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

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Date:	Fri, 29 Jan 2016 19:23:54 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <aduyck@...antis.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	alexander.duyck@...il.com,
	Sowmini Varadhan <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

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.

BTW, even a memcpy(&key_addrs->v4addrs, &iph->saddr, 8) could crash, as
the compiler can certainly assume src and dst are 4 bytes aligned, and
could use word accesses when inlining memcpy() even on Sparc.

Apparently the compiler used by Sowmini is gentle.

Thanks.