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SubjectRe: [PATCH nf-next] netfilter: xt_CHECKSUM: avoid bad offload warnings on GSO packets
On Thu, Aug 24, 2017 at 03:17:22PM +0200, Florian Westphal wrote:
> Davide Caratti <> wrote:
> > Small nit: may I suggest you to call skb_csum_hwoffload_help() instead of
> > skb_checksum_help(), so that we avoid corrupting SCTP packets in case they
> > hit xt_CHECKSUM target?
> Alternatively we could restrict the target to udp only.
> AFAIU the only reason this thing exists is to fix up udp checksum
> for old dhcp clients that use AF_PACKET without evaluating the extra
> metadata that indicates when a 'bad' checksum is in fact ok because it
> is supposed to be filled in by hardware later.
> This can happen in virtual environemnt when such skb is directly passed
> to vm.

Based on what the documentation and the commit message of the commit
introducing xt_CHECKSUM module say, it seems so. But I must admit I'm
not sure where is the target is used and how (and why). In particular,
our issue was most likely result of

where they explicitely confine it to TCP packets. Unfortunately these
lines come from "Initial testing commit" so it's hard to say what the
intention behind that was.

Michal Kubecek

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