linux-kernel - Re: [PATCH] ipv6: ip6mr: Recalc UDP checksum before forwarding

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Message-ID: <1513187564.25033.65.camel@gmail.com>
Date:   Wed, 13 Dec 2017 09:52:44 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Brendan McGrath <redmcg@...mandi.dyndns.org>,
        "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv6: ip6mr: Recalc UDP checksum before forwarding

On Wed, 2017-12-13 at 22:20 +1100, Brendan McGrath wrote:
> Currently, when forwarding from a Virtual Interface to a Physical
> Interface, ip_summed is set to a value of CHECKSUM_UNNECESSARY and
> the UDP checksum has not been calculated.
> 

This seems a bug then ?
CHECKSUM_UNNECESSARY means checksum has been validated.
Not that we want it being computed later in the stack.

If we force a checksum here, what guarantee do we have packet was not
corrupted before we do this ?