nl80211: fix null-ptr dereference on invalid mesh configuration

If TX rates are specified during mesh join, the channel must
also be specified. Check the channel pointer to avoid a null
pointer dereference if it isn't.
Reported-by: NJouni Malinen <j@w1.fi>
Fixes: 8564e382 ("cfg80211: add checks for beacon rate, extend to mesh")
Signed-off-by: NJohannes Berg <johannes.berg@intel.com>

net/wireless/nl80211.c

@@ -9987,6 +9987,9 @@ static int nl80211_join_mesh(struct sk_buff *skb, struct genl_info *info)
 		if (err)
 			return err;
 
+		if (!setup.chandef.chan)
+			return -EINVAL;
+
 		err = validate_beacon_tx_rate(rdev, setup.chandef.chan->band,
 					      &setup.beacon_rate);
 		if (err)