ath9k: add compile time checking for the size of the channel list

This prevents random memory corruption if the number of channels ever gets
changed without an update to the internal channel array size.
Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/hw.h

@@ -61,6 +61,8 @@
 
 #define ATH9K_RSSI_BAD			-128
 
+#define ATH9K_NUM_CHANNELS	38
+
 /* Register read/write primitives */
 #define REG_WRITE(_ah, _reg, _val) \
 	ath9k_hw_common(_ah)->ops->write((_ah), (_val), (_reg))
@@ -618,7 +620,7 @@ struct ath_hw {
 	struct ath9k_hw_version hw_version;
 	struct ath9k_ops_config config;
 	struct ath9k_hw_capabilities caps;
-	struct ath9k_channel channels[38];
+	struct ath9k_channel channels[ATH9K_NUM_CHANNELS];
 	struct ath9k_channel *curchan;
 
 	union {

drivers/net/wireless/ath/ath9k/init.c

@@ -481,6 +481,10 @@ static int ath9k_init_channels_rates(struct ath_softc *sc)
 {
 	void *channels;
 
+	BUILD_BUG_ON(ARRAY_SIZE(ath9k_2ghz_chantable) +
+		     ARRAY_SIZE(ath9k_5ghz_chantable) !=
+		     ATH9K_NUM_CHANNELS);
+
 	if (test_bit(ATH9K_MODE_11G, sc->sc_ah->caps.wireless_modes)) {
 		channels = kmemdup(ath9k_2ghz_chantable,
 			sizeof(ath9k_2ghz_chantable), GFP_KERNEL);