netdev - Re: [PATCH net] netfilter: set skb transport_header before calling sctp_compute

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Date:   Fri, 8 Mar 2019 16:50:49 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>,
        netfilter-devel@...r.kernel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>
Subject: Re: [PATCH net] netfilter: set skb transport_header before calling
 sctp_compute_cksum

Hi,

On Sun, Mar 03, 2019 at 04:17:21PM +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() -> sctp_compute_cksum().
> 
> 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 setting skb transport_header before calling
> sctp_compute_cksum().

I see a few more calls to sctp_compute_cksum() in the netfilter tree.
I guess they are broken too.

In netfilter, skb->transport_header is never set from the input path,
I think this introduces an assymmetry with other transport protocols.

May we have a variant of sctp_compute_cksum() which does not rely on
sctp_hdr() instead?