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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdbool.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <unistd.h>
#include "base-filesystem.h"
#include "chase-symlinks.h"
#include "fd-util.h"
#include "log.h"
#include "missing_syscall.h"
#include "mkdir-label.h"
#include "mount-util.h"
#include "mountpoint-util.h"
#include "path-util.h"
#include "rm-rf.h"
#include "stdio-util.h"
#include "string-util.h"
#include "strv.h"
#include "switch-root.h"
#include "user-util.h"
#include "util.h"
int switch_root(const char *new_root,
const char *old_root_after, /* path below the new root, where to place the old root after the transition */
bool unmount_old_root,
unsigned long mount_flags) { /* MS_MOVE or MS_BIND */
_cleanup_free_ char *resolved_old_root_after = NULL;
_cleanup_close_ int old_root_fd = -1;
int r;
assert(new_root);
assert(old_root_after);
if (path_equal(new_root, "/"))
return 0;
/* Check if we shall remove the contents of the old root */
old_root_fd = open("/", O_RDONLY | O_CLOEXEC | O_DIRECTORY);
if (old_root_fd < 0)
return log_error_errno(errno, "Failed to open root directory: %m");
r = fd_is_temporary_fs(old_root_fd);
if (r < 0)
return log_error_errno(r, "Failed to stat root directory: %m");
if (r > 0)
log_debug("Root directory is on tmpfs, will do cleanup later.");
else
old_root_fd = safe_close(old_root_fd);
/* Determine where we shall place the old root after the transition */
r = chase_symlinks(old_root_after, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &resolved_old_root_after, NULL);
if (r < 0)
return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, old_root_after);
if (r == 0) /* Doesn't exist yet. Let's create it */
(void) mkdir_p_label(resolved_old_root_after, 0755);
/* Work-around for kernel design: the kernel refuses MS_MOVE if any file systems are mounted MS_SHARED. Hence
* remount them MS_PRIVATE here as a work-around.
*
* https://bugzilla.redhat.com/show_bug.cgi?id=847418 */
if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)
return log_error_errno(errno, "Failed to set \"/\" mount propagation to private: %m");
FOREACH_STRING(path, "/sys", "/dev", "/run", "/proc") {
_cleanup_free_ char *chased = NULL;
r = chase_symlinks(path, new_root, CHASE_PREFIX_ROOT|CHASE_NONEXISTENT, &chased, NULL);
if (r < 0)
return log_error_errno(r, "Failed to resolve %s/%s: %m", new_root, path);
if (r > 0) {
/* Already exists. Let's see if it is a mount point already. */
r = path_is_mount_point(chased, NULL, 0);
if (r < 0)
return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", chased);
if (r > 0) /* If it is already mounted, then do nothing */
continue;
} else
/* Doesn't exist yet? */
(void) mkdir_p_label(chased, 0755);
if (mount(path, chased, NULL, mount_flags, NULL) < 0)
return log_error_errno(errno, "Failed to mount %s to %s: %m", path, chased);
}
/* Do not fail if base_filesystem_create() fails. Not all switch roots are like base_filesystem_create() wants
* them to look like. They might even boot, if they are RO and don't have the FS layout. Just ignore the error
* and switch_root() nevertheless. */
(void) base_filesystem_create(new_root, UID_INVALID, GID_INVALID);
if (chdir(new_root) < 0)
return log_error_errno(errno, "Failed to change directory to %s: %m", new_root);
/* We first try a pivot_root() so that we can umount the old root dir. In many cases (i.e. where rootfs is /),
* that's not possible however, and hence we simply overmount root */
if (pivot_root(new_root, resolved_old_root_after) >= 0) {
/* Immediately get rid of the old root, if detach_oldroot is set.
* Since we are running off it we need to do this lazily. */
if (unmount_old_root) {
r = umount_recursive(old_root_after, MNT_DETACH);
if (r < 0)
log_warning_errno(r, "Failed to unmount old root directory tree, ignoring: %m");
}
} else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0)
return log_error_errno(errno, "Failed to move %s to /: %m", new_root);
if (chroot(".") < 0)
return log_error_errno(errno, "Failed to change root: %m");
if (chdir("/") < 0)
return log_error_errno(errno, "Failed to change directory: %m");
if (old_root_fd >= 0) {
struct stat rb;
if (fstat(old_root_fd, &rb) < 0)
return log_error_errno(errno, "Failed to stat old root directory: %m");
(void) rm_rf_children(TAKE_FD(old_root_fd), 0, &rb); /* takes possession of the dir fd, even on failure */
}
return 0;
}
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