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SubjectRe: [PATCH] ipv6: ip6mr: Recalc UDP checksum before forwarding
Hi,

On Wed, Dec 13, 2017 at 10:20:48PM +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.
>
> When the packet is then forwarded by a Multicast Router, the checksum
> value is left as is and therefore rejected by the receiving
> machine(s).
>
> This patch ensures the checksum is recalculated before forwarding.
>
> Signed-off-by: Brendan McGrath <redmcg@redmandi.dyndns.org>
> ---
>
> It's a bit ugly putting UDP specific code in this spot - but I'm not
> aware of any other protocols that are:
> a) multicast;
> b) forwarded; and
> c) checksummed
>
> net/ipv6/ip6mr.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
> index 890f9bda..ee4370a 100644
> --- a/net/ipv6/ip6mr.c
> +++ b/net/ipv6/ip6mr.c
> @@ -2077,6 +2077,13 @@ static int ip6mr_forward2(struct net *net, struct mr6_table *mrt,
> ipv6h = ipv6_hdr(skb);
> ipv6h->hop_limit--;
>
> + if (ipv6h->nexthdr == NEXTHDR_UDP &&
> + skb->ip_summed != CHECKSUM_PARTIAL) {
^

This indentation is wrong. The 2nd line should start right after the (
column in the 1st line, like:
+ if (ipv6h->nexthdr == NEXTHDR_UDP &&
+ skb->ip_summed != CHECKSUM_PARTIAL) {
Adjust with spaces as needed.

Running the patch through scripts/checkpatch.pl before posting will
catch these.

> + struct udphdr *uh = udp_hdr(skb);
> + udp6_set_csum(false, skb, &ipv6_hdr(skb)->saddr,
> + &ipv6_hdr(skb)->daddr, ntohs(uh->len));
^ same deal here.

> + }
> +
> IP6CB(skb)->flags |= IP6SKB_FORWARDED;
>
> return NF_HOOK(NFPROTO_IPV6, NF_INET_FORWARD,
> --
> 2.7.4
>

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