[PATCH 4.4 23/35] USB: serial: safe_serial: fix information leak in completion handler

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johan Hovold <jo...@kernel.org>

commit 8c76d7cd520ebffc1ea9ea0850d87a224a50c7f2 upstream.

Add missing sanity check to the bulk-in completion handler to avoid an
integer underflow that could be triggered by a malicious device.

This avoids leaking up to 56 bytes from after the URB transfer buffer to
user space.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Johan Hovold <jo...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/usb/serial/safe_serial.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/usb/serial/safe_serial.c
+++ b/drivers/usb/serial/safe_serial.c
@@ -205,6 +205,11 @@ static void safe_process_read_urb(struct
        if (!safe)
                goto out;
 
+       if (length < 2) {
+               dev_err(&port->dev, "malformed packet\n");
+               return;
+       }
+
        fcs = fcs_compute10(data, length, CRC10_INITFCS);
        if (fcs) {
                dev_err(&port->dev, "%s - bad CRC %x\n", __func__, fcs);