Re: [net-next] netfiler: conntrack: Add the option to set ct tcp flag - BE_LIBERAL per-ct basis.

[Numan Siddique <nusiddiq@redhat.com>]

On Tue, Nov 10, 2020 at 3:06 AM Florian Westphal <fw@strlen.de> wrote:
>
> nusiddiq@redhat.com <nusiddiq@redhat.com> wrote:
> > From: Numan Siddique <nusiddiq@redhat.com>
> >
> > Before calling nf_conntrack_in(), caller can set this flag in the
> > connection template for a tcp packet and any errors in the
> > tcp_in_window() will be ignored.
> >
> > A helper function - nf_ct_set_tcp_be_liberal(nf_conn) is added which
> > sets this flag for both the directions of the nf_conn.
> >
> > openvswitch makes use of this feature so that any out of window tcp
> > packets are not marked invalid. Prior to this there was no easy way
> > to distinguish if conntracked packet is marked invalid because of
> > tcp_in_window() check error or because it doesn't belong to an
> > existing connection.
> >
> > An earlier attempt (see the link) tried to solve this problem for
> > openvswitch in a different way. Florian Westphal instead suggested
> > to be liberal in openvswitch for tcp packets.
> >
> > Link: https://patchwork.ozlabs.org/project/netdev/patch/20201006083355.121018-1-nusiddiq@redhat.com/
> >
> > Suggested-by: Florian Westphal <fw@strlen.de>
> > Signed-off-by: Numan Siddique <nusiddiq@redhat.com>
> > ---
> >  include/net/netfilter/nf_conntrack_l4proto.h |  6 ++++++
> >  net/netfilter/nf_conntrack_core.c            | 13 +++++++++++--
> >  net/openvswitch/conntrack.c                  |  1 +
> >  3 files changed, 18 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/net/netfilter/nf_conntrack_l4proto.h b/include/net/netfilter/nf_conntrack_l4proto.h
> > index 88186b95b3c2..572ae8d2a622 100644
> > --- a/include/net/netfilter/nf_conntrack_l4proto.h
> > +++ b/include/net/netfilter/nf_conntrack_l4proto.h
> > @@ -203,6 +203,12 @@ static inline struct nf_icmp_net *nf_icmpv6_pernet(struct net *net)
> >  {
> >       return &net->ct.nf_ct_proto.icmpv6;
> >  }
> > +
> > +static inline void nf_ct_set_tcp_be_liberal(struct nf_conn *ct)
> > +{
> > +     ct->proto.tcp.seen[0].flags |= IP_CT_TCP_FLAG_BE_LIBERAL;
> > +     ct->proto.tcp.seen[1].flags |= IP_CT_TCP_FLAG_BE_LIBERAL;
> > +}
> >  #endif
> >
> >  #ifdef CONFIG_NF_CT_PROTO_DCCP
> > diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
> > index 234b7cab37c3..8290c5b04e88 100644
> > --- a/net/netfilter/nf_conntrack_core.c
> > +++ b/net/netfilter/nf_conntrack_core.c
> > @@ -1748,10 +1748,18 @@ static int nf_conntrack_handle_packet(struct nf_conn *ct,
> >                                     struct sk_buff *skb,
> >                                     unsigned int dataoff,
> >                                     enum ip_conntrack_info ctinfo,
> > -                                   const struct nf_hook_state *state)
> > +                                   const struct nf_hook_state *state,
> > +                                   union nf_conntrack_proto *tmpl_proto)
>
> I would prefer if we could avoid adding yet another function argument.
>
> AFAICS its enough to call the new nf_ct_set_tcp_be_liberal() helper
> before nf_conntrack_confirm() in ovs_ct_commit(), e.g.:

Thanks for the comments. I actually tried this approach first, but it
doesn't seem to work.
I noticed that for the committed connections, the ct tcp flag -
IP_CT_TCP_FLAG_BE_LIBERAL is
not set when nf_conntrack_in() calls resolve_normal_ct().

Would you expect that the tcp ct flags should have been preserved once
the connection is committed ?

Thanks
Numan

>
> diff --git a/net/openvswitch/conntrack.c b/net/openvswitch/conntrack.c
> --- a/net/openvswitch/conntrack.c
> +++ b/net/openvswitch/conntrack.c
> @@ -1235,10 +1235,13 @@ static int ovs_ct_commit(struct net *net, struct sw_flow_key *key,
>         if (!nf_ct_is_confirmed(ct)) {
>                 err = ovs_ct_init_labels(ct, key, &info->labels.value,
>                                          &info->labels.mask);
>                 if (err)
>                         return err;
> +
> +               if (nf_ct_protonum(ct) == IPPROTO_TCP)
> +                       nf_ct_set_tcp_be_liberal(ct);
>