Hello,
On Tue, 23 Jul 2013, Joe Stringer wrote:
> This patch consolidates the SCTP checksum calculation code from various
> places to a single new function, sctp_compute_cksum(skb, offset).
>
> Signed-off-by: Joe Stringer <joe@xxxxxxxxxxx>
> ---
> include/net/sctp/checksum.h | 15 +++++++++++++++
> net/netfilter/ipvs/ip_vs_proto_sctp.c | 23 ++++-------------------
> net/netfilter/nf_nat_proto_sctp.c | 8 +-------
> net/sctp/input.c | 10 +---------
> 4 files changed, 21 insertions(+), 35 deletions(-)
>
> diff --git a/include/net/sctp/checksum.h b/include/net/sctp/checksum.h
> index 0cb08e6..8675564 100644
> --- a/include/net/sctp/checksum.h
> +++ b/include/net/sctp/checksum.h
> @@ -85,4 +85,19 @@ static inline __le32 sctp_end_cksum(__u32 crc32)
> return cpu_to_le32(~crc32);
> }
>
> +/* Calculate the CRC32C checksum of an SCTP packet. */
> +static inline __le32 sctp_compute_cksum(const struct sk_buff *skb,
> + unsigned int offset)
> +{
> + const struct sk_buff *iter;
> +
> + __u32 crc32 = sctp_start_cksum((__u8 *)sctp_hdr(skb),
> + skb_headlen(skb) - offset);
sctp_hdr() is valid in INPUT hook after commit
21d1196a35f5686c4323e42a62fdb4b23b0ab4a3 (ipv4: set transport header
earlier) but I'm not sure for the OUTPUT hook where
IPVS is working. I guess the same is valid for Netfilter.
IPVS uses skb_network_header(skb) + offset but
I guess it can work with skb->data, just like Netfilter:
__u32 crc32 = sctp_start_cksum(skb->data + offset,
This should work also in SCTP where skb->data points
to the SCTP header when sctp_rcv_checksum() is called.
> + skb_walk_frags(skb, iter)
> + crc32 = sctp_update_cksum((__u8 *) iter->data,
> + skb_headlen(iter), crc32);
> +
> + return sctp_end_cksum(crc32);
> +}
> +
> #endif /* __sctp_checksum_h__ */
> diff --git a/net/netfilter/ipvs/ip_vs_proto_sctp.c b/net/netfilter/ipvs/ip_vs_proto_sctp.c
> index 3c0da87..b2e422d 100644
> --- a/net/netfilter/ipvs/ip_vs_proto_sctp.c
> +++ b/net/netfilter/ipvs/ip_vs_proto_sctp.c
> @@ -66,15 +66,9 @@ sctp_conn_schedule(int af, struct sk_buff *skb, struct ip_vs_proto_data *pd,
> 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);
> + __le32 crc32 = sctp_compute_cksum(skb, sctphoff);
crc32 var is not needed anymore, eg:
sctph->checksum = sctp_compute_cksum(skb, sctphoff);
> + sctph->checksum = crc32;
> skb->ip_summed = CHECKSUM_UNNECESSARY;
> }
>
> @@ -151,10 +145,7 @@ sctp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp)
> {
> unsigned int sctphoff;
> struct sctphdr *sh, _sctph;
> - struct sk_buff *iter;
> - __le32 cmp;
> - __le32 val;
> - __u32 tmp;
> + __le32 cmp, val;
>
> #ifdef CONFIG_IP_VS_IPV6
> if (af == AF_INET6)
> @@ -168,13 +159,7 @@ sctp_csum_check(int af, struct sk_buff *skb, struct ip_vs_protocol *pp)
> return 0;
>
> cmp = sh->checksum;
> -
> - tmp = sctp_start_cksum((__u8 *) sh, skb_headlen(skb));
> - skb_walk_frags(skb, iter)
> - tmp = sctp_update_cksum((__u8 *) iter->data,
> - skb_headlen(iter), tmp);
> -
> - val = sctp_end_cksum(tmp);
> + val = sctp_compute_cksum(skb, 0);
The original code has bug here, still the code
was never used because there are no IPVS apps with
SCTP support. You can safely use sctphoff here, not 0, eg:
val = sctp_compute_cksum(skb, sctphoff);
> if (val != cmp) {
> /* CRC failure, dump it. */
Regards
--
Julian Anastasov <ja@xxxxxx>
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