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

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Date:   Sat, 9 Mar 2019 17:07:17 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>,
        Neil Horman <nhorman@...driver.com>
Cc:     network dev <netdev@...r.kernel.org>,
        netfilter-devel@...r.kernel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCH net] netfilter: set skb transport_header before calling sctp_compute_cksum

On Fri, Mar 8, 2019 at 11:50 PM Pablo Neira Ayuso <pablo@...filter.org> wrote:
>
> 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?
I posted one before this:
  https://marc.info/?l=linux-netdev&m=155109395226858&w=2
But from sctp side, Neil preferred sctp_hdr().

We need to either add skb_set_transport_header() in sctp_s/dnat_handler()
and sctp_manip_pkt(), or bring that patch back?

Now it seems not good to set skb->transport_header in netfilter code.
Hi Neil, what's your point now?