Re: [PATCH -mm] vmscan: make mapped executable pages the first class citizen

Elladan
2009-05-08T03:43:11Z

On Thu, May 07, 2009 at 01:11:41PM -0400, Rik van Riel wrote:
> Christoph Lameter wrote:
>
>> We need some way to control this. If there would be a way to simply switch
>> off eviction of exec pages (via /proc/sys/vm/never_reclaim_exec_pages or
>> so) I'd use it.
>
> Nobody (except you) is proposing that we completely disable
> the eviction of executable pages. I believe that your idea
> could easily lead to a denial of service attack, with a user
> creating a very large executable file and mmaping it.
>
> Giving executable pages some priority over other file cache
> pages is nowhere near as dangerous wrt. unexpected side effects
> and should work just as well.

I don't think this sort of DOS is relevant for a single user or trusted user
system.

I don't know of any distro that applies default ulimits, so desktops are
already susceptible to the far more trivial "call malloc a lot" or "fork bomb"
attacks. Plus, ulimits don't help, since they only apply per process - you'd
need a default mem cgroup before this mattered, I think.

Thanks,
Elladan