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