audit: Guarantee forward progress of chunk untagging

When removing chunk from a tree, we do shrink the chunk. This can fail
for various reasons (due to races, ENOMEM, etc.) and in some cases we
just bail from untag_chunk() relying on someone else to cleanup.
Although this currently works, later we will need to add new failure
situation which would break. Also this simplifies the code and will
allow us to make locking around untag_chunk() less awkward.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

kernel/audit_tree.c

@@ -309,16 +309,28 @@ static void replace_chunk(struct audit_chunk *new, struct audit_chunk *old,
 	list_replace_rcu(&old->hash, &new->hash);
 }
 
+static void remove_chunk_node(struct audit_chunk *chunk, struct node *p)
+{
+	struct audit_tree *owner = p->owner;
+
+	if (owner->root == chunk) {
+		list_del_init(&owner->same_root);
+		owner->root = NULL;
+	}
+	list_del_init(&p->list);
+	p->owner = NULL;
+	put_tree(owner);
+}
+
 static void untag_chunk(struct node *p)
 {
 	struct audit_chunk *chunk = find_chunk(p);
 	struct fsnotify_mark *entry = chunk->mark;
 	struct audit_chunk *new = NULL;
-	struct audit_tree *owner;
 	int size = chunk->count - 1;
 
+	remove_chunk_node(chunk, p);
 	fsnotify_get_mark(entry);
-
 	spin_unlock(&hash_lock);
 
 	if (size)
@@ -336,15 +348,10 @@ static void untag_chunk(struct node *p)
 		goto out;
 	}
 
-	owner = p->owner;
-
 	if (!size) {
 		chunk->dead = 1;
 		spin_lock(&hash_lock);
 		list_del_init(&chunk->trees);
-		if (owner->root == chunk)
-			owner->root = NULL;
-		list_del_init(&p->list);
 		list_del_rcu(&chunk->hash);
 		spin_unlock(&hash_lock);
 		fsnotify_detach_mark(entry);
@@ -354,21 +361,16 @@ static void untag_chunk(struct node *p)
 	}
 
 	if (!new)
-		goto Fallback;
+		goto out_mutex;
 
 	if (fsnotify_add_mark_locked(new->mark, entry->connector->obj,
 				     FSNOTIFY_OBJ_TYPE_INODE, 1)) {
 		fsnotify_put_mark(new->mark);
-		goto Fallback;
+		goto out_mutex;
 	}
 
 	chunk->dead = 1;
 	spin_lock(&hash_lock);
-	if (owner->root == chunk) {
-		list_del_init(&owner->same_root);
-		owner->root = NULL;
-	}
-	list_del_init(&p->list);
 	/*
 	 * This has to go last when updating chunk as once replace_chunk() is
 	 * called, new RCU readers can see the new chunk.
@@ -381,17 +383,7 @@ static void untag_chunk(struct node *p)
 	fsnotify_put_mark(new->mark);	/* drop initial reference */
 	goto out;
 
-Fallback:
-	// do the best we can
-	spin_lock(&hash_lock);
-	if (owner->root == chunk) {
-		list_del_init(&owner->same_root);
-		owner->root = NULL;
-	}
-	list_del_init(&p->list);
-	p->owner = NULL;
-	put_tree(owner);
-	spin_unlock(&hash_lock);
+out_mutex:
 	mutex_unlock(&entry->group->mark_mutex);
 out:
 	fsnotify_put_mark(entry);