netfilter: nf_tables: bail out early if hardware offload is not supported

If user requests for NFT_CHAIN_HW_OFFLOAD, then check if either device
provides the .ndo_setup_tc interface or there is an indirect flow block
that has been registered. Otherwise, bail out early from the preparation
phase. Moreover, validate that family == NFPROTO_NETDEV and hook is
NF_NETDEV_INGRESS.

Fixes: c9626a2c ("netfilter: nf_tables: add hardware offload support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/flow_offload.h

@@ -612,5 +612,6 @@ int flow_indr_dev_setup_offload(struct net_device *dev, struct Qdisc *sch,
 				enum tc_setup_type type, void *data,
 				struct flow_block_offload *bo,
 				void (*cleanup)(struct flow_block_cb *block_cb));
+bool flow_indr_dev_exists(void);
 
 #endif /* _NET_FLOW_OFFLOAD_H */

include/net/netfilter/nf_tables_offload.h

@@ -92,7 +92,7 @@ int nft_flow_rule_offload_commit(struct net *net);
 	NFT_OFFLOAD_MATCH(__key, __base, __field, __len, __reg)		\
 	memset(&(__reg)->mask, 0xff, (__reg)->len);
 
-int nft_chain_offload_priority(struct nft_base_chain *basechain);
+bool nft_chain_offload_support(const struct nft_base_chain *basechain);
 
 int nft_offload_init(void);
 void nft_offload_exit(void);

net/core/flow_offload.c

@@ -595,3 +595,9 @@ int flow_indr_dev_setup_offload(struct net_device *dev,	struct Qdisc *sch,
 	return (bo && list_empty(&bo->cb_list)) ? -EOPNOTSUPP : count;
 }
 EXPORT_SYMBOL(flow_indr_dev_setup_offload);
+
+bool flow_indr_dev_exists(void)
+{
+	return !list_empty(&flow_block_indr_dev_list);
+}
+EXPORT_SYMBOL(flow_indr_dev_exists);

net/netfilter/nf_tables_api.c

@@ -2166,7 +2166,7 @@ static int nft_basechain_init(struct nft_base_chain *basechain, u8 family,
 	chain->flags |= NFT_CHAIN_BASE | flags;
 	basechain->policy = NF_ACCEPT;
 	if (chain->flags & NFT_CHAIN_HW_OFFLOAD &&
-	    nft_chain_offload_priority(basechain) < 0)
+	    !nft_chain_offload_support(basechain))
 		return -EOPNOTSUPP;
 
 	flow_block_init(&basechain->flow_block);

net/netfilter/nf_tables_offload.c

@@ -208,7 +208,7 @@ static int nft_setup_cb_call(enum tc_setup_type type, void *type_data,
 	return 0;
 }
 
-int nft_chain_offload_priority(struct nft_base_chain *basechain)
+static int nft_chain_offload_priority(const struct nft_base_chain *basechain)
 {
 	if (basechain->ops.priority <= 0 ||
 	    basechain->ops.priority > USHRT_MAX)
@@ -217,6 +217,27 @@ int nft_chain_offload_priority(struct nft_base_chain *basechain)
 	return 0;
 }
 
+bool nft_chain_offload_support(const struct nft_base_chain *basechain)
+{
+	struct net_device *dev;
+	struct nft_hook *hook;
+
+	if (nft_chain_offload_priority(basechain) < 0)
+		return false;
+
+	list_for_each_entry(hook, &basechain->hook_list, list) {
+		if (hook->ops.pf != NFPROTO_NETDEV ||
+		    hook->ops.hooknum != NF_NETDEV_INGRESS)
+			return false;
+
+		dev = hook->ops.dev;
+		if (!dev->netdev_ops->ndo_setup_tc && !flow_indr_dev_exists())
+			return false;
+	}
+
+	return true;
+}
+
 static void nft_flow_cls_offload_setup(struct flow_cls_offload *cls_flow,
 				       const struct nft_base_chain *basechain,
 				       const struct nft_rule *rule,