linux-ext4 - Re: [PATCH] fscrypt: add a documentation file for filesystem-level encryption

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Message-ID: <94e45437-c71c-1d45-ffcb-2cf2447261b8@oracle.com>
Date:   Mon, 28 Aug 2017 20:18:55 +0800
From:   Anand Jain <anand.jain@...cle.com>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     "Theodore Y . Ts'o" <tytso@....edu>, linux-fscrypt@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, Jaegeuk Kim <jaegeuk@...nel.org>,
        Richard Weinberger <richard@....at>,
        Michael Halcrow <mhalcrow@...gle.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH] fscrypt: add a documentation file for filesystem-level
 encryption



On 08/23/2017 01:36 AM, Eric Biggers wrote:
> On Tue, Aug 22, 2017 at 11:35:20PM +0800, Anand Jain wrote:
>>>>
>>>>    I think AE is the only good solution for this, File-name encryption at
>>>> this stage won't solve any kind of Evil Maid attack, (as it was quoted
>>>> somewhere else in ML).
>>>>
>>>>
>>>>   Further, below,  is define but not used.
>>>> -----
>>>>   #define FS_AES_256_GCM_KEY_SIZE		32
>>>> -----
>>>>
>>>
>>> Yes, authenticated encryption with AES-256-GCM was in an older version of the
>>> ext4 encryption design document.  But unfortunately it was never really thought
>>> through. The primary problem, even ignoring rollback protection, is that there
>>> is nowhere to store the per-block metadata (GCM authentication tag and IV) *and*
>>> have it updated atomicly with the block contents.  Recently, dm-integrity solves
>>> this at the block device layer, but it uses data journaling which is very
>>> inefficient.  This maybe could be implemented more efficiently on a COW
>>> filesystem like BTRFS.  But even after that, another problem is that
>>> authenticated encryption of file contents only would not stop an attacker from
>>> swapping around blocks, files, directories, or creating links, etc.
>>
>>
>>   Some of the problems to be solved in this area are quite
>> interesting and challenging and IMO BTRFS fits nicely. Per extent AE
>> for BTRFS is drafted, it needs scrutiny and constructive feedback.
>>
>> Thanks, Anand
>>
>>
>>> Eric
>>>
> 
> Where is the code?  Is there a design document, and it is it readable by people
> not as familiar with btrfs?  Is the API compatible with ext4, f2fs, and ubifs?
> 
> Eric

  (sorry for the delay in replay due to my vacation).

  Eric, No code yet, proposed encryption method is seeking review. Link 
sent to you.

Thanks, Anand