mac80211: fix HT-Control field reception for management frames

If we receive management frames with an HT-Control field, we cannot
parse them properly, as we assume a fixed length management header.

Since we don't even need the HTC field (for these frames, or really
at all), just remove it at the beginning of RX.
Reported-by: Haggai Abramovsky <haggai.abramovsky@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Link: https://lore.kernel.org/r/20200526143346.cf5ce70521c5.I333251a084ec4cfe67b7ef7efe2d2f1a33883931@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/rx.c

@@ -93,13 +93,44 @@ static u8 *ieee80211_get_bssid(struct ieee80211_hdr *hdr, size_t len,
  * This function cleans up the SKB, i.e. it removes all the stuff
  * only useful for monitoring.
  */
-static void remove_monitor_info(struct sk_buff *skb,
-				unsigned int present_fcs_len,
-				unsigned int rtap_space)
+static struct sk_buff *ieee80211_clean_skb(struct sk_buff *skb,
+					   unsigned int present_fcs_len,
+					   unsigned int rtap_space)
 {
+	struct ieee80211_hdr *hdr;
+	unsigned int hdrlen;
+	__le16 fc;
+
 	if (present_fcs_len)
 		__pskb_trim(skb, skb->len - present_fcs_len);
 	__pskb_pull(skb, rtap_space);
+
+	hdr = (void *)skb->data;
+	fc = hdr->frame_control;
+
+	/*
+	 * Remove the HT-Control field (if present) on management
+	 * frames after we've sent the frame to monitoring. We
+	 * (currently) don't need it, and don't properly parse
+	 * frames with it present, due to the assumption of a
+	 * fixed management header length.
+	 */
+	if (likely(!ieee80211_is_mgmt(fc) || !ieee80211_has_order(fc)))
+		return skb;
+
+	hdrlen = ieee80211_hdrlen(fc);
+	hdr->frame_control &= ~cpu_to_le16(IEEE80211_FCTL_ORDER);
+
+	if (!pskb_may_pull(skb, hdrlen)) {
+		dev_kfree_skb(skb);
+		return NULL;
+	}
+
+	memmove(skb->data + IEEE80211_HT_CTL_LEN, skb->data,
+		hdrlen - IEEE80211_HT_CTL_LEN);
+	__pskb_pull(skb, IEEE80211_HT_CTL_LEN);
+
+	return skb;
 }
 
 static inline bool should_drop_frame(struct sk_buff *skb, int present_fcs_len,
@@ -827,8 +858,8 @@ ieee80211_rx_monitor(struct ieee80211_local *local, struct sk_buff *origskb,
 			return NULL;
 		}
 
-		remove_monitor_info(origskb, present_fcs_len, rtap_space);
-		return origskb;
+		return ieee80211_clean_skb(origskb, present_fcs_len,
+					   rtap_space);
 	}
 
 	ieee80211_handle_mu_mimo_mon(monitor_sdata, origskb, rtap_space);
@@ -871,8 +902,7 @@ ieee80211_rx_monitor(struct ieee80211_local *local, struct sk_buff *origskb,
 	if (!origskb)
 		return NULL;
 
-	remove_monitor_info(origskb, present_fcs_len, rtap_space);
-	return origskb;
+	return ieee80211_clean_skb(origskb, present_fcs_len, rtap_space);
 }
 
 static void ieee80211_parse_qos(struct ieee80211_rx_data *rx)