src/nspawn.c

   1 /*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
   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 <signal.h>
  23 #include <sched.h>
  24 #include <unistd.h>
  25 #include <sys/types.h>
  26 #include <sys/syscall.h>
  27 #include <sys/mount.h>
  28 #include <sys/wait.h>
  29 #include <stdlib.h>
  30 #include <string.h>
  31 #include <stdio.h>
  32 #include <errno.h>
  33 #include <sys/prctl.h>
  34 #include <sys/capability.h>
  35 #include <getopt.h>
  36 #include <sys/epoll.h>
  37 #include <termios.h>
  38 #include <sys/signalfd.h>
  39 #include <grp.h>
  40
  41 #include "log.h"
  42 #include "util.h"
  43 #include "missing.h"
  44 #include "cgroup-util.h"
  45 #include "sd-daemon.h"
  46 #include "strv.h"
  47
  48 static char *arg_directory = NULL;
  49 static char *arg_user = NULL;
  50
  51 static int help(void) {
  52
  53         printf("%s [OPTIONS...] [PATH] [ARGUMENTS...]\n\n"
  54                "Spawn a minimal namespace container for debugging, testing and building.\n\n"
  55                "  -h --help            Show this help\n"
  56                "  -D --directory=NAME  Root directory for the container\n"
  57                "  -u --user=USER       Run the command under specified user or uid\n",
  58                program_invocation_short_name);
  59
  60         return 0;
  61 }
  62
  63 static int parse_argv(int argc, char *argv[]) {
  64
  65         static const struct option options[] = {
  66                 { "help",      no_argument,       NULL, 'h' },
  67                 { "directory", required_argument, NULL, 'D' },
  68                 { "user",      optional_argument, NULL, 'u' },
  69                 { NULL,        0,                 NULL, 0   }
  70         };
  71
  72         int c;
  73
  74         assert(argc >= 0);
  75         assert(argv);
  76
  77         while ((c = getopt_long(argc, argv, "+hD:u:", options, NULL)) >= 0) {
  78
  79                 switch (c) {
  80
  81                 case 'h':
  82                         help();
  83                         return 0;
  84
  85                 case 'D':
  86                         free(arg_directory);
  87                         if (!(arg_directory = strdup(optarg))) {
  88                                 log_error("Failed to duplicate root directory.");
  89                                 return -ENOMEM;
  90                         }
  91
  92                         break;
  93
  94                 case 'u':
  95                         free(arg_user);
  96                         if (!(arg_user = strdup(optarg))) {
  97                                 log_error("Failed to duplicate user name.");
  98                                 return -ENOMEM;
  99                         }
 100
 101                         break;
 102
 103                 case '?':
 104                         return -EINVAL;
 105
 106                 default:
 107                         log_error("Unknown option code %c", c);
 108                         return -EINVAL;
 109                 }
 110         }
 111
 112         return 1;
 113 }
 114
 115 static int mount_all(const char *dest) {
 116
 117         typedef struct MountPoint {
 118                 const char *what;
 119                 const char *where;
 120                 const char *type;
 121                 const char *options;
 122                 unsigned long flags;
 123                 bool fatal;
 124         } MountPoint;
 125
 126         static const MountPoint mount_table[] = {
 127                 { "proc",      "/proc",     "proc",      NULL,        MS_NOSUID|MS_NOEXEC|MS_NODEV, true },
 128                 { "/proc/sys", "/proc/sys", "bind",      NULL,        MS_BIND, true },                      /* Bind mount first */
 129                 { "/proc/sys", "/proc/sys", "bind",      NULL,        MS_BIND|MS_RDONLY|MS_REMOUNT, true }, /* Then, make it r/o */
 130                 { "sysfs",     "/sys",      "sysfs",     NULL,        MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, true },
 131                 { "tmpfs",     "/dev",      "tmpfs",     "mode=755",  MS_NOSUID, true },
 132                 { "/dev/pts",  "/dev/pts",  "bind",      NULL,        MS_BIND, true },
 133                 { "tmpfs",     "/run",      "tmpfs",     "mode=755",  MS_NOSUID|MS_NODEV, true },
 134 #ifdef HAVE_SELINUX
 135                 { "selinux",   "/selinux",  "selinuxfs", NULL,        MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_RDONLY, false },
 136 #endif
 137         };
 138
 139         unsigned k;
 140         int r = 0;
 141         char *where;
 142
 143         for (k = 0; k < ELEMENTSOF(mount_table); k++) {
 144                 int t;
 145
 146                 if (asprintf(&where, "%s/%s", dest, mount_table[k].where) < 0) {
 147                         log_error("Out of memory");
 148
 149                         if (r == 0)
 150                                 r = -ENOMEM;
 151
 152                         break;
 153                 }
 154
 155                 if ((t = path_is_mount_point(where)) < 0) {
 156                         log_error("Failed to detect whether %s is a mount point: %s", where, strerror(-t));
 157                         free(where);
 158
 159                         if (r == 0)
 160                                 r = t;
 161
 162                         continue;
 163                 }
 164
 165                 mkdir_p(where, 0755);
 166
 167                 if (mount(mount_table[k].what,
 168                           where,
 169                           mount_table[k].type,
 170                           mount_table[k].flags,
 171                           mount_table[k].options) < 0 &&
 172                     mount_table[k].fatal) {
 173
 174                         log_error("mount(%s) failed: %m", where);
 175
 176                         if (r == 0)
 177                                 r = -errno;
 178                 }
 179
 180                 free(where);
 181         }
 182
 183         /* Fix the timezone, if possible */
 184         if (asprintf(&where, "%s/%s", dest, "/etc/localtime") >= 0) {
 185                 mount("/etc/localtime", where, "bind", MS_BIND, NULL);
 186                 mount("/etc/localtime", where, "bind", MS_BIND|MS_REMOUNT|MS_RDONLY, NULL);
 187                 free(where);
 188         }
 189
 190         return r;
 191 }
 192
 193 static int copy_devnodes(const char *dest, const char *console) {
 194
 195         static const char devnodes[] =
 196                 "null\0"
 197                 "zero\0"
 198                 "full\0"
 199                 "random\0"
 200                 "urandom\0"
 201                 "tty\0"
 202                 "ptmx\0"
 203                 "kmsg\0"
 204                 "rtc0\0";
 205
 206         const char *d;
 207         int r = 0, k;
 208         mode_t u;
 209         struct stat st;
 210         char *from = NULL, *to = NULL;
 211
 212         assert(dest);
 213         assert(console);
 214
 215         u = umask(0000);
 216
 217         NULSTR_FOREACH(d, devnodes) {
 218                 from = to = NULL;
 219
 220                 asprintf(&from, "/dev/%s", d);
 221                 asprintf(&to, "%s/dev/%s", dest, d);
 222
 223                 if (!from || !to) {
 224                         log_error("Failed to allocate devnode path");
 225
 226                         free(from);
 227                         free(to);
 228
 229                         from = to = NULL;
 230
 231                         if (r == 0)
 232                                 r = -ENOMEM;
 233
 234                         break;
 235                 }
 236
 237                 if (stat(from, &st) < 0) {
 238
 239                         if (errno != ENOENT) {
 240                                 log_error("Failed to stat %s: %m", from);
 241                                 if (r == 0)
 242                                         r = -errno;
 243                         }
 244
 245                 } else if (!S_ISCHR(st.st_mode) && !S_ISBLK(st.st_mode)) {
 246
 247                         log_error("%s is not a char or block device, cannot copy.", from);
 248                         if (r == 0)
 249                                 r = -EIO;
 250
 251                 } else if (mknod(to, st.st_mode, st.st_rdev) < 0) {
 252
 253                         log_error("mknod(%s) failed: %m", dest);
 254                         if (r == 0)
 255                                 r = -errno;
 256                 }
 257
 258                 free(from);
 259                 free(to);
 260         }
 261
 262         if (stat(console, &st) < 0) {
 263
 264                 log_error("Failed to stat %s: %m", console);
 265                 if (r == 0)
 266                         r = -errno;
 267
 268                 goto finish;
 269
 270         } else if (!S_ISCHR(st.st_mode)) {
 271
 272                 log_error("/dev/console is not a char device.");
 273                 if (r == 0)
 274                         r = -EIO;
 275
 276                 goto finish;
 277         }
 278
 279         if (asprintf(&to, "%s/dev/console", dest) < 0) {
 280
 281                 log_error("Out of memory");
 282                 if (r == 0)
 283                         r = -ENOMEM;
 284
 285                  goto finish;
 286         }
 287
 288         /* We need to bind mount the right tty to /dev/console since
 289          * ptys can only exist on pts file systems. To have something
 290          * to bind mount things on we create a device node first, that
 291          * has the right major/minor (note that the major minor
 292          * doesn't actually matter here, since we mount it over
 293          * anyway). */
 294
 295         if (mknod(to, (st.st_mode & ~07777) | 0600, st.st_rdev) < 0)
 296                 log_error("mknod for /dev/console failed: %m");
 297
 298         if (mount(console, to, "bind", MS_BIND, NULL) < 0) {
 299                 log_error("bind mount for /dev/console failed: %m");
 300
 301                 if (r == 0)
 302                         r = -errno;
 303         }
 304
 305         free(to);
 306
 307         if ((k = chmod_and_chown(console, 0600, 0, 0)) < 0) {
 308                 log_error("Failed to correct access mode for TTY: %s", strerror(-k));
 309
 310                 if (r == 0)
 311                         r = k;
 312         }
 313
 314 finish:
 315
 316         umask(u);
 317
 318         return r;
 319 }
 320
 321 static int drop_capabilities(void) {
 322         static const unsigned long retain[] = {
 323                 CAP_CHOWN,
 324                 CAP_DAC_OVERRIDE,
 325                 CAP_DAC_READ_SEARCH,
 326                 CAP_FOWNER,
 327                 CAP_FSETID,
 328                 CAP_IPC_OWNER,
 329                 CAP_KILL,
 330                 CAP_LEASE,
 331                 CAP_LINUX_IMMUTABLE,
 332                 CAP_NET_BIND_SERVICE,
 333                 CAP_NET_BROADCAST,
 334                 CAP_NET_RAW,
 335                 CAP_SETGID,
 336                 CAP_SETFCAP,
 337                 CAP_SETPCAP,
 338                 CAP_SETUID,
 339                 CAP_SYS_ADMIN,
 340                 CAP_SYS_CHROOT,
 341                 CAP_SYS_NICE,
 342                 CAP_SYS_PTRACE,
 343                 CAP_SYS_TTY_CONFIG
 344         };
 345
 346         unsigned long l;
 347
 348         for (l = 0; l <= MAX(63LU, (unsigned long) CAP_LAST_CAP); l++) {
 349                 unsigned i;
 350
 351                 for (i = 0; i < ELEMENTSOF(retain); i++)
 352                         if (retain[i] == l)
 353                                 break;
 354
 355                 if (i < ELEMENTSOF(retain))
 356                         continue;
 357
 358                 if (prctl(PR_CAPBSET_DROP, l) < 0) {
 359
 360                         /* If this capability is not known, EINVAL
 361                          * will be returned, let's ignore this. */
 362                         if (errno == EINVAL)
 363                                 break;
 364
 365                         log_error("PR_CAPBSET_DROP failed: %m");
 366                         return -errno;
 367                 }
 368         }
 369
 370         return 0;
 371 }
 372
 373 static int is_os_tree(const char *path) {
 374         int r;
 375         char *p;
 376         /* We use /bin/sh as flag file if something is an OS */
 377
 378         if (asprintf(&p, "%s/bin/sh", path) < 0)
 379                 return -ENOMEM;
 380
 381         r = access(p, F_OK);
 382         free(p);
 383
 384         return r < 0 ? 0 : 1;
 385 }
 386
 387 #define BUFFER_SIZE 1024
 388
 389 static int process_pty(int master, sigset_t *mask) {
 390
 391         char in_buffer[BUFFER_SIZE], out_buffer[BUFFER_SIZE];
 392         size_t in_buffer_full = 0, out_buffer_full = 0;
 393         struct epoll_event stdin_ev, stdout_ev, master_ev, signal_ev;
 394         bool stdin_readable = false, stdout_writable = false, master_readable = false, master_writable = false;
 395         int ep = -1, signal_fd = -1, r;
 396
 397         fd_nonblock(STDIN_FILENO, 1);
 398         fd_nonblock(STDOUT_FILENO, 1);
 399         fd_nonblock(master, 1);
 400
 401         if ((signal_fd = signalfd(-1, mask, SFD_NONBLOCK|SFD_CLOEXEC)) < 0) {
 402                 log_error("signalfd(): %m");
 403                 r = -errno;
 404                 goto finish;
 405         }
 406
 407         if ((ep = epoll_create1(EPOLL_CLOEXEC)) < 0) {
 408                 log_error("Failed to create epoll: %m");
 409                 r = -errno;
 410                 goto finish;
 411         }
 412
 413         zero(stdin_ev);
 414         stdin_ev.events = EPOLLIN|EPOLLET;
 415         stdin_ev.data.fd = STDIN_FILENO;
 416
 417         zero(stdout_ev);
 418         stdout_ev.events = EPOLLOUT|EPOLLET;
 419         stdout_ev.data.fd = STDOUT_FILENO;
 420
 421         zero(master_ev);
 422         master_ev.events = EPOLLIN|EPOLLOUT|EPOLLET;
 423         master_ev.data.fd = master;
 424
 425         zero(signal_ev);
 426         signal_ev.events = EPOLLIN;
 427         signal_ev.data.fd = signal_fd;
 428
 429         if (epoll_ctl(ep, EPOLL_CTL_ADD, STDIN_FILENO, &stdin_ev) < 0 ||
 430             epoll_ctl(ep, EPOLL_CTL_ADD, STDOUT_FILENO, &stdout_ev) < 0 ||
 431             epoll_ctl(ep, EPOLL_CTL_ADD, master, &master_ev) < 0 ||
 432             epoll_ctl(ep, EPOLL_CTL_ADD, signal_fd, &signal_ev) < 0) {
 433                 log_error("Failed to regiser fds in epoll: %m");
 434                 r = -errno;
 435                 goto finish;
 436         }
 437
 438         for (;;) {
 439                 struct epoll_event ev[16];
 440                 ssize_t k;
 441                 int i, nfds;
 442
 443                 if ((nfds = epoll_wait(ep, ev, ELEMENTSOF(ev), -1)) < 0) {
 444
 445                         if (errno == EINTR || errno == EAGAIN)
 446                                 continue;
 447
 448                         log_error("epoll_wait(): %m");
 449                         r = -errno;
 450                         goto finish;
 451                 }
 452
 453                 assert(nfds >= 1);
 454
 455                 for (i = 0; i < nfds; i++) {
 456                         if (ev[i].data.fd == STDIN_FILENO) {
 457
 458                                 if (ev[i].events & (EPOLLIN|EPOLLHUP))
 459                                         stdin_readable = true;
 460
 461                         } else if (ev[i].data.fd == STDOUT_FILENO) {
 462
 463                                 if (ev[i].events & (EPOLLOUT|EPOLLHUP))
 464                                         stdout_writable = true;
 465
 466                         } else if (ev[i].data.fd == master) {
 467
 468                                 if (ev[i].events & (EPOLLIN|EPOLLHUP))
 469                                         master_readable = true;
 470
 471                                 if (ev[i].events & (EPOLLOUT|EPOLLHUP))
 472                                         master_writable = true;
 473
 474                         } else if (ev[i].data.fd == signal_fd) {
 475                                 struct signalfd_siginfo sfsi;
 476                                 ssize_t n;
 477
 478                                 if ((n = read(signal_fd, &sfsi, sizeof(sfsi))) != sizeof(sfsi)) {
 479
 480                                         if (n >= 0) {
 481                                                 log_error("Failed to read from signalfd: invalid block size");
 482                                                 r = -EIO;
 483                                                 goto finish;
 484                                         }
 485
 486                                         if (errno != EINTR && errno != EAGAIN) {
 487                                                 log_error("Failed to read from signalfd: %m");
 488                                                 r = -errno;
 489                                                 goto finish;
 490                                         }
 491                                 } else {
 492
 493                                         if (sfsi.ssi_signo == SIGWINCH) {
 494                                                 struct winsize ws;
 495
 496                                                 /* The window size changed, let's forward that. */
 497                                                 if (ioctl(STDIN_FILENO, TIOCGWINSZ, &ws) >= 0)
 498                                                         ioctl(master, TIOCSWINSZ, &ws);
 499                                         } else {
 500                                                 r = 0;
 501                                                 goto finish;
 502                                         }
 503                                 }
 504                         }
 505                 }
 506
 507                 while ((stdin_readable && in_buffer_full <= 0) ||
 508                        (master_writable && in_buffer_full > 0) ||
 509                        (master_readable && out_buffer_full <= 0) ||
 510                        (stdout_writable && out_buffer_full > 0)) {
 511
 512                         if (stdin_readable && in_buffer_full < BUFFER_SIZE) {
 513
 514                                 if ((k = read(STDIN_FILENO, in_buffer + in_buffer_full, BUFFER_SIZE - in_buffer_full)) < 0) {
 515
 516                                         if (errno == EAGAIN || errno == EPIPE || errno == ECONNRESET || errno == EIO)
 517                                                 stdin_readable = false;
 518                                         else {
 519                                                 log_error("read(): %m");
 520                                                 r = -errno;
 521                                                 goto finish;
 522                                         }
 523                                 } else
 524                                         in_buffer_full += (size_t) k;
 525                         }
 526
 527                         if (master_writable && in_buffer_full > 0) {
 528
 529                                 if ((k = write(master, in_buffer, in_buffer_full)) < 0) {
 530
 531                                         if (errno == EAGAIN || errno == EPIPE || errno == ECONNRESET || errno == EIO)
 532                                                 master_writable = false;
 533                                         else {
 534                                                 log_error("write(): %m");
 535                                                 r = -errno;
 536                                                 goto finish;
 537                                         }
 538
 539                                 } else {
 540                                         assert(in_buffer_full >= (size_t) k);
 541                                         memmove(in_buffer, in_buffer + k, in_buffer_full - k);
 542                                         in_buffer_full -= k;
 543                                 }
 544                         }
 545
 546                         if (master_readable && out_buffer_full < BUFFER_SIZE) {
 547
 548                                 if ((k = read(master, out_buffer + out_buffer_full, BUFFER_SIZE - out_buffer_full)) < 0) {
 549
 550                                         if (errno == EAGAIN || errno == EPIPE || errno == ECONNRESET || errno == EIO)
 551                                                 master_readable = false;
 552                                         else {
 553                                                 log_error("read(): %m");
 554                                                 r = -errno;
 555                                                 goto finish;
 556                                         }
 557                                 }  else
 558                                         out_buffer_full += (size_t) k;
 559                         }
 560
 561                         if (stdout_writable && out_buffer_full > 0) {
 562
 563                                 if ((k = write(STDOUT_FILENO, out_buffer, out_buffer_full)) < 0) {
 564
 565                                         if (errno == EAGAIN || errno == EPIPE || errno == ECONNRESET || errno == EIO)
 566                                                 stdout_writable = false;
 567                                         else {
 568                                                 log_error("write(): %m");
 569                                                 r = -errno;
 570                                                 goto finish;
 571                                         }
 572
 573                                 } else {
 574                                         assert(out_buffer_full >= (size_t) k);
 575                                         memmove(out_buffer, out_buffer + k, out_buffer_full - k);
 576                                         out_buffer_full -= k;
 577                                 }
 578                         }
 579                 }
 580         }
 581
 582 finish:
 583         if (ep >= 0)
 584                 close_nointr_nofail(ep);
 585
 586         if (signal_fd >= 0)
 587                 close_nointr_nofail(signal_fd);
 588
 589         return r;
 590 }
 591
 592 int main(int argc, char *argv[]) {
 593         pid_t pid = 0;
 594         int r = EXIT_FAILURE, k;
 595         char *oldcg = NULL, *newcg = NULL;
 596         int master = -1;
 597         const char *console = NULL;
 598         struct termios saved_attr, raw_attr;
 599         sigset_t mask;
 600         bool saved_attr_valid = false;
 601         struct winsize ws;
 602
 603         log_parse_environment();
 604         log_open();
 605
 606         if ((r = parse_argv(argc, argv)) <= 0)
 607                 goto finish;
 608
 609         if (arg_directory) {
 610                 char *p;
 611
 612                 p = path_make_absolute_cwd(arg_directory);
 613                 free(arg_directory);
 614                 arg_directory = p;
 615         } else
 616                 arg_directory = get_current_dir_name();
 617
 618         if (!arg_directory) {
 619                 log_error("Failed to determine path");
 620                 goto finish;
 621         }
 622
 623         path_kill_slashes(arg_directory);
 624
 625         if (geteuid() != 0) {
 626                 log_error("Need to be root.");
 627                 goto finish;
 628         }
 629
 630         if (sd_booted() <= 0) {
 631                 log_error("Not running on a systemd system.");
 632                 goto finish;
 633         }
 634
 635         if (path_equal(arg_directory, "/")) {
 636                 log_error("Spawning container on root directory not supported.");
 637                 goto finish;
 638         }
 639
 640         if (is_os_tree(arg_directory) <= 0) {
 641                 log_error("Directory %s doesn't look like an OS root directory. Refusing.", arg_directory);
 642                 goto finish;
 643         }
 644
 645         if ((k = cg_get_by_pid(SYSTEMD_CGROUP_CONTROLLER, 0, &oldcg)) < 0) {
 646                 log_error("Failed to determine current cgroup: %s", strerror(-k));
 647                 goto finish;
 648         }
 649
 650         if (asprintf(&newcg, "%s/nspawn-%lu", oldcg, (unsigned long) getpid()) < 0) {
 651                 log_error("Failed to allocate cgroup path.");
 652                 goto finish;
 653         }
 654
 655         if ((k = cg_create_and_attach(SYSTEMD_CGROUP_CONTROLLER, newcg, 0)) < 0)  {
 656                 log_error("Failed to create cgroup: %s", strerror(-k));
 657                 goto finish;
 658         }
 659
 660         if ((master = posix_openpt(O_RDWR|O_NOCTTY|O_CLOEXEC|O_NDELAY)) < 0) {
 661                 log_error("Failed to acquire pseudo tty: %m");
 662                 goto finish;
 663         }
 664
 665         if (!(console = ptsname(master))) {
 666                 log_error("Failed to determine tty name: %m");
 667                 goto finish;
 668         }
 669
 670         log_info("Spawning namespace container on %s (console is %s).", arg_directory, console);
 671
 672         if (ioctl(STDIN_FILENO, TIOCGWINSZ, &ws) >= 0)
 673                 ioctl(master, TIOCSWINSZ, &ws);
 674
 675         if (unlockpt(master) < 0) {
 676                 log_error("Failed to unlock tty: %m");
 677                 goto finish;
 678         }
 679
 680         if (tcgetattr(STDIN_FILENO, &saved_attr) < 0) {
 681                 log_error("Failed to get terminal attributes: %m");
 682                 goto finish;
 683         }
 684
 685         saved_attr_valid = true;
 686
 687         raw_attr = saved_attr;
 688         cfmakeraw(&raw_attr);
 689         raw_attr.c_lflag &= ~ECHO;
 690
 691         if (tcsetattr(STDIN_FILENO, TCSANOW, &raw_attr) < 0) {
 692                 log_error("Failed to set terminal attributes: %m");
 693                 goto finish;
 694         }
 695
 696         assert_se(sigemptyset(&mask) == 0);
 697         sigset_add_many(&mask, SIGCHLD, SIGWINCH, SIGTERM, SIGINT, -1);
 698         assert_se(sigprocmask(SIG_BLOCK, &mask, NULL) == 0);
 699
 700         if ((pid = syscall(__NR_clone, SIGCHLD|CLONE_NEWIPC|CLONE_NEWNS|CLONE_NEWPID|CLONE_NEWUTS, NULL)) < 0) {
 701                 log_error("clone() failed: %m");
 702                 goto finish;
 703         }
 704
 705         if (pid == 0) {
 706                 /* child */
 707
 708                 const char *hn;
 709                 const char *home = NULL;
 710                 uid_t uid = (uid_t) -1;
 711                 gid_t gid = (gid_t) -1;
 712                 const char *envp[] = {
 713                         "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
 714                         NULL, /* TERM */
 715                         NULL, /* HOME */
 716                         NULL, /* USER */
 717                         NULL, /* LOGNAME */
 718                         NULL
 719                 };
 720
 721                 envp[1] = strv_find_prefix(environ, "TERM=");
 722
 723                 close_nointr_nofail(master);
 724
 725                 close_nointr(STDIN_FILENO);
 726                 close_nointr(STDOUT_FILENO);
 727                 close_nointr(STDERR_FILENO);
 728
 729                 close_all_fds(NULL, 0);
 730
 731                 reset_all_signal_handlers();
 732
 733                 assert_se(sigemptyset(&mask) == 0);
 734                 assert_se(sigprocmask(SIG_SETMASK, &mask, NULL) == 0);
 735
 736                 if (setsid() < 0)
 737                         goto child_fail;
 738
 739                 if (prctl(PR_SET_PDEATHSIG, SIGKILL) < 0)
 740                         goto child_fail;
 741
 742                 if (mount_all(arg_directory) < 0)
 743                         goto child_fail;
 744
 745                 if (copy_devnodes(arg_directory, console) < 0)
 746                         goto child_fail;
 747
 748                 if (chdir(arg_directory) < 0) {
 749                         log_error("chdir(%s) failed: %m", arg_directory);
 750                         goto child_fail;
 751                 }
 752
 753                 if (open_terminal("dev/console", O_RDWR) != STDIN_FILENO ||
 754                     dup2(STDIN_FILENO, STDOUT_FILENO) != STDOUT_FILENO ||
 755                     dup2(STDIN_FILENO, STDERR_FILENO) != STDERR_FILENO)
 756                         goto child_fail;
 757
 758                 if (mount(arg_directory, "/", "bind", MS_BIND|MS_MOVE, NULL) < 0) {
 759                         log_error("mount(MS_MOVE) failed: %m");
 760                         goto child_fail;
 761                 }
 762
 763                 if (chroot(".") < 0) {
 764                         log_error("chroot() failed: %m");
 765                         goto child_fail;
 766                 }
 767
 768                 if (chdir("/") < 0) {
 769                         log_error("chdir() failed: %m");
 770                         goto child_fail;
 771                 }
 772
 773                 umask(0002);
 774
 775                 if (drop_capabilities() < 0)
 776                         goto child_fail;
 777
 778                 if (arg_user) {
 779
 780                         if (get_user_creds((const char**)&arg_user, &uid, &gid, &home) < 0) {
 781                                 log_error("get_user_creds() failed: %m");
 782                                 goto child_fail;
 783                         }
 784
 785                         if (mkdir_parents(home, 0775) < 0) {
 786                                 log_error("mkdir_parents() failed: %m");
 787                                 goto child_fail;
 788                         }
 789
 790                         if (safe_mkdir(home, 0775, uid, gid) < 0) {
 791                                 log_error("safe_mkdir() failed: %m");
 792                                 goto child_fail;
 793                         }
 794
 795                         if (initgroups((const char*)arg_user, gid) < 0) {
 796                                 log_error("initgroups() failed: %m");
 797                                 goto child_fail;
 798                         }
 799
 800                         if (setresgid(gid, gid, gid) < 0) {
 801                                 log_error("setregid() failed: %m");
 802                                 goto child_fail;
 803                         }
 804
 805                         if (setresuid(uid, uid, uid) < 0) {
 806                                 log_error("setreuid() failed: %m");
 807                                 goto child_fail;
 808                         }
 809                 }
 810
 811                 if ((asprintf((char**)(envp + 2), "HOME=%s", home? home: "/root") < 0) ||
 812                     (asprintf((char**)(envp + 3), "USER=%s", arg_user? arg_user : "root") < 0) ||
 813                     (asprintf((char**)(envp + 4), "LOGNAME=%s", arg_user? arg_user : "root") < 0)) {
 814                     log_error("Out of memory");
 815                     goto child_fail;
 816                 }
 817
 818                 if ((hn = file_name_from_path(arg_directory)))
 819                         sethostname(hn, strlen(hn));
 820
 821                 if (argc > optind)
 822                         execvpe(argv[optind], argv + optind, (char**) envp);
 823                 else {
 824                         chdir(home ? home : "/root");
 825                         execle("/bin/bash", "-bash", NULL, (char**) envp);
 826                 }
 827
 828                 log_error("execv() failed: %m");
 829
 830         child_fail:
 831                 _exit(EXIT_FAILURE);
 832         }
 833
 834         if (process_pty(master, &mask) < 0)
 835                 goto finish;
 836
 837         if (saved_attr_valid) {
 838                 tcsetattr(STDIN_FILENO, TCSANOW, &saved_attr);
 839                 saved_attr_valid = false;
 840         }
 841
 842         r = wait_for_terminate_and_warn(argc > optind ? argv[optind] : "bash", pid);
 843
 844         if (r < 0)
 845                 r = EXIT_FAILURE;
 846
 847 finish:
 848         if (saved_attr_valid)
 849                 tcsetattr(STDIN_FILENO, TCSANOW, &saved_attr);
 850
 851         if (master >= 0)
 852                 close_nointr_nofail(master);
 853
 854         if (oldcg)
 855                 cg_attach(SYSTEMD_CGROUP_CONTROLLER, oldcg, 0);
 856
 857         if (newcg)
 858                 cg_kill_recursive_and_wait(SYSTEMD_CGROUP_CONTROLLER, newcg, true);
 859
 860         free(arg_directory);
 861         free(oldcg);
 862         free(newcg);
 863
 864         return r;
 865 }