netfilter: nf_tables_offload: incorrect flow offload action array size

immediate verdict expression needs to allocate one slot in the flow offload
action array, however, immediate data expression does not need to do so.

fwd and dup expression need to allocate one slot, this is missing.

Add a new offload_action interface to report if this expression needs to
allocate one slot in the flow offload action array.

Fixes: be2861dc ("netfilter: nft_{fwd,dup}_netdev: add offload support")
Reported-and-tested-by: Nick Gregory <Nick.Gregory@Sophos.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables.h

@@ -905,9 +905,9 @@ struct nft_expr_ops {
 	int				(*offload)(struct nft_offload_ctx *ctx,
 						   struct nft_flow_rule *flow,
 						   const struct nft_expr *expr);
+	bool				(*offload_action)(const struct nft_expr *expr);
 	void				(*offload_stats)(struct nft_expr *expr,
 							 const struct flow_stats *stats);
-	u32				offload_flags;
 	const struct nft_expr_type	*type;
 	void				*data;
 };

include/net/netfilter/nf_tables_offload.h

@@ -67,8 +67,6 @@ struct nft_flow_rule {
 	struct flow_rule	*rule;
 };
 
-#define NFT_OFFLOAD_F_ACTION	(1 << 0)
-
 void nft_flow_rule_set_addr_type(struct nft_flow_rule *flow,
 				 enum flow_dissector_key_id addr_type);
 

net/netfilter/nf_tables_offload.c

@@ -94,7 +94,8 @@ struct nft_flow_rule *nft_flow_rule_create(struct net *net,
 
 	expr = nft_expr_first(rule);
 	while (nft_expr_more(rule, expr)) {
-		if (expr->ops->offload_flags & NFT_OFFLOAD_F_ACTION)
+		if (expr->ops->offload_action &&
+		    expr->ops->offload_action(expr))
 			num_actions++;
 
 		expr = nft_expr_next(expr);

net/netfilter/nft_dup_netdev.c

@@ -67,6 +67,11 @@ static int nft_dup_netdev_offload(struct nft_offload_ctx *ctx,
 	return nft_fwd_dup_netdev_offload(ctx, flow, FLOW_ACTION_MIRRED, oif);
 }
 
+static bool nft_dup_netdev_offload_action(const struct nft_expr *expr)
+{
+	return true;
+}
+
 static struct nft_expr_type nft_dup_netdev_type;
 static const struct nft_expr_ops nft_dup_netdev_ops = {
 	.type		= &nft_dup_netdev_type,
@@ -75,6 +80,7 @@ static const struct nft_expr_ops nft_dup_netdev_ops = {
 	.init		= nft_dup_netdev_init,
 	.dump		= nft_dup_netdev_dump,
 	.offload	= nft_dup_netdev_offload,
+	.offload_action	= nft_dup_netdev_offload_action,
 };
 
 static struct nft_expr_type nft_dup_netdev_type __read_mostly = {

net/netfilter/nft_fwd_netdev.c

@@ -79,6 +79,11 @@ static int nft_fwd_netdev_offload(struct nft_offload_ctx *ctx,
 	return nft_fwd_dup_netdev_offload(ctx, flow, FLOW_ACTION_REDIRECT, oif);
 }
 
+static bool nft_fwd_netdev_offload_action(const struct nft_expr *expr)
+{
+	return true;
+}
+
 struct nft_fwd_neigh {
 	u8			sreg_dev;
 	u8			sreg_addr;
@@ -222,6 +227,7 @@ static const struct nft_expr_ops nft_fwd_netdev_ops = {
 	.dump		= nft_fwd_netdev_dump,
 	.validate	= nft_fwd_validate,
 	.offload	= nft_fwd_netdev_offload,
+	.offload_action	= nft_fwd_netdev_offload_action,
 };
 
 static const struct nft_expr_ops *

net/netfilter/nft_immediate.c

@@ -213,6 +213,16 @@ static int nft_immediate_offload(struct nft_offload_ctx *ctx,
 	return 0;
 }
 
+static bool nft_immediate_offload_action(const struct nft_expr *expr)
+{
+	const struct nft_immediate_expr *priv = nft_expr_priv(expr);
+
+	if (priv->dreg == NFT_REG_VERDICT)
+		return true;
+
+	return false;
+}
+
 static const struct nft_expr_ops nft_imm_ops = {
 	.type		= &nft_imm_type,
 	.size		= NFT_EXPR_SIZE(sizeof(struct nft_immediate_expr)),
@@ -224,7 +234,7 @@ static const struct nft_expr_ops nft_imm_ops = {
 	.dump		= nft_immediate_dump,
 	.validate	= nft_immediate_validate,
 	.offload	= nft_immediate_offload,
-	.offload_flags	= NFT_OFFLOAD_F_ACTION,
+	.offload_action	= nft_immediate_offload_action,
 };
 
 struct nft_expr_type nft_imm_type __read_mostly = {