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

Fabio M. De Francesco
2021-08-22T10:59:18Z

On Sunday, August 22, 2021 12:09:29 PM CEST Pavel Skripkin wrote:
> 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;
> }
> }

It's up to the callers of _rtw_usb*() to check return values and then act
accordingly.

It doesn't matter whether or not *pdata is initialized because usb_read*()
returns data = 0 if usb_control_msg() has not initialized/changed its third
parameter. Then _rtw_read*() receive 0 or initialized data depending on errors
or no errors. Finally _rtw_read*() returns that same value to the callers (via
r_val).

So, it's up to the callers to test if (!_rtw_read*()) and then act
accordingly. If they get 0 they should know how to handle the errors.

Furthermore, we have already either adapt->bSurpriseRemoved = true or haldata-
>srestpriv.Wifi_Error_Status = USB_VEN_REQ_CMD_FAIL. Depending on contexts
where _rtw_read*() are called, perhaps they could also check the two variables
above.

In summation. if anything should be changed, it is the code of the callers of
_rtw_read*() if you find out they they don't properly handle the returning
values of this function. You should find every place where _rtw_read*() are
called and figure out if the returns are properly checked and handled; if not,
make some change only there.

Larry, Philip, where are you? Am I missing something?

Thanks,

Fabio

>
> 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