udf: Verify partition map count

Verify that number of partition maps isn't insanely high which can lead
to large allocation in udf_sb_alloc_partition_maps(). All partition maps
have to fit in the LVD which is in a single block.

Reported-by: [e-mail]
Signed-off-by: Jan Kara <[e-mail]>

fs/udf/super.c

···
 	struct genericPartitionMap *gpm;
 	uint16_t ident;
 	struct buffer_head *bh;
-	unsigned int table_len;
+	unsigned int table_len, part_map_count;
 	int ret;
 
 	bh = udf_read_tagged(sb, block, block, &ident);
···
 					   "logical volume");
 	if (ret)
 		goto out_bh;
-	ret = udf_sb_alloc_partition_maps(sb, le32_to_cpu(lvd->numPartitionMaps));
+
+	part_map_count = le32_to_cpu(lvd->numPartitionMaps);
+	if (part_map_count > table_len / sizeof(struct genericPartitionMap1)) {
+		udf_err(sb, "error loading logical volume descriptor: "
+			"Too many partition maps (%u > %u)\n", part_map_count,
+			table_len / (unsigned)sizeof(struct genericPartitionMap1));
+		ret = -EIO;
+		goto out_bh;
+	}
+	ret = udf_sb_alloc_partition_maps(sb, part_map_count);
 	if (ret)
 		goto out_bh;