diff options
Diffstat (limited to 'src/libshared/switch-root.c')
| -rw-r--r-- | src/libshared/switch-root.c | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/src/libshared/switch-root.c b/src/libshared/switch-root.c new file mode 100644 index 0000000000..47d3a5a1fa --- /dev/null +++ b/src/libshared/switch-root.c @@ -0,0 +1,156 @@ +/*** + 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 <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 + * 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; + + 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 + * 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; +} |