stuff

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;
+}