netdev - [PATCH 44/50] netfilter: nat: skip checksum on offload SCTP packets

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Date:   Wed,  7 Dec 2016 22:52:50 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org
Subject: [PATCH 44/50] netfilter: nat: skip checksum on offload SCTP packets

From: Davide Caratti <dcaratti@...hat.com>

SCTP GSO and hardware can do CRC32c computation after netfilter processing,
so we can avoid calling sctp_compute_checksum() on skb if skb->ip_summed
is equal to CHECKSUM_PARTIAL. Moreover, set skb->ip_summed to CHECKSUM_NONE
when the NAT code computes the CRC, to prevent offloaders from computing
it again (on ixgbe this resulted in a transmission with wrong L4 checksum).

Signed-off-by: Davide Caratti <dcaratti@...hat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 net/netfilter/nf_nat_proto_sctp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nf_nat_proto_sctp.c b/net/netfilter/nf_nat_proto_sctp.c
index 2e14108ff697..31d358691af0 100644
--- a/net/netfilter/nf_nat_proto_sctp.c
+++ b/net/netfilter/nf_nat_proto_sctp.c
@@ -47,7 +47,10 @@ sctp_manip_pkt(struct sk_buff *skb,
 		hdr->dest = tuple->dst.u.sctp.port;
 	}
 
-	hdr->checksum = sctp_compute_cksum(skb, hdroff);
+	if (skb->ip_summed != CHECKSUM_PARTIAL) {
+		hdr->checksum = sctp_compute_cksum(skb, hdroff);
+		skb->ip_summed = CHECKSUM_NONE;
+	}
 
 	return true;
 }
-- 
2.1.4