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Date:   Tue, 14 May 2019 10:20:44 +0800
From:   Eryu Guan <guaneryu@...il.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     fstests@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [RFC PATCH 4/7] common/encrypt: add helper for ciphertext
 verification tests

On Mon, May 13, 2019 at 12:12:05PM -0700, Eric Biggers wrote:
> Hi Eryu,
> 
> On Sun, May 12, 2019 at 08:27:03PM +0800, Eryu Guan wrote:
> > > +# Retrieve the filename stored on-disk for the given file.
> > > +# The name is printed to stdout in binary.
> > > +_get_on_disk_filename()
> > > +{
> > > +	local device=$1
> > > +	local inode=$2
> > > +	local dir_inode=$3
> > > +
> > > +	case $FSTYP in
> > > +	ext4)
> > > +		# Extract the filename from the debugfs output line like:
> > > +		#
> > > +		#  131075  100644 (1)      0      0       0 22-Apr-2019 16:54 \xa2\x85\xb0z\x13\xe9\x09\x86R\xed\xdc\xce\xad\x14d\x19
> > > +		#
> > > +		$DEBUGFS_PROG $device -R "ls -l -r <$dir_inode>" \
> > > +					2>>$seqres.full | perl -ne '
> > > +			next if not /^\s*'$inode'\s+/;
> > > +			s/.*?\d\d:\d\d //;
> > > +			chomp;
> > > +			s/\\x([[:xdigit:]]{2})/chr hex $1/eg;
> > > +			print;'
> > > +		;;
> > > +	f2fs)
> > > +		# Extract the filename from the dump.f2fs output line like:
> > > +		#
> > > +		#  i_name                        		[UpkzIPuts9by1oDmE+Ivfw]
> > > +		#
> > > +		# The name is base64-encoded, so we have to decode it here.
> > > +		#
> > > +		$DUMP_F2FS_PROG $device -i $inode | perl -ne '
> > > +			next if not /^i_name\s+\[([A-Za-z0-9+,]+)\]/;
> > > +			chomp $1;
> > > +			my @chars = split //, $1;
> > > +			my $ac = 0;
> > > +			my $bits = 0;
> > > +			my $table = join "", (A..Z, a..z, 0..9, "+", ",");
> > > +			foreach (@chars) {
> > > +				$ac += index($table, $_) << $bits;
> > > +				$bits += 6;
> > > +				if ($bits >= 8) {
> > > +					print chr($ac & 0xff);
> > > +					$ac >>= 8;
> > > +					$bits -= 8;
> > > +				}
> > > +			}
> > > +			if ($ac != 0) {
> > > +				print STDERR "Invalid base64-encoded string!\n";
> > > +			}'
> > > +		;;
> > > +	*)
> > > +		_notrun "_get_on_disk_filename() isn't implemented on $FSTYP"
> > 
> > And looks like this function has nothing to do with fs encryption, move it to
> > common/rc?
> 
> For ext4 that's true, but for f2fs the name is assumed to be base64-encoded,
> which f2fs-tools only does for encrypted filenames.  I'll update the comment to
> clarify that the function assumes the directory is encrypted.
> 
> > 
> > > +		;;
> > > +	esac
> > > +}
> > > +
> > > +# Require support for _get_on_disk_filename()
> > > +_require_get_on_disk_filename_support()
> > > +{
> > > +	echo "Checking for _get_on_disk_filename() support for $FSTYP" >> $seqres.full
> > > +	case $FSTYP in
> > > +	ext4)
> > > +		# Verify that the "ls -l -r" debugfs command is supported and
> > > +		# hex-encodes non-ASCII characters, rather than using an
> > > +		# ambiguous escaping method.  This requires the e2fsprogs patch
> > > +		# "debugfs: avoid ambiguity when printing filenames"
> > > +		# (https://marc.info/?l=linux-ext4&m=155596495624232&w=2).
> > > +		# TODO: once merged, list the minimum e2fsprogs version here.
> > > +		_require_command "$DEBUGFS_PROG" debugfs
> > > +		_scratch_mount
> > > +		touch $SCRATCH_MNT/$'\xc1'
> > > +		_scratch_unmount
> > > +		if ! $DEBUGFS_PROG $SCRATCH_DEV -R "ls -l -r /" 2>&1 \
> > > +			| tee -a $seqres.full | grep -E -q '\s+\\xc1\s*$'; then
> > > +			_notrun "debugfs (e2fsprogs) is too old; doesn't support showing unambiguous on-disk filenames"
> > > +		fi
> > > +		;;
> > > +	f2fs)
> > > +		# Verify that dump.f2fs shows encrypted filenames in full.  This
> > > +		# requires the patch "f2fs-tools: improve filename printing"
> > > +		# (https://sourceforge.net/p/linux-f2fs/mailman/message/36648641/).
> > > +		# TODO: once merged, list the minimum f2fs-tools version here.
> > > +
> > > +		_require_command "$DUMP_F2FS_PROG" dump.f2fs
> > > +		_require_command "$KEYCTL_PROG" keyctl
> > > +		_scratch_mount
> > > +		_new_session_keyring
> > > +
> > > +		local keydesc=$(_generate_encryption_key)
> > > +		local dir=$SCRATCH_MNT/test.${FUNCNAME[0]}
> > > +		local file=$dir/$(perl -e 'print "A" x 255')
> > > +		mkdir $dir
> > > +		_set_encpolicy $dir $keydesc
> > > +		touch $file
> > > +		local inode=$(stat -c %i $file)
> > > +
> > > +		_scratch_unmount
> > > +		$KEYCTL_PROG clear @s
> > > +
> > > +		# 255-character filename should result in 340 base64 characters.
> > > +		if ! $DUMP_F2FS_PROG -i $inode $SCRATCH_DEV \
> > > +			| grep -E -q '^i_name[[:space:]]+\[[A-Za-z0-9+,]{340}\]'; then
> > > +			_notrun "dump.f2fs (f2fs-tools) is too old; doesn't support showing unambiguous on-disk filenames"
> > > +		fi
> > > +		;;
> > > +	*)
> > > +		_notrun "_get_on_disk_filename() isn't implemented on $FSTYP"
> > > +		;;
> > > +	esac
> > > +}
> > > +
> > > +# Get the file's list of on-disk blocks as a comma-separated list of block
> > > +# offsets from the start of the device.  "Blocks" are 512 bytes each here.
> > > +_get_file_block_list()
> > > +{
> > > +	local file=$1
> > > +
> > > +	sync
> > > +	$XFS_IO_PROG -c fiemap $file | perl -ne '
> > > +		next if not /^\s*\d+: \[\d+\.\.\d+\]: (\d+)\.\.(\d+)/;
> > > +		print $_ . "," foreach $1..$2;' | sed 's/,$//'
> > > +}
> > > +
> > > +# Dump a block list that was previously saved by _get_file_block_list().
> > > +_dump_file_blocks()
> > > +{
> > > +	local device=$1
> > > +	local blocklist=$2
> > > +	local block
> > > +
> > > +	for block in $(tr ',' ' ' <<< $blocklist); do
> > > +		dd if=$device bs=512 count=1 skip=$block status=none
> > > +	done
> > > +}
> > 
> > Above two functions seem generic enough to be moved to common/rc
> 
> I feel that would be premature because common/rc is kind of bloated, and there's
> a good chance these functions will only ever be used for encryption tests.
> Normally, xfstests only test for user-visible behavior, so tests just 'cat' the
> file contents, or 'ls' the filenames.  The encryption tests are somewhat special
> in that they really care about what's *actually* stored on-disk.
> 
> So I think that common/encrypt is the most logical location for now.  But I

Yeah, that makes sense to me. Perhaps the functions should be renamed to
reflect that they're encryption-related?

Thanks,
Eryu

> don't feel too strongly, and I can move it if you prefer.
> 
> Thanks for the review!
> 
> - Eric

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