CVE-2026-64538

In the Linux kernel, the following vulnerability has been resolved:

ipv6: Fix null-ptr-deref in fib6_nh_mtu_change().

fib6_nh_mtu_change() re-fetches idev via __in6_dev_get(arg->dev) and

dereferences idev->cnf.mtu6 without a NULL check. addrconf_ifdown()

clears dev->ip6_ptr with RCU_INIT_POINTER() after rt6_disable_ip() has

released tb6_lock, so the RA-driven MTU walk can observe a NULL idev and

oops. The caller rt6_mtu_change_route() guards its own __in6_dev_get(),

but this re-fetch is unguarded; nexthop-backed routes survive

addrconf_ifdown()'s flush, so the walk still reaches it after ip6_ptr is

nulled.

Return 0 when idev is NULL, matching rt6_mtu_change_route() and the

fib6_mtu() fix in commit 5ad509c1fdad ("ipv6: Fix null-ptr-deref in

fib6_mtu().").

Oops: general protection fault, ... KASAN: null-ptr-deref in range

[0x00000000000002a8-0x00000000000002af]

RIP: 0010:fib6_nh_mtu_change+0x203/0x990

rt6_mtu_change_route+0x141/0x1d0

__fib6_clean_all+0xd0/0x160

rt6_mtu_change+0xb4/0x100

ndisc_router_discovery+0x24b5/0x2cb0

icmpv6_rcv+0x12e9/0x1710

ipv6_rcv+0x39b/0x410