netfilter: nft_hash: track register operations

Check if the destination register already contains the data that this
osf expression performs. Always cancel register tracking for jhash since
this requires tracking multiple source registers in case of
concatenations. Perform register tracking (without bitwise) for symhash
since input does not come from source register.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_hash.c

@@ -165,6 +165,16 @@ static int nft_jhash_dump(struct sk_buff *skb,
 	return -1;
 }
 
+static bool nft_jhash_reduce(struct nft_regs_track *track,
+			     const struct nft_expr *expr)
+{
+	const struct nft_jhash *priv = nft_expr_priv(expr);
+
+	nft_reg_track_cancel(track, priv->dreg, sizeof(u32));
+
+	return false;
+}
+
 static int nft_symhash_dump(struct sk_buff *skb,
 			    const struct nft_expr *expr)
 {
@@ -185,6 +195,30 @@ static int nft_symhash_dump(struct sk_buff *skb,
 	return -1;
 }
 
+static bool nft_symhash_reduce(struct nft_regs_track *track,
+			       const struct nft_expr *expr)
+{
+	struct nft_symhash *priv = nft_expr_priv(expr);
+	struct nft_symhash *symhash;
+
+	if (!nft_reg_track_cmp(track, expr, priv->dreg)) {
+		nft_reg_track_update(track, expr, priv->dreg, sizeof(u32));
+		return false;
+	}
+
+	symhash = nft_expr_priv(track->regs[priv->dreg].selector);
+	if (priv->offset != symhash->offset ||
+	    priv->modulus != symhash->modulus) {
+		nft_reg_track_update(track, expr, priv->dreg, sizeof(u32));
+		return false;
+	}
+
+	if (!track->regs[priv->dreg].bitwise)
+		return true;
+
+	return false;
+}
+
 static struct nft_expr_type nft_hash_type;
 static const struct nft_expr_ops nft_jhash_ops = {
 	.type		= &nft_hash_type,
@@ -192,6 +226,7 @@ static const struct nft_expr_ops nft_jhash_ops = {
 	.eval		= nft_jhash_eval,
 	.init		= nft_jhash_init,
 	.dump		= nft_jhash_dump,
+	.reduce		= nft_jhash_reduce,
 };
 
 static const struct nft_expr_ops nft_symhash_ops = {
@@ -200,6 +235,7 @@ static const struct nft_expr_ops nft_symhash_ops = {
 	.eval		= nft_symhash_eval,
 	.init		= nft_symhash_init,
 	.dump		= nft_symhash_dump,
+	.reduce		= nft_symhash_reduce,
 };
 
 static const struct nft_expr_ops *