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

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Message-ID: <20140917035448.GZ7996@ZenIV.linux.org.uk>
Date:	Wed, 17 Sep 2014 04:54:48 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Shea Levy <shea@...alevy.com>
Cc:	linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Setting FS_USERNS_MOUNT in btrfs_fs_type.fs_flags

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?
Because without that FS_USERNS_MOUNT could open one hell of security hole;
things like user being able to execute an arbitrary code in kernel mode,
etc.
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