CVE-2026-23304

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

ipv6: fix NULL pointer deref in ip6rtgetdevrcu()

l3mdevmasterdevrcu() 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 ip6rtpcpualloc() -> ip6rtgetdevrcu() with commit 4832c30d5458 ("net: ipv6: put host and anycast routes on device with address").

KASAN: null-ptr-deref in range [0x0000000000000108-0x000000000000010f] RIP: 0010:ip6rtpcpualloc (net/ipv6/route.c:1418) Call Trace: ip6polroute (net/ipv6/route.c:2318) fib6rulelookup (net/ipv6/fib6rules.c:115) ip6routeoutputflags (net/ipv6/route.c:2607) vrfprocessv6outbound (drivers/net/vrf.c:437)

I was tempted to rework the un-slaving code to clear the flag first and insert synchronizercu() before we remove the upper. But looks like the explicit fallback to loopbackdev is an established pattern. And I guess avoiding the synchronize_rcu() is nice, too.