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

[Takashi Iwai]

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@xxxxxxxxxxxxxxx>
> Reported-by: syzbot+f02665daa2abeef4a947@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=f02665daa2abeef4a947
> Fixes: 0718a78f6a9f ("ALSA: usb-audio: Kill timer properly at removal")
> Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>

Thanks, applied now.


Takashi