Merge tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull mount fixes from Al Viro:
"Fixes for several recent mount-related regressions"

* tag 'pull-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
change_mnt_propagation(): calculate propagation source only if we'll need it
use uniform permission checks for all mount propagation changes
propagate_umount(): only surviving overmounts should be reparented
fix the softlockups in attach_recursive_mnt()

fs/namespace.c

···
 
 	if (!mnt_ns_attached(mnt)) {
 		for (struct mount *m = mnt; m; m = next_mnt(m, mnt))
-			if (unlikely(mnt_ns_attached(m)))
-				m = skip_mnt_tree(m);
-			else
-				mnt_add_to_ns(n, m);
+			mnt_add_to_ns(n, m);
 		n->nr_mounts += n->pending_mounts;
 		n->pending_mounts = 0;
 	}
···
 			lock_mnt_tree(child);
 		q = __lookup_mnt(&child->mnt_parent->mnt,
 				 child->mnt_mountpoint);
+		commit_tree(child);
 		if (q) {
 			struct mountpoint *mp = root.mp;
 			struct mount *r = child;
···
 				mp = shorter;
 			mnt_change_mountpoint(r, mp, q);
 		}
-		commit_tree(child);
 	}
 	unpin_mountpoint(&root);
 	unlock_mount_hash();
···
 	return attach_recursive_mnt(mnt, p, mp);
 }
 
+static int may_change_propagation(const struct mount *m)
+{
+        struct mnt_namespace *ns = m->mnt_ns;
+
+	 // it must be mounted in some namespace
+	 if (IS_ERR_OR_NULL(ns))         // is_mounted()
+		 return -EINVAL;
+	 // and the caller must be admin in userns of that namespace
+	 if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
+		 return -EPERM;
+	 return 0;
+}
+
 /*
  * Sanity check the flags to change_mnt_propagation.
  */
···
 		return -EINVAL;
 
 	namespace_lock();
-	if (!check_mnt(mnt)) {
-		err = -EINVAL;
+	err = may_change_propagation(mnt);
+	if (err)
 		goto out_unlock;
-	}
+
 	if (type == MS_SHARED) {
 		err = invent_group_ids(mnt, recurse);
 		if (err)
···
 
 	namespace_lock();
 
-	err = -EINVAL;
-	/* To and From must be mounted */
-	if (!is_mounted(&from->mnt))
+	err = may_change_propagation(from);
+	if (err)
 		goto out;
-	if (!is_mounted(&to->mnt))
-		goto out;
-
-	err = -EPERM;
-	/* We should be allowed to modify mount namespaces of both mounts */
-	if (!ns_capable(from->mnt_ns->user_ns, CAP_SYS_ADMIN))
-		goto out;
-	if (!ns_capable(to->mnt_ns->user_ns, CAP_SYS_ADMIN))
+	err = may_change_propagation(to);
+	if (err)
 		goto out;
 
 	err = -EINVAL;

fs/pnode.c

···
 		return;
 	}
 	if (IS_MNT_SHARED(mnt)) {
-		m = propagation_source(mnt);
+		if (type == MS_SLAVE || !hlist_empty(&mnt->mnt_slave_list))
+			m = propagation_source(mnt);
 		if (list_empty(&mnt->mnt_share)) {
 			mnt_release_group_id(mnt);
 		} else {
···
 	}
 
 	// now to_umount consists of all acceptable candidates
-	// deal with reparenting of remaining overmounts on those
+	// deal with reparenting of surviving overmounts on those
 	list_for_each_entry(m, &to_umount, mnt_list) {
-		if (m->overmount)
-			reparent(m->overmount);
+		struct mount *over = m->overmount;
+		if (over && !will_be_unmounted(over))
+			reparent(over);
 	}
 
 	// and fold them into the set