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/statfs.h>
  27 #include <sys/param.h>
  28 #include <fcntl.h>
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31 #include <unistd.h>
  32 #include <string.h>
  33 #include <errno.h>
  34 #include <ctype.h>
  35 #include <dirent.h>
  36
  37 #include "c.h"
  38 #include "nls.h"
  39 #include "closestream.h"
  40 #include "statfs_magic.h"
  41
  42 #ifndef MS_MOVE
  43 #define MS_MOVE 8192
  44 #endif
  45
  46 #ifndef MNT_DETACH
  47 #define MNT_DETACH       0x00000002     /* Just detach from the tree */
  48 #endif
  49
  50 /* remove all files/directories below dirName -- don't cross mountpoints */
  51 static int recursiveRemove(int fd)
  52 {
  53         struct stat rb;
  54         DIR *dir;
  55         int rc = -1;
  56         int dfd;
  57
  58         if (!(dir = fdopendir(fd))) {
  59                 warn(_("failed to open directory"));
  60                 goto done;
  61         }
  62
  63         /* fdopendir() precludes us from continuing to use the input fd */
  64         dfd = dirfd(dir);
  65
  66         if (fstat(dfd, &rb)) {
  67                 warn(_("stat failed"));
  68                 goto done;
  69         }
  70
  71         while(1) {
  72                 struct dirent *d;
  73                 int isdir = 0;
  74
  75                 errno = 0;
  76                 if (!(d = readdir(dir))) {
  77                         if (errno) {
  78                                 warn(_("failed to read directory"));
  79                                 goto done;
  80                         }
  81                         break;  /* end of directory */
  82                 }
  83
  84                 if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
  85                         continue;
  86 #ifdef _DIRENT_HAVE_D_TYPE
  87                 if (d->d_type == DT_DIR || d->d_type == DT_UNKNOWN)
  88 #endif
  89                 {
  90                         struct stat sb;
  91
  92                         if (fstatat(dfd, d->d_name, &sb, AT_SYMLINK_NOFOLLOW)) {
  93                                 warn(_("stat of %s failed"), d->d_name);
  94                                 continue;
  95                         }
  96
  97                         /* skip if device is not the same */
  98                         if (sb.st_dev != rb.st_dev)
  99                                 continue;
 100
 101                         /* remove subdirectories */
 102                         if (S_ISDIR(sb.st_mode)) {
 103                                 int cfd;
 104
 105                                 cfd = openat(dfd, d->d_name, O_RDONLY);
 106                                 if (cfd >= 0) {
 107                                         recursiveRemove(cfd);
 108                                         close(cfd);
 109                                 }
 110                                 isdir = 1;
 111                         }
 112                 }
 113
 114                 if (unlinkat(dfd, d->d_name, isdir ? AT_REMOVEDIR : 0))
 115                         warn(_("failed to unlink %s"), d->d_name);
 116         }
 117
 118         rc = 0; /* success */
 119
 120 done:
 121         if (dir)
 122                 closedir(dir);
 123         return rc;
 124 }
 125
 126 static int switchroot(const char *newroot)
 127 {
 128         /*  Don't try to unmount the old "/", there's no way to do it. */
 129         const char *umounts[] = { "/dev", "/proc", "/sys", "/run", NULL };
 130         int i;
 131         int cfd;
 132         pid_t pid;
 133         struct stat newroot_stat, sb;
 134
 135         if (stat(newroot, &newroot_stat) != 0) {
 136                 warn(_("stat of %s failed"), newroot);
 137                 return -1;
 138         }
 139
 140         for (i = 0; umounts[i] != NULL; i++) {
 141                 char newmount[PATH_MAX];
 142
 143                 snprintf(newmount, sizeof(newmount), "%s%s", newroot, umounts[i]);
 144
 145                 if ((stat(newmount, &sb) != 0) || (sb.st_dev != newroot_stat.st_dev)) {
 146                         /* mount point seems to be mounted already or stat failed */
 147                         umount2(umounts[i], MNT_DETACH);
 148                         continue;
 149                 }
 150
 151                 if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
 152                         warn(_("failed to mount moving %s to %s"),
 153                                 umounts[i], newmount);
 154                         warnx(_("forcing unmount of %s"), umounts[i]);
 155                         umount2(umounts[i], MNT_FORCE);
 156                 }
 157         }
 158
 159         if (chdir(newroot)) {
 160                 warn(_("failed to change directory to %s"), newroot);
 161                 return -1;
 162         }
 163
 164         cfd = open("/", O_RDONLY);
 165         if (cfd < 0) {
 166                 warn(_("cannot open %s"), "/");
 167                 return -1;
 168         }
 169
 170         if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
 171                 close(cfd);
 172                 warn(_("failed to mount moving %s to /"), newroot);
 173                 return -1;
 174         }
 175
 176         if (chroot(".")) {
 177                 close(cfd);
 178                 warn(_("failed to change root"));
 179                 return -1;
 180         }
 181
 182         pid = fork();
 183         if (pid <= 0) {
 184                 struct statfs stfs;
 185
 186                 if (fstatfs(cfd, &stfs) == 0 &&
 187                     (F_TYPE_EQUAL(stfs.f_type, STATFS_RAMFS_MAGIC) ||
 188                      F_TYPE_EQUAL(stfs.f_type, STATFS_TMPFS_MAGIC)))
 189                         recursiveRemove(cfd);
 190                 else
 191                         warn(_("old root filesystem is not an initramfs"));
 192                 if (pid == 0)
 193                         exit(EXIT_SUCCESS);
 194         }
 195
 196         close(cfd);
 197         return 0;
 198 }
 199
 200 static void __attribute__((__noreturn__)) usage(FILE *output)
 201 {
 202         fputs(USAGE_HEADER, output);
 203         fprintf(output, _(" %s [options] <newrootdir> <init> <args to init>\n"),
 204                 program_invocation_short_name);
 205
 206         fputs(USAGE_SEPARATOR, output);
 207         fputs(_("Switch to another filesystem as the root of the mount tree.\n"), output);
 208
 209         fputs(USAGE_OPTIONS, output);
 210         fputs(USAGE_HELP, output);
 211         fputs(USAGE_VERSION, output);
 212         fprintf(output, USAGE_MAN_TAIL("switch_root(8)"));
 213
 214         exit(output == stderr ? EXIT_FAILURE : EXIT_SUCCESS);
 215 }
 216
 217 int main(int argc, char *argv[])
 218 {
 219         char *newroot, *init, **initargs;
 220         atexit(close_stdout);
 221
 222         if (argv[1] && (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")))
 223                 usage(stdout);
 224         if (argv[1] && (!strcmp(argv[1], "--version") || !strcmp(argv[1], "-V"))) {
 225                 printf(UTIL_LINUX_VERSION);
 226                 return EXIT_SUCCESS;
 227         }
 228         if (argc < 3)
 229                 usage(stderr);
 230
 231         newroot = argv[1];
 232         init = argv[2];
 233         initargs = &argv[2];
 234
 235         if (!*newroot || !*init)
 236                 usage(stderr);
 237
 238         if (switchroot(newroot))
 239                 errx(EXIT_FAILURE, _("failed. Sorry."));
 240
 241         if (access(init, X_OK))
 242                 warn(_("cannot access %s"), init);
 243
 244         execv(init, initargs);
 245         err(EXIT_FAILURE, _("failed to execute %s"), init);
 246 }
 247