mac80211: ensure that mgmt tx skbs have tailroom for encryption

Some drivers use IEEE80211_KEY_FLAG_SW_MGMT_TX to indicate that management
frames need to be software encrypted. Since normal data packets are still
encrypted by the hardware, crypto_tx_tailroom_needed_cnt gets decremented
after key upload to hw. This can lead to passing skbs to ccmp_encrypt_skb,
which don't have the necessary tailroom for software encryption.

Change the code to add tailroom for encrypted management packets, even if
crypto_tx_tailroom_needed_cnt is 0.

Cc: stable@vger.kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/tx.c

@@ -1938,9 +1938,16 @@ static int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
 				int head_need, bool may_encrypt)
 {
 	struct ieee80211_local *local = sdata->local;
+	struct ieee80211_hdr *hdr;
+	bool enc_tailroom;
 	int tail_need = 0;
 
-	if (may_encrypt && sdata->crypto_tx_tailroom_needed_cnt) {
+	hdr = (struct ieee80211_hdr *) skb->data;
+	enc_tailroom = may_encrypt &&
+		       (sdata->crypto_tx_tailroom_needed_cnt ||
+			ieee80211_is_mgmt(hdr->frame_control));
+
+	if (enc_tailroom) {
 		tail_need = IEEE80211_ENCRYPT_TAILROOM;
 		tail_need -= skb_tailroom(skb);
 		tail_need = max_t(int, tail_need, 0);
@@ -1948,8 +1955,7 @@ static int ieee80211_skb_resize(struct ieee80211_sub_if_data *sdata,
 
 	if (skb_cloned(skb) &&
 	    (!ieee80211_hw_check(&local->hw, SUPPORTS_CLONED_SKBS) ||
-	     !skb_clone_writable(skb, ETH_HLEN) ||
-	     (may_encrypt && sdata->crypto_tx_tailroom_needed_cnt)))
+	     !skb_clone_writable(skb, ETH_HLEN) || enc_tailroom))
 		I802_DEBUG_INC(local->tx_expand_skb_head_cloned);
 	else if (head_need || tail_need)
 		I802_DEBUG_INC(local->tx_expand_skb_head);