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 #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(int fd)
  43 {
  44         struct stat rb;
  45         DIR *dir;
  46         int rc = -1;
  47         int dfd;
  48
  49         if (!(dir = fdopendir(fd))) {
  50                 warn("failed to open directory");
  51                 goto done;
  52         }
  53
  54         /* fdopendir() precludes us from continuing to use the input fd */
  55         dfd = dirfd(dir);
  56
  57         if (fstat(dfd, &rb)) {
  58                 warn("failed to stat directory");
  59                 goto done;
  60         }
  61
  62         while(1) {
  63                 struct dirent *d;
  64
  65                 errno = 0;
  66                 if (!(d = readdir(dir))) {
  67                         if (errno) {
  68                                 warn("failed to read directory");
  69                                 goto done;
  70                         }
  71                         break;  /* end of directory */
  72                 }
  73
  74                 if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
  75                         continue;
  76
  77                 if (d->d_type == DT_DIR) {
  78                         struct stat sb;
  79
  80                         if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
  81                                 warn("failed to stat %s", d->d_name);
  82                                 continue;
  83                         }
  84
  85                         /* remove subdirectories if device is same as dir */
  86                         if (sb.st_dev == rb.st_dev) {
  87                                 int cfd;
  88
  89                                 cfd = openat(dfd, d->d_name, O_RDONLY);
  90                                 if (cfd >= 0) {
  91                                         recursiveRemove(cfd);
  92                                         close(cfd);
  93                                 }
  94                         } else
  95                                 continue;
  96                 }
  97
  98                 if (unlinkat(dfd, d->d_name,
  99                              d->d_type == DT_DIR ? AT_REMOVEDIR : 0))
 100                         warn("failed to unlink %s", d->d_name);
 101         }
 102
 103         rc = 0; /* success */
 104
 105 done:
 106         if (dir)
 107                 closedir(dir);
 108         return rc;
 109 }
 110
 111 static int switchroot(const char *newroot)
 112 {
 113         /*  Don't try to unmount the old "/", there's no way to do it. */
 114         const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
 115         int i;
 116         int cfd;
 117
 118         for (i = 0; umounts[i] != NULL; i++) {
 119                 char newmount[PATH_MAX];
 120
 121                 snprintf(newmount, sizeof(newmount), "%s%s", newroot, umounts[i]);
 122
 123                 if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
 124                         warn("failed to mount moving %s to %s",
 125                                 umounts[i], newmount);
 126                         warnx("forcing unmount of %s", umounts[i]);
 127                         umount2(umounts[i], MNT_FORCE);
 128                 }
 129         }
 130
 131         if (chdir(newroot)) {
 132                 warn("failed to change directory to %s", newroot);
 133                 return -1;
 134         }
 135
 136         cfd = open("/", O_RDONLY);
 137         if (cfd >= 0) {
 138                 recursiveRemove(cfd);
 139                 close(cfd);
 140         }
 141
 142         if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
 143                 warn("failed to mount moving %s to /", newroot);
 144                 return -1;
 145         }
 146
 147         if (chroot(".")) {
 148                 warn("failed to change root");
 149                 return -1;
 150         }
 151         return 0;
 152 }
 153
 154 static void usage(FILE *output)
 155 {
 156         fprintf(output, "usage: %s <newrootdir> <init> <args to init>\n",
 157                         program_invocation_short_name);
 158         exit(output == stderr ? EXIT_FAILURE : EXIT_SUCCESS);
 159 }
 160
 161 static void version(void)
 162 {
 163         fprintf(stdout,  "%s from %s\n", program_invocation_short_name,
 164                         PACKAGE_STRING);
 165         exit(EXIT_SUCCESS);
 166 }
 167
 168 int main(int argc, char *argv[])
 169 {
 170         char *newroot, *init, **initargs;
 171
 172         if (argv[1] && (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
 173                 usage(stdout);
 174         if (argv[1] && (!strcmp(argv[1], "--version") || !strcmp(argv[1], "-V")))
 175                 version();
 176         if (argc < 3)
 177                 usage(stderr);
 178
 179         newroot = argv[1];
 180         init = argv[2];
 181         initargs = &argv[2];
 182
 183         if (!*newroot || !*init)
 184                 usage(stderr);
 185
 186         if (switchroot(newroot))
 187                 errx(EXIT_FAILURE, "failed. Sorry.");
 188
 189         if (access(init, X_OK))
 190                 warn("cannot access %s", init);
 191
 192         /* get session leader */
 193         setsid();
 194
 195         /* set controlling terminal */
 196         if (ioctl (0, TIOCSCTTY, 1))
 197                 warn("failed to TIOCSCTTY");
 198
 199         execv(init, initargs);
 200         err(EXIT_FAILURE, "failed to execute %s", init);
 201 }
 202