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

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Date:   Thu, 8 Mar 2018 15:29:48 -0800
From:   sathyanarayanan kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Oliver Neukum <oneukum@...e.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     johan@...nel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v1 1/1] USB: serial: Add boundry check for read_urbs array
 access



On 03/08/2018 12:54 AM, Oliver Neukum wrote:
> Am Mittwoch, den 07.03.2018, 13:41 -0800 schrieb sathyanarayanan
> kuppuswamy       :
>> On 03/07/2018 12:58 PM, Greg KH wrote:
>>> 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?
>> void usb_serial_generic_read_bulk_callback(struct urb *urb)
>>
>> 385         for (i = 0; i < ARRAY_SIZE(port->read_urbs); ++i) {
>> 386                 if (urb == port->read_urbs[i])
>> 387                         break;
>> 388         }
>>
>> In here, after this for loop is done (without any matching urb), i value
>> will be equal to ARRAY_SIZE(port->read_urbs). So there is a possibility
>> of usb_serial_generic_submit_read_urb() getting called with this invalid
>> index.
> If this happens the function was called for a stray URB.
> Your check comes to late. We have called set_bit with an invalid index
> and other shit.
> We definitely do not just want to return an error in that case.
In that case do you think we should use some WARN_ON() for invalid index 
in usb_serial_generic_read_bulk_callback()?
>
> 	Regards
> 		Oliver
>
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-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer