linux-kernel - Re: [PATCH] ipvs: Fix checksumming on GSO of SCTP packets

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Message-ID: <fd234180-4d6f-313a-0edd-13c821bd4423@ssi.bg>
Date: Sun, 21 Apr 2024 14:01:21 +0300 (EEST)
From: Julian Anastasov <ja@....bg>
To: Ismael Luceno <iluceno@...e.de>
cc: linux-kernel@...r.kernel.org, Firo Yang <firo.yang@...e.com>,
        Andreas Taschner <andreas.taschner@...e.com>,
        Michal Kubeček <mkubecek@...e.com>,
        Simon Horman <horms@...ge.net.au>, lvs-devel@...r.kernel.org,
        netfilter-devel@...r.kernel.org, netdev@...r.kernel.org,
        coreteam@...filter.org
Subject: Re: [PATCH] ipvs: Fix checksumming on GSO of SCTP packets


	Hello,

On Thu, 18 Apr 2024, 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.
> 
> Co-developed-by: Firo Yang <firo.yang@...e.com>
> Signed-off-by: Ismael Luceno <iluceno@...e.de>
> Tested-by: Andreas Taschner <andreas.taschner@...e.com>
> CC: Michal Kubeček <mkubecek@...e.com>
> CC: Simon Horman <horms@...ge.net.au>
> CC: Julian Anastasov <ja@....bg>
> CC: lvs-devel@...r.kernel.org
> CC: netfilter-devel@...r.kernel.org
> CC: netdev@...r.kernel.org
> CC: coreteam@...filter.org

	Thanks for the fix, I'll accept this but skb_is_gso_sctp()
has comment for pre-condition: skb_is_gso(skb). Can you send v2
with it?

	I'm guessing what should be the Fixes line, may be?:

Fixes: 90017accff61 ("sctp: Add GSO support")

	because SCTP GSO was added after the IPVS code? Or the
more recent commit d02f51cbcf12 which adds skb_is_gso_sctp ?

> ---
>  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..3205b45ce161 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_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_sctp(skb))
> +			sctp_nat_csum(skb, sctph, sctphoff);
>  	} else if (skb->ip_summed != CHECKSUM_PARTIAL) {
>  		skb->ip_summed = CHECKSUM_UNNECESSARY;
>  	}

Regards

--
Julian Anastasov <ja@....bg>