netfilter: nft_socket: track register operations

Check if the destination register already contains the data that this
socket expression performs. This allows to skip this redundant
operation.  If the destination contains a different selector, update the
register tracking information.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_socket.c

@@ -10,6 +10,7 @@
 struct nft_socket {
 	enum nft_socket_keys		key:8;
 	u8				level;
+	u8				len;
 	union {
 		u8			dreg;
 	};
@@ -179,6 +180,7 @@ static int nft_socket_init(const struct nft_ctx *ctx,
 		return -EOPNOTSUPP;
 	}
 
+	priv->len = len;
 	return nft_parse_register_store(ctx, tb[NFTA_SOCKET_DREG], &priv->dreg,
 					NULL, NFT_DATA_VALUE, len);
 }
@@ -198,6 +200,31 @@ static int nft_socket_dump(struct sk_buff *skb,
 	return 0;
 }
 
+static bool nft_socket_reduce(struct nft_regs_track *track,
+			      const struct nft_expr *expr)
+{
+	const struct nft_socket *priv = nft_expr_priv(expr);
+	const struct nft_socket *socket;
+
+	if (!nft_reg_track_cmp(track, expr, priv->dreg)) {
+		nft_reg_track_update(track, expr, priv->dreg, priv->len);
+		return false;
+	}
+
+	socket = nft_expr_priv(track->regs[priv->dreg].selector);
+	if (priv->key != socket->key ||
+	    priv->dreg != socket->dreg ||
+	    priv->level != socket->level) {
+		nft_reg_track_update(track, expr, priv->dreg, priv->len);
+		return false;
+	}
+
+	if (!track->regs[priv->dreg].bitwise)
+		return true;
+
+	return nft_expr_reduce_bitwise(track, expr);
+}
+
 static struct nft_expr_type nft_socket_type;
 static const struct nft_expr_ops nft_socket_ops = {
 	.type		= &nft_socket_type,
@@ -205,6 +232,7 @@ static const struct nft_expr_ops nft_socket_ops = {
 	.eval		= nft_socket_eval,
 	.init		= nft_socket_init,
 	.dump		= nft_socket_dump,
+	.reduce		= nft_socket_reduce,
 };
 
 static struct nft_expr_type nft_socket_type __read_mostly = {