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 <limits.h>
  25 #include <stdbool.h>
  26 #include <stdio.h>
  27 #include <sys/mount.h>
  28 #include <sys/stat.h>
  29 #include <unistd.h>
  30
  31 #include "base-filesystem.h"
  32 #include "fd-util.h"
  33 #include "log.h"
  34 #include "missing.h"
  35 #include "mkdir.h"
  36 #include "path-util.h"
  37 #include "rm-rf.h"
  38 #include "string-util.h"
  39 #include "switch-root.h"
  40 #include "user-util.h"
  41 #include "util.h"
  42
  43 int switch_root(const char *new_root, const char *oldroot, bool detach_oldroot,  unsigned long mountflags) {
  44
  45         /*  Don't try to unmount/move the old "/", there's no way to do it. */
  46         static const char move_mounts[] =
  47                 "/dev\0"
  48                 "/proc\0"
  49                 "/sys\0"
  50                 "/run\0";
  51
  52         _cleanup_close_ int old_root_fd = -1;
  53         struct stat new_root_stat;
  54         bool old_root_remove;
  55         const char *i, *temporary_old_root;
  56
  57         if (path_equal(new_root, "/"))
  58                 return 0;
  59
  60         temporary_old_root = strjoina(new_root, oldroot);
  61         mkdir_p_label(temporary_old_root, 0755);
  62
  63         old_root_remove = in_initrd();
  64
  65         if (stat(new_root, &new_root_stat) < 0)
  66                 return log_error_errno(errno, "Failed to stat directory %s: %m", new_root);
  67
  68         /* Work-around for kernel design: the kernel refuses switching
  69          * root if any file systems are mounted MS_SHARED. Hence
  70          * remount them MS_PRIVATE here as a work-around.
  71          *
  72          * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
  73         if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
  74                 log_warning_errno(errno, "Failed to make \"/\" private mount: %m");
  75
  76         NULSTR_FOREACH(i, move_mounts) {
  77                 char new_mount[PATH_MAX];
  78                 struct stat sb;
  79
  80                 snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
  81
  82                 mkdir_p_label(new_mount, 0755);
  83
  84                 if ((stat(new_mount, &sb) < 0) ||
  85                     sb.st_dev != new_root_stat.st_dev) {
  86
  87                         /* Mount point seems to be mounted already or
  88                          * stat failed. Unmount the old mount
  89                          * point. */
  90                         if (umount2(i, MNT_DETACH) < 0)
  91                                 log_warning_errno(errno, "Failed to unmount %s: %m", i);
  92                         continue;
  93                 }
  94
  95                 if (mount(i, new_mount, NULL, mountflags, NULL) < 0) {
  96                         if (mountflags & MS_MOVE) {
  97                                 log_error_errno(errno, "Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
  98
  99                                 if (umount2(i, MNT_FORCE) < 0)
 100                                         log_warning_errno(errno, "Failed to unmount %s: %m", i);
 101                         }
 102                         if (mountflags & MS_BIND)
 103                                 log_error_errno(errno, "Failed to bind mount %s to %s: %m", i, new_mount);
 104
 105                 }
 106         }
 107
 108         /* Do not fail, if base_filesystem_create() fails. Not all
 109          * switch roots are like base_filesystem_create() wants them
 110          * to look like. They might even boot, if they are RO and
 111          * don't have the FS layout. Just ignore the error and
 112          * switch_root() nevertheless. */
 113         (void) base_filesystem_create(new_root, UID_INVALID, GID_INVALID);
 114
 115         if (chdir(new_root) < 0)
 116                 return log_error_errno(errno, "Failed to change directory to %s: %m", new_root);
 117
 118         if (old_root_remove) {
 119                 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
 120                 if (old_root_fd < 0)
 121                         log_warning_errno(errno, "Failed to open root directory: %m");
 122         }
 123
 124         /* We first try a pivot_root() so that we can umount the old
 125          * root dir. In many cases (i.e. where rootfs is /), that's
 126          * not possible however, and hence we simply overmount root */
 127         if (pivot_root(new_root, temporary_old_root) >= 0) {
 128
 129                 /* Immediately get rid of the old root, if detach_oldroot is set.
 130                  * Since we are running off it we need to do this lazily. */
 131                 if (detach_oldroot && umount2(oldroot, MNT_DETACH) < 0)
 132                         log_error_errno(errno, "Failed to lazily umount old root dir %s, %s: %m",
 133                                   oldroot,
 134                                   errno == ENOENT ? "ignoring" : "leaving it around");
 135
 136         } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0)
 137                 return log_error_errno(errno, "Failed to mount moving %s to /: %m", new_root);
 138
 139         if (chroot(".") < 0)
 140                 return log_error_errno(errno, "Failed to change root: %m");
 141
 142         if (chdir("/") < 0)
 143                 return log_error_errno(errno, "Failed to change directory: %m");
 144
 145         if (old_root_fd >= 0) {
 146                 struct stat rb;
 147
 148                 if (fstat(old_root_fd, &rb) < 0)
 149                         log_warning_errno(errno, "Failed to stat old root directory, leaving: %m");
 150                 else {
 151                         (void) rm_rf_children(old_root_fd, 0, &rb);
 152                         old_root_fd = -1;
 153                 }
 154         }
 155
 156         return 0;
 157 }