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 is zero).
But IPv6 doesn't have such header 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..e9917d74 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->src.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);
+ }
+ memcpy(from, to, sizeof (struct in6_addr));
return true;
}
--
1.9.1
--
Maxime
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