IPv4 and IPv6 input preserve an skb->sk association installed by bpf_sk_assign() so that local delivery can use the selected socket under RCU. IPv6 can also get such an association from udp_v6_early_demux(), which runs in ip6_rcv_finish_core(), after ip6_rcv_core(). The reproduced UDPv6 packet has a multicast IP destination but a unicast destination MAC address. It is therefore classified as PACKET_HOST and passes the UDP early-demux check. When the multicast packet is not locally deliverable, IPv6 hands the original skb to ip6_mr_input(). IPv4's ip_mr_input() similarly keeps the original skb when local delivery is not needed. Either path can put the skb on an unresolved multicast route queue or forward it after the receive-side RCU section ends. After the prefetched socket is destroyed, a later skb free invokes sock_pfree() and dereferences the stale skb->sk. Orphan the skb before each non-local multicast forwarding path. Local delivery retains the original skb; the existing skb_clone() calls provide multicast forwarding with a socket-free clone. Fixes: cf7fbe660f2d ("bpf: Add socket assign support") Fixes: 08842c43d016 ("udp: no longer touch sk->sk_refcnt in early demux") Cc: stable@vger.kernel.org Reported-by: Vega Signed-off-by: Zhiling Zou --- changes in v2: - Cover the IPv4 multicast forwarding path. - Correct the IPv6 early-demux ordering and document the unicast-MAC PACKET_HOST condition used by the reproducer. - Add the BPF socket-assignment and UDP early-demux Fixes tags. - v1 Link: https://lore.kernel.org/all/02db4590d0161e31a789dcdfa8d1be1a3212ec2e.1785724784.git.zhilinz@nebusec.ai/ net/ipv4/ipmr.c | 3 +++ net/ipv6/ip6_input.c | 1 + 2 files changed, 4 insertions(+) diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c index 1d9a4ac14fcef..e5f2b1c6150d2 100644 --- a/net/ipv4/ipmr.c +++ b/net/ipv4/ipmr.c @@ -2213,6 +2213,9 @@ int ip_mr_input(struct sk_buff *skb) if (IPCB(skb)->flags & IPSKB_FORWARDED) goto dont_forward; + if (!local) + skb_orphan(skb); + mrt = ipmr_rt_fib_lookup(net, skb); if (IS_ERR(mrt)) { kfree_skb(skb); diff --git a/net/ipv6/ip6_input.c b/net/ipv6/ip6_input.c index 8972863c93ee5..d332ec60f9150 100644 --- a/net/ipv6/ip6_input.c +++ b/net/ipv6/ip6_input.c @@ -622,6 +622,7 @@ int ip6_mc_input(struct sk_buff *skb) if (deliver) { skb2 = skb_clone(skb, GFP_ATOMIC); } else { + skb_orphan(skb); skb2 = skb; skb = NULL; } -- 2.43.0