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

Takashi Iwai
2018-02-12T06:59:53Z

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@suse.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@suse.de>
> [bwh: Backported to 3.2: adjust context]
> Signed-off-by: Ben Hutchings <ben@decadent.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;
>