CVE-2026-23304ipv6: fix NULL pointer deref in ip6_rt_get_dev_rcu()

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/d542e2ac7f9e288d49735be0775611547ca4e0ee
• https://git.kernel.org/stable/c/a73fe9f4ae84a239d5b2686f47a58c158aee2eb4
• https://git.kernel.org/stable/c/4a48fe59f29f673a3d042d679f26629a9c3e29d4
• https://git.kernel.org/stable/c/581800298313c9fd75e94985e6d37d21b7e35d34
• https://git.kernel.org/stable/c/3310fc11fc47387d1dd4759b0bc961643ea11c7f
• https://git.kernel.org/stable/c/0b5a7826020706057cc5a9d9009e667027f221ee
• https://git.kernel.org/stable/c/ae88c8256547b63980770a9ea7be73a15900d27e
• https://git.kernel.org/stable/c/2ffb4f5c2ccb2fa1c049dd11899aee7967deef5a
• https://cert-portal.siemens.com/productcert/html/ssa-082556.html
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html
• https://cert-portal.siemens.com/productcert/html/ssa-457936.html
• https://cert-portal.siemens.com/productcert/html/ssa-784472.html