src/shared/switch-root.c

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