On 10/25/2013 11:00 PM, Julian Anastasov wrote:
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.
Thanks for all your feedback Julian !
Let me think about this, and come back to you w/ a 2nd version
of the set at latest on Monday.
+ 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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