netdev - Re: IPv6-UDP 0x0000 checksum

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Message-ID: <1485442164.14760.11.camel@sipsolutions.net>
Date:   Thu, 26 Jan 2017 15:49:24 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org,
        linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: IPv6-UDP 0x0000 checksum

On Thu, 2017-01-26 at 06:45 -0800, Eric Dumazet wrote:
> On Thu, 2017-01-26 at 14:49 +0100, Johannes Berg wrote:
> 
> > Oops, sorry - receive. We can only indicate "CHECKSUM_UNNECESSARY",
> > nothing more advanced right now, but right now we'd indicate that
> > if
> > the packet had 0x0000 in the checksum field, but should've had
> > 0xffff.
> > 
> > On TX I believe we actually do in HW exactly what your patch just
> > did.
> 
> Can you describe the visible effects of this problem ?
> 
> Is that because of a conversion we might do later to
> CHECKSUM_COMPLETE ?

Unfortunately, I haven't been able to actually test this yet. I also
didn't find the code that would drop frames with CSUM 0 either, so I'm
thinking - for now - that if all the csum handling is skipped, dropping
0 csum frames would also be, and then we'd accept a frame we should
actually have dropped.

I'll go test this I guess :)

Any pointers to where 0 csum frames are dropped?

johannes