netfilter: move nat hlist_head to nf_conn

The nat extension structure is 32bytes in size on x86_64:

struct nf_conn_nat {
        struct hlist_node          bysource;             /*     0    16 */
        struct nf_conn *           ct;                   /*    16     8 */
        union nf_conntrack_nat_help help;                /*    24     4 */
        int                        masq_index;           /*    28     4 */
        /* size: 32, cachelines: 1, members: 4 */
        /* last cacheline: 32 bytes */
};

The hlist is needed to quickly check for possible tuple collisions
when installing a new nat binding. Storing this in the extension
area has two drawbacks:

1. We need ct backpointer to get the conntrack struct from the extension.
2. When reallocation of extension area occurs we need to fixup the bysource
   hash head via hlist_replace_rcu.

We can avoid both by placing the hlist_head in nf_conn and place nf_conn in
the bysource hash rather than the extenstion.

We can also remove the ->move support; no other extension needs it.

Moving the entire nat extension into nf_conn would be possible as well but
then we have to add yet another callback for deletion from the bysource
hash table rather than just using nat extension ->destroy hook for this.

nf_conn size doesn't increase due to aligment, followup patch replaces
hlist_node with single pointer.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 2 insertions, 13 deletions

diff --git a/net/netfilter/nf_conntrack_extend.c b/net/netfilter/nf_conntrack_extend.c
index 1a9545965c0d28..02bcf00c24920b 100644
--- a/net/netfilter/nf_conntrack_extend.c
+++ b/net/netfilter/nf_conntrack_extend.c
@@ -73,7 +73,7 @@ void *__nf_ct_ext_add_length(struct nf_conn *ct, enum nf_ct_ext_id id,
 			     size_t var_alloc_len, gfp_t gfp)
 {
 	struct nf_ct_ext *old, *new;
-	int i, newlen, newoff;
+	int newlen, newoff;
 	struct nf_ct_ext_type *t;
 
 	/* Conntrack must not be confirmed to avoid races on reallocation. */
@@ -99,19 +99,8 @@ void *__nf_ct_ext_add_length(struct nf_conn *ct, enum nf_ct_ext_id id,
 		return NULL;
 
 	if (new != old) {
-		for (i = 0; i < NF_CT_EXT_NUM; i++) {
-			if (!__nf_ct_ext_exist(old, i))
-				continue;
-
-			rcu_read_lock();
-			t = rcu_dereference(nf_ct_ext_types[i]);
-			if (t && t->move)
-				t->move((void *)new + new->offset[i],
-					(void *)old + old->offset[i]);
-			rcu_read_unlock();
-		}
 		kfree_rcu(old, rcu);
-		ct->ext = new;
+		rcu_assign_pointer(ct->ext, new);
 	}
 
 	new->offset[id] = newoff;