linux-kernel - Re: [patch 021/104] lib/idr.c: fix rcu related race with idr

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Date:	Tue, 9 Dec 2008 18:32:05 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Dave Airlie" <airlied@...il.com>
Cc:	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Greg KH" <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	"Randy Dunlap" <rdunlap@...otime.net>,
	"Chuck Ebbert" <cebbert@...hat.com>,
	"Domenico Andreoli" <cavokz@...il.com>, alan@...rguk.ukuu.org.uk,
	"Manfred Spraul" <manfred@...orfullife.com>,
	"Clement Calmels" <cboulte@...il.com>,
	"Nadia Derbey" <Nadia.Derbey@...l.net>,
	"Pierre Peiffer" <peifferp@...il.com>
Subject: Re: [patch 021/104] lib/idr.c: fix rcu related race with idr_find

On Wed, 10 Dec 2008 12:08:13 +1000 "Dave Airlie" <airlied@...il.com> wrote:

> >> if my usage is illegal over just overlooked.
> >
> >
> > <greps for a while>
> >
> > I assume we're talking about drivers/gpu/drm/drm_stub.c:drm_minor_get_id()?
> >
> > I don't immediately see anything in the idr code which special-cases a
> > NULL caller pointer?
> >
> 
> Actually now that I'm starting to wrap my head around it I think it
> might be the fact that I call
> idr_get_new_above with 64, then later with 0. I'm not sure the new
> code is dealing with that case so
> well.
> 
> We don't do that in the standard kernel tree yet, so it explains why
> nobody's noticed, however the KMS
> changes introduce it, and we have those in f10.
> 
> http://git.kernel.org/?p=linux/kernel/git/airlied/drm-2.6.git;a=blob;f=drivers/gpu/drm/drm_stub.c;h=5ca132afa4f2e128999e319e44e31ad156e6ab74;hb=drm-next
> 
> is the drm_stub.c from drm-next that will trigger the issue.
> 
> Again I'm not sure if this is a legal use of idrs.
> 

Well nobody really maintains or owns the idr code, so there's nobody we
can ask about design intent.  Various people do hit-n-run attacks on it
when the need presents.

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