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

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Date:   Mon, 12 Feb 2018 07:59:51 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Ben Hutchings <ben@...adent.org.uk>
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 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,

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;
>