netfilter: nft_fib: add reduce support

The fib expression stores to a register, so we can't add empty stub.
Check that the register that is being written is in fact redundant.

In most cases, this is expected to cancel tracking as re-use is
unlikely.
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nft_fib.h

@@ -37,4 +37,7 @@ void nft_fib6_eval(const struct nft_expr *expr, struct nft_regs *regs,
 
 void nft_fib_store_result(void *reg, const struct nft_fib *priv,
 			  const struct net_device *dev);
+
+bool nft_fib_reduce(struct nft_regs_track *track,
+		    const struct nft_expr *expr);
 #endif

net/ipv4/netfilter/nft_fib_ipv4.c

@@ -152,6 +152,7 @@ static const struct nft_expr_ops nft_fib4_type_ops = {
 	.init		= nft_fib_init,
 	.dump		= nft_fib_dump,
 	.validate	= nft_fib_validate,
+	.reduce		= nft_fib_reduce,
 };
 
 static const struct nft_expr_ops nft_fib4_ops = {
@@ -161,6 +162,7 @@ static const struct nft_expr_ops nft_fib4_ops = {
 	.init		= nft_fib_init,
 	.dump		= nft_fib_dump,
 	.validate	= nft_fib_validate,
+	.reduce		= nft_fib_reduce,
 };
 
 static const struct nft_expr_ops *

net/ipv6/netfilter/nft_fib_ipv6.c

@@ -211,6 +211,7 @@ static const struct nft_expr_ops nft_fib6_type_ops = {
 	.init		= nft_fib_init,
 	.dump		= nft_fib_dump,
 	.validate	= nft_fib_validate,
+	.reduce		= nft_fib_reduce,
 };
 
 static const struct nft_expr_ops nft_fib6_ops = {
@@ -220,6 +221,7 @@ static const struct nft_expr_ops nft_fib6_ops = {
 	.init		= nft_fib_init,
 	.dump		= nft_fib_dump,
 	.validate	= nft_fib_validate,
+	.reduce		= nft_fib_reduce,
 };
 
 static const struct nft_expr_ops *

net/netfilter/nft_fib.c

@@ -156,5 +156,47 @@ void nft_fib_store_result(void *reg, const struct nft_fib *priv,
 }
 EXPORT_SYMBOL_GPL(nft_fib_store_result);
 
+bool nft_fib_reduce(struct nft_regs_track *track,
+		    const struct nft_expr *expr)
+{
+	const struct nft_fib *priv = nft_expr_priv(expr);
+	unsigned int len = NFT_REG32_SIZE;
+	const struct nft_fib *fib;
+
+	switch (priv->result) {
+	case NFT_FIB_RESULT_OIF:
+		break;
+	case NFT_FIB_RESULT_OIFNAME:
+		if (priv->flags & NFTA_FIB_F_PRESENT)
+			len = NFT_REG32_SIZE;
+		else
+			len = IFNAMSIZ;
+		break;
+	case NFT_FIB_RESULT_ADDRTYPE:
+	     break;
+	default:
+		WARN_ON_ONCE(1);
+		break;
+	}
+
+	if (!nft_reg_track_cmp(track, expr, priv->dreg)) {
+		nft_reg_track_update(track, expr, priv->dreg, len);
+		return false;
+	}
+
+	fib = nft_expr_priv(track->regs[priv->dreg].selector);
+	if (priv->result != fib->result ||
+	    priv->flags != fib->flags) {
+		nft_reg_track_update(track, expr, priv->dreg, len);
+		return false;
+	}
+
+	if (!track->regs[priv->dreg].bitwise)
+		return true;
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(nft_fib_reduce);
+
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");

net/netfilter/nft_fib_inet.c

@@ -49,6 +49,7 @@ static const struct nft_expr_ops nft_fib_inet_ops = {
 	.init		= nft_fib_init,
 	.dump		= nft_fib_dump,
 	.validate	= nft_fib_validate,
+	.reduce		= nft_fib_reduce,
 };
 
 static struct nft_expr_type nft_fib_inet_type __read_mostly = {

net/netfilter/nft_fib_netdev.c

@@ -58,6 +58,7 @@ static const struct nft_expr_ops nft_fib_netdev_ops = {
 	.init		= nft_fib_init,
 	.dump		= nft_fib_dump,
 	.validate	= nft_fib_validate,
+	.reduce		= nft_fib_reduce,
 };
 
 static struct nft_expr_type nft_fib_netdev_type __read_mostly = {