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

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Date:	Thu, 17 Jan 2013 00:03:49 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] Avoid making inappropriate requests of
 NETIF_F_V[46]_CSUM devices

On Wed, 2013-01-16 at 18:00 -0500, David Miller wrote:
> I'm saying that tun can't inject unchecked crap into our stack.

That's a very strange way of putting it.

Our stack has explicit support for sane hardware devices with
NETIF_F_HW_CSUM capability that can checksum anything.

And it has checks (harmonize_features) on output, so that if the device
on which a packet is being emitted *doesn't* have appropriate hardware
checksum capability, we'll do the checksum in software.

Except that the check in harmonize_features() doesn't do that check
*properly*. It only catches *some* of the packets that the device can't
handle, and lets others through.

So we basically can't use NETIF_F_HW_CSUM in the general case, for
anything like SCTP or any other protocol, because harmonize_features()
is buggy and will let it go out a device that can't handle it.

Um, SCTP *does* use CHECKSUM_PARTIAL. Am I missing something or does
that suffer the same problem?

-- 
dwmw2

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