CVE-2026-64542

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.