Re: [PATCH v3 0/3] Add file-system authentication to BTRFS

[David Sterba <dsterba@suse.cz>]

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.

That's a good point.

The v1 space cache will be phased out but it won't be in a timeframe
we'll get in the authentication. At this point we don't even have a way
to select v2 at mkfs time (it's work in progress though), so it would be
required to switch to v2 on the first mount.

> - 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.

Fallocate is a standard file operation, not supporting would be quite
strange. What's the problem with fallocate and authentication?