linux-kernel - Re: [lxc-devel] Kernel bug? Setuid apps and user namespaces

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Date:	Fri, 04 Apr 2014 11:13:50 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"Serge E. Hallyn" <serge@...lyn.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Sean Pajot <sean.pajot@...culink.com>,
	lxc-devel@...ts.linuxcontainers.org, linux-kernel@...r.kernel.org
Subject: Re: [lxc-devel] Kernel bug? Setuid apps and user namespaces

On 04/02/2014 10:32 AM, Serge E. Hallyn wrote:
> (Sorry - the lxc-devel list has moved, so replying to all with the
> correct list address;   please reply to this rather than my previous
> email)
> 
> Quoting Serge Hallyn (serge.hallyn@...ntu.com):
>> Hi Eric,
>>
>> (sorry, I don't seem to have the email I actually wanted to reply
>> to in my mbox, but it is
>> https://lists.linuxcontainers.org/pipermail/lxc-devel/2013-October/005857.html)
>>
>> You'd said,
>>> Someone needs to read and think through all of the corner cases and see
>>> if we can ever have a time when task_dumpable is false but root in the
>>> container would not or should not be able to see everything.
>>>
>>> In particular I am worried about the case of a setuid app calling setns,
>>> and entering a lesser privileged user namespace.  In my foggy mind that
>>> might be a security problem.  And there might be other similar crazy
>>> cases.
>>
>> Can we make use of current->mm->exe_file->f_cred->user_ns?
>>
>> So either always use 
>> make_kgid(current->mm->exe_file->f_cred->user_ns, 0)
>> instead of make_kuid(cred->user_ns, 0), or check that
>> (current->mm->exe_file->f_cred->user_ns == cred->user_ns)
>> and, if not, assume that the caller has done a setns?

Do you have a summary of the issue?  I'm a little lost here.

I suspect that what we really need is to revoke a bunch of proc files
every time a task does anything involving setuid (or, more generally,
any of the LSM_UNSAFE_PTRACE things).

--Andy
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