netdev - Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from uninitialized memory in __alloc

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Message-ID: <1303182557.4152.48.camel@edumazet-laptop>
Date:	Tue, 19 Apr 2011 05:09:17 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	netdev@...r.kernel.org, bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org, casteyde.christian@...e.fr,
	Vegard Nossum <vegardno@....uio.no>,
	Pekka Enberg <penberg@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from
 uninitialized memory in __alloc_skb

Le mardi 19 avril 2011 à 04:51 +0200, Eric Dumazet a écrit :

> Hmm, looking at mm/slub.c, I wonder what prevents "object" from pointing
> to a now freed and unreachable zone of memory. (Say we are interrupted,
> object given to interrupt handler and this one wants to change page bits
> to trap access)


Yes, I suspect this whole business is not kmemcheck compatable, or
DEBUG_PAGEALLOC

get_freepointer(s, object) can access to freed memory and kmemcheck
triggers the fault, while this_cpu_cmpxchg_double() would presumably
detect a change of tid and would not perform the freelist/tid change.




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