CVE-2025-71097ipv4: Fix reference count leak when using error routes with nexthop objects

Official description

In the Linux kernel, the following vulnerability has been resolved: ipv4: Fix reference count leak when using error routes with nexthop objects When a nexthop object is deleted, it is marked as dead and then fib_table_flush() is called to flush all the routes that are using the dead nexthop. The current logic in fib_table_flush() is to only flush error routes (e.g., blackhole) when it is called as part of network namespace dismantle (i.e., with flush_all=true). Therefore, error routes are not flushed when their nexthop object is deleted: # ip link add name dummy1 up type dummy # ip nexthop add id 1 dev dummy1 # ip route add 198.51.100.1/32 nhid 1 # ip route add blackhole 198.51.100.2/32 nhid 1 # ip nexthop del id 1 # ip route show blackhole 198.51.100.2 nhid 1 dev dummy1 As such, they keep holding a reference on the nexthop object which in turn holds a reference on the nexthop device, resulting in a reference count leak: # ip link del dev dummy1 [ 70.516258] unregister_netdevice: waiting for dummy1 to become free. Usage count = 2 Fix by flushing error routes when their nexthop is marked as dead. IPv6 does not suffer from this problem.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/5de7ad7e18356e39e8fbf7edd185a5faaf4f385a
• https://git.kernel.org/stable/c/33ff5c207c873215e54e6176624ed57423cb7dea
• https://git.kernel.org/stable/c/30386e090c49e803c0616a7147e43409c32a2b0e
• https://git.kernel.org/stable/c/5979338c83012110ccd45cae6517591770bfe536
• https://git.kernel.org/stable/c/ee4183501ea556dca31f5ffd8690aa9fd25b609f
• https://git.kernel.org/stable/c/e3fc381320d04e4a74311e576a86cac49a16fc43
• https://git.kernel.org/stable/c/ac782f4e3bfcde145b8a7f8af31d9422d94d172a
• https://cert-portal.siemens.com/productcert/html/ssa-019113.html
• https://cert-portal.siemens.com/productcert/html/ssa-457936.html