netfilter: nft_exthdr: add reduce support

Check if we can elide the load. Cancel if the new candidate
isn't identical to previous store.
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_exthdr.c

@@ -603,12 +603,40 @@ static int nft_exthdr_dump_strip(struct sk_buff *skb, const struct nft_expr *exp
 	return nft_exthdr_dump_common(skb, priv);
 }
 
+static bool nft_exthdr_reduce(struct nft_regs_track *track,
+			       const struct nft_expr *expr)
+{
+	const struct nft_exthdr *priv = nft_expr_priv(expr);
+	const struct nft_exthdr *exthdr;
+
+	if (!nft_reg_track_cmp(track, expr, priv->dreg)) {
+		nft_reg_track_update(track, expr, priv->dreg, priv->len);
+		return false;
+	}
+
+	exthdr = nft_expr_priv(track->regs[priv->dreg].selector);
+	if (priv->type != exthdr->type ||
+	    priv->op != exthdr->op ||
+	    priv->flags != exthdr->flags ||
+	    priv->offset != exthdr->offset ||
+	    priv->len != exthdr->len) {
+		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 const struct nft_expr_ops nft_exthdr_ipv6_ops = {
 	.type		= &nft_exthdr_type,
 	.size		= NFT_EXPR_SIZE(sizeof(struct nft_exthdr)),
 	.eval		= nft_exthdr_ipv6_eval,
 	.init		= nft_exthdr_init,
 	.dump		= nft_exthdr_dump,
+	.reduce		= nft_exthdr_reduce,
 };
 
 static const struct nft_expr_ops nft_exthdr_ipv4_ops = {
@@ -617,6 +645,7 @@ static const struct nft_expr_ops nft_exthdr_ipv4_ops = {
 	.eval		= nft_exthdr_ipv4_eval,
 	.init		= nft_exthdr_ipv4_init,
 	.dump		= nft_exthdr_dump,
+	.reduce		= nft_exthdr_reduce,
 };
 
 static const struct nft_expr_ops nft_exthdr_tcp_ops = {
@@ -625,6 +654,7 @@ static const struct nft_expr_ops nft_exthdr_tcp_ops = {
 	.eval		= nft_exthdr_tcp_eval,
 	.init		= nft_exthdr_init,
 	.dump		= nft_exthdr_dump,
+	.reduce		= nft_exthdr_reduce,
 };
 
 static const struct nft_expr_ops nft_exthdr_tcp_set_ops = {
@@ -633,6 +663,7 @@ static const struct nft_expr_ops nft_exthdr_tcp_set_ops = {
 	.eval		= nft_exthdr_tcp_set_eval,
 	.init		= nft_exthdr_tcp_set_init,
 	.dump		= nft_exthdr_dump_set,
+	.reduce		= NFT_REDUCE_READONLY,
 };
 
 static const struct nft_expr_ops nft_exthdr_tcp_strip_ops = {
@@ -641,6 +672,7 @@ static const struct nft_expr_ops nft_exthdr_tcp_strip_ops = {
 	.eval		= nft_exthdr_tcp_strip_eval,
 	.init		= nft_exthdr_tcp_strip_init,
 	.dump		= nft_exthdr_dump_strip,
+	.reduce		= NFT_REDUCE_READONLY,
 };
 
 static const struct nft_expr_ops nft_exthdr_sctp_ops = {
@@ -649,6 +681,7 @@ static const struct nft_expr_ops nft_exthdr_sctp_ops = {
 	.eval		= nft_exthdr_sctp_eval,
 	.init		= nft_exthdr_init,
 	.dump		= nft_exthdr_dump,
+	.reduce		= nft_exthdr_reduce,
 };
 
 static const struct nft_expr_ops *