iwlwifi: check for valid band for channel info

when display channel info in debugfs, always check for valid band
before access the pointer and display information

for 1000 NIC, it only support "bgn" mode, so there is no 5.2GHz channels
available to display.
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-debugfs.c

@@ -380,50 +380,53 @@ static ssize_t iwl_dbgfs_channels_read(struct file *file, char __user *user_buf,
 	}
 
 	supp_band = iwl_get_hw_mode(priv, IEEE80211_BAND_2GHZ);
-	channels = supp_band->channels;
+	if (supp_band) {
+		channels = supp_band->channels;
 
-	pos += scnprintf(buf + pos, bufsz - pos,
-			"Displaying %d channels in 2.4GHz band 802.11bg):\n",
-			 supp_band->n_channels);
-
-	for (i = 0; i < supp_band->n_channels; i++)
 		pos += scnprintf(buf + pos, bufsz - pos,
-				"%d: %ddBm: BSS%s%s, %s.\n",
-				ieee80211_frequency_to_channel(
-				channels[i].center_freq),
-				channels[i].max_power,
-				channels[i].flags & IEEE80211_CHAN_RADAR ?
-				" (IEEE 802.11h required)" : "",
-				((channels[i].flags & IEEE80211_CHAN_NO_IBSS)
-				|| (channels[i].flags &
-				IEEE80211_CHAN_RADAR)) ? "" :
-				", IBSS",
-				channels[i].flags &
-				IEEE80211_CHAN_PASSIVE_SCAN ?
-				"passive only" : "active/passive");
+				"Displaying %d channels in 2.4GHz band 802.11bg):\n",
+				supp_band->n_channels);
 
+		for (i = 0; i < supp_band->n_channels; i++)
+			pos += scnprintf(buf + pos, bufsz - pos,
+					"%d: %ddBm: BSS%s%s, %s.\n",
+					ieee80211_frequency_to_channel(
+					channels[i].center_freq),
+					channels[i].max_power,
+					channels[i].flags & IEEE80211_CHAN_RADAR ?
+					" (IEEE 802.11h required)" : "",
+					((channels[i].flags & IEEE80211_CHAN_NO_IBSS)
+					|| (channels[i].flags &
+					IEEE80211_CHAN_RADAR)) ? "" :
+					", IBSS",
+					channels[i].flags &
+					IEEE80211_CHAN_PASSIVE_SCAN ?
+					"passive only" : "active/passive");
+	}
 	supp_band = iwl_get_hw_mode(priv, IEEE80211_BAND_5GHZ);
-	channels = supp_band->channels;
+	if (supp_band) {
+		channels = supp_band->channels;
 
-	pos += scnprintf(buf + pos, bufsz - pos,
-			"Displaying %d channels in 5.2GHz band (802.11a)\n",
-			supp_band->n_channels);
-
-	for (i = 0; i < supp_band->n_channels; i++)
 		pos += scnprintf(buf + pos, bufsz - pos,
-				"%d: %ddBm: BSS%s%s, %s.\n",
-				ieee80211_frequency_to_channel(
-				channels[i].center_freq),
-				channels[i].max_power,
-				channels[i].flags & IEEE80211_CHAN_RADAR ?
-				" (IEEE 802.11h required)" : "",
-				((channels[i].flags & IEEE80211_CHAN_NO_IBSS)
-				|| (channels[i].flags &
-				IEEE80211_CHAN_RADAR)) ? "" :
-				", IBSS",
-				channels[i].flags &
-				IEEE80211_CHAN_PASSIVE_SCAN ?
-				"passive only" : "active/passive");
+				"Displaying %d channels in 5.2GHz band (802.11a)\n",
+				supp_band->n_channels);
+
+		for (i = 0; i < supp_band->n_channels; i++)
+			pos += scnprintf(buf + pos, bufsz - pos,
+					"%d: %ddBm: BSS%s%s, %s.\n",
+					ieee80211_frequency_to_channel(
+					channels[i].center_freq),
+					channels[i].max_power,
+					channels[i].flags & IEEE80211_CHAN_RADAR ?
+					" (IEEE 802.11h required)" : "",
+					((channels[i].flags & IEEE80211_CHAN_NO_IBSS)
+					|| (channels[i].flags &
+					IEEE80211_CHAN_RADAR)) ? "" :
+					", IBSS",
+					channels[i].flags &
+					IEEE80211_CHAN_PASSIVE_SCAN ?
+					"passive only" : "active/passive");
+	}
 	ret = simple_read_from_buffer(user_buf, count, ppos, buf, pos);
 	kfree(buf);
 	return ret;