linux-kernel - Re: [PATCH RFC 0/3] staging: r8188eu: avoid uninit value bugs

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Date:   Sun, 22 Aug 2021 13:09:29 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Larry.Finger@...inger.net, phil@...lpotter.co.uk,
        gregkh@...uxfoundation.org, straube.linux@...il.com
Cc:     linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Martin Kaiser <martin@...ser.cx>
Subject: Re: [PATCH RFC 0/3] staging: r8188eu: avoid uninit value bugs

On 8/22/21 12:53 PM, Fabio M. De Francesco wrote:
> On Friday, August 20, 2021 7:07:28 PM CEST Pavel Skripkin wrote:
>> Hi, Greg, Larry and Phillip!
>> 
>> I noticed, that new staging driver was added like 3 weeks ago and I decided
>> to look at the code, because drivers in staging directory are always buggy.
>> 
>> The first thing I noticed is *no one* was checking read operations result, 
> but
>> it can fail and driver may start writing random stack values into registers. 
> It
>> can cause driver misbehavior or device misbehavior.
> 
> After the messages I wrote yesterday, I had some minutes to look deeper at the
> code that would be changed by these patches.
> 
> I think that it does not look like that the driver could return "random stack
> values into registers" and I think this entire series in unnecessary.
> 
> As far as I understand this driver (though I must admit that I really don't
> know how to write drivers, and I'm not interested in understanding - at the
> moment, at least), all the usb_read*() call usbctrl_vendorreq() and the latter
> *does* proper error checking before returning to the callers the read data.
> 
> Please, look at the code copied from usbctrl_vendorreq() and pasted here (some
> comments are mine):
> 
> /* start of code */
> static int usbctrl_vendorreq(struct intf_hdl *pintfhdl, u16 value, void
> *pdata, u16 len, u8 requesttype)
> {
> 
> /* test if everything is OK for transfers and setup the necessary variables */
> [...]
> 
> status = usb_control_msg(udev, pipe, REALTEK_USB_VENQT_CMD_REQ,
>                                           reqtype, value,
> REALTEK_USB_VENQT_CMD_IDX,
>                                           pIo_buf, len,
> RTW_USB_CONTROL_MSG_TIMEOUT);
> 
>                  if (status == len) {   /*  Success this control transfer. */
>                          rtw_reset_continual_urb_error(dvobjpriv);
>                          if (requesttype == 0x01)
>                                  memcpy(pdata, pIo_buf,  len); /* pdata
> receives the read data */
> 	} else { /*  error cases */
> 
> [...]
> 
> }
> /* end of code */
> 
> So, *I cannot ack this RFC*, unless maintainers say I'm missing something.
> 
> Larry, Philip, since you have much more knowledge than me about r8188eu (and,
> more in general, on device drivers) may you please say what you think about my
> arguments against this series?
> 

Hi, Fabio!

Thank you for looking into this, but I still can see the case when pdata 
won't be initialized:


pdata is initialized only in case of successful transfer, i.e len > 0. 
It means some data was received (maybe not full length, but anyway). In 
case of usb_control_msg() error (for example -ENOMEM) code only does 
this code block:

if (status < 0) {
	if (status == (-ESHUTDOWN) || status == -ENODEV) {
		adapt->bSurpriseRemoved = true;
	} else {
		struct hal_data_8188e	*haldata = GET_HAL_DATA(adapt);
		haldata->srestpriv.Wifi_Error_Status = USB_VEN_REQ_CMD_FAIL;
	}
}


And then just loops further. In case of 10 ENOMEM in a row,. passed 
pdata won't be initialized at all and driver doesn't do anything about 
it. I believe, it's not good approach to play with random values. We 
should somehow handle transfer errors all across the driver.

If I am missing something, please, let me know :)



With regards,
Pavel Skripkin