xfs: abort dir/attr btree operation if btree is obviously weird

Abort an dir/attr btree operation if the attr btree has obvious problems
like loops back to the root or pointers don't point down the tree.
Found by fuzzing btree[0].before to zero in xfs/402, which livelocks on
the cycle in the attr btree.

Apply the same checks to xfs_da3_node_lookup_int.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>

fs/xfs/libxfs/xfs_da_btree.c

@@ -1466,6 +1466,7 @@ xfs_da3_node_lookup_int(
 	int			max;
 	int			error;
 	int			retval;
+	unsigned int		expected_level = 0;
 	struct xfs_inode	*dp = state->args->dp;
 
 	args = state->args;
@@ -1474,7 +1475,7 @@ xfs_da3_node_lookup_int(
 	 * Descend thru the B-tree searching each level for the right
 	 * node to use, until the right hashval is found.
 	 */
-	blkno = (args->whichfork == XFS_DATA_FORK)? args->geo->leafblk : 0;
+	blkno = args->geo->leafblk;
 	for (blk = &state->path.blk[0], state->path.active = 1;
 			 state->path.active <= XFS_DA_NODE_MAXDEPTH;
 			 blk++, state->path.active++) {
@@ -1517,6 +1518,18 @@ xfs_da3_node_lookup_int(
 		dp->d_ops->node_hdr_from_disk(&nodehdr, node);
 		btree = dp->d_ops->node_tree_p(node);
 
+		/* Tree taller than we can handle; bail out! */
+		if (nodehdr.level >= XFS_DA_NODE_MAXDEPTH)
+			return -EFSCORRUPTED;
+
+		/* Check the level from the root. */
+		if (blkno == args->geo->leafblk)
+			expected_level = nodehdr.level - 1;
+		else if (expected_level != nodehdr.level)
+			return -EFSCORRUPTED;
+		else
+			expected_level--;
+
 		max = nodehdr.count;
 		blk->hashval = be32_to_cpu(btree[max - 1].hashval);
 
@@ -1562,8 +1575,15 @@ xfs_da3_node_lookup_int(
 			blk->index = probe;
 			blkno = be32_to_cpu(btree[probe].before);
 		}
+
+		/* We can't point back to the root. */
+		if (blkno == args->geo->leafblk)
+			return -EFSCORRUPTED;
 	}
 
+	if (expected_level != 0)
+		return -EFSCORRUPTED;
+
 	/*
 	 * A leaf block that ends in the hashval that we are interested in
 	 * (final hashval == search hashval) means that the next block may

fs/xfs/xfs_attr_list.c

@@ -223,6 +223,7 @@ xfs_attr_node_list_lookup(
 	struct xfs_buf			*bp;
 	int				i;
 	int				error = 0;
+	unsigned int			expected_level = 0;
 	uint16_t			magic;
 
 	ASSERT(*pbp == NULL);
@@ -246,6 +247,18 @@ xfs_attr_node_list_lookup(
 
 		dp->d_ops->node_hdr_from_disk(&nodehdr, node);
 
+		/* Tree taller than we can handle; bail out! */
+		if (nodehdr.level >= XFS_DA_NODE_MAXDEPTH)
+			goto out_corruptbuf;
+
+		/* Check the level from the root node. */
+		if (cursor->blkno == 0)
+			expected_level = nodehdr.level - 1;
+		else if (expected_level != nodehdr.level)
+			goto out_corruptbuf;
+		else
+			expected_level--;
+
 		btree = dp->d_ops->node_tree_p(node);
 		for (i = 0; i < nodehdr.count; btree++, i++) {
 			if (cursor->hashval <= be32_to_cpu(btree->hashval)) {
@@ -259,8 +272,15 @@ xfs_attr_node_list_lookup(
 
 		if (i == nodehdr.count)
 			return 0;
+
+		/* We can't point back to the root. */
+		if (cursor->blkno == 0)
+			return -EFSCORRUPTED;
 	}
 
+	if (expected_level != 0)
+		goto out_corruptbuf;
+
 	*pbp = bp;
 	return 0;