On Thu, Oct 8, 2015 at 1:26 PM, Maxime Bizon <mbizon@xxxxxxxxxx> wrote:
>
> With this setup:
>
> * non IPv6 checksumming capable network hardware
> * GRO off
> * IPv6 SNAT
>
> I get this when I receive an UDPv6 reply: "<unknown>: hw csum failure"
>
> Call trace:
>
> * nf_ip6_checksum() calls __skb_checksum_complete()
> * nf_nat_ipv6_csum_update() & nf_nat_ipv6_manip_pkt()
> * __udp6_lib_rcv() => udp6_csum_init()
> * __skb_checksum_validate_complete() "fastpath" fails because
> skb->csum is incorrect.
> * udpv6_recvmsg() => skb_copy_and_csum_datagram_msg()
>
> The last call computes a valid checksum despite CHECKSUM_COMPLETE and
> triggers the warning.
>
> When we perform NAT on IPv4, we also update the IPv4 checksum, so
> there is no side effect on skb->csum (since the csum over a valid IPv4
> header area was already zero).
>
> But IPv6 doesn't have such checksum, so when performing NAT we need to
> update skb->csum.
>
> Signed-off-by: Maxime Bizon <mbizon@xxxxxxxxxx>
> ---
> net/ipv6/netfilter/nf_nat_l3proto_ipv6.c | 23 +++++++++++++++++++----
> 1 file changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c b/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c
> index 70fbaed..e44af9c 100644
> --- a/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c
> +++ b/net/ipv6/netfilter/nf_nat_l3proto_ipv6.c
> @@ -81,6 +81,8 @@ static bool nf_nat_ipv6_manip_pkt(struct sk_buff *skb,
> enum nf_nat_manip_type maniptype)
> {
> struct ipv6hdr *ipv6h;
> + const __be32 *to;
> + __be32 *from;
> __be16 frag_off;
> int hdroff;
> u8 nexthdr;
> @@ -100,11 +102,24 @@ static bool nf_nat_ipv6_manip_pkt(struct sk_buff *skb,
> target, maniptype))
> return false;
> manip_addr:
> - if (maniptype == NF_NAT_MANIP_SRC)
> - ipv6h->saddr = target->src.u3.in6;
> - else
> - ipv6h->daddr = target->dst.u3.in6;
> + if (maniptype == NF_NAT_MANIP_SRC) {
> + from = ipv6h->saddr.s6_addr32;
> + to = target->src.u3.in6.s6_addr32;
> + } else {
> + from = ipv6h->daddr.s6_addr32;
> + to = target->dst.u3.in6.s6_addr32;
> + }
> +
> + if (skb->ip_summed == CHECKSUM_COMPLETE) {
> + __be32 diff[] = {
> + ~from[0], ~from[1], ~from[2], ~from[3],
> + to[0], to[1], to[2], to[3],
> + };
> +
> + skb->csum = ~csum_partial(diff, sizeof(diff), ~skb->csum);
> + }
>
I think inet_proto_csum_replace16 should be called here.
> + memcpy(from, to, sizeof (struct in6_addr));
> return true;
> }
>
> --
> 1.9.1
>
>
> --
> Maxime
>
>
> --
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