HID: betop: check shape of output reports

betopff_init() only checks the total sum of the report counts for each
report field to be at least 4, but hid_betopff_play() expects 4 report
fields.
A device advertising an output report with one field and 4 report counts
would pass the check but crash the kernel with a NULL pointer dereference
in hid_betopff_play().

Fixes: 52cd778 ("HID: betop: add drivers/hid/hid-betopff.c")
Signed-off-by: Pietro Borrello <borrello@diag.uniroma1.it>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-betopff.c

@@ -60,7 +60,6 @@ static int betopff_init(struct hid_device *hid)
 	struct list_head *report_list =
 			&hid->report_enum[HID_OUTPUT_REPORT].report_list;
 	struct input_dev *dev;
-	int field_count = 0;
 	int error;
 	int i, j;
 
@@ -86,19 +85,21 @@ static int betopff_init(struct hid_device *hid)
 	 * -----------------------------------------
 	 * Do init them with default value.
 	 */
+	if (report->maxfield < 4) {
+		hid_err(hid, "not enough fields in the report: %d\n",
+				report->maxfield);
+		return -ENODEV;
+	}
 	for (i = 0; i < report->maxfield; i++) {
+		if (report->field[i]->report_count < 1) {
+			hid_err(hid, "no values in the field\n");
+			return -ENODEV;
+		}
 		for (j = 0; j < report->field[i]->report_count; j++) {
 			report->field[i]->value[j] = 0x00;
-			field_count++;
 		}
 	}
 
-	if (field_count < 4) {
-		hid_err(hid, "not enough fields in the report: %d\n",
-				field_count);
-		return -ENODEV;
-	}
-
 	betopff = kzalloc(sizeof(*betopff), GFP_KERNEL);
 	if (!betopff)
 		return -ENOMEM;