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

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Sun, Apr 21, 2024 at 04:22:32PM +0200, Ismael Luceno wrote:
> 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.

I am placing this into the nf.git tree for submission upstream in the
next pull request, unless stated otherwise.

Thanks.

> Fixes: 90017accff61 ("sctp: Add GSO support", 2016-06-02)
> Co-developed-by: Firo Yang <firo.yang@suse.com>
> Signed-off-by: Ismael Luceno <iluceno@suse.de>
> Tested-by: Andreas Taschner <andreas.taschner@suse.com>
> CC: Michal Kubeček <mkubecek@suse.com>
> CC: Simon Horman <horms@verge.net.au>
> CC: Julian Anastasov <ja@ssi.bg>
> CC: lvs-devel@vger.kernel.org
> CC: netfilter-devel@vger.kernel.org
> CC: netdev@vger.kernel.org
> CC: coreteam@netfilter.org
> ---
> 
> 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
> 
>