Re: Module loading in unpriveledged domains

[David Hopwood <david.nospam.hopwood@blueyonder.co.uk>]

Ian Pratt wrote:
>>Ian Pratt wrote:
>>
>>>>Is there any security risk in enabling loadable module support in the linux
>>>>kernel used for the unpriveledged domains? I ask this question in the context of
>>>>a virtual private server hosting provider.
>>>
>>>There shouldn't be any security risk at all -- Xen should provide
>>>all the isolation you need (modulo any bugs).
>>
>>So the answer to the original question is, "yes, enabling loadable module
>>support will increase your exposure to security risks due to any weaknesses
>>in Xen's isolation." Xen hasn't had particularly extensive security review
>>yet.
> 
> I don't think that preventing loadable module support is going to
> buy you anything. If your users have root they can write to the
> domain's memory image and hence in practice do anything that they
> could if they had kernel modules.

True, unless there are bugs that cause different behaviour depending
on whether a module is compiled-in or loaded (such as
<http://lists.jammed.com/linux-security-module/2003/12/0012.html>).
Nevertheless enabling loadable modules may allow a greater proportion
of script kiddies to be capable of exploiting any given bug.

This is all the same as in standard Linux, so perhaps I should have
said: enable loadable modules iff you would do so in standard Linux.

> Xen has been designed to provide secure isolation between
> guests. It has undergone code review by a bunch of different
> people. It may have security bugs, but at least they're
> relatively obscure...

I remain skeptical.

-- 
David Hopwood <david.nospam.hopwood@blueyonder.co.uk>



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