netdev - Re: [net PATCH] flow_dissector: Fix unaligned access in __skb_flow_dissector when used by eth_get

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Message-Id: <20160129.193520.477355610549821770.davem@davemloft.net>
Date:	Fri, 29 Jan 2016 19:35:20 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	aduyck@...antis.com, netdev@...r.kernel.org,
	alexander.duyck@...il.com, sowmini.varadhan@...cle.com,
	tom@...bertland.com
Subject: Re: [net PATCH] flow_dissector: Fix unaligned access in
 __skb_flow_dissector when used by eth_get_headlen

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 29 Jan 2016 19:23:54 -0800

> On Fri, 2016-01-29 at 18:49 -0800, Alexander Duyck wrote:
>> This patch fixes an issue with unaligned accesses when using
>> eth_get_headlen on a page that was DMA aligned instead of being IP aligned.
>> The fact is when trying to check the length we don't need to be looking at
>> the flow label so we can reorder the checks to first check if we are
>> supposed to gather the flow label and then make the call to actually get
>> it.
>> 
>> Reported-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
>> Signed-off-by: Alexander Duyck <aduyck@...antis.com>
>> ---
> 
> 
> You did not quite follow the discussion Alexander, we did not exactly
> took a decision about this bug.
> 
> As we mentioned, there are other parts that need care.
> 
> key_keyid->keyid = *keyid;
> 
> Please address them, instead of having to 'wait' for the next crash.

Indeed, this is a more fundamental issue.

This change in and of itself isn't bad, and is probably a suitable
micro-optimization for net-next, but it doesn't fix the bug in
question.