Re: [PATCHv2 net-next 3/5] net: sched: return NF_ACCEPT when fails to add nat ext in tcf_ct_act_nat

[Xin Long <lucien.xin@gmail.com>]

On Wed, Nov 23, 2022 at 9:24 AM Marcelo Ricardo Leitner
<marcelo.leitner@gmail.com> wrote:
>
> On Tue, Nov 22, 2022 at 12:32:19PM -0500, Xin Long wrote:
> > This patch changes to return NF_ACCEPT when fails to add nat
> > ext before doing NAT in tcf_ct_act_nat(), to keep consistent
> > with OVS' processing in ovs_ct_nat().
> >
> > Reviewed-by: Saeed Mahameed <saeed@kernel.org>
> > Signed-off-by: Xin Long <lucien.xin@gmail.com>
> > ---
> >  net/sched/act_ct.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c
> > index da0b7f665277..8869b3ef6642 100644
> > --- a/net/sched/act_ct.c
> > +++ b/net/sched/act_ct.c
> > @@ -994,7 +994,7 @@ static int tcf_ct_act_nat(struct sk_buff *skb,
> >
> >       /* Add NAT extension if not confirmed yet. */
> >       if (!nf_ct_is_confirmed(ct) && !nf_ct_nat_ext_add(ct))
> > -             return NF_DROP;   /* Can't NAT. */
> > +             return NF_ACCEPT;   /* Can't NAT. */
>
> I'm wondering if the fix should actually be in OVS, to make it drop
> the packet? Aaron, Eelco?
>
> If the user asked for NAT, and it can't NAT, it doesn't seem right to
> forward the packet while not performing the asked action.
>
> If we follow the code here, it may even commit the entry without the
> NAT extension, rendering the connection useless/broken per the first
> if condition above. It just won't try again.
nf_ct_nat_ext_add() returning NULL is caused by krealloc() failure
like an -ENOMEM error, and a similar thing could happen in
nfct_seqadj_ext_add() called by ovs_ct_nat() -> nf_nat_setup_info()
when doing NAT where it returns DROP. So I think it's right that
we should fix this in openvswitch instead of TC.

Anyway, in ovs_ct_nat():

        if (!nf_ct_is_confirmed(ct) && !nf_ct_nat_ext_add(ct))
                return NF_ACCEPT;   /* Can't NAT. */

git blame shows this was added at the beginning by:

    05752523e565 ("openvswitch: Interface with NAT.")

So add Jarno Rajahalme to Cc: list.

Thanks.

>
> >
> >       if (ctinfo != IP_CT_NEW && (ct->status & IPS_NAT_MASK) &&
> >           (ctinfo != IP_CT_RELATED || commit)) {
> > --
> > 2.31.1
> >