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Date:   Wed, 27 May 2020 15:11:35 +0200
From:   David Sterba <dsterba@suse.cz>
To:     Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc:     Johannes Thumshirn <jth@kernel.org>,
        David Sterba <dsterba@suse.cz>, linux-fsdevel@vger.kernel.org,
        linux-btrfs@vger.kernel.org, Eric Biggers <ebiggers@google.com>,
        Richard Weinberger <richard@nod.at>,
        Johannes Thumshirn <johannes.thumshirn@wdc.com>
Subject: Re: [PATCH v3 0/3] Add file-system authentication to BTRFS
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On Wed, May 27, 2020 at 10:08:06AM +0800, Qu Wenruo wrote:
> > Changes since v2:
> > - Select CONFIG_CRYPTO_HMAC and CONFIG_KEYS (kbuild robot)
> > - Fix double free in error path
> > - Fix memory leak in error path
> > - Disallow nodatasum and nodatacow when authetication is use (Eric)
> 
> Since we're disabling NODATACOW usages, can we also disable the
> following features?
> - v1 space cache
>   V1 space cache uses NODATACOW file to store space cache, althouhg it
>   has inline csum, but it's fixed to crc32c. So attacker can easily
>   utilize this hole to mess space cache, and do some DoS attack.
> 
> - fallocate
>   I'm not 100% sure about this, but since nodatacow is already a second
>   class citizen in btrfs, maybe not supporting fallocate is not a
>   strange move.

- swapfile
  NODATACOW is required for swapfile, so authentication and swapfile are
  mutualy exclusive.