CVE-2026-23304

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

ipv6: fix NULL pointer deref in ip6_rt_get_dev_rcu()

l3mdev_master_dev_rcu() can return NULL when the slave device is being

un-slaved from a VRF. All other callers deal with this, but we lost

the fallback to loopback in ip6_rt_pcpu_alloc() -> ip6_rt_get_dev_rcu()

with commit 4832c30d5458 ("net: ipv6: put host and anycast routes on

device with address").

KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f]

RIP: 0010:ip6_rt_pcpu_alloc (net/ipv6/route.c:1418)

Call Trace:

ip6_pol_route (net/ipv6/route.c:2318)

fib6_rule_lookup (net/ipv6/fib6_rules.c:115)

ip6_route_output_flags (net/ipv6/route.c:2607)

vrf_process_v6_outbound (drivers/net/vrf.c:437)

I was tempted to rework the un-slaving code to clear the flag first

and insert synchronize_rcu() before we remove the upper. But looks like

the explicit fallback to loopback_dev is an established pattern.

And I guess avoiding the synchronize_rcu() is nice, too.