linux-kernel - Re: [PATCH] OSS: keep index within bounds of midi

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Date:	Mon, 16 Nov 2009 17:46:56 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Roel Kluin <roel.kluin@...il.com>
Cc:	Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] OSS: keep index within bounds of midi_devs[]

At Mon, 16 Nov 2009 17:05:02 +0100,
Roel Kluin wrote:
> 
> When the {orig,midi}_dev equals num_midis, that's one too
> large already.
> 
> Signed-off-by: Roel Kluin <roel.kluin@...il.com>
> ---
> In MIDIbuf_open() sound/oss/midibuf.c:166
> 
>         if (num_midis > MAX_MIDI_DEV)
>         {
>                 printk(KERN_ERR "midi: Too many midi interfaces\n");
>                 num_midis = MAX_MIDI_DEV;
>         }
> 
> num_midis is at most MAX_MIDI_DEV.
> 
> `git grep -n MAX_MIDI_DEV' and note that when the index equals
> num_midis this causes reads/writes outside array bounds for
> midi_devs, midi2synth, dev_conf and others (below check in patch).

The fix looks correct to me.  Applied now.

Thanks.


Takashi

> 
>  sound/oss/midi_synth.c |    2 +-
>  sound/oss/mpu401.c     |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/oss/midi_synth.c b/sound/oss/midi_synth.c
> index 9e45098..3bc7104 100644
> --- a/sound/oss/midi_synth.c
> +++ b/sound/oss/midi_synth.c
> @@ -426,7 +426,7 @@ midi_synth_open(int dev, int mode)
>  	int             err;
>  	struct midi_input_info *inc;
>  
> -	if (orig_dev < 0 || orig_dev > num_midis || midi_devs[orig_dev] == NULL)
> +	if (orig_dev < 0 || orig_dev >= num_midis || midi_devs[orig_dev] == NULL)
>  		return -ENXIO;
>  
>  	midi2synth[orig_dev] = dev;
> diff --git a/sound/oss/mpu401.c b/sound/oss/mpu401.c
> index 734b8f9..0af9d24 100644
> --- a/sound/oss/mpu401.c
> +++ b/sound/oss/mpu401.c
> @@ -770,7 +770,7 @@ static int mpu_synth_ioctl(int dev, unsigned int cmd, void __user *arg)
>  
>  	midi_dev = synth_devs[dev]->midi_dev;
>  
> -	if (midi_dev < 0 || midi_dev > num_midis || midi_devs[midi_dev] == NULL)
> +	if (midi_dev < 0 || midi_dev >= num_midis || midi_devs[midi_dev] == NULL)
>  		return -ENXIO;
>  
>  	devc = &dev_conf[midi_dev];
> 
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