wifi: cfg80211: factor out bridge tunnel / RFC1042 header check

The same check is done in multiple places, unify it.
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20230213100855.34315-2-nbd@nbd.nameSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/util.c

@@ -542,6 +542,21 @@ unsigned int ieee80211_get_mesh_hdrlen(struct ieee80211s_hdr *meshhdr)
 }
 EXPORT_SYMBOL(ieee80211_get_mesh_hdrlen);
 
+static bool ieee80211_get_8023_tunnel_proto(const void *hdr, __be16 *proto)
+{
+	const __be16 *hdr_proto = hdr + ETH_ALEN;
+
+	if (!(ether_addr_equal(hdr, rfc1042_header) &&
+	      *hdr_proto != htons(ETH_P_AARP) &&
+	      *hdr_proto != htons(ETH_P_IPX)) &&
+	    !ether_addr_equal(hdr, bridge_tunnel_header))
+		return false;
+
+	*proto = *hdr_proto;
+
+	return true;
+}
+
 int ieee80211_data_to_8023_exthdr(struct sk_buff *skb, struct ethhdr *ehdr,
 				  const u8 *addr, enum nl80211_iftype iftype,
 				  u8 data_offset, bool is_amsdu)
@@ -633,14 +648,9 @@ int ieee80211_data_to_8023_exthdr(struct sk_buff *skb, struct ethhdr *ehdr,
 
 	if (likely(!is_amsdu &&
 		   skb_copy_bits(skb, hdrlen, &payload, sizeof(payload)) == 0 &&
-	           ((ether_addr_equal(payload.hdr, rfc1042_header) &&
-		     payload.proto != htons(ETH_P_AARP) &&
-		     payload.proto != htons(ETH_P_IPX)) ||
-		    ether_addr_equal(payload.hdr, bridge_tunnel_header)))) {
-		/* remove RFC1042 or Bridge-Tunnel encapsulation and
-		 * replace EtherType */
+		   ieee80211_get_8023_tunnel_proto(&payload, &tmp.h_proto))) {
+		/* remove RFC1042 or Bridge-Tunnel encapsulation */
 		hdrlen += ETH_ALEN + 2;
-		tmp.h_proto = payload.proto;
 		skb_postpull_rcsum(skb, &payload, ETH_ALEN + 2);
 	} else {
 		tmp.h_proto = htons(skb->len - hdrlen);
@@ -756,8 +766,6 @@ void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list,
 {
 	unsigned int hlen = ALIGN(extra_headroom, 4);
 	struct sk_buff *frame = NULL;
-	u16 ethertype;
-	u8 *payload;
 	int offset = 0, remaining;
 	struct ethhdr eth;
 	bool reuse_frag = skb->head_frag && !skb_has_frag_list(skb);
@@ -811,14 +819,8 @@ void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list,
 		frame->dev = skb->dev;
 		frame->priority = skb->priority;
 
-		payload = frame->data;
-		ethertype = (payload[6] << 8) | payload[7];
-		if (likely((ether_addr_equal(payload, rfc1042_header) &&
-			    ethertype != ETH_P_AARP && ethertype != ETH_P_IPX) ||
-			   ether_addr_equal(payload, bridge_tunnel_header))) {
-			eth.h_proto = htons(ethertype);
+		if (likely(ieee80211_get_8023_tunnel_proto(frame->data, &eth.h_proto)))
 			skb_pull(frame, ETH_ALEN + 2);
-		}
 
 		memcpy(skb_push(frame, sizeof(eth)), &eth, sizeof(eth));
 		__skb_queue_tail(list, frame);