mac80211: clean up remain-on-channel on interface stop

When any interface goes down, it could be the one that we
were doing a remain-on-channel with. We therefore need to
cancel the remain-on-channel and flush the related work
structs so they don't run after the interface has been
removed or even destroyed.

It's also possible in this case that an off-channel SKB
was never transmitted, so free it if this is the case.
Note that this can also happen if the driver finishes
the off-channel period without ever starting it.

Cc: stable@kernel.org
Reported-by: Nirav Shah <nirav.j2.shah@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/offchannel.c b/net/mac80211/offchannel.c
index f054e94..935aa4b 100644
--- a/net/mac80211/offchannel.c
+++ b/net/mac80211/offchannel.c
@@ -234,6 +234,22 @@
 		return;
 	}
 
+	/* was never transmitted */
+	if (local->hw_roc_skb) {
+		u64 cookie;
+
+		cookie = local->hw_roc_cookie ^ 2;
+
+		cfg80211_mgmt_tx_status(local->hw_roc_dev, cookie,
+					local->hw_roc_skb->data,
+					local->hw_roc_skb->len, false,
+					GFP_KERNEL);
+
+		kfree_skb(local->hw_roc_skb);
+		local->hw_roc_skb = NULL;
+		local->hw_roc_skb_for_status = NULL;
+	}
+
 	if (!local->hw_roc_for_tx)
 		cfg80211_remain_on_channel_expired(local->hw_roc_dev,
 						   local->hw_roc_cookie,