sys-utils/switch_root.c

   1 /*
   2  * switchroot.c - switch to new root directory and start init.
   3  *
   4  * Copyright 2002-2008 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 #ifndef MS_MOVE
  37 #define MS_MOVE 8192
  38 #endif
  39
  40 enum {
  41         ok,
  42         err_no_directory,
  43         err_usage,
  44 };
  45
  46 /* remove all files/directories below dirName -- don't cross mountpoints */
  47 static int recursiveRemove(char *dirName)
  48 {
  49         struct stat rb;
  50         DIR *dir;
  51         int rc = -1;
  52         int dfd;
  53
  54         if (!(dir = opendir(dirName))) {
  55                 printf("error opening %s: %m\n", dirName);
  56                 goto done;
  57         }
  58
  59         dfd = dirfd(dir);
  60
  61         if (fstat(dfd, &rb)) {
  62                 printf("unable to stat %s: %m\n", dirName);
  63                 goto done;
  64         }
  65
  66         while(1) {
  67                 struct dirent *d;
  68
  69                 errno = 0;
  70                 if (!(d = readdir(dir))) {
  71                         if (errno) {
  72                                 printf("error reading from %s: %m\n", dirName);
  73                                 goto done;
  74                         }
  75                         break;  /* end of directory */
  76                 }
  77
  78                 if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
  79                         continue;
  80
  81                 if (d->d_type == DT_DIR) {
  82                         struct stat sb;
  83
  84                         if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
  85                                 printf("failed to stat %s/%s: %m\n",
  86                                                 dirName, d->d_name);
  87                                 continue;
  88                         }
  89
  90                         /* remove subdirectories if device is same as dir */
  91                         if (sb.st_dev == rb.st_dev) {
  92                                 char subdir[ strlen(dirName) +
  93                                              strlen(d->d_name) + 2 ];
  94
  95                                 sprintf(subdir, "%s/%s", dirName, d->d_name);
  96                                 recursiveRemove(subdir);
  97                         } else
  98                                 continue;
  99                 }
 100
 101                 if (unlinkat(dfd, d->d_name,
 102                              d->d_type == DT_DIR ? AT_REMOVEDIR : 0))
 103                         printf("failed to unlink %s/%s: %m\n", dirName, d->d_name);
 104         }
 105
 106         rc = 0; /* success */
 107
 108 done:
 109         if (dir)
 110                 closedir(dir);
 111         return rc;
 112 }
 113
 114 static int switchroot(const char *newroot)
 115 {
 116         /*  Don't try to unmount the old "/", there's no way to do it. */
 117         const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
 118         int errnum;
 119         int i;
 120
 121         for (i = 0; umounts[i] != NULL; i++) {
 122                 char newmount[PATH_MAX];
 123                 strcpy(newmount, newroot);
 124                 strcat(newmount, umounts[i]);
 125                 if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
 126                         fprintf(stderr, "Error mount moving old %s %s %m\n",
 127                                 umounts[i], newmount);
 128                         fprintf(stderr, "Forcing unmount of %s\n", umounts[i]);
 129                         umount2(umounts[i], MNT_FORCE);
 130                 }
 131         }
 132
 133         if (chdir(newroot) < 0) {
 134                 errnum=errno;
 135                 fprintf(stderr, "switchroot: chdir failed: %m\n");
 136                 errno=errnum;
 137                 return -1;
 138         }
 139         recursiveRemove("/");
 140         if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
 141                 errnum = errno;
 142                 fprintf(stderr, "switchroot: mount failed: %m\n");
 143                 errno = errnum;
 144                 return -1;
 145         }
 146
 147         if (chroot(".")) {
 148                 errnum = errno;
 149                 fprintf(stderr, "switchroot: chroot failed: %m\n");
 150                 errno = errnum;
 151                 return -2;
 152         }
 153         return 1;
 154 }
 155
 156 static void usage(FILE *output)
 157 {
 158         fprintf(output, "usage: switchroot <newrootdir> <init> <args to init>\n");
 159         if (output == stderr)
 160                 exit(err_usage);
 161         exit(ok);
 162 }
 163
 164 int main(int argc, char *argv[])
 165 {
 166         char *newroot = argv[1];
 167         char *init = argv[2];
 168         char **initargs = &argv[2];
 169
 170         if (newroot == NULL || newroot[0] == '\0' ||
 171             init == NULL || init[0] == '\0' ) {
 172                 usage(stderr);
 173         }
 174
 175         if (switchroot(newroot) < 0) {
 176                 fprintf(stderr, "switchroot has failed.  Sorry.\n");
 177                 return 1;
 178         }
 179         if (access(initargs[0], X_OK))
 180                 fprintf(stderr, "WARNING: can't access %s\n", initargs[0]);
 181
 182         /* get session leader */
 183         setsid();
 184         /* set controlling terminal */
 185         ioctl (0, TIOCSCTTY, 1);
 186
 187         execv(initargs[0], initargs);
 188 }
 189