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Message-ID: <20110822095354.GA13836@openwall.com>
Date: Mon, 22 Aug 2011 13:53:54 +0400
From: Solar Designer <solar@...nwall.com>
To: kernel-hardening@...ts.openwall.com
Subject: Re: kmalloc() nofail allocations
Vasiliy,
On Mon, Aug 22, 2011 at 01:45:58PM +0400, Vasiliy Kulikov wrote:
> On Mon, Aug 22, 2011 at 13:38 +0400, Solar Designer wrote:
> > On Mon, Aug 22, 2011 at 01:24:29PM +0400, Vasiliy Kulikov wrote:
> > > Major problem with the idea in general:
> > ...
> > > Unlikely, but fully possible case - we want some memory and the OOM killer
> > > kills us for our wish.
> >
> > How/why is this a major problem with the idea in general? I am probably
> > missing something.
>
> Initially I wanted to "wrap" kmalloc calls, which cannot fail in any
> case. This would not change any mm code, but the caller (its
> expectation).
>
> Now I see that it's impossible without any mm code changes. It needs at
> least __GFP_NOFAIL flag addition, which is explicitly marked as "no new
> uses". Such kmalloc_nofail() wouldn't differ much from kmalloc(size,
> flags | __GFP_NOFAIL).
Thanks for the explanation.
However, is there any difference for the caller between kmalloc()
looping until success (and thus only returning on success) and it
OOM-killing the current process (and thus also only returning on
success)? Or does this question somehow not apply to the problem you
discovered?
Alexander
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