Re: Setting FS_USERNS_MOUNT in btrfs_fs_type.fs_flags

[Zach Brown]

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)
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