src/shared/switch-root.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2012 Harald Hoyer, Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <limits.h>
  23 #include <stdbool.h>
  24 #include <stdio.h>
  25 #include <sys/mount.h>
  26 #include <sys/stat.h>
  27 #include <unistd.h>
  28
  29 #include "base-filesystem.h"
  30 #include "fd-util.h"
  31 #include "log.h"
  32 #include "missing.h"
  33 #include "mkdir.h"
  34 #include "path-util.h"
  35 #include "rm-rf.h"
  36 #include "stdio-util.h"
  37 #include "string-util.h"
  38 #include "switch-root.h"
  39 #include "user-util.h"
  40 #include "util.h"
  41
  42 int switch_root(const char *new_root, const char *oldroot, bool detach_oldroot,  unsigned long mountflags) {
  43
  44         /*  Don't try to unmount/move the old "/", there's no way to do it. */
  45         static const char move_mounts[] =
  46                 "/dev\0"
  47                 "/proc\0"
  48                 "/sys\0"
  49                 "/run\0";
  50
  51         _cleanup_close_ int old_root_fd = -1;
  52         struct stat new_root_stat;
  53         bool old_root_remove;
  54         const char *i, *temporary_old_root;
  55
  56         if (path_equal(new_root, "/"))
  57                 return 0;
  58
  59         temporary_old_root = strjoina(new_root, oldroot);
  60         mkdir_p_label(temporary_old_root, 0755);
  61
  62         old_root_remove = in_initrd();
  63
  64         if (stat(new_root, &new_root_stat) < 0)
  65                 return log_error_errno(errno, "Failed to stat directory %s: %m", new_root);
  66
  67         /* Work-around for kernel design: the kernel refuses switching
  68          * root if any file systems are mounted MS_SHARED. Hence
  69          * remount them MS_PRIVATE here as a work-around.
  70          *
  71          * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
  72         if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
  73                 log_warning_errno(errno, "Failed to make \"/\" private mount: %m");
  74
  75         NULSTR_FOREACH(i, move_mounts) {
  76                 char new_mount[PATH_MAX];
  77                 struct stat sb;
  78
  79                 xsprintf(new_mount, "%s%s", new_root, i);
  80
  81                 mkdir_p_label(new_mount, 0755);
  82
  83                 if ((stat(new_mount, &sb) < 0) ||
  84                     sb.st_dev != new_root_stat.st_dev) {
  85
  86                         /* Mount point seems to be mounted already or
  87                          * stat failed. Unmount the old mount
  88                          * point. */
  89                         if (umount2(i, MNT_DETACH) < 0)
  90                                 log_warning_errno(errno, "Failed to unmount %s: %m", i);
  91                         continue;
  92                 }
  93
  94                 if (mount(i, new_mount, NULL, mountflags, NULL) < 0) {
  95                         if (mountflags & MS_MOVE) {
  96                                 log_error_errno(errno, "Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
  97
  98                                 if (umount2(i, MNT_FORCE) < 0)
  99                                         log_warning_errno(errno, "Failed to unmount %s: %m", i);
 100                         }
 101                         if (mountflags & MS_BIND)
 102                                 log_error_errno(errno, "Failed to bind mount %s to %s: %m", i, new_mount);
 103
 104                 }
 105         }
 106
 107         /* Do not fail, if base_filesystem_create() fails. Not all
 108          * switch roots are like base_filesystem_create() wants them
 109          * to look like. They might even boot, if they are RO and
 110          * don't have the FS layout. Just ignore the error and
 111          * switch_root() nevertheless. */
 112         (void) base_filesystem_create(new_root, UID_INVALID, GID_INVALID);
 113
 114         if (chdir(new_root) < 0)
 115                 return log_error_errno(errno, "Failed to change directory to %s: %m", new_root);
 116
 117         if (old_root_remove) {
 118                 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
 119                 if (old_root_fd < 0)
 120                         log_warning_errno(errno, "Failed to open root directory: %m");
 121         }
 122
 123         /* We first try a pivot_root() so that we can umount the old
 124          * root dir. In many cases (i.e. where rootfs is /), that's
 125          * not possible however, and hence we simply overmount root */
 126         if (pivot_root(new_root, temporary_old_root) >= 0) {
 127
 128                 /* Immediately get rid of the old root, if detach_oldroot is set.
 129                  * Since we are running off it we need to do this lazily. */
 130                 if (detach_oldroot && umount2(oldroot, MNT_DETACH) < 0)
 131                         log_error_errno(errno, "Failed to lazily umount old root dir %s, %s: %m",
 132                                   oldroot,
 133                                   errno == ENOENT ? "ignoring" : "leaving it around");
 134
 135         } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0)
 136                 return log_error_errno(errno, "Failed to mount moving %s to /: %m", new_root);
 137
 138         if (chroot(".") < 0)
 139                 return log_error_errno(errno, "Failed to change root: %m");
 140
 141         if (chdir("/") < 0)
 142                 return log_error_errno(errno, "Failed to change directory: %m");
 143
 144         if (old_root_fd >= 0) {
 145                 struct stat rb;
 146
 147                 if (fstat(old_root_fd, &rb) < 0)
 148                         log_warning_errno(errno, "Failed to stat old root directory, leaving: %m");
 149                 else {
 150                         (void) rm_rf_children(old_root_fd, 0, &rb);
 151                         old_root_fd = -1;
 152                 }
 153         }
 154
 155         return 0;
 156 }