netdev - Re: [RFC] Kernel unaligned access at __skb_flow

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Message-ID: <20160129194434.GC17127@oracle.com>
Date:	Fri, 29 Jan 2016 14:44:34 -0500
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [RFC] Kernel unaligned access at __skb_flow_dissect

On (01/29/16 11:37), Eric Dumazet wrote:
> 
> I have no idea why reading iph->saddr or iph->daddr would not hit the
> problem, but accessing the 32bit ipv6 flow label would be an issue.
> 
> Something is fishy.

I was wondering about this myself. Even on sparc, I only first
ran into the errors for ipv6. I dont know if the fact that the
saddr is memcpy'ed masks the error (even though the problem
is still there). 

But doing the check of: if (!IS_ALIGNED(..)) on the iph->saddr in the
code does result in a positive.

> But really adding unaligned() accesses in flow dissector would slow it
> quite a lot on MIPS and others.