Re: disable-cap-mlock

[Chris Wright <chrisw@osdl.org>]

* Andrea Arcangeli (andrea@suse.de) wrote:
> On Thu, Apr 01, 2004 at 06:21:27PM -0800, Chris Wright wrote:
> > Ah, yes I see what you are saying.  This is the same issue with normal
> > pages and SHM_LOCK that I mentioned earlier, I believe.  I don't see the
> > best solution, because once you detach w/out any destroy, there could be
> > nobody to assign the accounting to.  Do you agree?
> 
> yes, rlimit just can't account for shmget(SHM_HUGETLB) and
> shmctl(SHM_LOCK) either, because it can only account the stuff that you
> temporarily have in the address space.
> 
> the exploit is simply to shmget tons of 2M hugepage segments, and to
> shmat/shmdt all of them, then you'll pin N times those 2M largepages,
> and they will not be accounted anywhere allowing anybody to pin as much
> memory as they want.

Yup.  I had an earlier patch against 2.4 that created a max count for
pages lockable by unprivileged users.  So the accounting was done
against a global pool, and mitigated the DoS damage to those trying to
share this pool.  I think it was more of a hack, though.

thanks,
-chris
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