Re: [PATCH V2 net-next 2/6] sctp: Handle sctp packets with CHECKSUM_PARTIAL

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Tue, May 01, 2018 at 10:07:35PM -0400, Vladislav Yasevich wrote:
> With SCTP checksum offload available in virtio, it is now
> possible for virtio to receive a sctp packet with CHECKSUM_PARTIAL
> set (guest-to-guest traffic).  SCTP doesn't really have a
> partial checksum like TCP does, because CRC32c can't do partial
> additive checksumming.  It's all or nothing.  So an SCTP packet
> with CHECKSUM_PARTIAL will have checksum set to 0.  Let SCTP
> treat this as a valid checksum if CHECKSUM_PARTIAL is set.
>
> Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
> ---
>  net/sctp/input.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/net/sctp/input.c b/net/sctp/input.c
> index ba8a6e6..055b8ffa 100644
> --- a/net/sctp/input.c
> +++ b/net/sctp/input.c
> @@ -80,8 +80,17 @@ static inline int sctp_rcv_checksum(struct net *net, struct sk_buff *skb)
>  {
>  	struct sctphdr *sh = sctp_hdr(skb);
>  	__le32 cmp = sh->checksum;
> -	__le32 val = sctp_compute_cksum(skb, 0);
> +	__le32 val = 0;
>
> +	/* In sctp PARTIAL checksum is always 0.  This is a case of
> +	 * a packet received from guest that supports checksum offload.
> +	 * Assume it's correct as there is really no way to verify,
> +	 * and we want to avaoid computing it unnecesarily.
               nit, typos --^                     --^
> +	 */
> +	if (skb->ip_summed == CHECKSUM_PARTIAL)
> +		return 0;
> +
> +	val = sctp_compute_cksum(skb, 0);
>  	if (val != cmp) {
>  		/* CRC failure, dump it. */
>  		__SCTP_INC_STATS(net, SCTP_MIB_CHECKSUMERRORS);
> --
> 2.9.5
>
> --
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