CVE-2022-50043

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

net: fix potential refcount leak in ndisc_router_discovery()

The issue happens on specific paths in the function. After both the object rt and neigh are grabbed successfully, when lifetime is nonzero but the metric needs change, the function just deletes the route and set rt to NULL. Then, it may try grabbing rt and neigh again if above conditions hold. The function simply overwrite neigh if succeeds or returns if fails, without decreasing the reference count of previous neigh. This may result in memory leaks.

Fix it by decrementing the reference count of neigh in place.