mac80211: fix an issue with allocated tailroom for encrypted mgmt packets

Fixes kernel warnings and connectivity issues in encrypted mesh networks

Signed-off-by: Felix Fietkau <nbd@nbd.name>

package/kernel/mac80211/patches/subsys/384-mac80211-ensure-that-management-tx-skbs-have-encrypt.patch

@@ -0,0 +1,48 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Mon, 28 Jan 2019 13:16:45 +0100
+Subject: [PATCH] mac80211: ensure that management tx skbs have encryption
+ tailroom
+
+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. This can lead to passing skbs to ccmp_encrypt_skb, which
+don't have the needed 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>
+---
+
+--- a/net/mac80211/tx.c
++++ b/net/mac80211/tx.c
+@@ -1912,9 +1912,16 @@ static int ieee80211_skb_resize(struct i
+ 				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);
+@@ -1922,8 +1929,7 @@ static int ieee80211_skb_resize(struct i
+ 
+ 	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);