mac80211: fix rts threshold check

commit a2c40249 upstream.

Currently whenever rts thresold is set, every packet will use RTS
protection no matter its size exceeds the threshold or not. This is
due to a bug in the rts threshold check.
	if (len > tx->local->hw.wiphy->rts_threshold) {
		txrc.rts = rts = true;
	}
Basically it is comparing an int (len) and a u32 (rts_threshold),
and the variable len is assigned as:
	len = min_t(int, tx->skb->len + FCS_LEN,
			 tx->local->hw.wiphy->frag_threshold);
However, when frag_threshold is "-1", len is always "-1", which is
0xffffffff therefore rts is always set to true.
Signed-off-by: Shanyu Zhao <shanyu.zhao@intel.com>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

net/mac80211/tx.c

@@ -584,7 +584,8 @@ ieee80211_tx_h_rate_ctrl(struct ieee80211_tx_data *tx)
 	struct ieee80211_hdr *hdr = (void *)tx->skb->data;
 	struct ieee80211_supported_band *sband;
 	struct ieee80211_rate *rate;
-	int i, len;
+	int i;
+	u32 len;
 	bool inval = false, rts = false, short_preamble = false;
 	struct ieee80211_tx_rate_control txrc;
 	u32 sta_flags;
@@ -593,7 +594,7 @@ ieee80211_tx_h_rate_ctrl(struct ieee80211_tx_data *tx)
 
 	sband = tx->local->hw.wiphy->bands[tx->channel->band];
 
-	len = min_t(int, tx->skb->len + FCS_LEN,
+	len = min_t(u32, tx->skb->len + FCS_LEN,
 			 tx->local->hw.wiphy->frag_threshold);
 
 	/* set up the tx rate control struct we give the RC algo */