linux-kernel - Re: [PATCH v1 1/1] USB: serial: Add boundry check for read

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Date:   Wed, 7 Mar 2018 12:58:40 -0800
From:   Greg KH <gregkh@...uxfoundation.org>
To:     sathyanarayanan.kuppuswamy@...ux.intel.com
Cc:     johan@...nel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/1] USB: serial: Add boundry check for read_urbs
 array access

On Wed, Mar 07, 2018 at 12:23:56PM -0800, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> In usb_serial_generic_submit_read_urb() function we are accessing the
> port->read_urbs array without any boundry checks. This might lead to
> kernel panic when index value goes above array length.
> 
> One posible call path for this issue is,
> 
> usb_serial_generic_read_bulk_callback()
> {
>  ...
>  if (!port->throttled) {
> 	usb_serial_generic_submit_read_urb(port, i, GFP_ATOMIC);
>  ...
> }

How does i ever get to be greater than the array size here in this
function?  It directly came from looking in that array in the first
place :)

So I don't see why your check is needed, what other code path would ever
call this function in a way that the bounds check would be needed?

thanks,

greg k-h