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
  24 #define _GNU_SOURCE 1
  25
  26 #include <sys/mount.h>
  27 #include <sys/types.h>
  28 #include <sys/stat.h>
  29 #include <sys/param.h>
  30 #include <fcntl.h>
  31 #include <stdio.h>
  32 #include <stdlib.h>
  33 #include <unistd.h>
  34 #include <string.h>
  35 #include <errno.h>
  36 #include <ctype.h>
  37 #include <dirent.h>
  38
  39 #ifndef MS_MOVE
  40 #define MS_MOVE 8192
  41 #endif
  42
  43 #ifndef MNT_DETACH
  44 #define MNT_DETACH 0x2
  45 #endif
  46
  47 enum {
  48         ok,
  49         err_no_directory,
  50         err_usage,
  51 };
  52
  53 /* remove all files/directories below dirName -- don't cross mountpoints */
  54 static int
  55 recursiveRemove(char * dirName)
  56  {
  57     struct stat sb,rb;
  58     DIR * dir;
  59     struct dirent * d;
  60     char * strBuf = alloca(strlen(dirName) + 1024);
  61
  62     if (!(dir = opendir(dirName))) {
  63         printf("error opening %s: %m\n", dirName);
  64         return 0;
  65     }
  66
  67     if (fstat(dirfd(dir),&rb)) {
  68         printf("unable to stat %s: %m\n", dirName);
  69         closedir(dir);
  70         return 0;
  71     }
  72
  73     errno = 0;
  74     while ((d = readdir(dir))) {
  75         errno = 0;
  76
  77         if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, "..")) {
  78             errno = 0;
  79             continue;
  80         }
  81
  82         strcpy(strBuf, dirName);
  83         strcat(strBuf, "/");
  84         strcat(strBuf, d->d_name);
  85
  86         if (lstat(strBuf, &sb)) {
  87             printf("failed to stat %s: %m\n", strBuf);
  88             errno = 0;
  89             continue;
  90         }
  91
  92         /* only descend into subdirectories if device is same as dir */
  93         if (S_ISDIR(sb.st_mode)) {
  94             if (sb.st_dev == rb.st_dev) {
  95                 recursiveRemove(strBuf);
  96                 if (rmdir(strBuf))
  97                     printf("failed to rmdir %s: %m\n", strBuf);
  98             }
  99             errno = 0;
 100             continue;
 101         }
 102         if (unlink(strBuf)) {
 103             printf("failed to remove %s: %m\n", strBuf);
 104             errno = 0;
 105             continue;
 106         }
 107     }
 108
 109     if (errno) {
 110         closedir(dir);
 111         printf("error reading from %s: %m\n", dirName);
 112         return 1;
 113     }
 114
 115     closedir(dir);
 116
 117     return 0;
 118  }
 119
 120 static int switchroot(const char *newroot)
 121 {
 122         /*  Don't try to unmount the old "/", there's no way to do it. */
 123         const char *umounts[] = { "/dev", "/proc", "/sys", NULL };
 124         int errnum;
 125         int i;
 126
 127         for (i = 0; umounts[i] != NULL; i++) {
 128                 char newmount[PATH_MAX];
 129                 strcpy(newmount, newroot);
 130                 strcat(newmount, umounts[i]);
 131                 if (mount(umounts[i], newmount, NULL, MS_MOVE, NULL) < 0) {
 132                         fprintf(stderr, "Error mount moving old %s %s %m\n",
 133                                 umounts[i], newmount);
 134                         fprintf(stderr, "Forcing unmount of %s\n", umounts[i]);
 135                         umount2(umounts[i], MNT_FORCE);
 136                 }
 137         }
 138
 139         if (chdir(newroot) < 0) {
 140           errnum=errno;
 141           fprintf(stderr, "switchroot: chdir failed: %m\n");
 142           errno=errnum;
 143           return -1;
 144         }
 145         recursiveRemove("/");
 146         if (mount(newroot, "/", NULL, MS_MOVE, NULL) < 0) {
 147                 errnum = errno;
 148                 fprintf(stderr, "switchroot: mount failed: %m\n");
 149                 errno = errnum;
 150                 return -1;
 151         }
 152
 153         if (chroot(".")) {
 154                 errnum = errno;
 155                 fprintf(stderr, "switchroot: chroot failed: %m\n");
 156                 errno = errnum;
 157                 return -2;
 158         }
 159         return 1;
 160 }
 161
 162 static void usage(FILE *output)
 163 {
 164         fprintf(output, "usage: switchroot <newrootdir> <init> <args to init>\n");
 165         if (output == stderr)
 166                 exit(err_usage);
 167         exit(ok);
 168 }
 169
 170 int main(int argc, char *argv[])
 171 {
 172         char *newroot = argv[1];
 173         char *init = argv[2];
 174         char **initargs = &argv[2];
 175
 176         if (newroot == NULL || newroot[0] == '\0' ||
 177             init == NULL || init[0] == '\0' ) {
 178                 usage(stderr);
 179         }
 180
 181         if (switchroot(newroot) < 0) {
 182           fprintf(stderr, "switchroot has failed.  Sorry.\n");
 183           return 1;
 184         }
 185         if (access(initargs[0], X_OK))
 186           fprintf(stderr, "WARNING: can't access %s\n", initargs[0]);
 187
 188         /* get session leader */
 189         setsid();
 190         /* set controlling terminal */
 191         ioctl (0, TIOCSCTTY, 1);
 192
 193         execv(initargs[0], initargs);
 194 }
 195
 196 /*
 197  * vim:noet:ts=8:sw=8:sts=8
 198  */