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SubjectRe: [PATCH 0/1] udf: fix silent AED tagLocation corruption
Hi!

Thanks for the fixes! This is just to let you know that I haven't forgotten
about them but I need to think a bit about them. Hopefully I'll be able to
find more time for them tomorrow.

Honza

On Thu 07-01-21 17:41:15, Steve Magnani wrote:
> From: Steven J. Magnani <magnani@ieee.org>
>
> Certain scenarios involving enlargement of a large and/or fragmented file
> result in corruption of the file's Allocation Extent Descriptor tag.
> Once this has happened, attempts to read the file in Windows 10 fail with
> "Data error (cyclic redundancy check)". A "chkdsk /f" in Windows causes
> extents of the file described by the corrupted AED (and any subsequent
> chained AEDs) to be truncated.
>
> No problems are noted when the file is accessed in Linux.
>
> The script below creates a toy UDF filesystem to illustrate the problem.
> The filesystem can be dd'd to a flash disk partition of the same size
> to observe how Windows handles the corruption.
> ---
> #!/bin/bash
>
> # Tool to illustrate / test fix for bug in UDF driver
> # that can result in corruption of Allocation Extent Descriptor tag location
> # Developed using mkudffs from udftools 2.2.
>
> # Terminology:
> # LSN == Logical Sector Number (media / volume relative)
> # LBN == Logical Block Number (UDF partition relative)
>
>
> TEST_UDFFS=/tmp/test.udf
>
> # Changing these may alter filesystem layout and/or invalidate the test
> UDFFS_SIZE=1M # --size argument to 'truncate' command
> UDF_BLOCKSIZE=512
> PD_LSN=98 # Expected UDF Partition Descriptor location
> AED_LSN=1343 # Location of Allocation Extent Descriptor under test
>
> require()
> {
> local APP_REALPATH=`which $1`
> local PACKAGE_NAME=${2:-$1}
> if [ -z "$APP_REALPATH" ] ; then
> echo This test requires $1. Please install the $PACKAGE_NAME package.
> exit 1
> fi
> }
>
> # "Quiet" dd command
> ddq()
> {
> dd $* 2> /dev/null
> }
>
> # Extract a 16-bit little-endian unsigned value at a specified byte offset ($2)
> # of a specified LSN ($1)
> #
> extract16()
> {
> local value=`ddq if=$TEST_UDFFS bs=$UDF_BLOCKSIZE skip=$1 count=1 | ddq bs=1 skip=$2 count=2 | od -A none -t u2 --endian=little`
> [ -z "$value" ] && value=0 # Fail in a sane manner
>
> echo -n $value
> }
>
> # Extract a 32-bit little-endian unsigned value at a specified byte offset ($2)
> # of a specified LSN ($1)
> #
> extract32()
> {
> local value=`ddq if=$TEST_UDFFS bs=$UDF_BLOCKSIZE skip=$1 count=1 | ddq bs=1 skip=$2 count=4 | od -A none -t u4 --endian=little`
> [ -z "$value" ] && value=0 # Fail in a sane manner
>
> echo -n $value
> }
>
>
> # $1 = LSN
> # $2 = Expected tag ID value (decimal) - i.e., 266 for EFE
> require_tag_id()
> {
> local found_tag=`extract16 $1 0`
>
> if [ $found_tag -ne $2 ] ; then
> echo Expected tag $2 in LSN $1, found $found_tag.
> echo Unexpected test conditions - results must be verified manually
> exit 1
> fi
> }
>
> gen_provoker_data()
> {
> ddq if=/dev/zero bs=$UDF_BLOCKSIZE count=1 of=/tmp/hole.$$
>
> openssl rand 172032
> cat /tmp/hole.$$
> openssl rand 149504
> cat /tmp/hole.$$
> openssl rand 22528
> cat /tmp/hole.$$
> openssl rand 2048
> cat /tmp/hole.$$
> openssl rand 4096
> cat /tmp/hole.$$
> openssl rand 4096
> cat /tmp/hole.$$
> openssl rand 8192
> cat /tmp/hole.$$
> openssl rand 184320
> cat /tmp/hole.$$
> openssl rand 131072
>
> rm -f /tmp/hole.$$
> }
>
> # $1 == loopback UDF filesystem to create
> make_test_udf()
> {
> rm -f $1
> truncate --size=$UDFFS_SIZE $1
> mkudffs --label=SPARSE --uid=$UID --blocksize=$UDF_BLOCKSIZE $1 > /dev/null
>
> mkdir -p /tmp/testudf.mnt
> echo Mounting test UDF filesystem. Please provide the root password if prompted.
> sudo mount $1 /tmp/testudf.mnt
> cp --sparse=always /tmp/provoker.$$ /tmp/testudf.mnt/provoker
> sync
> sudo umount /tmp/testudf.mnt
> rmdir /tmp/testudf.mnt
> echo Test UDF filesystem generated in $1.
> }
>
> ### MAIN
>
> require openssl
> require mkudffs udftools
>
> if [ -e $TEST_UDFFS ] ; then
> echo $TEST_UDFFS already exists - please dismount and remove it
> exit 1
> fi
>
> gen_provoker_data > /tmp/provoker.$$
> make_test_udf $TEST_UDFFS
>
> # Verify hardcoded LSNs involved in testing
> require_tag_id $PD_LSN 5 # PD
> require_tag_id $AED_LSN 258 # AED
>
> LBN_BASE=`extract32 $PD_LSN 188` # Partition Starting Location
> AED_LBN=`expr $AED_LSN - $LBN_BASE`
> AED_TAG_LOCATION=`extract32 $AED_LSN 12`
>
> if [ $AED_TAG_LOCATION -ne $AED_LBN ] ; then
> echo Test FAILED: expected AED tag location $AED_LBN, actual is $AED_TAG_LOCATION
> exit 1
> else
> echo Test PASSED. AED tag location field is correct.
> fi
> ------------------------------------------------------------------------
> Steven J. Magnani "I claim this network for MARS!
> Earthling, return my space modulator!"
> #include <standard.disclaimer>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR

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