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

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Date:   Tue, 22 Aug 2017 10:36:00 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     Anand Jain <anand.jain@...cle.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 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