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

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Date:   Mon, 12 Jul 2021 15:37:16 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Vadim Fedorenko <vfedorenko@...ek.ru>,
        David Ahern <dsahern@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Xin Long <lucien.xin@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net 2/3] udp: check encap socket in __udp_lib_err

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.

> > 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 ?

Thanks!

/P