Re: [RFC PATCH 1/3] Avoid making inappropriate requests of NETIF_F_V[46]_CSUM devices

[David Miller <davem@davemloft.net>]

From: David Woodhouse <dwmw2@infradead.org>
Date: Wed, 16 Jan 2013 22:34:18 +0000

> On Wed, 2013-01-16 at 15:54 -0500, David Miller wrote:
>> 
>> My opinion on this is that the injectors of packets are responsible
>> for ensuring checksum types are set on SKBs in an appropriate way.
>> 
>> So we ensure this in the local protocol stacks that generate packets,
>> and if foreign alien entities can inject SKBs with these checksum
>> settings (like the tun device can) the burdon of verification falls
>> upon whatever layer allows that to happen.
>> 
>> So really, the fix is in the tun device and the virtio layer.
> 
> The virtio layer (and the tun device) expose the equivalent of the
> NETIF_F_HW_CSUM capability to the guest. In the case where we have a
> real device on the host which *also* has NETIF_F_HW_CSUM capability, are
> you saying that the tun driver should do the checksum for non-UDP/TCP
> packets in software *anyway*, just because the packet might end up going
> out a device *without* that capability, and the check in
> harmonize_features() isn't sophisticated enough to cope properly?

I'm saying that tun can't inject unchecked crap into our stack.