netfilter: nf_tables: double hook unregistration in netns path

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

netfilter: nf_tables: double hook unregistration in netns path

__nft_release_hooks() is called from pre_netns exit path which

unregisters the hooks, then the NETDEV_UNREGISTER event is triggered

which unregisters the hooks again.

[ 565.221461] WARNING: CPU: 18 PID: 193 at net/netfilter/core.c:495 __nf_unregister_net_hook+0x247/0x270

[...]

[ 565.246890] CPU: 18 PID: 193 Comm: kworker/u64:1 Tainted: G E 5.18.0-rc7+ #27

[ 565.253682] Workqueue: netns cleanup_net

[ 565.257059] RIP: 0010:__nf_unregister_net_hook+0x247/0x270

[...]

[ 565.297120] Call Trace:

[ 565.300900] <TASK>

[ 565.304683] nf_tables_flowtable_event+0x16a/0x220 [nf_tables]

[ 565.308518] raw_notifier_call_chain+0x63/0x80

[ 565.312386] unregister_netdevice_many+0x54f/0xb50

Unregister and destroy netdev hook from netns pre_exit via kfree_rcu

so the NETDEV_UNREGISTER path see unregistered hooks.