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

https://git.kernel.org/stable/c/1451deca9896957159f0666520a792c1b861af4f

https://git.kernel.org/stable/c/302d57ed7872838b40e56a868fb4c7da7da606e9

https://git.kernel.org/stable/c/46c3b8191aad3d032776bf3bebf03efdf5f4b905

https://git.kernel.org/stable/c/6428634f7a0b7878144b4925c37856bef3224967

https://git.kernel.org/stable/c/80600b5d0f3ecb9324120dc95b5e915130f516c5

https://git.kernel.org/stable/c/b0d0eb13a0441a8ebf4f227843deaf494f1e2c33

https://git.kernel.org/stable/c/b2c70dd3326809429b709a9c7e9220d29923051a

https://git.kernel.org/stable/c/d08d019f2f43a6f9a71e81868bbc326b3afaf37b

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