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

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Date:	Wed, 20 Apr 2011 17:34:26 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	vegardno@....uio.no
Cc:	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	casteyde.christian@...e.fr,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org
Subject: Re: [Bugme-new] [Bug 33502] New: Caught 64-bit read from
 uninitialized memory in __alloc_skb

Le mercredi 20 avril 2011 à 17:15 +0200, Vegard Nossum a écrit :

>  Thanks, guys. I wonder: Is it possible to make a reproducible test-case 
>  (e.g. loadable module) for this?
> 

Not easy to code a specific test-case, but just use regular workload,
(and network trafic to get interrupts). Use CONFIG_PREEMPT to trigger
preemptions.

>  Also, pardon my ignorance, but can you explain why this is a bug with 
>  kmemcheck/page-alloc debug and not without them?

Without them, we can read object->next without trigerring a fault.
We can read garbage data (if object is in use, it was overwritten with
user data), but this doesnt matter because cmpxchg_double() wont perform
its work (since tid will have change)



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