[PATCH v2] ipvs: Fix checksumming on GSO of SCTP packets

[Ismael Luceno]

It was observed in the wild that pairs of consecutive packets would leave
the IPVS with the same wrong checksum, and the issue only went away when
disabling GSO.

IPVS needs to avoid computing the SCTP checksum when using GSO.

Fixes: 90017accff61 ("sctp: Add GSO support", 2016-06-02)
Co-developed-by: Firo Yang <firo.yang@xxxxxxxx>
Signed-off-by: Ismael Luceno <iluceno@xxxxxxx>
Tested-by: Andreas Taschner <andreas.taschner@xxxxxxxx>
CC: Michal Kubeček <mkubecek@xxxxxxxx>
CC: Simon Horman <horms@xxxxxxxxxxxx>
CC: Julian Anastasov <ja@xxxxxx>
CC: lvs-devel@xxxxxxxxxxxxxxx
CC: netfilter-devel@xxxxxxxxxxxxxxx
CC: netdev@xxxxxxxxxxxxxxx
CC: coreteam@xxxxxxxxxxxxx
---

Notes:
    Changes since v1:
    * Added skb_is_gso before skb_is_gso_sctp.
    * Added "Fixes" tag.

 net/netfilter/ipvs/ip_vs_proto_sctp.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/ipvs/ip_vs_proto_sctp.c b/net/netfilter/ipvs/ip_vs_proto_sctp.c
index a0921adc31a9..1e689c714127 100644
--- a/net/netfilter/ipvs/ip_vs_proto_sctp.c
+++ b/net/netfilter/ipvs/ip_vs_proto_sctp.c
@@ -126,7 +126,8 @@ sctp_snat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
 	if (sctph->source != cp->vport || payload_csum ||
 	    skb->ip_summed == CHECKSUM_PARTIAL) {
 		sctph->source = cp->vport;
-		sctp_nat_csum(skb, sctph, sctphoff);
+		if (!skb_is_gso(skb) || !skb_is_gso_sctp(skb))
+			sctp_nat_csum(skb, sctph, sctphoff);
 	} else {
 		skb->ip_summed = CHECKSUM_UNNECESSARY;
 	}
@@ -174,7 +175,8 @@ sctp_dnat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
 	    (skb->ip_summed == CHECKSUM_PARTIAL &&
 	     !(skb_dst(skb)->dev->features & NETIF_F_SCTP_CRC))) {
 		sctph->dest = cp->dport;
-		sctp_nat_csum(skb, sctph, sctphoff);
+		if (!skb_is_gso(skb) || !skb_is_gso_sctp(skb))
+			sctp_nat_csum(skb, sctph, sctphoff);
 	} else if (skb->ip_summed != CHECKSUM_PARTIAL) {
 		skb->ip_summed = CHECKSUM_UNNECESSARY;
 	}
-- 
2.43.0