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, 46 insertions, 34 deletions

diff --git a/net/netfilter/nft_set_hash.c b/net/netfilter/nft_set_hash.c
index e758b887ad86..0691565caa81 100644
--- a/net/netfilter/nft_set_hash.c
+++ b/net/netfilter/nft_set_hash.c
@@ -27,6 +27,7 @@ struct nft_rhash {
 };
 
 struct nft_rhash_elem {
+	struct nft_elem_priv		priv;
 	struct rhash_head		node;
 	struct nft_set_ext		ext;
 };
@@ -95,8 +96,9 @@ bool nft_rhash_lookup(const struct net *net, const struct nft_set *set,
 	return !!he;
 }
 
-static void *nft_rhash_get(const struct net *net, const struct nft_set *set,
-			   const struct nft_set_elem *elem, unsigned int flags)
+static struct nft_elem_priv *
+nft_rhash_get(const struct net *net, const struct nft_set *set,
+	      const struct nft_set_elem *elem, unsigned int flags)
 {
 	struct nft_rhash *priv = nft_set_priv(set);
 	struct nft_rhash_elem *he;
@@ -108,13 +110,14 @@ static void *nft_rhash_get(const struct net *net, const struct nft_set *set,
 
 	he = rhashtable_lookup(&priv->ht, &arg, nft_rhash_params);
 	if (he != NULL)
-		return he;
+		return &he->priv;
 
 	return ERR_PTR(-ENOENT);
 }
 
 static bool nft_rhash_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 *regs),
 			     const struct nft_expr *expr,
@@ -123,6 +126,7 @@ static bool nft_rhash_update(struct nft_set *set, const u32 *key,
 {
 	struct nft_rhash *priv = nft_set_priv(set);
 	struct nft_rhash_elem *he, *prev;
+	struct nft_elem_priv *elem_priv;
 	struct nft_rhash_cmp_arg arg = {
 		.genmask = NFT_GENMASK_ANY,
 		.set	 = set,
@@ -133,10 +137,11 @@ static bool nft_rhash_update(struct nft_set *set, const u32 *key,
 	if (he != NULL)
 		goto out;
 
-	he = new(set, expr, regs);
-	if (he == NULL)
+	elem_priv = new(set, expr, regs);
+	if (!elem_priv)
 		goto err1;
 
+	he = nft_elem_priv_cast(elem_priv);
 	prev = rhashtable_lookup_get_insert_key(&priv->ht, &arg, &he->node,
 						nft_rhash_params);
 	if (IS_ERR(prev))
@@ -144,7 +149,7 @@ static bool nft_rhash_update(struct nft_set *set, const u32 *key,
 
 	/* Another cpu may race to insert the element with the same key */
 	if (prev) {
-		nft_set_elem_destroy(set, he, true);
+		nft_set_elem_destroy(set, &he->priv, true);
 		atomic_dec(&set->nelems);
 		he = prev;
 	}
@@ -154,7 +159,7 @@ out:
 	return true;
 
 err2:
-	nft_set_elem_destroy(set, he, true);
+	nft_set_elem_destroy(set, &he->priv, true);
 	atomic_dec(&set->nelems);
 err1:
 	return false;
@@ -164,8 +169,8 @@ static int nft_rhash_insert(const struct net *net, const struct nft_set *set,
 			    const struct nft_set_elem *elem,
 			    struct nft_set_ext **ext)
 {
+	struct nft_rhash_elem *he = nft_elem_priv_cast(elem->priv);
 	struct nft_rhash *priv = nft_set_priv(set);
-	struct nft_rhash_elem *he = elem->priv;
 	struct nft_rhash_cmp_arg arg = {
 		.genmask = nft_genmask_next(net),
 		.set	 = set,
@@ -187,22 +192,23 @@ static int nft_rhash_insert(const struct net *net, const struct nft_set *set,
 static void nft_rhash_activate(const struct net *net, const struct nft_set *set,
 			       const struct nft_set_elem *elem)
 {
-	struct nft_rhash_elem *he = elem->priv;
+	struct nft_rhash_elem *he = nft_elem_priv_cast(elem->priv);
 
 	nft_set_elem_change_active(net, set, &he->ext);
 }
 
 static void nft_rhash_flush(const struct net *net,
-			    const struct nft_set *set, void *priv)
+			    const struct nft_set *set,
+			    struct nft_elem_priv *elem_priv)
 {
-	struct nft_rhash_elem *he = priv;
+	struct nft_rhash_elem *he = nft_elem_priv_cast(elem_priv);
 
 	nft_set_elem_change_active(net, set, &he->ext);
 }
 
-static void *nft_rhash_deactivate(const struct net *net,
-				  const struct nft_set *set,
-				  const struct nft_set_elem *elem)
+static struct nft_elem_priv *
+nft_rhash_deactivate(const struct net *net, const struct nft_set *set,
+		     const struct nft_set_elem *elem)
 {
 	struct nft_rhash *priv = nft_set_priv(set);
 	struct nft_rhash_elem *he;
@@ -219,15 +225,15 @@ static void *nft_rhash_deactivate(const struct net *net,
 
 	rcu_read_unlock();
 
-	return he;
+	return &he->priv;
 }
 
 static void nft_rhash_remove(const struct net *net,
 			     const struct nft_set *set,
 			     const struct nft_set_elem *elem)
 {
+	struct nft_rhash_elem *he = nft_elem_priv_cast(elem->priv);
 	struct nft_rhash *priv = nft_set_priv(set);
-	struct nft_rhash_elem *he = elem->priv;
 
 	rhashtable_remove_fast(&priv->ht, &he->node, nft_rhash_params);
 }
@@ -278,7 +284,7 @@ static void nft_rhash_walk(const struct nft_ctx *ctx, struct nft_set *set,
 		if (!nft_set_elem_active(&he->ext, iter->genmask))
 			goto cont;
 
-		elem.priv = he;
+		elem.priv = &he->priv;
 
 		iter->err = iter->fn(ctx, set, iter, &elem);
 		if (iter->err < 0)
@@ -404,6 +410,8 @@ static int nft_rhash_init(const struct nft_set *set,
 	struct rhashtable_params params = nft_rhash_params;
 	int err;
 
+	BUILD_BUG_ON(offsetof(struct nft_rhash_elem, priv) != 0);
+
 	params.nelem_hint = desc->size ?: NFT_RHASH_ELEMENT_HINT;
 	params.key_len	  = set->klen;
 
@@ -426,8 +434,9 @@ struct nft_rhash_ctx {
 static void nft_rhash_elem_destroy(void *ptr, void *arg)
 {
 	struct nft_rhash_ctx *rhash_ctx = arg;
+	struct nft_rhash_elem *he = ptr;
 
-	nf_tables_set_elem_destroy(&rhash_ctx->ctx, rhash_ctx->set, ptr);
+	nf_tables_set_elem_destroy(&rhash_ctx->ctx, rhash_ctx->set, &he->priv);
 }
 
 static void nft_rhash_destroy(const struct nft_ctx *ctx,
@@ -474,6 +483,7 @@ struct nft_hash {
 };
 
 struct nft_hash_elem {
+	struct nft_elem_priv		priv;
 	struct hlist_node		node;
 	struct nft_set_ext		ext;
 };
@@ -499,8 +509,9 @@ bool nft_hash_lookup(const struct net *net, const struct nft_set *set,
 	return false;
 }
 
-static void *nft_hash_get(const struct net *net, const struct nft_set *set,
-			  const struct nft_set_elem *elem, unsigned int flags)
+static struct nft_elem_priv *
+nft_hash_get(const struct net *net, const struct nft_set *set,
+	     const struct nft_set_elem *elem, unsigned int flags)
 {
 	struct nft_hash *priv = nft_set_priv(set);
 	u8 genmask = nft_genmask_cur(net);
@@ -512,7 +523,7 @@ static void *nft_hash_get(const struct net *net, const struct nft_set *set,
 	hlist_for_each_entry_rcu(he, &priv->table[hash], node) {
 		if (!memcmp(nft_set_ext_key(&he->ext), elem->key.val.data, set->klen) &&
 		    nft_set_elem_active(&he->ext, genmask))
-			return he;
+			return &he->priv;
 	}
 	return ERR_PTR(-ENOENT);
 }
@@ -562,7 +573,7 @@ static int nft_hash_insert(const struct net *net, const struct nft_set *set,
 			   const struct nft_set_elem *elem,
 			   struct nft_set_ext **ext)
 {
-	struct nft_hash_elem *this = elem->priv, *he;
+	struct nft_hash_elem *this = nft_elem_priv_cast(elem->priv), *he;
 	struct nft_hash *priv = nft_set_priv(set);
 	u8 genmask = nft_genmask_next(net);
 	u32 hash;
@@ -583,25 +594,26 @@ static int nft_hash_insert(const struct net *net, const struct nft_set *set,
 static void nft_hash_activate(const struct net *net, const struct nft_set *set,
 			      const struct nft_set_elem *elem)
 {
-	struct nft_hash_elem *he = elem->priv;
+	struct nft_hash_elem *he = nft_elem_priv_cast(elem->priv);
 
 	nft_set_elem_change_active(net, set, &he->ext);
 }
 
 static void nft_hash_flush(const struct net *net,
-			   const struct nft_set *set, void *priv)
+			   const struct nft_set *set,
+			   struct nft_elem_priv *elem_priv)
 {
-	struct nft_hash_elem *he = priv;
+	struct nft_hash_elem *he = nft_elem_priv_cast(elem_priv);
 
 	nft_set_elem_change_active(net, set, &he->ext);
 }
 
-static void *nft_hash_deactivate(const struct net *net,
-				 const struct nft_set *set,
-				 const struct nft_set_elem *elem)
+static struct nft_elem_priv *
+nft_hash_deactivate(const struct net *net, const struct nft_set *set,
+		    const struct nft_set_elem *elem)
 {
+	struct nft_hash_elem *this = nft_elem_priv_cast(elem->priv), *he;
 	struct nft_hash *priv = nft_set_priv(set);
-	struct nft_hash_elem *this = elem->priv, *he;
 	u8 genmask = nft_genmask_next(net);
 	u32 hash;
 
@@ -611,7 +623,7 @@ static void *nft_hash_deactivate(const struct net *net,
 			    set->klen) &&
 		    nft_set_elem_active(&he->ext, genmask)) {
 			nft_set_elem_change_active(net, set, &he->ext);
-			return he;
+			return &he->priv;
 		}
 	}
 	return NULL;
@@ -621,7 +633,7 @@ static void nft_hash_remove(const struct net *net,
 			    const struct nft_set *set,
 			    const struct nft_set_elem *elem)
 {
-	struct nft_hash_elem *he = elem->priv;
+	struct nft_hash_elem *he = nft_elem_priv_cast(elem->priv);
 
 	hlist_del_rcu(&he->node);
 }
@@ -641,7 +653,7 @@ static void nft_hash_walk(const struct nft_ctx *ctx, struct nft_set *set,
 			if (!nft_set_elem_active(&he->ext, iter->genmask))
 				goto cont;
 
-			elem.priv = he;
+			elem.priv = &he->priv;
 
 			iter->err = iter->fn(ctx, set, iter, &elem);
 			if (iter->err < 0)
@@ -682,7 +694,7 @@ static void nft_hash_destroy(const struct nft_ctx *ctx,
 	for (i = 0; i < priv->buckets; i++) {
 		hlist_for_each_entry_safe(he, next, &priv->table[i], node) {
 			hlist_del_rcu(&he->node);
-			nf_tables_set_elem_destroy(ctx, set, he);
+			nf_tables_set_elem_destroy(ctx, set, &he->priv);
 		}
 	}
 }