sys-utils/switch_root.c

   1 /*
   2  * switchroot.c - switch to new root directory and start init.
   3  *
   4  * Copyright 2002-2009 Red Hat, Inc.  All rights reserved.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  *
  19  * Authors:
  20  *      Peter Jones <pjones@redhat.com>
  21  *      Jeremy Katz <katzj@redhat.com>
  22  */
  23 #include <sys/mount.h>
  24 #include <sys/types.h>
  25 #include <sys/stat.h>
  26 #include <sys/param.h>
  27 #include <fcntl.h>
  28 #include <stdio.h>
  29 #include <stdlib.h>
  30 #include <unistd.h>
  31 #include <string.h>
  32 #include <errno.h>
  33 #include <ctype.h>
  34 #include <dirent.h>
  35
  36 #include "c.h"
  37 #include "nls.h"
  38 #include "closestream.h"
  39
  40 #ifndef MS_MOVE
  41 #define MS_MOVE 8192
  42 #endif
  43
  44 #ifndef MNT_DETACH
  45 #define MNT_DETACH       0x00000002     /* Just detach from the tree */
  46 #endif
  47
  48 /* remove all files/directories below dirName -- don't cross mountpoints */
  49 static int recursiveRemove(int fd)
  50 {
  51         struct stat rb;
  52         DIR *dir;
  53         int rc = -1;
  54         int dfd;
  55
  56         if (!(dir = fdopendir(fd))) {
  57                 warn(_("failed to open directory"));
  58                 goto done;
  59         }
  60
  61         /* fdopendir() precludes us from continuing to use the input fd */
  62         dfd = dirfd(dir);
  63
  64         if (fstat(dfd, &rb)) {
  65                 warn(_("failed to stat directory"));
  66                 goto done;
  67         }
  68
  69         while(1) {
  70                 struct dirent *d;
  71
  72                 errno = 0;
  73                 if (!(d = readdir(dir))) {
  74                         if (errno) {
  75                                 warn(_("failed to read directory"));
  76                                 goto done;
  77                         }
  78                         break;  /* end of directory */
  79                 }
  80
  81                 if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
  82                         continue;
  83
  84                 if (d->d_type == DT_DIR) {
  85                         struct stat sb;
  86
  87                         if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
  88                                 warn(_("failed to stat %s"), d->d_name);
  89                                 continue;
  90                         }
  91
  92                         /* remove subdirectories if device is same as dir */
  93                         if (sb.st_dev == rb.st_dev) {
  94                                 int cfd;
  95
  96                                 cfd = openat(dfd, d->d_name, O_RDONLY);
  97                                 if (cfd >= 0) {
  98                                         recursiveRemove(cfd);
  99                                         close(cfd);
 100                                 }
 101                         } else
 102                                 continue;
 103                 }
 104
 105                 if (unlinkat(dfd, d->d_name,
 106                              d->d_type == DT_DIR ? AT_REMOVEDIR : 0))
 107                         warn(_("failed to unlink %s"), d->d_name);
 108         }
 109
 110         rc = 0; /* success */
 111
 112 done:
 113         if (dir)
 114                 closedir(dir);
 115         return rc;
 116 }
 117
 118 static int switchroot(const char *newroot)
 119 {
 120         /*  Don't try to unmount the old "/", there's no way to do it. */
 121         const char *umounts[] = { "/dev", "/proc", "/sys", "/run", NULL };
 122         int i;
 123         int cfd;
 124         pid_t pid;
 125         struct stat newroot_stat, sb;
 126
 127         if (stat(newroot, &newroot_stat) != 0) {
 128                 warn(_("failed to stat directory %s"), newroot);
 129                 return -1;
 130         }
 131
 132         for (i = 0; umounts[i] != NULL; i++) {
 133                 char newmount[PATH_MAX];
 134
 135                 snprintf(newmount, sizeof(newmount), "%s%s", newroot, umounts[i]);
 136
 137                 if ((stat(newmount, &sb) != 0) || (sb.st_dev != newroot_stat.st_dev)) {
 138                         /* mount point seems to be mounted already or stat failed */
 139                         umount2(umounts[i], MNT_DETACH);
 140                         continue;
 141                 }
 142
 143                 if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
 144                         warn(_("failed to mount moving %s to %s"),
 145                                 umounts[i], newmount);
 146                         warnx(_("forcing unmount of %s"), umounts[i]);
 147                         umount2(umounts[i], MNT_FORCE);
 148                 }
 149         }
 150
 151         if (chdir(newroot)) {
 152                 warn(_("failed to change directory to %s"), newroot);
 153                 return -1;
 154         }
 155
 156         cfd = open("/", O_RDONLY);
 157
 158         if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
 159                 close(cfd);
 160                 warn(_("failed to mount moving %s to /"), newroot);
 161                 return -1;
 162         }
 163
 164         if (chroot(".")) {
 165                 close(cfd);
 166                 warn(_("failed to change root"));
 167                 return -1;
 168         }
 169
 170         if (cfd >= 0) {
 171                 pid = fork();
 172                 if (pid <= 0) {
 173                         recursiveRemove(cfd);
 174                         if (pid == 0)
 175                                 exit(EXIT_SUCCESS);
 176                 }
 177                 close(cfd);
 178         }
 179         return 0;
 180 }
 181
 182 static void __attribute__((__noreturn__)) usage(FILE *output)
 183 {
 184         fputs(USAGE_HEADER, output);
 185         fprintf(output, _(" %s [options] <newrootdir> <init> <args to init>\n"),
 186                 program_invocation_short_name);
 187         fputs(USAGE_OPTIONS, output);
 188         fputs(USAGE_HELP, output);
 189         fputs(USAGE_VERSION, output);
 190         fprintf(output, USAGE_MAN_TAIL("switch_root(8)"));
 191
 192         exit(output == stderr ? EXIT_FAILURE : EXIT_SUCCESS);
 193 }
 194
 195 int main(int argc, char *argv[])
 196 {
 197         char *newroot, *init, **initargs;
 198         atexit(close_stdout);
 199
 200         if (argv[1] && (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
 201                 usage(stdout);
 202         if (argv[1] && (!strcmp(argv[1], "--version") || !strcmp(argv[1], "-V"))) {
 203                 printf(UTIL_LINUX_VERSION);
 204                 return EXIT_SUCCESS;
 205         }
 206         if (argc < 3)
 207                 usage(stderr);
 208
 209         newroot = argv[1];
 210         init = argv[2];
 211         initargs = &argv[2];
 212
 213         if (!*newroot || !*init)
 214                 usage(stderr);
 215
 216         if (switchroot(newroot))
 217                 errx(EXIT_FAILURE, _("failed. Sorry."));
 218
 219         if (access(init, X_OK))
 220                 warn(_("cannot access %s"), init);
 221
 222         execv(init, initargs);
 223         err(EXIT_FAILURE, _("failed to execute %s"), init);
 224 }
 225