Btrfs: check btree node's nritems

When btree node (level = 1) has nritems which equals to zero,
we can end up with panic due to insert_ptr()'s

BUG_ON(slot > nritems);

where slot is 1 and nritems is 0, as copy_for_split() calls
insert_ptr(.., path->slots[1] + 1, ...);

A invalid value results in the whole mess, this adds the check
for btree's node nritems so that we stop reading block when
when something is wrong.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/disk-io.c

@@ -613,6 +613,19 @@ static noinline int check_leaf(struct btrfs_root *root,
 	return 0;
 }
 
+static int check_node(struct btrfs_root *root, struct extent_buffer *node)
+{
+	unsigned long nr = btrfs_header_nritems(node);
+
+	if (nr == 0 || nr > BTRFS_NODEPTRS_PER_BLOCK(root)) {
+		btrfs_crit(root->fs_info,
+			   "corrupt node: block %llu root %llu nritems %lu",
+			   node->start, root->objectid, nr);
+		return -EIO;
+	}
+	return 0;
+}
+
 static int btree_readpage_end_io_hook(struct btrfs_io_bio *io_bio,
 				      u64 phy_offset, struct page *page,
 				      u64 start, u64 end, int mirror)
@@ -683,6 +696,9 @@ static int btree_readpage_end_io_hook(struct btrfs_io_bio *io_bio,
 		ret = -EIO;
 	}
 
+	if (found_level > 0 && check_node(root, eb))
+		ret = -EIO;
+
 	if (!ret)
 		set_extent_buffer_uptodate(eb);
 err: