Re: [net-next] net/sctp: Refactor SCTP skb checksum computation

[Joe Stringer <joe@wand.net.nz>]

Thanks for the quick response. I'll fix up these issues and repost.

On Tue, Jul 23, 2013 at 4:14 PM, Julian Anastasov <ja@ssi.bg> wrote:
>
>         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@wand.net.nz>
>> ---
>>  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@ssi.bg>