Re: [patch 1/2] c/r: prctl: Add ability to set newmm_struct::exe_file

[Cyrill Gorcunov]

On Tue, Mar 20, 2012 at 12:02:44AM +0100, richard -rw- weinberger wrote:
> On Mon, Mar 19, 2012 at 11:46 PM, Andrew Morton
> <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > Well, let's discuss this more completely.  In what ways could an
> > attacker use this?  How serious is the problem?  What actions can be
> > taken to lessen it?  etcetera.
> 
> After considering the problem a bit more I think it's not a big problem.
> We must not trust /proc/pid/exe in anyway.

Well, Richard, we probably do not trust it anyway but sysadmins might do
(and this was another reason for one-shot behaviour -- to not bring
 heart attacks to sysadmins, and everyone would know this link might
 be changed only one time ;)

> An attacker can always execute another binary without calling execve().

That's what c/r basically does :)

> 
> So, why makes that one-short fashion the feature more secure?
> Let the user change the exe symlink as often as he wants.
> From a security point of view the exe symlink is anyway useless.

Maybe better to call it 'predictable' then rather than 'secure'?

	Cyrill
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