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

[Pavel Skripkin]

On 8/24/21 3:10 AM, Fabio M. De Francesco wrote:
> On Tuesday, August 24, 2021 1:33:46 AM CEST Phillip Potter wrote:
> > On Sun, 22 Aug 2021 at 15:36, Pavel Skripkin <paskripkin@xxxxxxxxx> 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*().

Hi, guys!


Sorry for breaking your system, Phillip. This code was part of "last 
minute" changes and yes, it's broken :)

I get what Phillip said, because I _should_ read into tmp variable 
instead of directly to data, but I don't get Fabio's idea, sorry.

Data from chip comes in little-endian, so we _should_ convert it to 
cpu's endian. Temp variable is needed to make smatch and all other 
static anylis tools happy about this code.


If I am missing something, please, let me know :) v3 is on the way...





With regards,
Pavel Skripkin