netdev - Re: [PATCH net 2/3] udp: check encap socket in __udp_lib

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Date:   Fri, 16 Jul 2021 13:50:00 -0400
From:   Xin Long <lucien.xin@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Vadim Fedorenko <vfedorenko@...ek.ru>,
        David Ahern <dsahern@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        network dev <netdev@...r.kernel.org>
Subject: Re: [PATCH net 2/3] udp: check encap socket in __udp_lib_err

On Mon, Jul 12, 2021 at 9:37 AM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On Mon, 2021-07-12 at 13:45 +0100, Vadim Fedorenko wrote:
> >
> > > After this patch, the above chunk will not clear 'sk' for packets
> > > targeting ESP in UDP sockets, but AFAICS we will still enter the
> > > following conditional, preserving the current behavior - no ICMP
> > > processing.
> >
> > We will not enter following conditional for ESP in UDP case because
> > there is no more check for encap_type or encap_enabled.
>
> I see. You have a bug in the ipv6 code-path. With your patch applied:
>
> ---
>         sk = __udp6_lib_lookup(net, daddr, uh->dest, saddr, uh->source,
>                                inet6_iif(skb), inet6_sdif(skb), udptable, NULL);
>         if (sk && udp_sk(sk)->encap_enabled) {
>                 //...
>         }
>
>         if (!sk || udp_sk(sk)->encap_enabled) {
>         // can still enter here...
> ---
>
> > I maybe missing something but d26796ae5894 doesn't actually explain
> > which particular situation should be avoided by this additional check
> > and no tests were added to simply reproduce the problem. If you can
> > explain it a bit more it would greatly help me to improve the fix.
>
> Xin knows better, but AFAICS it used to cover the situation you
> explicitly tests in patch 3/3 - incoming packet with src-port == dst-
> port == tunnel port - for e.g. vxlan tunnels.
Thanks Paolo and sorry for late.

Right, __udp4/6_lib_err_encap() was introduced to process the ICMP error
packets for UDP tunnels. But it will only work when there's no socket
found with src + dst port, as when the src == dst port a socket might
be found(if the bind addr is ANY) and the code will be called.



>
> > > Why can't you use something alike the following instead?
> > >
> > > ---
> > > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > > index c0f9f3260051..96a3b640e4da 100644
> > > --- a/net/ipv4/udp.c
> > > +++ b/net/ipv4/udp.c
> > > @@ -707,7 +707,7 @@ int __udp4_lib_err(struct sk_buff *skb, u32 info, struct udp_table *udptable)
> > >          sk = __udp4_lib_lookup(net, iph->daddr, uh->dest,
> > >                                 iph->saddr, uh->source, skb->dev->ifindex,
> > >                                 inet_sdif(skb), udptable, NULL);
> > > -       if (!sk || udp_sk(sk)->encap_type) {
> > > +       if (!sk || READ_ONCE(udp_sk(sk)->encap_err_lookup)) {
> > >                  /* No socket for error: try tunnels before discarding */
> > >                  sk = ERR_PTR(-ENOENT);
> > >                  if (static_branch_unlikely(&udp_encap_needed_key)) {
> > >
> > > ---
>
> Could you please have a look at the above ?
If not all udp tunnels want to do further validation for ICMP error packet,
This looks good to me.

>
> Thanks!
>
> /P
>