mac80211: fix monitor mode tx radiotap header handling

When an injected frame gets buffered for a powersave STA or filtered
and retransmitted, mac80211 attempts to parse the radiotap header
again, which doesn't work because it's gone at that point.
This patch adds a new flag for checking the availability of a radiotap
header, so that it only attempts to parse it once, reusing the tx info
on the next call to ieee80211_tx().
This fixes severe issues with rekeying in AP mode.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

include/net/mac80211.h

@@ -275,6 +275,8 @@ struct ieee80211_bss_conf {
  * @IEEE80211_TX_INTFL_RETRANSMISSION: This frame is being retransmitted
  *	after TX status because the destination was asleep, it must not
  *	be modified again (no seqno assignment, crypto, etc.)
+ * @IEEE80211_TX_INTFL_HAS_RADIOTAP: This frame was injected and still
+ *	has a radiotap header at skb->data.
  */
 enum mac80211_tx_control_flags {
 	IEEE80211_TX_CTL_REQ_TX_STATUS		= BIT(0),
@@ -296,6 +298,7 @@ enum mac80211_tx_control_flags {
 	IEEE80211_TX_CTL_PSPOLL_RESPONSE	= BIT(17),
 	IEEE80211_TX_CTL_MORE_FRAMES		= BIT(18),
 	IEEE80211_TX_INTFL_RETRANSMISSION	= BIT(19),
+	IEEE80211_TX_INTFL_HAS_RADIOTAP		= BIT(20),
 };
 
 /**

net/mac80211/tx.c

@@ -1108,7 +1108,7 @@ ieee80211_tx_prepare(struct ieee80211_sub_if_data *sdata,
 	tx->flags |= IEEE80211_TX_FRAGMENTED;
 
 	/* process and remove the injection radiotap header */
-	if (unlikely(info->flags & IEEE80211_TX_CTL_INJECTED)) {
+	if (unlikely(info->flags & IEEE80211_TX_INTFL_HAS_RADIOTAP)) {
 		if (!__ieee80211_parse_tx_radiotap(tx, skb))
 			return TX_DROP;
 
@@ -1117,6 +1117,7 @@ ieee80211_tx_prepare(struct ieee80211_sub_if_data *sdata,
 		 * the radiotap header that was present and pre-filled
 		 * 'tx' with tx control information.
 		 */
+		info->flags &= ~IEEE80211_TX_INTFL_HAS_RADIOTAP;
 	}
 
 	/*
@@ -1499,7 +1500,8 @@ static void ieee80211_xmit(struct ieee80211_sub_if_data *sdata,
 		int hdrlen;
 		u16 len_rthdr;
 
-		info->flags |= IEEE80211_TX_CTL_INJECTED;
+		info->flags |= IEEE80211_TX_CTL_INJECTED |
+			       IEEE80211_TX_INTFL_HAS_RADIOTAP;
 
 		len_rthdr = ieee80211_get_radiotap_len(skb->data);
 		hdr = (struct ieee80211_hdr *)(skb->data + len_rthdr);