Re: CVE-2014-4014: Linux kernel user namespace bug

[Andy Lutomirski <luto () amacapital net>]

On Tue, Jun 10, 2014 at 2:49 PM, Andy Lutomirski <luto () amacapital net> wrote:
> The internal function inode_capable was used inappropriately.
> Depending on configuration, this may be usable to escalate privileges.
> A cursory inspection of my Fedora box suggests that it is not
> vulnerable to the obvious way to exploit this bug.
>
> The fix should appear in Linus' -master shortly, and it's tagged for
> stable.  In the mean time, I've attached it here.

The commit that fixes this is:

23adbe12ef7d3d4195e80800ab36b37bee28cd03

The bug is that, if you created a user namespace and retained
capabilities in that namespace, then you could use chmod to set the
setgid bit on any file you owned, including files with, say, group 0.

The impact depends on what files are available that have gids that
shouldn't be available to the users who own the file.  For example,
the existence of a uid != 0, gid == 0 file would allow that uid to
escalate privileges to gid 0, which is likely good enough for full
root.

--Andy