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authorLuke Shumaker <lukeshu@sbcglobal.net>2016-07-27 17:24:48 -0400
committerLuke Shumaker <lukeshu@sbcglobal.net>2016-07-27 17:24:48 -0400
commitcce8d84b2e8a010f4b5a313e3866b0dcf2ed5854 (patch)
treeda8f7ac1275dac579531546de8e8609cf51be97d /src/libshared/switch-root.c
parentef98f526dafb8206cc4fd895a691eda0ea0894ec (diff)
./move.sh
Diffstat (limited to 'src/libshared/switch-root.c')
-rw-r--r--src/libshared/switch-root.c156
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;
+}