btrfs-progs: print-tree: do sanity checks for dir items

There is a bug report that with UBSAN enabled, fuzz/006 test case
crashes.

It turns out that the image bko-154021-invalid-drop-level.raw has
invalid dir items, that the name/data len is beyond the item.

And if we try to read beyond the eb boundary, UBSAN got triggered.

Normally in kernel tree-checker would reject such metadata in the first
place, but in btrfs-progs we can not be that strict or we cannot do a
lot of repair.

So here just enhance print_dir_item() to do extra sanity checks for
data/name len before reading the contents.

Issue: #805
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: adam900710

kernel-shared/print-tree.c

@@ -78,6 +78,11 @@ static void print_dir_item(struct extent_buffer *eb, u32 size,
 		printf("\n");
 		name_len = btrfs_dir_name_len(eb, di);
 		data_len = btrfs_dir_data_len(eb, di);
+		if (data_len + name_len + cur > size) {
+			error("invalid length, cur=%u name_len=%u data_len=%u size=%u",
+			      cur, name_len, data_len, size);
+			break;
+		}
 		len = (name_len <= sizeof(namebuf))? name_len: sizeof(namebuf);
 		printf("\t\ttransid %llu data_len %u name_len %u\n",
 				btrfs_dir_transid(eb, di),