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Hello,
On Fri, 25 Oct 2013, Daniel Borkmann wrote:
> Unlike UDP or TCP, we do not take the pseudo-header into account
> in SCTP checksums [1]. So in case port mapping is the very same, we
> do not need to recalculate the whole SCTP checksum in software, which
> is expensive.
>
> Also, similarly as in IPVS/TCP, take into account when a private
> helper mangled the packet. In that case, we also need to recalculate
> the checksum even if ports might be same.
>
> [1] http://tools.ietf.org/html/rfc4960#section-6.8
>
> Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
> ---
> net/netfilter/ipvs/ip_vs_proto_sctp.c | 30 ++++++++++++++++++++++++------
> 1 file changed, 24 insertions(+), 6 deletions(-)
>
> diff --git a/net/netfilter/ipvs/ip_vs_proto_sctp.c
> b/net/netfilter/ipvs/ip_vs_proto_sctp.c
> index 9ca7aa0..e56661e 100644
> --- a/net/netfilter/ipvs/ip_vs_proto_sctp.c
> +++ b/net/netfilter/ipvs/ip_vs_proto_sctp.c
> @@ -81,6 +81,7 @@ sctp_snat_handler(struct sk_buff *skb, struct
> ip_vs_protocol *pp,
> {
> sctp_sctphdr_t *sctph;
> unsigned int sctphoff = iph->len;
> + bool payload_csum = false;
>
> #ifdef CONFIG_IP_VS_IPV6
> if (cp->af == AF_INET6 && iph->fragoffs)
> @@ -92,19 +93,27 @@ sctp_snat_handler(struct sk_buff *skb, struct
> ip_vs_protocol *pp,
...
> - sctp_nat_csum(skb, sctph, sctphoff);
> + /* Only update csum if we really have to */
> + if (sctph->source != cp->vport || payload_csum) {
The above check should be little more complicated
because local SCTP can decide to avoid setting ->checksum,
there is a case when we can see CHECKSUM_PARTIAL for
locally generated packets. And it happens both for
requests (dnat_handler) and replies (snat_handler).
I mean both places should be fixed because you can
see in ip_vs_ops[] that in NF_INET_LOCAL_OUT we can call both
snat_handler and dnat_handler.
May be the simplest change can be to add check for
!skb->dev to catch the LOCAL_OUT hook, so that we can
perform full recalculation. We can further optimize this
check for dnat_handler because the dnat_handler can look
at the skb_dst()->dev->features as done by sctp_packet_transmit().
The idea is that SCTP decides to avoid csum calculation
if hardware supports offloading. IPVS can change the
device after rerouting to real server but we can preserve
the CHECKSUM_PARTIAL mode if the new device supports
offloading too. This works because skb dst is changed
before dnat_handler and we see the new device.
For snat_handler it is more complex. skb contains
the original route and ip_vs_route_me_harder() can change
the route after snat_handler. So, for locally generated
replies from local server we can not preserve the
CHECKSUM_PARTIAL mode. It is an chicken or egg dilemma:
snat_handler needs the device after rerouting (to
check for NETIF_F_SCTP_CSUM), while ip_route_me_harder() wants
the snat_handler() to put the new saddr for proper rerouting.
So, for snat_handler we need just the !skb->dev check,
sort of:
if (sctph->source != cp->vport || payload_csum ||
(!skb->dev && skb->ip_summed == CHECKSUM_PARTIAL)) {
But I have to think more whether we can preserve
the ip_summed value in other cases, see skb_forward_csum()
for reference.
> + sctph->source = cp->vport;
> + sctp_nat_csum(skb, sctph, sctphoff);
> + }
>
> return 1;
> }
> @@ -126,19 +136,27 @@ sctp_dnat_handler(struct sk_buff *skb, struct
> ip_vs_protocol *pp,
...
> - sctp_nat_csum(skb, sctph, sctphoff);
> + /* Only update csum if we really have to */
> + if (sctph->dest != cp->dport || payload_csum) {
Here we can can preserve CHECKSUM_PARTIAL after
some checks, eg. when the new device in skb_dst supports
offloading.
> + sctph->dest = cp->dport;
> + sctp_nat_csum(skb, sctph, sctphoff);
> + }
>
> return 1;
> }
> --
> 1.7.11.7
Regards
--
Julian Anastasov <ja@xxxxxx>
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