netfilter: nf_nat: Fix possible memory leak in nf_nat_init()

In nf_nat_init(), register_nf_nat_bpf() can fail and return directly
without any error handling.
Then nf_nat_bysource will leak and registering of &nat_net_ops,
&follow_master_nat and nf_nat_hook won't be reverted.

This leaves wild ops in linkedlists and when another module tries to
call register_pernet_operations() or nf_ct_helper_expectfn_register()
it triggers page fault:

 BUG: unable to handle page fault for address: fffffbfff81b964c
 RIP: 0010:register_pernet_operations+0x1b9/0x5f0
 Call Trace:
 <TASK>
  register_pernet_subsys+0x29/0x40
  ebtables_init+0x58/0x1000 [ebtables]
  ...

Fixes: 820dc052 ("net: netfilter: move bpf_ct_set_nat_info kfunc in nf_nat_bpf.c")
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_nat_core.c

@@ -1152,7 +1152,16 @@ static int __init nf_nat_init(void)
 	WARN_ON(nf_nat_hook != NULL);
 	RCU_INIT_POINTER(nf_nat_hook, &nat_hook);
 
-	return register_nf_nat_bpf();
+	ret = register_nf_nat_bpf();
+	if (ret < 0) {
+		RCU_INIT_POINTER(nf_nat_hook, NULL);
+		nf_ct_helper_expectfn_unregister(&follow_master_nat);
+		synchronize_net();
+		unregister_pernet_subsys(&nat_net_ops);
+		kvfree(nf_nat_bysource);
+	}
+
+	return ret;
 }
 
 static void __exit nf_nat_cleanup(void)