ath5k: warn and correct rate for unknown hw rate indexes

ath5k sets up a mapping table from the hardware rate index to
the rate index used by mac80211; however, we have seen some
received frames with incorrect rate indexes.  Such frames
normally get dropped with a warning in __ieee80211_rx(),
but it doesn't include enough information to track down the
error.

This patch adds a warning to hw_to_driver_rix for any lookups
that result in a rate index of -1, then returns a valid rate so
the frame can be processed.

Changes-licensed-under: 3-Clause-BSD
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Cc: stable@kernel.org
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath5k/base.c

@@ -1088,9 +1088,18 @@ ath5k_mode_setup(struct ath5k_softc *sc)
 static inline int
 ath5k_hw_to_driver_rix(struct ath5k_softc *sc, int hw_rix)
 {
-	WARN(hw_rix < 0 || hw_rix >= AR5K_MAX_RATES,
-			"hw_rix out of bounds: %x\n", hw_rix);
-	return sc->rate_idx[sc->curband->band][hw_rix];
+	int rix;
+
+	/* return base rate on errors */
+	if (WARN(hw_rix < 0 || hw_rix >= AR5K_MAX_RATES,
+			"hw_rix out of bounds: %x\n", hw_rix))
+		return 0;
+
+	rix = sc->rate_idx[sc->curband->band][hw_rix];
+	if (WARN(rix < 0, "invalid hw_rix: %x\n", hw_rix))
+		rix = 0;
+
+	return rix;
 }
 
 /***************\

drivers/net/wireless/ath5k/base.h

@@ -112,7 +112,7 @@ struct ath5k_softc {
 	struct ieee80211_supported_band sbands[IEEE80211_NUM_BANDS];
 	struct ieee80211_channel channels[ATH_CHAN_MAX];
 	struct ieee80211_rate	rates[IEEE80211_NUM_BANDS][AR5K_MAX_RATES];
-	u8			rate_idx[IEEE80211_NUM_BANDS][AR5K_MAX_RATES];
+	s8			rate_idx[IEEE80211_NUM_BANDS][AR5K_MAX_RATES];
 	enum nl80211_iftype	opmode;
 	struct ath5k_hw		*ah;		/* Atheros HW */