linux-kernel - Re: [RFC][PATCH 2/7] RSS controller core

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Date:	Thu, 15 Mar 2007 18:55:45 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Dave Hansen <hansendc@...ibm.com>, menage@...gle.com,
	containers@...ts.osdl.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, xemul@...ru
Subject: Re: [RFC][PATCH 2/7] RSS controller core

Alan Cox <alan@...rguk.ukuu.org.uk> writes:

>> stuff is happening by comparing page->count and page->_mapcount, but it
>> certainly wouldn't be conclusive.  But, does this kind of nonsense even
>> happen in practice?  
>
> "Is it useful for me as a bad guy to make it happen ?"

To create a DOS attack.

- Allocate some memory you know your victim will want in the future,
  (shared libraries and the like).
- Wait until your victim is using the memory you allocated.
- Terminate your memory resource group.
- Victim is pushed over memory limits by your exiting.
- Victim can no longer allocate memory
- Victim dies

It's not quite that easy unless your victim calls mlockall(MCL_FUTURE),
but the potential is clearly there.

Am I missing something?  Or is this fundamental to any first touch scenario?

I just know I have problems with first touch because it is darn hard to
reason about.

Eric
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