linux-kernel - Re: [PATCH 3.2 57/79] ALSA: usb-audio: Fix potential zero-division at parsing FU

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Message-ID: <1518546535.2617.47.camel@decadent.org.uk>
Date:   Tue, 13 Feb 2018 18:28:55 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH 3.2 57/79] ALSA: usb-audio: Fix potential zero-division
 at parsing FU

On Mon, 2018-02-12 at 07:59 +0100, Takashi Iwai wrote:
> On Sun, 11 Feb 2018 05:20:06 +0100,
> Ben Hutchings wrote:
> > 
> > 3.2.99-rc1 review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Takashi Iwai <tiwai@...e.de>
> > 
> > commit 8428a8ebde2db1e988e41a58497a28beb7ce1705 upstream.
> 
> Please drop this.  This patch is broken, and was reverted in the later
> commit 3c02a6d94665.

Thanks, I've dropped this from 3.2 and 3.16 patch queues.

Ben.

> thanks,
> 
> Takashi
> 
> 
> > 
> > parse_audio_feature_unit() contains a code dividing potentially with
> > zero when a malformed FU descriptor is passed.  Although there is
> > already a sanity check, it checks only the value zero, hence it can
> > still lead to a zero-division when a value 1 is passed there.
> > 
> > Fix it by correcting the sanity check (and the error message
> > thereof).
> > 
> > Fixes: 23caaf19b11e ("ALSA: usb-mixer: Add support for Audio Class v2.0")
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > [bwh: Backported to 3.2: adjust context]
> > Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
> > ---
> >  sound/usb/mixer.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > --- a/sound/usb/mixer.c
> > +++ b/sound/usb/mixer.c
> > @@ -1262,9 +1262,9 @@ static int parse_audio_feature_unit(stru
> >  			return -EINVAL;
> >  		}
> >  		csize = hdr->bControlSize;
> > -		if (!csize) {
> > +		if (csize <= 1) {
> >  			snd_printdd(KERN_ERR "usbaudio: unit %u: "
> > -				    "invalid bControlSize == 0\n", unitid);
> > +				    "invalid bControlSize <= 1\n", unitid);
> >  			return -EINVAL;
> >  		}
> >  		channels = (hdr->bLength - 7) / csize - 1;
> > 
-- 
Ben Hutchings
friends: People who know you well, but like you anyway.


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