netfilter: nf_tables: Simplify set backend selection

Drop nft_set_type's ability to act as a container of multiple backend
implementations it chooses from. Instead consolidate the whole selection
logic in nft_select_set_ops() and the actual backend provided estimate()
callback.

This turns nf_tables_set_types into a list containing all available
backends which is traversed when selecting one matching userspace
requested criteria.

Also, this change allows to embed nft_set_ops structure into
nft_set_type and pull flags field into the latter as it's only used
during selection phase.

A crucial part of this change is to make sure the new layout respects
hash backend constraints formerly enforced by nft_hash_select_ops()
function: This is achieved by introduction of a specific estimate()
callback for nft_hash_fast_ops which returns false for key lengths != 4.
In turn, nft_hash_estimate() is changed to return false for key lengths
== 4 so it won't be chosen by accident. Also, both callbacks must return
false for unbounded sets as their size estimate depends on a known
maximum element count.

Note that this patch partially reverts commit 4f2921ca21b71 ("netfilter:
nf_tables: meter: pick a set backend that supports updates") by making
nft_set_ops_candidate() not explicitly look for an update callback but
make NFT_SET_EVAL a regular backend feature flag which is checked along
with the others. This way all feature requirements are checked in one
go.

Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 15 insertions, 19 deletions

diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index 123e82a2f8bb..de77d36e36b3 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -275,23 +275,6 @@ struct nft_set_estimate {
 	enum nft_set_class	space;
 };
 
-/**
- *      struct nft_set_type - nf_tables set type
- *
- *      @select_ops: function to select nft_set_ops
- *      @ops: default ops, used when no select_ops functions is present
- *      @list: used internally
- *      @owner: module reference
- */
-struct nft_set_type {
-	const struct nft_set_ops	*(*select_ops)(const struct nft_ctx *,
-						       const struct nft_set_desc *desc,
-						       u32 flags);
-	const struct nft_set_ops	*ops;
-	struct list_head		list;
-	struct module			*owner;
-};
-
 struct nft_set_ext;
 struct nft_expr;
 
@@ -310,7 +293,6 @@ struct nft_expr;
  *	@init: initialize private data of new set instance
  *	@destroy: destroy private data of set instance
  *	@elemsize: element private size
- *	@features: features supported by the implementation
  */
 struct nft_set_ops {
 	bool				(*lookup)(const struct net *net,
@@ -361,9 +343,23 @@ struct nft_set_ops {
 	void				(*destroy)(const struct nft_set *set);
 
 	unsigned int			elemsize;
+};
+
+/**
+ *      struct nft_set_type - nf_tables set type
+ *
+ *      @ops: set ops for this type
+ *      @list: used internally
+ *      @owner: module reference
+ *      @features: features supported by the implementation
+ */
+struct nft_set_type {
+	const struct nft_set_ops	ops;
+	struct list_head		list;
+	struct module			*owner;
 	u32				features;
-	const struct nft_set_type	*type;
 };
+#define to_set_type(o) container_of(o, struct nft_set_type, ops)
 
 int nft_register_set(struct nft_set_type *type);
 void nft_unregister_set(struct nft_set_type *type);