USB: serial: belkin_sa: validate interrupt status length

The Belkin interrupt callback treats interrupt data as a four-byte
status report and reads LSR/MSR fields at offsets 2 and 3. The
interrupt-in buffer length is derived from endpoint wMaxPacketSize, and
short interrupt transfers may complete successfully with a smaller
actual_length.

Check the completed interrupt packet length before parsing status
fields so short interrupt endpoints and short successful packets are
ignored instead of causing out-of-bounds or stale status-byte reads.

KASAN report as below:

BUG: KASAN: slab-out-of-bounds in belkin_sa_read_int_callback()
Read of size 1
Call trace:
  belkin_sa_read_int_callback() (drivers/usb/serial/belkin_sa.c:202)
  __usb_hcd_giveback_urb() (drivers/usb/core/hcd.c:1630)
  dummy_timer() (?:?)

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Assisted-by: Codex:gpt-5.5
Signed-off-by: Zhang Cen <rollkingzzc@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/belkin_sa.c b/drivers/usb/serial/belkin_sa.c
index 38ac910b1082defdde576e8d63af0d7a84964b44..7bbd9523d4e9c13c21ec7904d6494301fe080f6e 100644 (file)
--- a/drivers/usb/serial/belkin_sa.c
+++ b/drivers/usb/serial/belkin_sa.c
@@ -194,6 +194,9 @@ static void belkin_sa_read_int_callback(struct urb *urb)
 
        usb_serial_debug_data(&port->dev, __func__, urb->actual_length, data);
 
+       if (urb->actual_length < BELKIN_SA_MSR_INDEX + 1)
+               goto exit;
+
        /* Handle known interrupt data */
        /* ignore data[0] and data[1] */