HID: hid-steam: Better handling of serial number length

The second byte of the GET_STRING_ATTRIB report is a length, so we should set
the size of the buffer to be the size we're actually requesting, and only
reject the reply if the length out is nonsensical.

Signed-off-by: Vicki Pfau <vi@endrift.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>

Author: endrift

drivers/hid/hid-steam.c

@@ -274,7 +274,7 @@ enum {
 };
 
 /* Other random constants */
-#define STEAM_SERIAL_LEN 10
+#define STEAM_SERIAL_LEN 0x15
 
 struct steam_device {
 	struct list_head list;
@@ -421,10 +421,10 @@ static int steam_get_serial(struct steam_device *steam)
 {
 	/*
 	 * Send: 0xae 0x15 0x01
-	 * Recv: 0xae 0x15 0x01 serialnumber (10 chars)
+	 * Recv: 0xae 0x15 0x01 serialnumber
 	 */
 	int ret = 0;
-	u8 cmd[] = {ID_GET_STRING_ATTRIBUTE, 0x15, ATTRIB_STR_UNIT_SERIAL};
+	u8 cmd[] = {ID_GET_STRING_ATTRIBUTE, sizeof(steam->serial_no), ATTRIB_STR_UNIT_SERIAL};
 	u8 reply[3 + STEAM_SERIAL_LEN + 1];
 
 	mutex_lock(&steam->report_mutex);
@@ -434,12 +434,13 @@ static int steam_get_serial(struct steam_device *steam)
 	ret = steam_recv_report(steam, reply, sizeof(reply));
 	if (ret < 0)
 		goto out;
-	if (reply[0] != ID_GET_STRING_ATTRIBUTE || reply[1] != 0x15 || reply[2] != ATTRIB_STR_UNIT_SERIAL) {
+	if (reply[0] != ID_GET_STRING_ATTRIBUTE || reply[1] < 1 ||
+	    reply[1] > sizeof(steam->serial_no) || reply[2] != ATTRIB_STR_UNIT_SERIAL) {
 		ret = -EIO;
 		goto out;
 	}
 	reply[3 + STEAM_SERIAL_LEN] = 0;
-	strscpy(steam->serial_no, reply + 3, sizeof(steam->serial_no));
+	strscpy(steam->serial_no, reply + 3, reply[1]);
 out:
 	mutex_unlock(&steam->report_mutex);
 	return ret;