linux-kernel - Re: [PATCH RFC 0/3] staging: r8188eu: avoid uninit value bugs

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Date:   Sun, 22 Aug 2021 18:03:07 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Pavel Skripkin <paskripkin@...il.com>
Cc:     Larry.Finger@...inger.net, phil@...lpotter.co.uk,
        straube.linux@...il.com, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Martin Kaiser <martin@...ser.cx>
Subject: Re: [PATCH RFC 0/3] staging: r8188eu: avoid uninit value bugs

On Sunday, August 22, 2021 3:31:31 PM CEST Pavel Skripkin wrote:
> On 8/22/21 4:21 PM, Fabio M. De Francesco wrote:
> > On Sunday, August 22, 2021 2:39:34 PM CEST Greg KH wrote:
> >> On Sun, Aug 22, 2021 at 03:10:56PM +0300, Pavel Skripkin wrote:
> >> > On 8/22/21 1:59 PM, Fabio M. De Francesco wrote:
> >> > > On Sunday, August 22, 2021 12:09:29 PM CEST Pavel Skripkin wrote:
> > [...]
> >> > > So, it's up to the callers to test if (!_rtw_read*()) and then act
> >> > > accordingly. If they get 0 they should know how to handle the errors.
> >> > 
> >> > Yes, but _rtw_read*() == 0 indicates 2 states:
> >> > 	1. Error on transfer side
> >> > 	2. Actual register value is 0
> >> 
> >> That's not a good design, it should be fixed.  Note there is the new
> >> usb_control_msg_recv() function which should probably be used instead
> >> here, to prevent this problem from happening.
> > 
> > I think that no functions should return 0 for signaling FAILURE. If I'm not
> > wrong, the kernel quite always prefers to return 0 on SUCCESS and <0 on
> > FAILURE. Why don't you just fix this?
> > 
> That's what I've done in v2. All rtw_read* family will have following 
> prototype in v2:
> 
> int __must_check _rtw_read8(struct adapter *adapter, u32 addr, u8 *data);
> 
> Was it your idea, or you were talking about different approach?
> 
> With regards,
> Pavel Skripkin

Pavel,

Yes, it is correct.

However, after that I had time to look at the calls chain and understand what 
each function does and then I saw that my initial proposal should be made
along with another one...

The calls chain is:

(1)        _rtw_read8()  <--- (returns the data read from next function in chain) 
                                            (no errors returned, see possible fix in next function)
(2)                usb_read8() <--- (returns the data read from next function in chain) 
                                                 (_data_may_be_unitialised_, no errors returned)
		  (possible fix: from "u8 data"; to "char data = -1;")
(3)                           usbctrl_vendorreq() <---- (returns data read from next function in chain)
		                            (data is always a valid pointer saved to third argument)
		                            (if it fails, the third argument is unchanged because it
		                            still has the address of the "data" argument given by the caller)
(4)	                usb_control_msg() <---- (it always returns how many bytes read or valid error codes)
		                                  (it _never_ returns 0: either positive or negative values)
		
I have not yet looked at the usb_control_msg_recv() which Greg talked about.

To summarize: in function (2) "u8 data" should become "char data = -1;".

Regards,

Fabio

P.S.: I was about to send this message while I see that you sent v2. Since I've already have
this response to your question I send it and soon after I'm going to read your v2 patches.