mac80211: fix crash if bitrate calculation goes wrong

If a frame's timestamp is calculated, and the bitrate
calculation goes wrong and returns zero, the system
will attempt to divide by zero and crash. Catch this
case and print the rate information that the driver
reported when this happens.

Cc: stable@vger.kernel.org
Reported-by: Thomas Lindroth <thomas.lindroth@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/util.c

@@ -2238,6 +2238,10 @@ u64 ieee80211_calculate_rx_timestamp(struct ieee80211_local *local,
 	}
 
 	rate = cfg80211_calculate_bitrate(&ri);
+	if (WARN_ONCE(!rate,
+		      "Invalid bitrate: flags=0x%x, idx=%d, vht_nss=%d\n",
+		      status->flag, status->rate_idx, status->vht_nss))
+		return 0;
 
 	/* rewind from end of MPDU */
 	if (status->flag & RX_FLAG_MACTIME_END)