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

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Date:   Thu, 31 Aug 2017 11:14:42 -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 Mon, Aug 28, 2017 at 08:18:55PM +0800, Anand Jain wrote:
> 
> 
> 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

Thanks, I'll review it when I have time.  Can you please consider sending out a
public link to linux-fscrypt, linux-fsdevel, linux-btrfs, etc. so that other
people can review it too?

Eric