udf: Fix mounting of Win7 created UDF filesystems

Win7 is creating UDF filesystems with single partition with number 8192.
Current partition descriptor scanning code does not handle this well as
it incorrectly assumes that partition numbers will form mostly contiguous
space of small numbers. This results in unmountable media due to errors
like:

UDF-fs: error (device dm-1): udf_read_tagged: tag version 0x0000 != 0x0002 || 0x0003, block 0
UDF-fs: warning (device dm-1): udf_fill_super: No fileset found

Fix the problem by handling partition descriptors in a way that sparse
partition numbering does not matter.
Reported-and-tested-by: jean-luc malet <jeanluc.malet@gmail.com>
CC: stable@vger.kernel.org
Fixes: 7b78fd02Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/super.c

@@ -1510,10 +1510,16 @@ static void udf_load_logicalvolint(struct super_block *sb, struct kernel_extent_
  */
 #define PART_DESC_ALLOC_STEP 32
 
+struct part_desc_seq_scan_data {
+	struct udf_vds_record rec;
+	u32 partnum;
+};
+
 struct desc_seq_scan_data {
 	struct udf_vds_record vds[VDS_POS_LENGTH];
 	unsigned int size_part_descs;
-	struct udf_vds_record *part_descs_loc;
+	unsigned int num_part_descs;
+	struct part_desc_seq_scan_data *part_descs_loc;
 };
 
 static struct udf_vds_record *handle_partition_descriptor(
@@ -1522,10 +1528,14 @@ static struct udf_vds_record *handle_partition_descriptor(
 {
 	struct partitionDesc *desc = (struct partitionDesc *)bh->b_data;
 	int partnum;
+	int i;
 
 	partnum = le16_to_cpu(desc->partitionNumber);
-	if (partnum >= data->size_part_descs) {
-		struct udf_vds_record *new_loc;
+	for (i = 0; i < data->num_part_descs; i++)
+		if (partnum == data->part_descs_loc[i].partnum)
+			return &(data->part_descs_loc[i].rec);
+	if (data->num_part_descs >= data->size_part_descs) {
+		struct part_desc_seq_scan_data *new_loc;
 		unsigned int new_size = ALIGN(partnum, PART_DESC_ALLOC_STEP);
 
 		new_loc = kcalloc(new_size, sizeof(*new_loc), GFP_KERNEL);
@@ -1537,7 +1547,7 @@ static struct udf_vds_record *handle_partition_descriptor(
 		data->part_descs_loc = new_loc;
 		data->size_part_descs = new_size;
 	}
-	return &(data->part_descs_loc[partnum]);
+	return &(data->part_descs_loc[data->num_part_descs++].rec);
 }
 
 
@@ -1587,6 +1597,7 @@ static noinline int udf_process_sequence(
 
 	memset(data.vds, 0, sizeof(struct udf_vds_record) * VDS_POS_LENGTH);
 	data.size_part_descs = PART_DESC_ALLOC_STEP;
+	data.num_part_descs = 0;
 	data.part_descs_loc = kcalloc(data.size_part_descs,
 				      sizeof(*data.part_descs_loc),
 				      GFP_KERNEL);
@@ -1598,7 +1609,6 @@ static noinline int udf_process_sequence(
 	 * are in it.
 	 */
 	for (; (!done && block <= lastblock); block++) {
-
 		bh = udf_read_tagged(sb, block, block, &ident);
 		if (!bh)
 			break;
@@ -1670,13 +1680,10 @@ static noinline int udf_process_sequence(
 	}
 
 	/* Now handle prevailing Partition Descriptors */
-	for (i = 0; i < data.size_part_descs; i++) {
-		if (data.part_descs_loc[i].block) {
-			ret = udf_load_partdesc(sb,
-						data.part_descs_loc[i].block);
-			if (ret < 0)
-				return ret;
-		}
+	for (i = 0; i < data.num_part_descs; i++) {
+		ret = udf_load_partdesc(sb, data.part_descs_loc[i].rec.block);
+		if (ret < 0)
+			return ret;
 	}
 
 	return 0;