Re: [PATCH RFC v2 5/6] staging: r8188eu: add error handling of rtw_read32

Fabio M. De Francesco
2021-08-24T00:10:42Z

On Tuesday, August 24, 2021 1:33:46 AM CEST Phillip Potter wrote:
> On Sun, 22 Aug 2021 at 15:36, Pavel Skripkin <paskripkin@gmail.com> wrote:
> > -static u32 usb_read32(struct intf_hdl *pintfhdl, u32 addr)
> > +static int usb_read32(struct intf_hdl *pintfhdl, u32 addr, u32 *data)
> > {
> > u8 requesttype;
> > u16 wvalue;
> > u16 len;
> > - __le32 data;
> > + int res;
> > + __le32 tmp;
> > +
> > + if (WARN_ON(unlikely(!data)))
> > + return -EINVAL;
> >
> > requesttype = 0x01;/* read_in */
> >
> > wvalue = (u16)(addr & 0x0000ffff);
> > len = 4;
> >
> > - usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype);
> > + res = usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype);
> > + if (res < 0) {
> > + dev_err(dvobj_to_dev(pintfhdl->pintf_dev), "Failed to read 32 bytes: %d\n", res);
> > + } else {
> > + /* Noone cares about positive return value */
> > + *data = le32_to_cpu(tmp);
> > + res = 0;
> > + }
> >
> > - return le32_to_cpu(data);
> > + return res;
> > }
>
> Dear Pavel,
>
> OK, found the issue with decoded stack trace after reviewing this
> usb_read32 function. Your line:
> res = usbctrl_vendorreq(pintfhdl, wvalue, &data, len, requesttype);
>
> should read:
> res = usbctrl_vendorreq(pintfhdl, wvalue, &tmp, len, requesttype);

Dear Philip,

No, it should read:

res = usbctrl_vendorreq(pintfhdl, wvalue, data, len, requesttype);

I suspect that Pavel didn't notice he was reusing a line of the old code
wth no due changes.

> With this change, the driver runs fine with no crashes/oopses. I will
> explain the issue but you can probably see already, so I hope I'm not
> coming across as patronising, just trying to be helpful :-)
>
> Essentially, you are taking the address of the data function parameter
> on this line with &data, a pointer to u32, which is giving you a
> pointer to a pointer to u32 (u32 **) for this function parameter
> variable. When passed to usbctrl_vendorreq, it is being passed to
> memcpy inside this function as a void *, meaning that memcpy
> subsequently overwrites the value of the memory address inside data to
> point to a different location, which is problem when it is later
> deferenced at:
> *data = le32_to_cpu(tmp);
> causing the OOPS
>
> Also, as written, you can probably see that tmp is uninitialised. This
> looks like a typo, so guessing this wasn't your intention. Anyhow,
> with that small change, usbctrl_vendorreq reads into tmp, which is
> then passed to le32_to_cpu whose return value is stored via the
> deferenced data ptr (which now has its original address within and not
> inadvertently modified). Hope this helps, and I'd be happy to Ack the
> series if you want to resend this patch. Many thanks.

I think that another typo is having 'tmp', because that variable is unnecessary
and "*data = le32_to_cpu(tmp);" is wrong too.

Now I also see that also usb_read16() is wrong, while usb_read8() (the one that
I had read yesterday) is the only correct function of the three usb_read*().

Regards,

Fabio
>
> Regards,
> Phil
>