CVE-2021-47291: Out-of-bounds Read

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

ipv6: fix another slab-out-of-bounds in fib6_nh_flush_exceptions

While running the self-tests on a KASAN enabled kernel, I observed a slab-out-of-bounds splat very similar to the one reported in commit 821bbf79fe46 ("ipv6: Fix KASAN: slab-out-of-bounds Read in fib6_nh_flush_exceptions").

We additionally need to take care of fib6_metrics initialization failure when the caller provides an nh.

The fix is similar, explicitly free the route instead of calling fib6_info_release on a half-initialized object.