netfilter: conntrack: nf_ct_gre_keymap_flush() removal

nf_ct_gre_keymap_flush() is useless.
It is called from nf_conntrack_cleanup_net_list() only and tries to remove
nf_ct_gre_keymap entries from pernet gre keymap list. Though:
a) at this point the list should already be empty, all its entries were
deleted during the conntracks cleanup, because
nf_conntrack_cleanup_net_list() executes nf_ct_iterate_cleanup(kill_all)
before nf_conntrack_proto_pernet_fini():
 nf_conntrack_cleanup_net_list
  +- nf_ct_iterate_cleanup
  |   nf_ct_put
  |    nf_conntrack_put
  |     nf_conntrack_destroy
  |      destroy_conntrack
  |       destroy_gre_conntrack
  |        nf_ct_gre_keymap_destroy
  `- nf_conntrack_proto_pernet_fini
      nf_ct_gre_keymap_flush

b) Let's say we find that the keymap list is not empty. This means netns
still has a conntrack associated with gre, in which case we should not free
its memory, because this will lead to a double free and related crashes.
However I doubt it could have gone unnoticed for years, obviously
this does not happen in real life. So I think we can remove
both nf_ct_gre_keymap_flush() and nf_conntrack_proto_pernet_fini().

Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: vaverin

include/net/netfilter/nf_conntrack_core.h

@@ -30,7 +30,6 @@ void nf_conntrack_cleanup_net(struct net *net);
 void nf_conntrack_cleanup_net_list(struct list_head *net_exit_list);
 
 void nf_conntrack_proto_pernet_init(struct net *net);
-void nf_conntrack_proto_pernet_fini(struct net *net);
 
 int nf_conntrack_proto_init(void);
 void nf_conntrack_proto_fini(void);

net/netfilter/nf_conntrack_core.c

@@ -2457,7 +2457,6 @@ void nf_conntrack_cleanup_net_list(struct list_head *net_exit_list)
 	}
 
 	list_for_each_entry(net, net_exit_list, exit_list) {
-		nf_conntrack_proto_pernet_fini(net);
 		nf_conntrack_ecache_pernet_fini(net);
 		nf_conntrack_expect_pernet_fini(net);
 		free_percpu(net->ct.stat);

net/netfilter/nf_conntrack_proto.c

@@ -697,13 +697,6 @@ void nf_conntrack_proto_pernet_init(struct net *net)
 #endif
 }
 
-void nf_conntrack_proto_pernet_fini(struct net *net)
-{
-#ifdef CONFIG_NF_CT_PROTO_GRE
-	nf_ct_gre_keymap_flush(net);
-#endif
-}
-
 module_param_call(hashsize, nf_conntrack_set_hashsize, param_get_uint,
 		  &nf_conntrack_htable_size, 0600);
 

net/netfilter/nf_conntrack_proto_gre.c

@@ -55,19 +55,6 @@ static inline struct nf_gre_net *gre_pernet(struct net *net)
 	return &net->ct.nf_ct_proto.gre;
 }
 
-void nf_ct_gre_keymap_flush(struct net *net)
-{
-	struct nf_gre_net *net_gre = gre_pernet(net);
-	struct nf_ct_gre_keymap *km, *tmp;
-
-	spin_lock_bh(&keymap_lock);
-	list_for_each_entry_safe(km, tmp, &net_gre->keymap_list, list) {
-		list_del_rcu(&km->list);
-		kfree_rcu(km, rcu);
-	}
-	spin_unlock_bh(&keymap_lock);
-}
-
 static inline int gre_key_cmpfn(const struct nf_ct_gre_keymap *km,
 				const struct nf_conntrack_tuple *t)
 {