netfilter: nf_tables: expose opaque set element as struct nft_elem_priv

Add placeholder structure and place it at the beginning of each struct
nft_*_elem for each existing set backend, instead of exposing elements
as void type to the frontend which defeats compiler type checks. Use
this pointer to this new type to replace void *.

This patch updates the following set backend API to use this new struct
nft_elem_priv placeholder structure:

- update
- deactivate
- flush
- get

as well as the following helper functions:

- nft_set_elem_ext()
- nft_set_elem_init()
- nft_set_elem_destroy()
- nf_tables_set_elem_destroy()

This patch adds nft_elem_priv_cast() to cast struct nft_elem_priv to
native element representation from the corresponding set backend.
BUILD_BUG_ON() makes sure this .priv placeholder is always at the top
of the opaque set element representation.

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

1 files changed, 25 insertions, 13 deletions

diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index d0f5c477c254..d287a778be65 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -274,6 +274,9 @@ struct nft_userdata {
 	unsigned char		data[];
 };
 
+/* placeholder structure for opaque set element backend representation. */
+struct nft_elem_priv { };
+
 /**
  *	struct nft_set_elem - generic representation of set elements
  *
@@ -294,9 +297,14 @@ struct nft_set_elem {
 		u32		buf[NFT_DATA_VALUE_MAXLEN / sizeof(u32)];
 		struct nft_data val;
 	} data;
-	void			*priv;
+	struct nft_elem_priv	*priv;
 };
 
+static inline void *nft_elem_priv_cast(const struct nft_elem_priv *priv)
+{
+	return (void *)priv;
+}
+
 struct nft_set;
 struct nft_set_iter {
 	u8		genmask;
@@ -430,7 +438,8 @@ struct nft_set_ops {
 						  const struct nft_set_ext **ext);
 	bool				(*update)(struct nft_set *set,
 						  const u32 *key,
-						  void *(*new)(struct nft_set *,
+						  struct nft_elem_priv *
+							(*new)(struct nft_set *,
 							       const struct nft_expr *,
 							       struct nft_regs *),
 						  const struct nft_expr *expr,
@@ -446,19 +455,19 @@ struct nft_set_ops {
 	void				(*activate)(const struct net *net,
 						    const struct nft_set *set,
 						    const struct nft_set_elem *elem);
-	void *				(*deactivate)(const struct net *net,
+	struct nft_elem_priv *		(*deactivate)(const struct net *net,
 						      const struct nft_set *set,
 						      const struct nft_set_elem *elem);
 	void				(*flush)(const struct net *net,
 						 const struct nft_set *set,
-						 void *priv);
+						 struct nft_elem_priv *priv);
 	void				(*remove)(const struct net *net,
 						  const struct nft_set *set,
 						  const struct nft_set_elem *elem);
 	void				(*walk)(const struct nft_ctx *ctx,
 						struct nft_set *set,
 						struct nft_set_iter *iter);
-	void *				(*get)(const struct net *net,
+	struct nft_elem_priv *		(*get)(const struct net *net,
 					       const struct nft_set *set,
 					       const struct nft_set_elem *elem,
 					       unsigned int flags);
@@ -796,9 +805,9 @@ static inline bool nft_set_elem_expired(const struct nft_set_ext *ext)
 }
 
 static inline struct nft_set_ext *nft_set_elem_ext(const struct nft_set *set,
-						   void *elem)
+						   const struct nft_elem_priv *elem_priv)
 {
-	return elem + set->ops->elemsize;
+	return (void *)elem_priv + set->ops->elemsize;
 }
 
 static inline struct nft_object **nft_set_ext_obj(const struct nft_set_ext *ext)
@@ -810,16 +819,19 @@ struct nft_expr *nft_set_elem_expr_alloc(const struct nft_ctx *ctx,
 					 const struct nft_set *set,
 					 const struct nlattr *attr);
 
-void *nft_set_elem_init(const struct nft_set *set,
-			const struct nft_set_ext_tmpl *tmpl,
-			const u32 *key, const u32 *key_end, const u32 *data,
-			u64 timeout, u64 expiration, gfp_t gfp);
+struct nft_elem_priv *nft_set_elem_init(const struct nft_set *set,
+					const struct nft_set_ext_tmpl *tmpl,
+					const u32 *key, const u32 *key_end,
+					const u32 *data,
+					u64 timeout, u64 expiration, gfp_t gfp);
 int nft_set_elem_expr_clone(const struct nft_ctx *ctx, struct nft_set *set,
 			    struct nft_expr *expr_array[]);
-void nft_set_elem_destroy(const struct nft_set *set, void *elem,
+void nft_set_elem_destroy(const struct nft_set *set,
+			  const struct nft_elem_priv *elem_priv,
 			  bool destroy_expr);
 void nf_tables_set_elem_destroy(const struct nft_ctx *ctx,
-				const struct nft_set *set, void *elem);
+				const struct nft_set *set,
+				const struct nft_elem_priv *elem_priv);
 
 struct nft_expr_ops;
 /**