linux-kernel - Re: [PATCH] ipc,sem block sem_lock on sma->lock during sma initialization

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Message-ID: <546FA0A7.2010507@redhat.com>
Date:	Fri, 21 Nov 2014 15:29:27 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-kernel@...r.kernel.org,
	Manfred Spraul <manfred@...orfullife.com>,
	Davidlohr Bueso <davidlohr@...com>,
	Rafael Aquini <aquini@...hat.com>
Subject: Re: [PATCH] ipc,sem block sem_lock on sma->lock during sma initialization

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On 11/21/2014 03:09 PM, Andrew Morton wrote:
> On Fri, 21 Nov 2014 14:52:26 -0500 Rik van Riel <riel@...hat.com>
> wrote:
> 
>> When manipulating just one semaphore with semop, sem_lock only
>> takes that single semaphore's lock. This creates a problem during
>> initialization of the semaphore array, when the data structures
>> used by sem_lock have not been set up yet. The sma->lock is
>> already held by newary, and we just have to make sure everything
>> else waits on that lock during initialization.
>> 
>> Luckily it is easy to make sem_lock wait on the sma->lock, by
>> pretending there is a complex operation in progress while the sma
>> is being initialized.
>> 
>> The newary function already zeroes sma->complex_count before
>> unlocking the sma->lock.
> 
> What are the runtime effects of the bug?
> 

NULL pointer dereference in spin_lock from sem_lock,
if it is called before sma->sem_base has been pointed
somewhere valid.

- -- 
All rights reversed
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