From: Clemens Ladisch <clemens@ladisch.de>
Date: Wed, 11 Feb 2015 15:35:50 +0000
Subject: Re: [alsa-devel] [patch] ALSA: seq: potential out of bounds in do_control()
Message-Id: <54DB76D6.3090803@ladisch.de>
List-Id: <kernel-janitors.vger.kernel.org>
References: <20150211151054.GA30155@mwanda>
In-Reply-To: <20150211151054.GA30155@mwanda>
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To: Dan Carpenter <dan.carpenter@oracle.com>, Jaroslav Kysela <perex@perex.cz>
Cc: Takashi Iwai <tiwai@suse.de>, alsa-devel@alsa-project.org, kernel-janitors@vger.kernel.org

Dan Carpenter wrote:
> Smatch complains that "control" is user specifigy and needs to be
> capped.  The call tree to understand this warning is quite long.
>
> snd_seq_write()  <-- get the event from the user
>   snd_seq_client_enqueue_event()
>     snd_seq_deliver_event()
>       deliver_to_subscribers()
>         snd_seq_deliver_single_event()
>           snd_opl3_oss_event_input()
>             snd_midi_process_event()
>               do_control()
>
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> I have spent some time reviewing this code, but I may have missed
> something where we verify that control is in bounds.  I'm not very
> familiar with this code and the call tree is fairly long.

BTW, there are other ways to deliver events.  In any case, events are
pretty much opaque blobs, and most fields are not checked.

> diff --git a/sound/core/seq/seq_midi_emul.c b/sound/core/seq/seq_midi_emul.c
> index 9b6470c..7ba9373 100644
> --- a/sound/core/seq/seq_midi_emul.c
> +++ b/sound/core/seq/seq_midi_emul.c
> @@ -269,6 +269,9 @@ do_control(struct snd_midi_op *ops, void *drv, struct snd_midi_channel_set *chse
>  {
>  	int  i;
>
> +	if (control >= ARRAY_SIZE(chan->control))
> +		return;

Is this correct for an unsigned int converted to an int?


Regards,
Clemens