linux-kernel - Re: [PATCH 4.19 062/125] ALSA: usb-audio: Fix possible NULL dereference at create_yamaha_midi

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Message-ID: <20191118143352.GA22736@duo.ucw.cz>
Date:   Mon, 18 Nov 2019 15:33:52 +0100
From:   Pavel Machek <pavel@...x.de>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     Pavel Machek <pavel@...x.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH 4.19 062/125] ALSA: usb-audio: Fix possible NULL
 dereference at create_yamaha_midi_quirk()

Hi!

> > > Clearly code wants to allow at most one of them to be NULL.
> > > 
> > > > -	if (!snd_usb_validate_midi_desc(injd) ||
> > > > -	    !snd_usb_validate_midi_desc(outjd))
> > > > +	if (!(injd && snd_usb_validate_midi_desc(injd)) ||
> > > > +	    !(outjd && snd_usb_validate_midi_desc(outjd)))
> > > >  		return -ENODEV;
> > > 
> > > Yet it will return here if it is. Correct check would be
> > > 
> > > +     if (!(!injd || snd_usb_validate_midi_desc(injd)) ||
> > > +         !(!outjd || snd_usb_validate_midi_desc(outjd)))
> > > 
> > > AFAICT.
> > 
> > Erm, right, but a better representation is:
> > 
> > 	if ((injd && !snd_usb_validate_midi_desc(injd)) ||
> > 	    (outjd && !snd_usb_validate_midi_desc(injd)))
> 
> Of course, another typo:
> 
>  	if ((injd && !snd_usb_validate_midi_desc(injd)) ||
>  	    (outjd && !snd_usb_validate_midi_desc(outjd)))

Agreed, that is better. I was focusing on boolean algebra too much.

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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