src/shared/switch-root.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2012 Harald Hoyer, Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <limits.h>
  23 #include <stdbool.h>
  24 #include <stdio.h>
  25 #include <sys/mount.h>
  26 #include <sys/stat.h>
  27 #include <unistd.h>
  28
  29 #include "base-filesystem.h"
  30 #include "fd-util.h"
  31 #include "fs-util.h"
  32 #include "log.h"
  33 #include "missing.h"
  34 #include "mkdir.h"
  35 #include "mount-util.h"
  36 #include "path-util.h"
  37 #include "rm-rf.h"
  38 #include "stdio-util.h"
  39 #include "string-util.h"
  40 #include "strv.h"
  41 #include "switch-root.h"
  42 #include "user-util.h"
  43 #include "util.h"
  44
  45 int switch_root(const char *new_root,
  46                 const char *old_root_after, /* path below the new root, where to place the old root after the transition */
  47                 bool unmount_old_root,
  48                 unsigned long mount_flags) {  /* MS_MOVE or MS_BIND */
  49
  50         _cleanup_free_ char *resolved_old_root_after = NULL;
  51         _cleanup_close_ int old_root_fd = -1;
  52         bool old_root_remove;
  53         const char *i;
  54         int r;
  55
  56         assert(new_root);
  57         assert(old_root_after);
  58
  59         if (path_equal(new_root, "/"))
  60                 return 0;
  61
  62         /* Check if we shall remove the contents of the old root */
  63         old_root_remove = in_initrd();
  64         if (old_root_remove) {
  65                 old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);
  66                 if (old_root_fd < 0)
  67                         return log_error_errno(errno, "Failed to open root directory: %m");
  68         }
  69
  70         /* Determine where we shall place the old root after the transition */
  71         r = chase_symlinks(old_root_after, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &resolved_old_root_after);
  72         if (r < 0)
  73                 return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, old_root_after);
  74         if (r == 0) /* Doesn't exist yet. Let's create it */
  75                 (void) mkdir_p_label(resolved_old_root_after, 0755);
  76
  77         /* Work-around for kernel design: the kernel refuses MS_MOVE if any file systems are mounted MS_SHARED. Hence
  78          * remount them MS_PRIVATE here as a work-around.
  79          *
  80          * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
  81         if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
  82                 return log_error_errno(errno, "Failed to set \"/\" mount propagation to private: %m");
  83
  84         FOREACH_STRING(i, "/sys", "/dev", "/run", "/proc") {
  85                 _cleanup_free_ char *chased = NULL;
  86
  87                 r = chase_symlinks(i, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &chased);
  88                 if (r < 0)
  89                         return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, i);
  90                 if (r > 0) {
  91                         /* Already exists. Let's see if it is a mount point already. */
  92                         r = path_is_mount_point(chased, NULL, 0);
  93                         if (r < 0)
  94                                 return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", chased);
  95                         if (r > 0) /* If it is already mounted, then do nothing */
  96                                 continue;
  97                 } else
  98                          /* Doesn't exist yet? */
  99                         (void) mkdir_p_label(chased, 0755);
 100
 101                 if (mount(i, chased, NULL, mount_flags, NULL) < 0)
 102                         return log_error_errno(r, "Failed to mount %s to %s: %m", i, chased);
 103         }
 104
 105         /* Do not fail if base_filesystem_create() fails. Not all switch roots are like base_filesystem_create() wants
 106          * them to look like. They might even boot, if they are RO and don't have the FS layout. Just ignore the error
 107          * and switch_root() nevertheless. */
 108         (void) base_filesystem_create(new_root, UID_INVALID, GID_INVALID);
 109
 110         if (chdir(new_root) < 0)
 111                 return log_error_errno(errno, "Failed to change directory to %s: %m", new_root);
 112
 113         /* We first try a pivot_root() so that we can umount the old root dir. In many cases (i.e. where rootfs is /),
 114          * that's not possible however, and hence we simply overmount root */
 115         if (pivot_root(new_root, resolved_old_root_after) >= 0) {
 116
 117                 /* Immediately get rid of the old root, if detach_oldroot is set.
 118                  * Since we are running off it we need to do this lazily. */
 119                 if (unmount_old_root) {
 120                         r = umount_recursive(old_root_after, MNT_DETACH);
 121                         if (r < 0)
 122                                 log_warning_errno(r, "Failed to unmount old root directory tree, ignoring: %m");
 123                 }
 124
 125         } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0)
 126                 return log_error_errno(errno, "Failed to move %s to /: %m", new_root);
 127
 128         if (chroot(".") < 0)
 129                 return log_error_errno(errno, "Failed to change root: %m");
 130
 131         if (chdir("/") < 0)
 132                 return log_error_errno(errno, "Failed to change directory: %m");
 133
 134         if (old_root_fd >= 0) {
 135                 struct stat rb;
 136
 137                 if (fstat(old_root_fd, &rb) < 0)
 138                         log_warning_errno(errno, "Failed to stat old root directory, leaving: %m");
 139                 else {
 140                         (void) rm_rf_children(old_root_fd, 0, &rb);
 141                         old_root_fd = -1;
 142                 }
 143         }
 144
 145         return 0;
 146 }