btrfs: tree-checker: Check leaf chunk item size

Inspired by btrfs-progs github issue #208, where chunk item in chunk
tree has invalid num_stripes (0).

Although that can already be caught by current btrfs_check_chunk_valid(),
that function doesn't really check item size as it needs to handle chunk
item in super block sys_chunk_array().

This patch will add two extra checks for chunk items in chunk tree:

- Basic chunk item size
  If the item is smaller than btrfs_chunk (which already contains one
  stripe), exit right now as reading num_stripes may even go beyond
  eb boundary.

- Item size check against num_stripes
  If item size doesn't match with calculated chunk size, then either the
  item size or the num_stripes is corrupted. Error out anyway.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/tree-checker.c

@@ -738,6 +738,44 @@ int btrfs_check_chunk_valid(struct extent_buffer *leaf,
 	return 0;
 }
 
+/*
+ * Enhanced version of chunk item checker.
+ *
+ * The common btrfs_check_chunk_valid() doesn't check item size since it needs
+ * to work on super block sys_chunk_array which doesn't have full item ptr.
+ */
+static int check_leaf_chunk_item(struct extent_buffer *leaf,
+				 struct btrfs_chunk *chunk,
+				 struct btrfs_key *key, int slot)
+{
+	int num_stripes;
+
+	if (btrfs_item_size_nr(leaf, slot) < sizeof(struct btrfs_chunk)) {
+		chunk_err(leaf, chunk, key->offset,
+			"invalid chunk item size: have %u expect [%zu, %u)",
+			btrfs_item_size_nr(leaf, slot),
+			sizeof(struct btrfs_chunk),
+			BTRFS_LEAF_DATA_SIZE(leaf->fs_info));
+		return -EUCLEAN;
+	}
+
+	num_stripes = btrfs_chunk_num_stripes(leaf, chunk);
+	/* Let btrfs_check_chunk_valid() handle this error type */
+	if (num_stripes == 0)
+		goto out;
+
+	if (btrfs_chunk_item_size(num_stripes) !=
+	    btrfs_item_size_nr(leaf, slot)) {
+		chunk_err(leaf, chunk, key->offset,
+			"invalid chunk item size: have %u expect %lu",
+			btrfs_item_size_nr(leaf, slot),
+			btrfs_chunk_item_size(num_stripes));
+		return -EUCLEAN;
+	}
+out:
+	return btrfs_check_chunk_valid(leaf, chunk, key->offset);
+}
+
 __printf(3, 4)
 __cold
 static void dev_item_err(const struct extent_buffer *eb, int slot,
@@ -1384,7 +1422,7 @@ static int check_leaf_item(struct extent_buffer *leaf,
 		break;
 	case BTRFS_CHUNK_ITEM_KEY:
 		chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
-		ret = btrfs_check_chunk_valid(leaf, chunk, key->offset);
+		ret = check_leaf_chunk_item(leaf, chunk, key, slot);
 		break;
 	case BTRFS_DEV_ITEM_KEY:
 		ret = check_dev_item(leaf, key, slot);