netfilter: nft_flow_offload: skip dst neigh lookup for ppp devices

The dst entry does not contain a valid hardware address, so skip the lookup
in order to avoid running into errors here.
The proper hardware address is filled in from nft_dev_path_info

Fixes: 72efd58 ("netfilter: flowtable: add pppoe support")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_flow_offload.c

@@ -36,6 +36,15 @@ static void nft_default_forward_path(struct nf_flow_route *route,
 	route->tuple[dir].xmit_type	= nft_xmit_type(dst_cache);
 }
 
+static bool nft_is_valid_ether_device(const struct net_device *dev)
+{
+	if (!dev || (dev->flags & IFF_LOOPBACK) || dev->type != ARPHRD_ETHER ||
+	    dev->addr_len != ETH_ALEN || !is_valid_ether_addr(dev->dev_addr))
+		return false;
+
+	return true;
+}
+
 static int nft_dev_fill_forward_path(const struct nf_flow_route *route,
 				     const struct dst_entry *dst_cache,
 				     const struct nf_conn *ct,
@@ -47,6 +56,9 @@ static int nft_dev_fill_forward_path(const struct nf_flow_route *route,
 	struct neighbour *n;
 	u8 nud_state;
 
+	if (!nft_is_valid_ether_device(dev))
+		goto out;
+
 	n = dst_neigh_lookup(dst_cache, daddr);
 	if (!n)
 		return -1;
@@ -60,6 +72,7 @@ static int nft_dev_fill_forward_path(const struct nf_flow_route *route,
 	if (!(nud_state & NUD_VALID))
 		return -1;
 
+out:
 	return dev_fill_forward_path(dev, ha, stack);
 }
 
@@ -78,15 +91,6 @@ struct nft_forward_info {
 	enum flow_offload_xmit_type xmit_type;
 };
 
-static bool nft_is_valid_ether_device(const struct net_device *dev)
-{
-	if (!dev || (dev->flags & IFF_LOOPBACK) || dev->type != ARPHRD_ETHER ||
-	    dev->addr_len != ETH_ALEN || !is_valid_ether_addr(dev->dev_addr))
-		return false;
-
-	return true;
-}
-
 static void nft_dev_path_info(const struct net_device_path_stack *stack,
 			      struct nft_forward_info *info,
 			      unsigned char *ha, struct nf_flowtable *flowtable)