linux-ext4 - Re: [PATCH] fscrypto: make XTS tweak initialization endian-independent

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Date:   Tue, 4 Oct 2016 10:46:54 +0200
From:   Richard Weinberger <richard@....at>
To:     Eric Biggers <ebiggers@...gle.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        Theodore Ts'o <tytso@....edu>, jaegeuk@...nel.org,
        David Gstir <david@...ma-star.at>
Subject: Re: [PATCH] fscrypto: make XTS tweak initialization
 endian-independent

Eric,

On 03.10.2016 20:03, Eric Biggers wrote:
>>>  {
>>> -       u8 xts_tweak[FS_XTS_TWEAK_SIZE];
>>> +       struct {
>>> +               __le64 index;
>>> +               u8 padding[FS_XTS_TWEAK_SIZE - sizeof(__le64)];
>>> +       } xts_tweak;
>>
>> While we are here, wouldn't it make sense to rename the variable to "iv"?
>> In aes-xts mode the IV is used as tweak. But it is still an IV and passed
>> as IV parameter to the crypto API.
>>
>> Especially when other cipher modes are used this is confusing.
>>
> 
> Good idea --- I agree that "iv" is a better name, so as to not tie the code to
> XTS specifically.  But I think the renaming should be a separate patch.

Sure. I can do that.

> Also, currently this code *is* only supposed to be used for XTS.  There's a bug
> where a specially crafted filesystem can cause this code path to be entered with
> CTS, but I have a patch pending in the ext4 tree to fix that.

David and I are currently working on UBIFS encryption and we have to support other cipher
modes than XTS. So, keeping fscrypto as generic as possible would be nice. :-)

Thanks,
//richard
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