Hello,
On Tue, 5 Feb 2013, Daniel Borkmann wrote:
> In our test lab, we have a simple SCTP client connecting to a SCTP
> server via an IPVS load balancer. On some machines, load balancing
> works, but on others the initial handshake just fails, thus no
> SCTP connection whatsoever can be established!
>
> We observed that the SCTP INIT-ACK handshake reply from the IPVS
> machine to the client had a correct IP checksum, but corrupt SCTP
> checksum when forwarded, thus on the client-side the packet was
> dropped and an intial handshake retriggered until all attempts
> run into the void.
>
> To fix this issue, this patch i) adds a missing CHECKSUM_UNNECESSARY
> after the full checksum (re-)calculation (as done in IPVS TCP and UDP
> code as well), ii) calculates the checksum in little-endian format
> (as fixed with the SCTP code in commit 4458f04c: sctp: Clean up sctp
> checksumming code) and iii) refactors duplicate checksum code into a
> common function. Tested by myself.
>
> Cc: Simon Horman <horms@xxxxxxxxxxxx>
> Cc: Julian Anastasov <ja@xxxxxx>
> Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
Looks good to me. Simon, please apply as bugfix.
It seems we have this problem from day 1 (2.6.34).
Acked-by: Julian Anastasov <ja@xxxxxx>
> ---
> net/netfilter/ipvs/ip_vs_proto_sctp.c | 35 ++++++++++++++++-----------------
> 1 files changed, 17 insertions(+), 18 deletions(-)
>
> diff --git a/net/netfilter/ipvs/ip_vs_proto_sctp.c b/net/netfilter/ipvs/ip_vs_proto_sctp.c
> index 746048b..ae8ec6f 100644
> --- a/net/netfilter/ipvs/ip_vs_proto_sctp.c
> +++ b/net/netfilter/ipvs/ip_vs_proto_sctp.c
> @@ -61,14 +61,27 @@ sctp_conn_schedule(int af, struct sk_buff *skb, struct ip_vs_proto_data *pd,
> return 1;
> }
>
> +static void sctp_nat_csum(struct sk_buff *skb, sctp_sctphdr_t *sctph,
> + unsigned int sctphoff)
> +{
> + __u32 crc32;
> + struct sk_buff *iter;
> +
> + crc32 = sctp_start_cksum((__u8 *)sctph, skb_headlen(skb) - sctphoff);
> + skb_walk_frags(skb, iter)
> + crc32 = sctp_update_cksum((u8 *) iter->data,
> + skb_headlen(iter), crc32);
> + sctph->checksum = sctp_end_cksum(crc32);
> +
> + skb->ip_summed = CHECKSUM_UNNECESSARY;
> +}
> +
> static int
> sctp_snat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
> struct ip_vs_conn *cp, struct ip_vs_iphdr *iph)
> {
> sctp_sctphdr_t *sctph;
> unsigned int sctphoff = iph->len;
> - struct sk_buff *iter;
> - __be32 crc32;
>
> #ifdef CONFIG_IP_VS_IPV6
> if (cp->af == AF_INET6 && iph->fragoffs)
> @@ -92,13 +105,7 @@ sctp_snat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
> sctph = (void *) skb_network_header(skb) + sctphoff;
> sctph->source = cp->vport;
>
> - /* Calculate the checksum */
> - crc32 = sctp_start_cksum((u8 *) sctph, skb_headlen(skb) - sctphoff);
> - skb_walk_frags(skb, iter)
> - crc32 = sctp_update_cksum((u8 *) iter->data, skb_headlen(iter),
> - crc32);
> - crc32 = sctp_end_cksum(crc32);
> - sctph->checksum = crc32;
> + sctp_nat_csum(skb, sctph, sctphoff);
>
> return 1;
> }
> @@ -109,8 +116,6 @@ sctp_dnat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
> {
> sctp_sctphdr_t *sctph;
> unsigned int sctphoff = iph->len;
> - struct sk_buff *iter;
> - __be32 crc32;
>
> #ifdef CONFIG_IP_VS_IPV6
> if (cp->af == AF_INET6 && iph->fragoffs)
> @@ -134,13 +139,7 @@ sctp_dnat_handler(struct sk_buff *skb, struct ip_vs_protocol *pp,
> sctph = (void *) skb_network_header(skb) + sctphoff;
> sctph->dest = cp->dport;
>
> - /* Calculate the checksum */
> - crc32 = sctp_start_cksum((u8 *) sctph, skb_headlen(skb) - sctphoff);
> - skb_walk_frags(skb, iter)
> - crc32 = sctp_update_cksum((u8 *) iter->data, skb_headlen(iter),
> - crc32);
> - crc32 = sctp_end_cksum(crc32);
> - sctph->checksum = crc32;
> + sctp_nat_csum(skb, sctph, sctphoff);
>
> return 1;
> }
> --
> 1.7.1
Regards
--
Julian Anastasov <ja@xxxxxx>
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