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

Pavel Skripkin
2021-08-24T06:40:22Z

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@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*().
>

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