[PATCH v3] ipvs: Fix checksumming on GSO of SCTP packets

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 <[email protected]>
Signed-off-by: Ismael Luceno <[email protected]>
Tested-by: Andreas Taschner <[email protected]>
CC: Michal Kubeček <[email protected]>
CC: Simon Horman <[email protected]>
CC: Julian Anastasov <[email protected]>
CC: [email protected]
CC: [email protected]
CC: [email protected]
CC: [email protected]
---

Notes:
    Changes since v2:
    * Use only skb_is_gso, no need to check for GSO type
    
    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..83e452916403 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))
+			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))
+			sctp_nat_csum(skb, sctph, sctphoff);
 	} else if (skb->ip_summed != CHECKSUM_PARTIAL) {
 		skb->ip_summed = CHECKSUM_UNNECESSARY;
 	}
-- 
2.43.0