netdev - Re: [PATCH net] sctp: get sctphdr by offset in sctp_compute

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Date:   Mon, 25 Feb 2019 07:46:14 -0500
From:   Neil Horman <nhorman@...driver.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     linux-kernel@...r.kernel.org, network dev <netdev@...r.kernel.org>,
        linux-sctp@...r.kernel.org, davem@...emloft.net,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCH net] sctp: get sctphdr by offset in sctp_compute_cksum

On Mon, Feb 25, 2019 at 07:25:37PM +0800, Xin Long wrote:
> sctp_hdr(skb) only works when skb->transport_header is set properly.
> 
> But in the path of nf_conntrack_in: sctp_packet() -> sctp_error()
> 
> skb->transport_header is not guaranteed to be right value for sctp.
> It will cause to fail to check the checksum for sctp packets.
> 
> So fix it by using offset, which is always right in all places.
> 
> Fixes: e6d8b64b34aa ("net: sctp: fix and consolidate SCTP checksumming code")
> Reported-by: Li Shuang <shuali@...hat.com>
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  include/net/sctp/checksum.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/net/sctp/checksum.h b/include/net/sctp/checksum.h
> index 32ee65a..1c6e6c0 100644
> --- a/include/net/sctp/checksum.h
> +++ b/include/net/sctp/checksum.h
> @@ -61,7 +61,7 @@ static inline __wsum sctp_csum_combine(__wsum csum, __wsum csum2,
>  static inline __le32 sctp_compute_cksum(const struct sk_buff *skb,
>  					unsigned int offset)
>  {
> -	struct sctphdr *sh = sctp_hdr(skb);
> +	struct sctphdr *sh = (struct sctphdr *)(skb->data + offset);
>  	const struct skb_checksum_ops ops = {
>  		.update  = sctp_csum_update,
>  		.combine = sctp_csum_combine,
> -- 
> 2.1.0
> 
> 
Shouldn't you use skb_set_transport_header and skb_transport_header here?

Neil