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 #include <err.h>
  36
  37 #ifndef MS_MOVE
  38 #define MS_MOVE 8192
  39 #endif
  40
  41 /* remove all files/directories below dirName -- don't cross mountpoints */
  42 static int recursiveRemove(char *dirName)
  43 {
  44         struct stat rb;
  45         DIR *dir;
  46         int rc = -1;
  47         int dfd;
  48
  49         if (!(dir = opendir(dirName))) {
  50                 warn("failed to open %s", dirName);
  51                 goto done;
  52         }
  53
  54         dfd = dirfd(dir);
  55
  56         if (fstat(dfd, &rb)) {
  57                 warn("failed to stat %s", dirName);
  58                 goto done;
  59         }
  60
  61         while(1) {
  62                 struct dirent *d;
  63
  64                 errno = 0;
  65                 if (!(d = readdir(dir))) {
  66                         if (errno) {
  67                                 warn("failed to read %s", dirName);
  68                                 goto done;
  69                         }
  70                         break;  /* end of directory */
  71                 }
  72
  73                 if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
  74                         continue;
  75
  76                 if (d->d_type == DT_DIR) {
  77                         struct stat sb;
  78
  79                         if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
  80                                 warn("failed to stat %s/%s", dirName, d->d_name);
  81                                 continue;
  82                         }
  83
  84                         /* remove subdirectories if device is same as dir */
  85                         if (sb.st_dev == rb.st_dev) {
  86                                 char subdir[ strlen(dirName) +
  87                                              strlen(d->d_name) + 2 ];
  88
  89                                 sprintf(subdir, "%s/%s", dirName, d->d_name);
  90                                 recursiveRemove(subdir);
  91                         } else
  92                                 continue;
  93                 }
  94
  95                 if (unlinkat(dfd, d->d_name,
  96                              d->d_type == DT_DIR ? AT_REMOVEDIR : 0))
  97                         warn("failed to unlink %s/%s", dirName, d->d_name);
  98         }
  99
 100         rc = 0; /* success */
 101
 102 done:
 103         if (dir)
 104                 closedir(dir);
 105         return rc;
 106 }
 107
 108 static int switchroot(const char *newroot)
 109 {
 110         /*  Don't try to unmount the old "/", there's no way to do it. */
 111         const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
 112         int i;
 113
 114         for (i = 0; umounts[i] != NULL; i++) {
 115                 char newmount[PATH_MAX];
 116
 117                 snprintf(newmount, sizeof(newmount), "%s%s", newroot, umounts[i]);
 118
 119                 if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
 120                         warn("failed to mount moving %s to %s",
 121                                 umounts[i], newmount);
 122                         warnx("forcing unmount of %s", umounts[i]);
 123                         umount2(umounts[i], MNT_FORCE);
 124                 }
 125         }
 126
 127         if (chdir(newroot)) {
 128                 warn("failed to change directory to %s", newroot);
 129                 return -1;
 130         }
 131
 132         recursiveRemove("/");
 133
 134         if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
 135                 warn("failed to mount moving %s to /", newroot);
 136                 return -1;
 137         }
 138
 139         if (chroot(".")) {
 140                 warn("failed to change root");
 141                 return -1;
 142         }
 143         return 0;
 144 }
 145
 146 static void usage(FILE *output)
 147 {
 148         fprintf(output, "usage: %s <newrootdir> <init> <args to init>\n",
 149                         program_invocation_short_name);
 150         exit(output == stderr ? EXIT_FAILURE : EXIT_SUCCESS);
 151 }
 152
 153 static void version(void)
 154 {
 155         fprintf(stdout,  "%s from %s\n", program_invocation_short_name,
 156                         PACKAGE_STRING);
 157         exit(EXIT_SUCCESS);
 158 }
 159
 160 int main(int argc, char *argv[])
 161 {
 162         char *newroot, *init, **initargs;
 163
 164         if (argv[1] && (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
 165                 usage(stdout);
 166         if (argv[1] && (!strcmp(argv[1], "--version") || !strcmp(argv[1], "-V")))
 167                 version();
 168         if (argc < 3)
 169                 usage(stderr);
 170
 171         newroot = argv[1];
 172         init = argv[2];
 173         initargs = &argv[2];
 174
 175         if (!*newroot || !*init)
 176                 usage(stderr);
 177
 178         if (switchroot(newroot))
 179                 errx(EXIT_FAILURE, "failed. Sorry.");
 180
 181         if (access(init, X_OK))
 182                 warn("cannot access %s", init);
 183
 184         /* get session leader */
 185         setsid();
 186
 187         /* set controlling terminal */
 188         if (ioctl (0, TIOCSCTTY, 1))
 189                 warn("failed to TIOCSCTTY");
 190
 191         execv(init, initargs);
 192         err(EXIT_FAILURE, "failed to execute %s", init);
 193 }
 194