Re: [PATCH net] udp: resubmit encap packets for secondary mcast sockets

[Kuniyuki Iwashima]

On Fri, Sep 18, 2026 at 8:36 AM Mariano Baragiola <mbaragiola@xxxxxxxxx> wrote:
>
> Multicast delivery clones packets for listeners after the first one.
> Commit 3cb8d4b9bfeb ("udp: fix encapsulation packet resubmit in multicast
> deliver") fixed encapsulation packet resubmission for the primary
> listener by propagating positive return values from udp_queue_rcv_skb()
> to the outer IP layer. However, it left the loop over secondary matching
> sockets unchanged.

Did you see a real problem or is this triggered by an AI report?

https://lore.kernel.org/netdev/20260415203624.4057135-1-kuniyu@xxxxxxxxxx/


>
> When an encapsulation receive handler requests protocol resubmission for
> a clone (ret > 0), the secondary delivery loop currently calls
> consume_skb(nskb), silently dropping the packet.
>
> Resubmit cloned IPv4 and IPv6 packets directly to the returned protocol
> via ip_protocol_deliver_rcu() and ip6_protocol_deliver_rcu(..., true),
> matching the ownership and resubmission conventions used in the
> segmented GSO paths.
>
> Fixes: 3cb8d4b9bfeb ("udp: fix encapsulation packet resubmit in multicast deliver")
> Signed-off-by: Mariano Baragiola <mbaragiola@xxxxxxxxx>
> ---
>  net/ipv4/udp.c | 5 +++--
>  net/ipv6/udp.c | 5 +++--
>  2 files changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index bb8cfc62cb00..d79be57854e3 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -2522,8 +2522,9 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
>                         __UDP_INC_STATS(net, UDP_MIB_INERRORS);
>                         continue;
>                 }
> -               if (udp_queue_rcv_skb(sk, nskb) > 0)
> -                       consume_skb(nskb);
> +               ret = udp_queue_rcv_skb(sk, nskb);
> +               if (ret > 0)
> +                       ip_protocol_deliver_rcu(net, nskb, ret);
>         }
>
>         /* Also lookup *:port if we are using hash2 and haven't done so yet. */
> diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
> index 93478d1ad576..ca8d0a1844d2 100644
> --- a/net/ipv6/udp.c
> +++ b/net/ipv6/udp.c
> @@ -1001,8 +1001,9 @@ static int __udp6_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
>                         continue;
>                 }
>
> -               if (udpv6_queue_rcv_skb(sk, nskb) > 0)
> -                       consume_skb(nskb);
> +               ret = udpv6_queue_rcv_skb(sk, nskb);
> +               if (ret > 0)
> +                       ip6_protocol_deliver_rcu(net, nskb, ret, true);
>         }
>
>         /* Also lookup *:port if we are using hash2 and haven't done so yet. */
> --
> 2.55.0
>