netdev - Re: [PATCH net] udp: drop secpath before storing an skb in a receive queue

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Message-ID: <CANn89iKQYN1qTZoSW4+1v6scDgH53zi9pP_O_mEbTdYQYie1uQ@mail.gmail.com>
Date: Tue, 14 Oct 2025 04:34:52 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Michal Kubecek <mkubecek@...e.cz>
Cc: Paolo Abeni <pabeni@...hat.com>, Sabrina Dubroca <sd@...asysnail.net>, 
	"David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Simon Horman <horms@...nel.org>, 
	Willem de Bruijn <willemb@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net] udp: drop secpath before storing an skb in a receive queue

On Tue, Oct 14, 2025 at 4:20 AM Michal Kubecek <mkubecek@...e.cz> wrote:
>
> On Tue, Oct 14, 2025 at 01:27:13AM GMT, Eric Dumazet wrote:
> > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > index 95241093b7f0..932c21838b9b 100644
> > --- a/net/ipv4/udp.c
> > +++ b/net/ipv4/udp.c
> > @@ -1851,8 +1851,13 @@ void skb_consume_udp(struct sock *sk, struct
> > sk_buff *skb, int len)
> >                 sk_peek_offset_bwd(sk, len);
> >
> >         if (!skb_shared(skb)) {
> > -               if (unlikely(udp_skb_has_head_state(skb)))
> > -                       skb_release_head_state(skb);
> > +               if (unlikely(udp_skb_has_head_state(skb))) {
> > +                       /* Make sure that skb_release_head_state()
> > will have nothing to do. */
> > +                       DEBUG_NET_WARN_ON_ONCE(skb_dst(skb));
> > +                       DEBUG_NET_WARN_ON_ONCE(skb->destructor);
> > +                       DEBUG_NET_WARN_ON_ONCE(skb_nfct(skb));
> > +                       skb_ext_reset(skb);
> > +               }
> >                 skb_attempt_defer_free(skb);
> >                 return;
> >         }
>
> Tested this version on my system (with DEBUG_NET enabled) and everything
> seems to work fine so far.
>
> Tested-by: Michal Kubecek <mkubecek@...e.cz>

Thanks for testing. I will follow Sabrina suggestion and send :

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 95241093b7f0..d66f273f9070 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1851,8 +1851,13 @@ void skb_consume_udp(struct sock *sk, struct
sk_buff *skb, int len)
                sk_peek_offset_bwd(sk, len);

        if (!skb_shared(skb)) {
-               if (unlikely(udp_skb_has_head_state(skb)))
-                       skb_release_head_state(skb);
+               /* Make sure that this skb has no dst, destructor
+                * or conntracking parts, because it might stay
+                * in a remote cpu list for a very long time.
+                */
+               DEBUG_NET_WARN_ON_ONCE(skb_dst(skb));
+               DEBUG_NET_WARN_ON_ONCE(skb->destructor);
+               DEBUG_NET_WARN_ON_ONCE(skb_nfct(skb));
                skb_attempt_defer_free(skb);
                return;
        }