netdev - Re: [PATCH 1/2] tcp: Fix out of bounds access to tcpm

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Message-ID: <4FFE2C8B.7080802@gmail.com>
Date:	Wed, 11 Jul 2012 18:46:51 -0700
From:	Alexander Duyck <alexander.duyck@...il.com>
To:	David Miller <davem@...emloft.net>
CC:	alexander.h.duyck@...el.com, netdev@...r.kernel.org,
	jeffrey.t.kirsher@...el.com
Subject: Re: [PATCH 1/2] tcp: Fix out of bounds access to tcpm_vals

On 7/11/2012 5:32 PM, David Miller wrote:
> From: Alexander Duyck<alexander.h.duyck@...el.com>
> Date: Wed, 11 Jul 2012 17:18:04 -0700
>
>> The recent patch "tcp: Maintain dynamic metrics in local cache." introduced
>> an out of bounds access due to what appears to be a typo.   I believe this
>> change should resolve the issue by replacing the access to RTAX_CWND with
>> TCP_METRIC_CWND.
>>
>> Signed-off-by: Alexander Duyck<alexander.h.duyck@...el.com>
> Applied, thanks a lot.
>
> How did you spot this, did you get a compiler warning?
>
> I ask because while working on this, I at one point put the
> tcp timestamp members after the metrics array in the
> tcp_metrics_bucket struct.  And I got a warning from gcc about
> an array bounds violation that I could not figure out.
>
> I am pretty certain this bug here is what it was warning about.  And
> the problem is that if you put the array at the end gcc doesn't warn
> in order to handle things similar to what people use zero length
> arrays for.
It came up as a compiler warning.  I suspect it may have something to do 
with the optimizations I had turned on since it complained that the 
issue was in tcp_update_metrics but then reported it on the one line in 
tcp_metric_set.

Thanks,

Alex
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