[PATCH 2/3] ALSA: usb-audio: Fix return value check for usb_string()

[Jaejoong Kim <climbbb.kim@gmail.com>]

In case of failure, the usb_string() can return a negative number. Therefore,
the return value of snd_usb_copy_string_desc() and get_term_name() can also
be negative.

Check the return values for these functions as follows:

  len = snd_usb_copy_string_desc();
  if (!len) ...

If len is negative, the if-statement is false and fails to handle exceptions.
So, we need to change it to a value less than or equal to zero.

Signed-off-by: Jaejoong Kim <climbbb.kim@gmail.com>
---
 sound/usb/mixer.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index da7cbe7..8a434b7 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1235,7 +1235,7 @@ static void build_feature_ctl(struct mixer_build *state, void *raw_desc,
 {
 	struct uac_feature_unit_descriptor *desc = raw_desc;
 	struct usb_feature_control_info *ctl_info;
-	unsigned int len = 0;
+	int len = 0;
 	int mapped_name = 0;
 	int nameid = uac_feature_unit_iFeature(desc);
 	struct snd_kcontrol *kctl;
@@ -1313,14 +1313,14 @@ static void build_feature_ctl(struct mixer_build *state, void *raw_desc,
 		 * - if the connected output can be determined, use it.
 		 * - otherwise, anonymous name.
 		 */
-		if (!len) {
+		if (len <= 0) {
 			len = get_term_name(state, iterm, kctl->id.name,
 					    sizeof(kctl->id.name), 1);
-			if (!len)
+			if (len <= 0)
 				len = get_term_name(state, &state->oterm,
 						    kctl->id.name,
 						    sizeof(kctl->id.name), 1);
-			if (!len)
+			if (len <= 0)
 				snprintf(kctl->id.name, sizeof(kctl->id.name),
 					 "Feature %d", unitid);
 		}
@@ -1343,7 +1343,7 @@ static void build_feature_ctl(struct mixer_build *state, void *raw_desc,
 				" Switch" : " Volume");
 		break;
 	default:
-		if (!len)
+		if (len <= 0)
 			strlcpy(kctl->id.name, audio_feature_info[control-1].name,
 				sizeof(kctl->id.name));
 		break;
@@ -1610,7 +1610,8 @@ static void build_mixer_unit_ctl(struct mixer_build *state,
 {
 	struct usb_mixer_elem_info *cval;
 	unsigned int num_outs = uac_mixer_unit_bNrChannels(desc);
-	unsigned int i, len;
+	unsigned int i;
+	int len;
 	struct snd_kcontrol *kctl;
 	const struct usbmix_name_map *map;
 
@@ -1649,7 +1650,7 @@ static void build_mixer_unit_ctl(struct mixer_build *state,
 	if (!len)
 		len = get_term_name(state, iterm, kctl->id.name,
 				    sizeof(kctl->id.name), 0);
-	if (!len)
+	if (len <= 0)
 		len = sprintf(kctl->id.name, "Mixer Source %d", in_ch + 1);
 	append_ctl_name(kctl, " Volume");
 
@@ -1947,7 +1948,7 @@ static int build_audio_procunit(struct mixer_build *state, int unitid,
 				len = snd_usb_copy_string_desc(state, nameid,
 							       kctl->id.name,
 							       sizeof(kctl->id.name));
-			if (!len)
+			if (len <= 0)
 				strlcpy(kctl->id.name, name, sizeof(kctl->id.name));
 		}
 		append_ctl_name(kctl, " ");
@@ -2077,7 +2078,8 @@ static int parse_audio_selector_unit(struct mixer_build *state, int unitid,
 				     void *raw_desc)
 {
 	struct uac_selector_unit_descriptor *desc = raw_desc;
-	unsigned int i, nameid, len;
+	unsigned int i, nameid;
+	int len;
 	int err;
 	struct usb_mixer_elem_info *cval;
 	struct snd_kcontrol *kctl;
@@ -2138,9 +2140,10 @@ static int parse_audio_selector_unit(struct mixer_build *state, int unitid,
 		}
 		len = check_mapped_selector_name(state, unitid, i, namelist[i],
 						 MAX_ITEM_NAME_LEN);
-		if (! len && check_input_term(state, desc->baSourceID[i], &iterm) >= 0)
+		if (!len && check_input_term(state, desc->baSourceID[i], &iterm) >= 0)
 			len = get_term_name(state, &iterm, namelist[i], MAX_ITEM_NAME_LEN, 0);
-		if (! len)
+
+		if (len <= 0)
 			sprintf(namelist[i], "Input %u", i);
 	}
 
@@ -2164,7 +2167,7 @@ static int parse_audio_selector_unit(struct mixer_build *state, int unitid,
 	else {
 		len = get_term_name(state, &state->oterm,
 				    kctl->id.name, sizeof(kctl->id.name), 0);
-		if (!len)
+		if (len <= 0)
 			strlcpy(kctl->id.name, "USB", sizeof(kctl->id.name));
 
 		if (desc->bDescriptorSubtype == UAC2_CLOCK_SELECTOR)
-- 
2.7.4