netfilter: nft_payload: track register operations

Check if the destination register already contains the data that this
payload store 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_payload.c

@@ -210,6 +210,34 @@ static int nft_payload_dump(struct sk_buff *skb, const struct nft_expr *expr)
 	return -1;
 }
 
+static bool nft_payload_reduce(struct nft_regs_track *track,
+			       const struct nft_expr *expr)
+{
+	const struct nft_payload *priv = nft_expr_priv(expr);
+	const struct nft_payload *payload;
+
+	if (!track->regs[priv->dreg].selector ||
+	    track->regs[priv->dreg].selector->ops != expr->ops) {
+		track->regs[priv->dreg].selector = expr;
+		track->regs[priv->dreg].bitwise = NULL;
+		return false;
+	}
+
+	payload = nft_expr_priv(track->regs[priv->dreg].selector);
+	if (priv->base != payload->base ||
+	    priv->offset != payload->offset ||
+	    priv->len != payload->len) {
+		track->regs[priv->dreg].selector = expr;
+		track->regs[priv->dreg].bitwise = NULL;
+		return false;
+	}
+
+	if (!track->regs[priv->dreg].bitwise)
+		return true;
+
+	return false;
+}
+
 static bool nft_payload_offload_mask(struct nft_offload_reg *reg,
 				     u32 priv_len, u32 field_len)
 {
@@ -513,6 +541,7 @@ static const struct nft_expr_ops nft_payload_ops = {
 	.eval		= nft_payload_eval,
 	.init		= nft_payload_init,
 	.dump		= nft_payload_dump,
+	.reduce		= nft_payload_reduce,
 	.offload	= nft_payload_offload,
 };
 
@@ -522,6 +551,7 @@ const struct nft_expr_ops nft_payload_fast_ops = {
 	.eval		= nft_payload_eval,
 	.init		= nft_payload_init,
 	.dump		= nft_payload_dump,
+	.reduce		= nft_payload_reduce,
 	.offload	= nft_payload_offload,
 };