else {
  79                         pam_syslog(handle, LOG_ERR, "Unknown parameter '%s'.", argv[i]);
  80                         return -EINVAL;
  81                 }
  82         }
  83
  84         if (kill_session && *kill_session && kill_user)
  85                 *kill_user = true;
  86
  87         return 0;
  88 }
  89
  90 static int open_file_and_lock(const char *fn) {
  91         int fd;
  92
  93         assert(fn);
  94
  95         if ((fd = open(fn, O_RDWR|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW|O_CREAT, 0600)) < 0)
  96                 return -errno;
  97
  98         /* The BSD socket semantics are a lot nicer than those of
  99          * POSIX locks. Which is why we use flock() here. BSD locking
 100          * does not work across NFS which however is not needed here
 101          * as the filesystems in question should be local, and only
 102          * locally accessible, and most likely even tmpfs. */
 103
 104         if (flock(fd, LOCK_EX) < 0)
 105                 return -errno;
 106
 107         return fd;
 108 }
 109
 110 enum {
 111         SESSION_ID_AUDIT = 'a',
 112         SESSION_ID_COUNTER = 'c',
 113         SESSION_ID_RANDOM = 'r'
 114 };
 115
 116 static uint64_t get_session_id(int *mode) {
 117         char *s;
 118         int fd;
 119
 120         assert(mode);
 121
 122         /* First attempt: let's use the session ID of the audit
 123          * system, if it is available. */
 124         if (read_one_line_file("/proc/self/sessionid", &s) >= 0) {
 125                 uint32_t u;
 126                 int r;
 127
 128                 r = safe_atou32(s, &u);
 129                 free(s);
 130
 131                 if (r >= 0 && u != (uint32_t) -1) {
 132                         *mode = SESSION_ID_AUDIT;
 133                         return (uint64_t) u;
 134                 }
 135         }
 136
 137         /* Second attempt, use our own counter. */
 138         if ((fd = open_file_and_lock(RUNTIME_DIR "/user/.pam-systemd-session")) >= 0) {
 139                 uint64_t counter;
 140                 ssize_t r;
 141
 142                 /* We do a bit of endianess swapping here, just to be
 143                  * sure. /var should be machine specific anyway, and
 144                  * /var/run even mounted from tmpfs, so this
 145                  * byteswapping should really not be necessary. But
 146                  * then again, you never know, so let's avoid any
 147                  * risk. */
 148
 149                 if (loop_read(fd, &counter, sizeof(counter), false) != sizeof(counter))
 150                         counter = 1;
 151                 else
 152                         counter = le64toh(counter) + 1;
 153
 154                 if (lseek(fd, 0, SEEK_SET) == 0) {
 155                         uint64_t swapped = htole64(counter);
 156
 157                         r = loop_write(fd, &swapped, sizeof(swapped), false);
 158
 159                         if (r != sizeof(swapped))
 160                                 r = -EIO;
 161                 } else
 162                         r = -errno;
 163
 164                 close_nointr_nofail(fd);
 165
 166                 if (r >= 0) {
 167                         *mode = SESSION_ID_COUNTER;
 168                         return counter;
 169                 }
 170         }
 171
 172         *mode = SESSION_ID_RANDOM;
 173
 174         /* Last attempt, pick a random value */
 175         return (uint64_t) random_ull();
 176 }
 177 static int get_user_data(
 178                 pam_handle_t *handle,
 179                 const char **ret_username,
 180                 struct passwd **ret_pw) {
 181
 182         const char *username;
 183         struct passwd *pw;
 184         int r;
 185
 186         assert(handle);
 187         assert(ret_username);
 188         assert(ret_pw);
 189
 190         if ((r = pam_get_user(handle, &username, NULL)) != PAM_SUCCESS) {
 191                 pam_syslog(handle, LOG_ERR, "Failed to get user name.");
 192                 return r;
 193         }
 194
 195         if (!username || !*username) {
 196                 pam_syslog(handle, LOG_ERR, "User name not valid.");
 197                 return PAM_AUTH_ERR;
 198         }
 199
 200         if (!(pw = pam_modutil_getpwnam(handle, username))) {
 201                 pam_syslog(handle, LOG_ERR, "Failed to get user data.");
 202                 return PAM_USER_UNKNOWN;
 203         }
 204
 205         *ret_pw = pw;
 206         *ret_username = username;
 207
 208         return PAM_SUCCESS;
 209 }
 210
 211 static int create_user_group(pam_handle_t *handle, const char *group, struct passwd *pw, bool attach) {
 212         int r;
 213
 214         assert(handle);
 215         assert(group);
 216
 217         if (attach)
 218                 r = cg_create_and_attach(SYSTEMD_CGROUP_CONTROLLER, group, 0);
 219         else
 220                 r = cg_create(SYSTEMD_CGROUP_CONTROLLER, group);
 221
 222         if (r < 0) {
 223                 pam_syslog(handle, LOG_ERR, "Failed to create cgroup: %s", strerror(-r));
 224                 return PAM_SESSION_ERR;
 225         }
 226
 227         if ((r = cg_set_task_access(SYSTEMD_CGROUP_CONTROLLER, group, 0755, pw->pw_uid, pw->pw_gid)) < 0 ||
 228             (r = cg_set_group_access(SYSTEMD_CGROUP_CONTROLLER, group, 0755, pw->pw_uid, pw->pw_gid)) < 0) {
 229                 pam_syslog(handle, LOG_ERR, "Failed to change access modes: %s", strerror(-r));
 230                 return PAM_SESSION_ERR;
 231         }
 232
 233         return PAM_SUCCESS;
 234 }
 235
 236 _public_ PAM_EXTERN int pam_sm_open_session(
 237                 pam_handle_t *handle,
 238                 int flags,
 239                 int argc, const char **argv) {
 240
 241         const char *username = NULL;
 242         struct passwd *pw;
 243         int r;
 244         char *buf = NULL;
 245         int lock_fd = -1;
 246         bool create_session = true;
 247
 248         assert(handle);
 249
 250         pam_syslog(handle, LOG_INFO, "pam-systemd initializing");
 251
 252         if (parse_argv(handle, argc, argv, &create_session, NULL, NULL) < 0)
 253                 return PAM_SESSION_ERR;
 254
 255         /* Make this a NOP on non-systemd systems */
 256         if (sd_booted() <= 0)
 257                 return PAM_SUCCESS;
 258
 259         if ((r = get_user_data(handle, &username, &pw)) != PAM_SUCCESS)
 260                 goto finish;
 261
 262         if (safe_mkdir(RUNTIME_DIR "/user", 0755, 0, 0) < 0) {
 263                 pam_syslog(handle, LOG_ERR, "Failed to create runtime directory: %m");
 264                 r = PAM_SYSTEM_ERR;
 265                 goto finish;
 266         }
 267
 268         if ((lock_fd = open_file_and_lock(RUNTIME_DIR "/user/.pam-systemd-lock")) < 0) {
 269                 pam_syslog(handle, LOG_ERR, "Failed to lock runtime directory: %m");
 270                 r = PAM_SYSTEM_ERR;
 271                 goto finish;
 272         }
 273
 274         /* Create /var/run/$USER */
 275         free(buf);
 276         if (asprintf(&buf, RUNTIME_DIR "/user/%s", username) < 0) {
 277                 r = PAM_BUF_ERR;
 278                 goto finish;
 279         }
 280
 281         if (safe_mkdir(buf, 0700, pw->pw_uid, pw->pw_gid) < 0) {
 282                 pam_syslog(handle, LOG_WARNING, "Failed to create runtime directory: %m");
 283                 r = PAM_SYSTEM_ERR;
 284                 goto finish;
 285         } else if ((r = pam_misc_setenv(handle, "XDG_RUNTIME_DIR", buf, 0)) != PAM_SUCCESS) {
 286                 pam_syslog(handle, LOG_ERR, "Failed to set runtime dir.");
 287                 goto finish;
 288         }
 289
 290         free(buf);
 291         buf = NULL;
 292
 293         if (create_session) {
 294                 const char *id;
 295
 296                 /* Reuse or create XDG session ID */
 297                 if (!(id = pam_getenv(handle, "XDG_SESSION_ID"))) {
 298                         int mode;
 299
 300                         if (asprintf(&buf, "%llux", (unsigned long long) get_session_id(&mode)) < 0) {
 301                                 r = PAM_BUF_ERR;
 302                                 goto finish;
 303                         }
 304
 305                         /* To avoid id clashes we add the session id
 306                          * source to our session ids. Note that the
 307                          * session id source might change during
 308                          * runtime, because a filesystem became
 309                          * writable or the system reconfigured. */
 310                         buf[strlen(buf)-1] =
 311                                 mode != SESSION_ID_AUDIT ? (char) mode : 0;
 312
 313                         if ((r = pam_misc_setenv(handle, "XDG_SESSION_ID", buf, 0)) != PAM_SUCCESS) {
 314                                 pam_syslog(handle, LOG_ERR, "Failed to set session id.");
 315                                 goto finish;
 316                         }
 317
 318                         if (!(id = pam_getenv(handle, "XDG_SESSION_ID"))) {
 319                                 pam_syslog(handle, LOG_ERR, "Failed to get session id.");
 320                                 r = PAM_SESSION_ERR;
 321                                 goto finish;
 322                         }
 323                 }
 324
 325                 r = asprintf(&buf, "/user/%s/%s", username, id);
 326         } else
 327                 r = asprintf(&buf, "/user/%s/no-session", username);
 328
 329         if (r < 0) {
 330                 r = PAM_BUF_ERR;
 331                 goto finish;
 332         }
 333
 334         if ((r = create_user_group(handle, buf, pw, true)) != PAM_SUCCESS)
 335                 goto finish;
 336
 337         r = PAM_SUCCESS;
 338
 339 finish:
 340         free(buf);
 341
 342         if (lock_fd >= 0)
 343                 close_nointr_nofail(lock_fd);
 344
 345         return r;
 346 }
 347
 348 static int session_remains(pam_handle_t *handle, const char *user_path) {
 349         int r;
 350         bool remains = false;
 351         DIR *d;
 352         char *subgroup;
 353
 354         if ((r = cg_enumerate_subgroups(SYSTEMD_CGROUP_CONTROLLER, user_path, &d)) < 0)
 355                 return r;
 356
 357         while ((r = cg_read_subgroup(d, &subgroup)) > 0) {
 358
 359                 remains = !streq(subgroup, "no-session");
 360                 free(subgroup);
 361
 362                 if (remains)
 363                         break;
 364         }
 365
 366         closedir(d);
 367
 368         if (r < 0)
 369                 return r;
 370
 371         return !!remains;
 372 }
 373
 374 _public_ PAM_EXTERN int pam_sm_close_session(
 375                 pam_handle_t *handle,
 376                 int flags,
 377                 int argc, const char **argv) {
 378
 379         const char *username = NULL;
 380         bool kill_session = false;
 381         bool kill_user = false;
 382         int lock_fd = -1, r;
 383         char *session_path = NULL, *nosession_path = NULL, *user_path = NULL;
 384         const char *id;
 385         struct passwd *pw;
 386
 387         assert(handle);
 388
 389         if (parse_argv(handle, argc, argv, NULL, &kill_session, &kill_user) < 0)
 390                 return PAM_SESSION_ERR;
 391
 392         /* Make this a NOP on non-systemd systems */
 393         if (sd_booted() <= 0)
 394                 return PAM_SUCCESS;
 395
 396         if ((r = get_user_data(handle, &username, &pw)) != PAM_SUCCESS)
 397                 goto finish;
 398
 399         if ((lock_fd = open_file_and_lock(RUNTIME_DIR "/user/.pam-systemd-lock")) < 0) {
 400                 pam_syslog(handle, LOG_ERR, "Failed to lock runtime directory: %m");
 401                 r = PAM_SYSTEM_ERR;
 402                 goto finish;
 403         }
 404
 405         /* We are probably still in some session/no-session dir. Move ourselves out of the way as first step */
 406         if ((r = cg_attach(SYSTEMD_CGROUP_CONTROLLER, "/user", 0)) < 0)
 407                 pam_syslog(handle, LOG_ERR, "Failed to move us away: %s", strerror(-r));
 408
 409         if (asprintf(&user_path, "/user/%s", username) < 0) {
 410                 r = PAM_BUF_ERR;
 411                 goto finish;
 412         }
 413
 414         if ((id = pam_getenv(handle, "XDG_SESSION_ID"))) {
 415
 416                 if (asprintf(&session_path, "/user/%s/%s", username, id) < 0 ||
 417                     asprintf(&nosession_path, "/user/%s/no-session", username) < 0) {
 418                         r = PAM_BUF_ERR;
 419                         goto finish;
 420                 }
 421
 422                 if (kill_session)  {
 423                         /* Kill processes in session cgroup, and delete it */
 424                         if ((r = cg_kill_recursive_and_wait(SYSTEMD_CGROUP_CONTROLLER, session_path, true)) < 0)
 425                                 pam_syslog(handle, LOG_ERR, "Failed to kill session cgroup: %s", strerror(-r));
 426                 } else {
 427                         /* Migrate processes from session to
 428                          * no-session cgroup. First, try to create the
 429                          * no-session group in case it doesn't exist
 430                          * yet. Also, delete the session group. */
 431                         create_user_group(handle, nosession_path, pw, 0);
 432
 433                         if ((r = cg_migrate_recursive(SYSTEMD_CGROUP_CONTROLLER, session_path, nosession_path, false, true)) < 0)
 434                                 pam_syslog(handle, LOG_ERR, "Failed to migrate session cgroup: %s", strerror(-r));
 435                 }
 436         }
 437
 438         /* GC user tree */
 439         cg_trim(SYSTEMD_CGROUP_CONTROLLER, user_path, false);
 440
 441         if ((r = session_remains(handle, user_path)) < 0)
 442                 pam_syslog(handle, LOG_ERR, "Failed to determine whether a session remains: %s", strerror(-r));
 443
 444         /* Kill user processes not attached to any session */
 445         if (kill_user && r == 0) {
 446
 447                 /* Kill no-session cgroup */
 448                 if ((r = cg_kill_recursive_and_wait(SYSTEMD_CGROUP_CONTROLLER, user_path, true)) < 0)
 449                         pam_syslog(handle, LOG_ERR, "Failed to kill user cgroup: %s", strerror(-r));
 450         } else {
 451
 452                 if ((r = cg_is_empty_recursive(SYSTEMD_CGROUP_CONTROLLER, user_path, true)) < 0)
 453                         pam_syslog(handle, LOG_ERR, "Failed to check user cgroup: %s", strerror(-r));
 454
 455                 /* Remove user cgroup */
 456                 if (r > 0) {
 457                         if ((r = cg_delete(SYSTEMD_CGROUP_CONTROLLER, user_path)) < 0)
 458                                 pam_syslog(handle, LOG_ERR, "Failed to delete user cgroup: %s", strerror(-r));
 459
 460                 /* If we managed to find somebody, don't cleanup the cgroup. */
 461                 } else if (r == 0)
 462                         r = -EBUSY;
 463         }
 464
 465         if (r >= 0) {
 466                 const char *runtime_dir;
 467
 468                 /* This will migrate us to the /user cgroup. */
 469
 470                 if ((runtime_dir = pam_getenv(handle, "XDG_RUNTIME_DIR")))
 471                         if ((r = rm_rf(runtime_dir, false, true)) < 0)
 472                                 pam_syslog(handle, LOG_ERR, "Failed to remove runtime directory: %s", strerror(-r));
 473         }
 474
 475         r = PAM_SUCCESS;
 476
 477 finish:
 478         if (lock_fd >= 0)
 479                 close_nointr_nofail(lock_fd);
 480
 481         free(session_path);
 482         free(nosession_path);
 483         free(user_path);
 484
 485         return r;
 486 }