udf: Use correct partition reference number for metadata

UDF/OSTA terminology is confusing. Partition Numbers (PNs) are arbitrary
16-bit values, one for each physical partition in the volume.  Partition
Reference Numbers (PRNs) are indices into the the Partition Map Table
and do not necessarily equal the PN of the mapped partition.

The current metadata code mistakenly uses the PN instead of the PRN when
mapping metadata blocks to physical/sparable blocks.  Windows-created
UDF 2.5 discs for some reason use large, arbitrary PNs, resulting in
mount failure and KASAN read warnings in udf_read_inode().

For example, a NetBSD UDF 2.5 partition might look like this:

PRN PN Type
--- -- ----
  0  0 Sparable
  1  0 Metadata

Since PRN == PN, we are fine.

But Windows could gives us:

PRN PN   Type
--- ---- ----
  0 8192 Sparable
  1 8192 Metadata

So udf_read_inode() will start out by checking the partition length in
sbi->s_partmaps[8192], which is obviously out of bounds.

Fix this by creating a new field (s_phys_partition_ref) in struct
udf_meta_data, referencing whatever physical or sparable map has the
same partition number as the metadata partition.

[JK: Add comment about s_phys_partition_ref, change its name]

Signed-off-by: Alden Tondettar <alden.tondettar@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/udf/udf_sb.h b/fs/udf/udf_sb.h
index 27b5335730c9..c13875d669c0 100644
--- a/fs/udf/udf_sb.h
+++ b/fs/udf/udf_sb.h
@@ -61,6 +61,11 @@ struct udf_meta_data {
 	__u32	s_bitmap_file_loc;
 	__u32	s_alloc_unit_size;
 	__u16	s_align_unit_size;
+	/*
+	 * Partition Reference Number of the associated physical / sparable
+	 * partition
+	 */
+	__u16   s_phys_partition_ref;
 	int	s_flags;
 	struct inode *s_metadata_fe;
 	struct inode *s_mirror_fe;