[PATCH 1/2] namespaces: introduce sys_hijack (v10)

Stephen Smalley sds at tycho.nsa.gov
Tue Nov 27 10:09:24 PST 2007


On Tue, 2007-11-27 at 10:11 -0600, Serge E. Hallyn wrote:
> Quoting Crispin Cowan (crispin at crispincowan.com):
> > Just the name "sys_hijack" makes me concerned.
> > 
> > This post describes a bunch of "what", but doesn't tell us about "why"
> > we would want this. What is it for?
> 
> Please see my response to Casey's email.
> 
> > And I second Casey's concern about careful management of the privilege
> > required to "hijack" a process.
> 
> Absolutely.  We're definately still in RFC territory.
> 
> Note that there are currently several proposed (but no upstream) ways to
> accomplish entering a namespace:
> 
> 	1. bind_ns() is a new pair of syscalls proposed by Cedric.  An
> 	nsproxy is given an integer id.  The id can be used to enter
> 	an nsproxy, basically a straight current->nsproxy = target_nsproxy;
> 
> 	2. I had previously posted a patchset on top of the nsproxy
> 	cgroup which allowed entering a nsproxy through the ns cgroup
> 	interface.
> 
> There are objections to both those patchsets because simply switching a
> task's nsproxy using a syscall or file write in the middle of running a
> binary is quite unsafe.  Eric Biederman had suggested using ptrace or
> something like it to accomplish the goal.
> 
> Just using ptrace is however not safe either.  You are inheriting *all*
> of the target's context, so it shouldn't be difficult for a nefarious
> container/vserver admin to trick the host admin into running something
> which gives the container/vserver admin full access to the host.

I don't follow the above - with ptrace, you are controlling a process
already within the container (hence in theory already limited to its
container), and it continues to execute within that container.  What's
the issue there?

> That's where the hijack idea came from.  Yes, I called it hijack to make
> sure alarm bells went off :) bc it's definately still worrisome.  But at
> this point I believe it is the safest solution suggested so far.

-- 
Stephen Smalley
National Security Agency



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