USB: serial: safe_serial: fix memory corruption with small endpoint

Make sure that the bulk-out buffer size is at least eight bytes to avoid
user-controlled slab corruption in "safe" mode should a malicious device
report a smaller size.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/safe_serial.c b/drivers/usb/serial/safe_serial.c
index 238b54993446cf37431b310a86c40021e7d164b9..d267a31dcccf111e530fd015a81c49e00af4857b 100644 (file)
--- a/drivers/usb/serial/safe_serial.c
+++ b/drivers/usb/serial/safe_serial.c
@@ -259,6 +259,7 @@ static int safe_prepare_write_buffer(struct usb_serial_port *port,
 static int safe_startup(struct usb_serial *serial)
 {
        struct usb_interface_descriptor *desc;
+       int bulk_out_size;
 
        if (serial->dev->descriptor.bDeviceClass != CDC_DEVICE_CLASS)
                return -ENODEV;
@@ -279,6 +280,16 @@ static int safe_startup(struct usb_serial *serial)
        default:
                return -EINVAL;
        }
+
+       /*
+        * The bulk-out buffer needs to be large enough for the two-byte
+        * trailer in safe mode, but assume anything smaller than eight bytes
+        * is broken.
+        */
+       bulk_out_size = serial->port[0]->bulk_out_size;
+       if (bulk_out_size > 0 && bulk_out_size < 8)
+               return -EINVAL;
+
        return 0;
 }