Re: [PATCH] common/encrypt: allow the use of 'fscrypt:' as key prefix

["Luís Henriques" <lhenriques@suse.de>]

Eric Biggers <ebiggers@kernel.org> writes:

> On Fri, Apr 01, 2022 at 11:45:53AM +0100, Luís Henriques wrote:
>> fscrypt keys have used the $FSTYP as prefix.  However this format is being
>> deprecated -- newer kernels already allow the usage of the generic
>> 'fscrypt:' prefix for ext4 and f2fs.  This patch allows the usage of this
>> new prefix for testing filesystems that have never supported the old
>> format, but keeping the $FSTYP prefix for filesystems that support it, so
>> that old kernels can be tested.
>> 
>> Signed-off-by: Luís Henriques <lhenriques@suse.de>
>> ---
>>  common/encrypt | 38 +++++++++++++++++++++++++++-----------
>>  1 file changed, 27 insertions(+), 11 deletions(-)
>> 
>> diff --git a/common/encrypt b/common/encrypt
>> index f90c4ef05a3f..897c97e0f6fa 100644
>> --- a/common/encrypt
>> +++ b/common/encrypt
>> @@ -250,6 +250,27 @@ _num_to_hex()
>>  	fi
>>  }
>>  
>> +# Keys are named $FSTYP:KEYDESC where KEYDESC is the 16-character key descriptor
>> +# hex string.  Newer kernels (ext4 4.8 and later, f2fs 4.6 and later) also allow
>> +# the common key prefix "fscrypt:" in addition to their filesystem-specific key
>> +# prefix ("ext4:", "f2fs:").  It would be nice to use the common key prefix, but
>> +# for now use the filesystem- specific prefix for these 2 filesystems to make it
>> +# possible to test older kernels, and the "fscrypt" prefix for anything else.
>> +_get_fs_keyprefix()
>> +{
>> +	local prefix=""
>> +
>> +	case $FSTYP in
>> +	ext4|f2fs|ubifs)
>> +		prefix="$FSTYP"
>> +		;;
>> +	*)
>> +		prefix="fscrypt"
>> +		;;
>> +	esac
>> +	echo $prefix
>> +}
>
> ubifs can use the "fscrypt" prefix, since there was never a kernel that
> supported ubifs encryption but not the "fscrypt" prefix.  Also, the "prefix"
> local variable is unnecessary.  So:
>
> 	case $FSTYP in
> 	ext4|f2fs)
> 		echo $FSTYP
> 		;;
> 	*)
> 		echo fscrypt
> 		;;
> 	esac
>
> Otherwise, this patch looks fine if we want to keep supporting testing kernels
> older than 4.8.  However, since 4.4 is no longer a supported LTS kernel, perhaps
> this is no longer needed and we could just always use "fscrypt"?  I'm not sure
> what xfstests's policy on old kernels is.

Thank you for your feedback.  I'll resend the patch with your changes.  I
am, of course, OK dropping support for older kernels on fstests, but I'll
leave that decision for the maintainers; if anyone thinks that support
should be dropped, I can send another version of the patch doing that.

Cheers,
-- 
Luís