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Subject: Re: [PATCH RFC v2 5/6] staging: r8188eu: add error handling of
 rtw_read32
To:     Phillip Potter <phil@philpotter.co.uk>
Cc:     Larry Finger <Larry.Finger@lwfinger.net>,
        Greg KH <gregkh@linuxfoundation.org>,
        Michael Straube <straube.linux@gmail.com>,
        "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
        "open list:STAGING SUBSYSTEM" <linux-staging@lists.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <cover.1629642658.git.paskripkin@gmail.com>
 <9004eb2972780455db4cba9694244a2c572abba8.1629642658.git.paskripkin@gmail.com>
 <CAA=Fs0=gX66TW3qoHYWcoSsvai6YZn=U81a34V45oij7NrMJrQ@mail.gmail.com>
From:   Pavel Skripkin <paskripkin@gmail.com>
Message-ID: <ba9e0634-6cc6-161f-f4f9-3538f44448f8@gmail.com>
Date:   Tue, 24 Aug 2021 09:53:37 +0300
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On 8/24/21 2:33 AM, 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);
> 
> 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
> 

The most strange thing is why gcc didn't complain about different 
pointer types... I think, that gcc must complain about this type of not 
explicit casts, because 99% it's a bug.


Again big thanks for analysis :)


With regards,
Pavel Skripkin