/*-*- 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 <errno.h> #include <fcntl.h> #include <stdbool.h> #include <string.h> #include <sys/mount.h> #include <sys/stat.h> #include <unistd.h> #include "base-filesystem.h" #include "fd-util.h" #include "missing.h" #include "mkdir.h" #include "path-util.h" #include "rm-rf.h" #include "string-util.h" #include "switch-root.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 * 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_errno(errno, "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); 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 * stat failed. Unmount the old mount * point. */ 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 * 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); 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 * 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, if detach_oldroot is set. * Since we are running off it we need to do this lazily. */ 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; }