linux-kernel - Re: Setting FS_USERNS_MOUNT in btrfs_fs_type.fs

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Message-ID: <20140917203135.GC2068@nixos>
Date:	Wed, 17 Sep 2014 16:31:35 -0400
From:	Shea Levy <shea@...alevy.com>
To:	Zach Brown <zab@...bo.net>
Cc:	Al Viro <viro@...IV.linux.org.uk>, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Setting FS_USERNS_MOUNT in btrfs_fs_type.fs_flags

On Wed, Sep 17, 2014 at 09:12:14AM -0700, Zach Brown wrote:
> On Wed, Sep 17, 2014 at 04:54:48AM +0100, Al Viro wrote:
> > On Tue, Sep 16, 2014 at 11:05:00PM -0400, Shea Levy wrote:
> > > Hi all,
> > > 
> > > What work would be required to mark btrfs_fs_type with FS_USERNS_MOUNT
> > > so that btrfs images can be mounted by unprivileged users within a user
> > > namespace (along with something like [1])? I'd like to be able to create
> > > disk images without having to start a VM (and --rootdir isn't flexible
> > > enough because I want to make subvolumes).
> > 
> > Er...  Which is to say, you have an audit of btrfs code making sure that
> > it can cope with arbitrary image hand-crafted by potential attacker?
> 
> It definitely can't cope. The easiest places to find bugs are the
> hundreds of BUG_ON() sites, many can be triggered by on-disk structures.
> The sheer volume of those makes me trust that you could find much worse
> if you did a thorough audit.
> 
> - z
> (fun related fact: distros automount btrfs images)

OK, so it seems like the answer to my question is "a helluva lot". Guess
I won't count on seeing it any time soon :)

Thanks,
Shea
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