linux-kernel - Re: [PATCH][next] ALSA: 6fire: Fix undefined behavior bug in struct midi

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Message-ID: <87o7hcw2dq.wl-tiwai@suse.de>
Date:   Fri, 06 Oct 2023 11:01:37 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Torsten Schenk <torsten.schenk@...o.com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] ALSA: 6fire: Fix undefined behavior bug in struct midi_runtime

On Fri, 29 Sep 2023 18:06:32 +0200,
Gustavo A. R. Silva wrote:
> 
> `struct urb` is a flexible structure, which means that it contains a
> flexible-array member at the bottom. This could potentially lead to an
> overwrite of the objects following `out_urb` in `struct midi_runtime`,
> among them a function pointer.
> 
> Fix this by placing the declaration of object `out_urb` at the end of
> `struct midi_runtime`.
> 
> Fixes: c6d43ba816d1 ("ALSA: usb/6fire - Driver for TerraTec DMX 6Fire USB")
> Cc: stable@...r.kernel.org
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

The same question as your another 6fire patch is applied here: does it
"fix" anything real?


thanks,

Takashi

> ---
>  sound/usb/6fire/midi.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/usb/6fire/midi.h b/sound/usb/6fire/midi.h
> index 47640c845903..df3f41913274 100644
> --- a/sound/usb/6fire/midi.h
> +++ b/sound/usb/6fire/midi.h
> @@ -22,12 +22,12 @@ struct midi_runtime {
>  	spinlock_t in_lock;
>  	spinlock_t out_lock;
>  	struct snd_rawmidi_substream *out;
> -	struct urb out_urb;
>  	u8 out_serial; /* serial number of out packet */
>  	u8 *out_buffer;
>  	int buffer_offset;
>  
>  	void (*in_received)(struct midi_runtime *rt, u8 *data, int length);
> +	struct urb out_urb;
>  };
>  
>  int usb6fire_midi_init(struct sfire_chip *chip);
> -- 
> 2.34.1
>