In the Linux kernel, the following vulnerability has been resolved: netfilter: nf_log: unregister loggers before per-net teardown nf_log_s

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

netfilter: nf_log: unregister loggers before per-net teardown

nf_log_syslog and nfnetlink_log unregister their per-network namespace
operations before unregistering their global logger backends. This
leaves a window where a sysctl or netlink writer can rebind the still-
registered logger after the per-net pre-exit callback cleared the old
selection.

The race looks like this:

CPU 0 CPU 1

unregister_pernet_subsys()
nf_log_unset(net, logger)
net->nf.nf_loggers[pf] = NULL

 1                                    lock nf_log_mutex
 2                                    find logger in loggers[][]
 3                                    net->nf.nf_loggers[pf] = logger
 4                                    unlock nf_log_mutex

nf_log_unregister(logger)
lock nf_log_mutex
loggers[pf][type] = NULL
unlock nf_log_mutex
synchronize_rcu()
module exit returns
module core frees backend memory

Later, a sysctl read or packet logging operation can dereference the
stale per-net logger pointer.

Fix this by unregistering the global logger backends before tearing down
per-net state. Once the global registrations are gone, later writers can
no longer rebind the logger. unregister_pernet_subsys() already waits
for an RCU grace period after the pre-exit callback clears the per-net
selection, while nf_log_unregister() continues to cover readers of the
global logger table.

Apply this ordering fix to both nf_log backends that combine per-net
teardown with global logger registration.