mac80211: handle lack of sband->bitrates in rates

Even though a driver or mac80211 shouldn't produce a
legacy bitrate if sband->bitrates doesn't exist, don't
crash if that is the case either.

This fixes a kernel panic if station dump is run before
last_rate can be updated with a data frame when
sband->bitrates is missing (eg. in S1G bands).

Signed-off-by: Thomas Pedersen <thomas@adapt-ip.com>
Link: https://lore.kernel.org/r/20201005164522.18069-1-thomas@adapt-ip.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/cfg.c

@@ -709,7 +709,8 @@ void sta_set_rate_info_tx(struct sta_info *sta,
 		u16 brate;
 
 		sband = ieee80211_get_sband(sta->sdata);
-		if (sband) {
+		WARN_ON_ONCE(sband && !sband->bitrates);
+		if (sband && sband->bitrates) {
 			brate = sband->bitrates[rate->idx].bitrate;
 			rinfo->legacy = DIV_ROUND_UP(brate, 1 << shift);
 		}

net/mac80211/sta_info.c

@@ -2122,6 +2122,10 @@ static void sta_stats_decode_rate(struct ieee80211_local *local, u32 rate,
 		int rate_idx = STA_STATS_GET(LEGACY_IDX, rate);
 
 		sband = local->hw.wiphy->bands[band];
+
+		if (WARN_ON_ONCE(!sband->bitrates))
+			break;
+
 		brate = sband->bitrates[rate_idx].bitrate;
 		if (rinfo->bw == RATE_INFO_BW_5)
 			shift = 2;