[cbr79] ALSA: usb-audio: Fix out of bounds reads when finding clock sources

sound/usb/clock.c

@@ -35,6 +35,10 @@
 #include "clock.h"
 #include "quirks.h"
 
+/* check whether the descriptor bLength has the minimal length */
+#define DESC_LENGTH_CHECK(p) \
+	 (p->bLength >= sizeof(*p))
+
 static void *find_uac_clock_desc(struct usb_host_interface *iface, int id,
 				 bool (*validator)(void *, int), u8 type)
 {
@@ -52,36 +56,60 @@ static void *find_uac_clock_desc(struct usb_host_interface *iface, int id,
 static bool validate_clock_source_v2(void *p, int id)
 {
 	struct uac_clock_source_descriptor *cs = p;
+	if (!DESC_LENGTH_CHECK(cs))
+		return false;
 	return cs->bClockID == id;
 }
 
 static bool validate_clock_source_v3(void *p, int id)
 {
 	struct uac3_clock_source_descriptor *cs = p;
+	if (!DESC_LENGTH_CHECK(cs))
+		return false;
 	return cs->bClockID == id;
 }
 
 static bool validate_clock_selector_v2(void *p, int id)
 {
 	struct uac_clock_selector_descriptor *cs = p;
-	return cs->bClockID == id;
+	if (!DESC_LENGTH_CHECK(cs))
+		return false;
+	if (cs->bClockID != id)
+		return false;
+	/* additional length check for baCSourceID array (in bNrInPins size)
+	 * and two more fields (which sizes depend on the protocol)
+	 */
+	return cs->bLength >= sizeof(*cs) + cs->bNrInPins +
+		1 /* bmControls */ + 1 /* iClockSelector */;
 }
 
 static bool validate_clock_selector_v3(void *p, int id)
 {
 	struct uac3_clock_selector_descriptor *cs = p;
-	return cs->bClockID == id;
+	if (!DESC_LENGTH_CHECK(cs))
+		return false;
+	if (cs->bClockID != id)
+		return false;
+	/* additional length check for baCSourceID array (in bNrInPins size)
+	 * and two more fields (which sizes depend on the protocol)
+	 */
+	return cs->bLength >= sizeof(*cs) + cs->bNrInPins +
+		4 /* bmControls */ + 2 /* wCSelectorDescrStr */;
 }
 
 static bool validate_clock_multiplier_v2(void *p, int id)
 {
 	struct uac_clock_multiplier_descriptor *cs = p;
+	if (!DESC_LENGTH_CHECK(cs))
+		return false;
 	return cs->bClockID == id;
 }
 
 static bool validate_clock_multiplier_v3(void *p, int id)
 {
 	struct uac3_clock_multiplier_descriptor *cs = p;
+	if (!DESC_LENGTH_CHECK(cs))
+		return false;
 	return cs->bClockID == id;
 }