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Subject: Re: [PATCH RFC v2 5/6] staging: r8188eu: add error handling of
 rtw_read32
To:     Dan Carpenter <dan.carpenter@oracle.com>
Cc:     Larry.Finger@lwfinger.net, phil@philpotter.co.uk,
        gregkh@linuxfoundation.org, straube.linux@gmail.com,
        fmdefrancesco@gmail.com, linux-staging@lists.linux.dev,
        linux-kernel@vger.kernel.org
References: <cover.1629642658.git.paskripkin@gmail.com>
 <9004eb2972780455db4cba9694244a2c572abba8.1629642658.git.paskripkin@gmail.com>
 <20210824065825.GL1931@kadam>
From:   Pavel Skripkin <paskripkin@gmail.com>
Message-ID: <e50d266f-410c-34cb-e28f-f27dc429ef37@gmail.com>
Date:   Tue, 24 Aug 2021 10:01:23 +0300
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On 8/24/21 9:58 AM, Dan Carpenter wrote:
> On Sun, Aug 22, 2021 at 05:36:01PM +0300, Pavel Skripkin 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);
> 
> Add a return here.  Try to keep the success path and the failure path
> as separate as possible.  Try to keep the success path indented at one
> tab so the code looks like this:
> 
> 	success();
> 	success();
> 	if (fail)
> 		handle_failure();
> 	success();
> 	success();
> 
> Try to deal with exceptions as quickly as possible so that the reader
> has less to remember.
> 
>> +	} else {
>> +		/* Noone cares about positive return value */
> 
> Ugh...  That's unfortunate.  We should actually care.  The
> usbctrl_vendorreq() has an information leak where it copies len (4)
> bytes of data even if usb_control_msg() is not able to read len bytes.
> 
> The best fix would be to remove the information leak and make
> usbctrl_vendorreq() return zero on success.  In other words something
> like:
> 
> 	status = usb_control_msg();
> 	if (status < 0)
> 		return status;
> 	if (status != len)
> 		return -EIO;
> 	status = 0;
> 

I see, thank you for reviewing, will fix in v3! I fully forgot, that 
usb_control_msg() can receive only part of the message :)


With regards,
Pavel Skripkin