#include <errno.h>

#include <fcntl.h>

#include <limits.h>

#include <stdbool.h>

#include <stdio.h>

#include <sys/mount.h>

#include <sys/stat.h>

#include <unistd.h>

#include "base-filesystem.h"

#include "fd-util.h"

#include "log.h"

#include "missing.h"

#include "mkdir.h"

#include "path-util.h"

#include "rm-rf.h"

#include "stdio-util.h"

#include "string-util.h"

#include "switch-root.h"

#include "user-util.h"

#include "util.h"

int switch_root(const char *new_root, const char *oldroot, bool detach_oldroot, unsigned long mountflags) {

/* Don't try to unmount/move the old "/", there's no way to do it. */

static const char move_mounts[] =

"/dev\0"

"/proc\0"

"/sys\0"

"/run\0";

_cleanup_close_ int old_root_fd = -1;

struct stat new_root_stat;

bool old_root_remove;

const char *i, *temporary_old_root;

if (path_equal(new_root, "/"))

return 0;

temporary_old_root = strjoina(new_root, oldroot);

mkdir_p_label(temporary_old_root, 0755);

old_root_remove = in_initrd();

if (stat(new_root, &new_root_stat) < 0)

return log_error_errno(errno, "Failed to stat directory %s: %m", new_root);

/* Work-around for kernel design: the kernel refuses switching

if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)

log_warning_errno(errno, "Failed to make \"/\" private mount: %m");

NULSTR_FOREACH(i, move_mounts) {

char new_mount[PATH_MAX];

struct stat sb;

xsprintf(new_mount, "%s%s", new_root, i);

mkdir_p_label(new_mount, 0755);

if ((stat(new_mount, &sb) < 0) ||

sb.st_dev != new_root_stat.st_dev) {

/* Mount point seems to be mounted already or

if (umount2(i, MNT_DETACH) < 0)

log_warning_errno(errno, "Failed to unmount %s: %m", i);

continue;

}

if (mount(i, new_mount, NULL, mountflags, NULL) < 0) {

if (mountflags & MS_MOVE) {

log_error_errno(errno, "Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);

if (umount2(i, MNT_FORCE) < 0)

log_warning_errno(errno, "Failed to unmount %s: %m", i);

}

if (mountflags & MS_BIND)

log_error_errno(errno, "Failed to bind mount %s to %s: %m", i, new_mount);

}

}

/* Do not fail, if base_filesystem_create() fails. Not all

(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);

if (old_root_remove) {

old_root_fd = open("/", O_RDONLY|O_NONBLOCK|O_CLOEXEC|O_NOCTTY|O_DIRECTORY);

if (old_root_fd < 0)

log_warning_errno(errno, "Failed to open root directory: %m");

}

/* We first try a pivot_root() so that we can umount the old

if (pivot_root(new_root, temporary_old_root) >= 0) {

/* Immediately get rid of the old root, if detach_oldroot is set.

if (detach_oldroot && umount2(oldroot, MNT_DETACH) < 0)

log_error_errno(errno, "Failed to lazily umount old root dir %s, %s: %m",

oldroot,

errno == ENOENT ? "ignoring" : "leaving it around");

} else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0)

return log_error_errno(errno, "Failed to mount moving %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)

log_warning_errno(errno, "Failed to stat old root directory, leaving: %m");

else {

(void) rm_rf_children(old_root_fd, 0, &rb);

old_root_fd = -1;

}

}

return 0;

}