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/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
/***
This file is part of systemd.
Copyright 2012 Harald Hoyer, Lennart Poettering
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <sys/stat.h>
#include <stdbool.h>
#include <errno.h>
#include <string.h>
#include <sys/mount.h>
#include <unistd.h>
#include <fcntl.h>
#include "util.h"
#include "path-util.h"
#include "switch-root.h"
#include "missing.h"
int switch_root(const char *new_root) {
/* 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;
/* When using pivot_root() we assume that /mnt exists as place
* we can temporarily move the old root to. As we immediately
* unmount it from there it doesn't matter much which
* directory we choose for this, but it should be more likely
* than not that /mnt exists and is suitable as mount point
* and is on the same fs as the old root dir */
temporary_old_root = strappenda(new_root, "/mnt");
old_root_remove = in_initrd();
if (stat(new_root, &new_root_stat) < 0) {
log_error("Failed to stat directory %s: %m", new_root);
return -errno;
}
/* Work-around for a kernel bug: for some reason the kernel
* refuses switching root 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)
log_warning("Failed to make \"/\" private mount: %m");
NULSTR_FOREACH(i, move_mounts) {
char new_mount[PATH_MAX];
struct stat sb;
snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
char_array_0(new_mount);
if ((stat(new_mount, &sb) < 0) ||
sb.st_dev != new_root_stat.st_dev) {
/* Mount point seems to be mounted already or
* stat failed. Unmount the old mount
* point. */
if (umount2(i, MNT_DETACH) < 0)
log_warning("Failed to unmount %s: %m", i);
continue;
}
if (mount(i, new_mount, NULL, MS_MOVE, NULL) < 0) {
log_error("Failed to move mount %s to %s, forcing unmount: %m", i, new_mount);
if (umount2(i, MNT_FORCE) < 0)
log_warning("Failed to unmount %s: %m", i);
}
}
if (chdir(new_root) < 0) {
log_error("Failed to change directory to %s: %m", new_root);
return -errno;
}
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("Failed to open root directory: %m");
}
/* 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, temporary_old_root) >= 0) {
/* Immediately get rid of the old root. Since we are
* running off it we need to do this lazily. */
if (umount2(temporary_old_root, MNT_DETACH) < 0) {
log_error("Failed to umount old root dir %s: %m", temporary_old_root);
return -errno;
}
} else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
log_error("Failed to mount moving %s to /: %m", new_root);
return -errno;
}
if (chroot(".") < 0) {
log_error("Failed to change root: %m");
return -errno;
}
if (chdir("/") < 0) {
log_error("Failed to change directory: %m");
return -errno;
}
if (old_root_fd >= 0) {
struct stat rb;
if (fstat(old_root_fd, &rb) < 0)
log_warning("Failed to stat old root directory, leaving: %m");
else {
rm_rf_children(old_root_fd, false, false, &rb);
old_root_fd = -1;
}
}
return 0;
}
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