linux-kernel - Re: [PATCH v2] ALSA: usb-audio: fix race condition to UAF in snd_usbmidi

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Message-ID: <875xd39jgn.wl-tiwai@suse.de>
Date: Sun, 28 Sep 2025 08:31:20 +0200
From: Takashi Iwai <tiwai@...e.de>
To: Jeongjun Park <aha310510@...il.com>
Cc: clemens@...isch.de,
	perex@...ex.cz,
	tiwai@...e.com,
	hdanton@...a.com,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	stable@...r.kernel.org,
	syzbot+f02665daa2abeef4a947@...kaller.appspotmail.com
Subject: Re: [PATCH v2] ALSA: usb-audio: fix race condition to UAF in snd_usbmidi_free

On Sat, 27 Sep 2025 19:39:24 +0200,
Jeongjun Park wrote:
> 
> The previous commit 0718a78f6a9f ("ALSA: usb-audio: Kill timer properly at
> removal") patched a UAF issue caused by the error timer.
> 
> However, because the error timer kill added in this patch occurs after the
> endpoint delete, a race condition to UAF still occurs, albeit rarely.
> 
> Additionally, since kill-cleanup for urb is also missing, freed memory can
> be accessed in interrupt context related to urb, which can cause UAF.
> 
> Therefore, to prevent this, error timer and urb must be killed before
> freeing the heap memory.
> 
> Cc: <stable@...r.kernel.org>
> Reported-by: syzbot+f02665daa2abeef4a947@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=f02665daa2abeef4a947
> Fixes: 0718a78f6a9f ("ALSA: usb-audio: Kill timer properly at removal")
> Signed-off-by: Jeongjun Park <aha310510@...il.com>

Thanks, applied now.


Takashi