CVE-2026-64542ipv6: ndisc: fix NULL deref in accept_untracked_na()

Official description

In the Linux kernel, the following vulnerability has been resolved: ipv6: ndisc: fix NULL deref in accept_untracked_na() accept_untracked_na() re-fetches the inet6_dev with __in6_dev_get(dev) and dereferences idev->cnf.accept_untracked_na without a NULL check, even though its only caller ndisc_recv_na() already fetched and NULL-checked idev for the same device. Both reads of dev->ip6_ptr run in the same RCU read-side critical section, but a concurrent addrconf_ifdown() can clear dev->ip6_ptr between them: lowering the MTU below IPV6_MIN_MTU calls addrconf_ifdown() without the synchronize_net() that orders the unregister path, so the re-fetch returns NULL and oopses: BUG: KASAN: null-ptr-deref in ndisc_recv_na (net/ipv6/ndisc.c:974) Read of size 4 at addr 0000000000000364 Call Trace: <IRQ> ndisc_recv_na (net/ipv6/ndisc.c:974) icmpv6_rcv (net/ipv6/icmp.c:1193) ip6_protocol_deliver_rcu (net/ipv6/ip6_input.c:479) ip6_input_finish (net/ipv6/ip6_input.c:534) ip6_input (net/ipv6/ip6_input.c:545) ip6_mc_input (net/ipv6/ip6_input.c:635) ipv6_rcv (net/ipv6/ip6_input.c:351) </IRQ> It is reachable by an unprivileged user via a network namespace. Pass the caller's already validated idev instead of re-fetching it; the idev stays alive for the whole RCU critical section, so it is safe even after dev->ip6_ptr has been cleared.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/e5ba3017e46f275ad347e762e8eecacec5efa41d
• https://git.kernel.org/stable/c/160d3f0d7a556ceae505dcab521a37057b4ce28f
• https://git.kernel.org/stable/c/62c719203cb521b64fab74da94a81bdde5c18808
• https://git.kernel.org/stable/c/a6450f7cfae57b382cbaf66a577765c9a88b3c58
• https://git.kernel.org/stable/c/63d1c23764de2309cedbb779c75188d257a09d9b
• https://git.kernel.org/stable/c/d186e942365acece7c56d39da05dd63bf95b280a