Subject: Re: [PATCHv2 RESEND] {xfrm, sctp} Stick to software crc32 even if hardware is capable of that

From: Daniel Borkmann <[email-masked]>
Date: Mon, 14 Oct 2013 10:07:22 +0200

On 10/14/2013 09:27 AM, Fan Du wrote:
> igb/ixgbe have hardware sctp checksum support, when this feature is enabled
> and also IPsec is armed to protect sctp traffic, ugly things happened as
> xfrm_output checks CHECKSUM_PARTIAL to do check sum operation(sum every thing
> up and pack the 16bits result in the checksum field). The result is fail
> establishment of sctp communication.
>
> Signed-off-by: Fan Du <[email-masked]>
> Cc: Vlad Yasevich <[email-masked]>
> Cc: Neil Horman <[email-masked]>
> Cc: Steffen Klassert <[email-masked]>
> Acked-by: Vlad Yasevich <[email-masked]>
> ---
>   net/sctp/output.c |   14 +++++++++++++-
>   1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/net/sctp/output.c b/net/sctp/output.c
> index 0ac3a65..6de6402 100644
> --- a/net/sctp/output.c
> +++ b/net/sctp/output.c
> @@ -372,6 +372,16 @@ static void sctp_packet_set_owner_w(struct sk_buff *skb, struct sock *sk)
>   	atomic_inc(&sk->sk_wmem_alloc);
>   }
>
> +static int is_xfrm_armed(struct dst_entry *dst)
> +{
> +#ifdef CONFIG_XFRM
> +	/* If dst->xfrm is valid, this skb needs to be transformed */
> +	return dst->xfrm != NULL;
> +#else
> +	return 0;
> +#endif
> +}

Instead of putting this into SCTP code, isn't the above rather a candidate for
include/net/xfrm.h, e.g. as ... bool xfrm_is_armed(...) ?

>   /* All packets are sent to the network through this function from
>    * sctp_outq_tail().
>    *
> @@ -536,7 +546,9 @@ int sctp_packet_transmit(struct sctp_packet *packet)
>   	 * by CRC32-C as described in <draft-ietf-tsvwg-sctpcsum-02.txt>.
>   	 */
>   	if (!sctp_checksum_disable) {
> -		if (!(dst->dev->features & NETIF_F_SCTP_CSUM)) {
> +		if ((!(dst->dev->features & NETIF_F_SCTP_CSUM)) ||
> +			is_xfrm_armed(dst)) {
> +
>   			__u32 crc32 = sctp_start_cksum((__u8 *)sh, cksum_buf_len);
>
>   			/* 3) Put the resultant value into the checksum field in the
>