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udf: support 2048-byte spacing of VRS descriptors on 4K media

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Some UDF creators (specifically Microsoft, but perhaps others) mishandle
the ECMA-167 corner case that requires descriptors within a Volume
Recognition Sequence to be placed at 4096-byte intervals on media where
the block size is 4K. Instead, the descriptors are placed at the 2048-
byte interval mandated for media with smaller blocks. This nonconformity
currently prevents Linux from recognizing the filesystem as UDF.

Modify the driver to tolerate a misformatted VRS on 4K media.

[JK: Simplified descriptor checking]
Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Tested-by: Steven J. Magnani <steve@digidescorp.com>
Link: https://lore.kernel.org/r/20190711133852.16887-2-steve@digidescorp.com
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Steven J. Magnani 2019-07-11 08:38:52 -05:00 committed by Jan Kara
parent ba54aef031
commit 6fbacb8539
1 changed files with 16 additions and 0 deletions
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16
fs/udf/super.c
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@ -739,6 +739,22 @@ static int udf_check_vsd(struct super_block *sb)
vsd = (struct volStructDesc *)(bh->b_data +
(sector & (sb->s_blocksize - 1)));
nsr = identify_vsd(vsd);
/* Found NSR or end? */
if (nsr) {
brelse(bh);
break;
}
/*
* Special handling for improperly formatted VRS (e.g., Win10)
* where components are separated by 2048 bytes even though
* sectors are 4K
*/
if (sb->s_blocksize == 4096) {
nsr = identify_vsd(vsd + 1);
/* Ignore unknown IDs... */
if (nsr < 0)
nsr = 0;
}
brelse(bh);
}