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 "stdio-util.h"
  39 #include "string-util.h"
  40 #include "switch-root.h"
  41 #include "user-util.h"
  42 #include "util.h"
  43
  44 int switch_root(const char *new_root, const char *oldroot, bool detach_oldroot,  unsigned long mountflags) {
  45
  46         /*  Don't try to unmount/move the old "/", there's no way to do it. */
  47         static const char move_mounts[] =
  48                 "/dev\0"
  49                 "/proc\0"
  50                 "/sys\0"
  51                 "/run\0";
  52
  53         _cleanup_close_ int old_root_fd = -1;
  54         struct stat new_root_stat;
  55         bool old_root_remove;
  56         const char *i, *temporary_old_root;
  57
  58         if (path_equal(new_root, "/"))
  59                 return 0;
  60
  61         temporary_old_root = strjoina(new_root, oldroot);
  62         mkdir_p_label(temporary_old_root, 0755);
  63
  64         old_root_remove = in_initrd();
  65
  66         if (stat(new_root, &new_root_stat) < 0)
  67                 return log_error_errno(errno, "Failed to stat directory %s: %m", new_root);
  68
  69         /* Work-around for kernel design: the kernel refuses switching
  70          * root if any file systems are mounted MS_SHARED. Hence
  71          * remount them MS_PRIVATE here as a work-around.
  72          *
  73          * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
  74         if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
  75                 log_warning_errno(errno, "Failed to make \"/\" private mount: %m");
  76
  77         NULSTR_FOREACH(i, move_mounts) {
  78                 char new_mount[PATH_MAX];
  79                 struct stat sb;
  80
  81                 xsprintf(new_mount, "%s%s", new_root, i);
  82
  83                 mkdir_p_label(new_mount, 0755);
  84
  85                 if ((stat(new_mount, &sb) < 0) ||
  86                     sb.st_dev != new_root_stat.st_dev) {
  87
  88                         /* Mount point seems to be mounted already or
  89                          * stat failed. Unmount the old mount
  90                          * point. */
  91                         if (umount2(i, MNT_DETACH) < 0)
  92                                 log_warning_errno(errno, "Failed to unmount %s: %m", i);
  93                         continue;
  94                 }
  95
  96                 if (mount(i, new_mount, NULL, mountflags, NULL) < 0) {
  97                         if (mountflags & MS_MOVE) {
  98                                 log_error_errno(errno, "Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
  99
 100                                 if (umount2(i, MNT_FORCE) < 0)
 101                                         log_warning_errno(errno, "Failed to unmount %s: %m", i);
 102                         }
 103                         if (mountflags & MS_BIND)
 104                                 log_error_errno(errno, "Failed to bind mount %s to %s: %m", i, new_mount);
 105
 106                 }
 107         }
 108
 109         /* Do not fail, if base_filesystem_create() fails. Not all
 110          * switch roots are like base_filesystem_create() wants them
 111          * to look like. They might even boot, if they are RO and
 112          * don't have the FS layout. Just ignore the error and
 113          * switch_root() nevertheless. */
 114         (void) base_filesystem_create(new_root, UID_INVALID, GID_INVALID);
 115
 116         if (chdir(new_root) < 0)
 117                 return log_error_errno(errno, "Failed to change directory to %s: %m", new_root);
 118
 119         if (old_root_remove) {
 120                 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
 121                 if (old_root_fd < 0)
 122                         log_warning_errno(errno, "Failed to open root directory: %m");
 123         }
 124
 125         /* We first try a pivot_root() so that we can umount the old
 126          * root dir. In many cases (i.e. where rootfs is /), that's
 127          * not possible however, and hence we simply overmount root */
 128         if (pivot_root(new_root, temporary_old_root) >= 0) {
 129
 130                 /* Immediately get rid of the old root, if detach_oldroot is set.
 131                  * Since we are running off it we need to do this lazily. */
 132                 if (detach_oldroot && umount2(oldroot, MNT_DETACH) < 0)
 133                         log_error_errno(errno, "Failed to lazily umount old root dir %s, %s: %m",
 134                                   oldroot,
 135                                   errno == ENOENT ? "ignoring" : "leaving it around");
 136
 137         } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0)
 138                 return log_error_errno(errno, "Failed to mount moving %s to /: %m", new_root);
 139
 140         if (chroot(".") < 0)
 141                 return log_error_errno(errno, "Failed to change root: %m");
 142
 143         if (chdir("/") < 0)
 144                 return log_error_errno(errno, "Failed to change directory: %m");
 145
 146         if (old_root_fd >= 0) {
 147                 struct stat rb;
 148
 149                 if (fstat(old_root_fd, &rb) < 0)
 150                         log_warning_errno(errno, "Failed to stat old root directory, leaving: %m");
 151                 else {
 152                         (void) rm_rf_children(old_root_fd, 0, &rb);
 153                         old_root_fd = -1;
 154                 }
 155         }
 156
 157         return 0;
 158 }