[v1] ipvs: Fix checksumming on GSO of SCTP packets

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

Posted by Ismael Luceno 2 weeks, 1 day ago

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@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
---
 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;
 	}
-- 
2.43.0

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

Posted by Julian Anastasov 1 week, 5 days ago

	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@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

	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@ssi.bg>

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

Posted by Ismael Luceno 1 week, 5 days ago

On 21/Apr/2024 14:01, Julian Anastasov wrote:
<...>
> 	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?

Thanks; sent!

> 	I'm guessing what should be the Fixes line, may be?:
> 
> Fixes: 90017accff61 ("sctp: Add GSO support")

This seems like the right one.

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

That doesn't seem related at all.

Do we need to check .gso_type in cases like this?

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

Posted by Julian Anastasov 1 week, 5 days ago

	Hello,

On Sun, 21 Apr 2024, Ismael Luceno wrote:

> On 21/Apr/2024 14:01, Julian Anastasov wrote:
> 
> > 	I'm guessing what should be the Fixes line, may be?:
> > 
> > Fixes: 90017accff61 ("sctp: Add GSO support")
> 
> This seems like the right one.
> 
> > 	because SCTP GSO was added after the IPVS code? Or the
> > more recent commit d02f51cbcf12 which adds skb_is_gso_sctp ?
> 
> That doesn't seem related at all.
> 
> Do we need to check .gso_type in cases like this?

	Just skb_is_gso(skb) ? IMHO, this should work.

Regards

--
Julian Anastasov <ja@ssi.bg>