CVE-2026-89564ip: orphan prefetched skbs before multicast forwarding

Official description

In the Linux kernel, the following vulnerability has been resolved: ip: orphan prefetched skbs before multicast forwarding 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. Both address families can also prefetch a socket in UDP early demux. In both paths (BPF and UDP early demux) a reference is not guaranteed to be held on the socket. When a 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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/592b91f41d4f35e37c9e0be1c46a4c28437642cd
• https://git.kernel.org/stable/c/882212d317a7c16ab70d20656f6b1c42abada9f6
• https://git.kernel.org/stable/c/e62aef7d6a5b27569bf540bbe11a9482117ff588
• https://git.kernel.org/stable/c/a8af6fbac895f057c4b8ff8a2e3fb4c5827fe4ce
• https://git.kernel.org/stable/c/f1281d4b99089fbaf0d3579bba62a814ebb4de4d
• https://git.kernel.org/stable/c/e36ce6e78fe3fc3c071a26750783b7ba081ce10d