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