netfilter: lift one-nat-hook-only restriction

This reverts commit f92b40a8
("netfilter: core: only allow one nat hook per hook point"), this
limitation is no longer needed.  The nat core now invokes these
functions and makes sure that hook evaluation stops after a mapping is
created and a null binding is created otherwise.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter.h

@@ -67,7 +67,6 @@ struct nf_hook_ops {
 	struct net_device	*dev;
 	void			*priv;
 	u_int8_t		pf;
-	bool			nat_hook;
 	unsigned int		hooknum;
 	/* Hooks are ordered in ascending priority. */
 	int			priority;

net/netfilter/core.c

@@ -138,11 +138,6 @@ nf_hook_entries_grow(const struct nf_hook_entries *old,
 			continue;
 		}
 
-		if (reg->nat_hook && orig_ops[i]->nat_hook) {
-			kvfree(new);
-			return ERR_PTR(-EBUSY);
-		}
-
 		if (inserted || reg->priority > orig_ops[i]->priority) {
 			new_ops[nhooks] = (void *)orig_ops[i];
 			new->hooks[nhooks] = old->hooks[i];

net/netfilter/nf_tables_api.c

@@ -74,64 +74,12 @@ static void nft_trans_destroy(struct nft_trans *trans)
 	kfree(trans);
 }
 
-/* removal requests are queued in the commit_list, but not acted upon
- * until after all new rules are in place.
- *
- * Therefore, nf_register_net_hook(net, &nat_hook) runs before pending
- * nf_unregister_net_hook().
- *
- * nf_register_net_hook thus fails if a nat hook is already in place
- * even if the conflicting hook is about to be removed.
- *
- * If collision is detected, search commit_log for DELCHAIN matching
- * the new nat hooknum; if we find one collision is temporary:
- *
- * Either transaction is aborted (new/colliding hook is removed), or
- * transaction is committed (old hook is removed).
- */
-static bool nf_tables_allow_nat_conflict(const struct net *net,
-					 const struct nf_hook_ops *ops)
-{
-	const struct nft_trans *trans;
-	bool ret = false;
-
-	if (!ops->nat_hook)
-		return false;
-
-	list_for_each_entry(trans, &net->nft.commit_list, list) {
-		const struct nf_hook_ops *pending_ops;
-		const struct nft_chain *pending;
-
-		if (trans->msg_type != NFT_MSG_NEWCHAIN &&
-		    trans->msg_type != NFT_MSG_DELCHAIN)
-			continue;
-
-		pending = trans->ctx.chain;
-		if (!nft_is_base_chain(pending))
-			continue;
-
-		pending_ops = &nft_base_chain(pending)->ops;
-		if (pending_ops->nat_hook &&
-		    pending_ops->pf == ops->pf &&
-		    pending_ops->hooknum == ops->hooknum) {
-			/* other hook registration already pending? */
-			if (trans->msg_type == NFT_MSG_NEWCHAIN)
-				return false;
-
-			ret = true;
-		}
-	}
-
-	return ret;
-}
-
 static int nf_tables_register_hook(struct net *net,
 				   const struct nft_table *table,
 				   struct nft_chain *chain)
 {
 	const struct nft_base_chain *basechain;
-	struct nf_hook_ops *ops;
-	int ret;
+	const struct nf_hook_ops *ops;
 
 	if (table->flags & NFT_TABLE_F_DORMANT ||
 	    !nft_is_base_chain(chain))
@@ -143,14 +91,7 @@ static int nf_tables_register_hook(struct net *net,
 	if (basechain->type->ops_register)
 		return basechain->type->ops_register(net, ops);
 
-	ret = nf_register_net_hook(net, ops);
-	if (ret == -EBUSY && nf_tables_allow_nat_conflict(net, ops)) {
-		ops->nat_hook = false;
-		ret = nf_register_net_hook(net, ops);
-		ops->nat_hook = true;
-	}
-
-	return ret;
+	return nf_register_net_hook(net, ops);
 }
 
 static void nf_tables_unregister_hook(struct net *net,
@@ -1418,9 +1359,6 @@ static int nf_tables_addchain(struct nft_ctx *ctx, u8 family, u8 genmask,
 		ops->hook	= hook.type->hooks[ops->hooknum];
 		ops->dev	= hook.dev;
 
-		if (basechain->type->type == NFT_CHAIN_T_NAT)
-			ops->nat_hook = true;
-
 		chain->flags |= NFT_BASE_CHAIN;
 		basechain->policy = policy;
 	} else {