netfilter: nf_tables: shrink memory consumption of set elements

Instead of copying struct nft_set_elem into struct nft_trans_elem, store
the pointer to the opaque set element object in the transaction. Adapt
set backend API (and set backend implementations) to take the pointer to
opaque set element representation whenever required.

This patch deconstifies .remove() and .activate() set backend API since
these modify the set element opaque object. And it also constify
nft_set_elem_ext() this provides access to the nft_set_ext struct
without updating the object.

According to pahole on x86_64, this patch shrinks struct nft_trans_elem
size from 216 to 24 bytes.

This patch also reduces stack memory consumption by removing the
template struct nft_set_elem object, using the opaque set element object
instead such as from the set iterator API, catchall elements and the get
element command.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: ummakynes

include/net/netfilter/nf_tables.h

@@ -314,7 +314,7 @@ struct nft_set_iter {
 	int		(*fn)(const struct nft_ctx *ctx,
 			      struct nft_set *set,
 			      const struct nft_set_iter *iter,
-			      struct nft_set_elem *elem);
+			      struct nft_elem_priv *elem_priv);
 };
 
 /**
@@ -454,7 +454,7 @@ struct nft_set_ops {
 						  struct nft_set_ext **ext);
 	void				(*activate)(const struct net *net,
 						    const struct nft_set *set,
-						    const struct nft_set_elem *elem);
+						    struct nft_elem_priv *elem_priv);
 	struct nft_elem_priv *		(*deactivate)(const struct net *net,
 						      const struct nft_set *set,
 						      const struct nft_set_elem *elem);
@@ -463,7 +463,7 @@ struct nft_set_ops {
 						 struct nft_elem_priv *priv);
 	void				(*remove)(const struct net *net,
 						  const struct nft_set *set,
-						  const struct nft_set_elem *elem);
+						  struct nft_elem_priv *elem_priv);
 	void				(*walk)(const struct nft_ctx *ctx,
 						struct nft_set *set,
 						struct nft_set_iter *iter);
@@ -1073,7 +1073,7 @@ struct nft_chain {
 int nft_chain_validate(const struct nft_ctx *ctx, const struct nft_chain *chain);
 int nft_setelem_validate(const struct nft_ctx *ctx, struct nft_set *set,
 			 const struct nft_set_iter *iter,
-			 struct nft_set_elem *elem);
+			 struct nft_elem_priv *elem_priv);
 int nft_set_catchall_validate(const struct nft_ctx *ctx, struct nft_set *set);
 int nf_tables_bind_chain(const struct nft_ctx *ctx, struct nft_chain *chain);
 void nf_tables_unbind_chain(const struct nft_ctx *ctx, struct nft_chain *chain);
@@ -1650,14 +1650,14 @@ struct nft_trans_table {
 
 struct nft_trans_elem {
 	struct nft_set			*set;
-	struct nft_set_elem		elem;
+	struct nft_elem_priv		*elem_priv;
 	bool				bound;
 };
 
 #define nft_trans_elem_set(trans)	\
 	(((struct nft_trans_elem *)trans->data)->set)
-#define nft_trans_elem(trans)	\
-	(((struct nft_trans_elem *)trans->data)->elem)
+#define nft_trans_elem_priv(trans)	\
+	(((struct nft_trans_elem *)trans->data)->elem_priv)
 #define nft_trans_elem_set_bound(trans)	\
 	(((struct nft_trans_elem *)trans->data)->bound)
 
@@ -1698,7 +1698,7 @@ struct nft_trans_gc {
 	struct nft_set		*set;
 	u32			seq;
 	u16			count;
-	void			*priv[NFT_TRANS_GC_BATCHCOUNT];
+	struct nft_elem_priv	*priv[NFT_TRANS_GC_BATCHCOUNT];
 	struct rcu_head		rcu;
 };
 
@@ -1721,7 +1721,7 @@ struct nft_trans_gc *nft_trans_gc_catchall_sync(struct nft_trans_gc *gc);
 
 void nft_setelem_data_deactivate(const struct net *net,
 				 const struct nft_set *set,
-				 struct nft_set_elem *elem);
+				 struct nft_elem_priv *elem_priv);
 
 int __init nft_chain_filter_init(void);
 void nft_chain_filter_fini(void);