[PATCH -next v2] ALSA: timer: Fix use-after-free problem

[Takashi Iwai]

On Wed, 03 Nov 2021 04:35:17 +0100,
Wang Wensheng wrote:
> 
> When the timer instance was add into ack_list but was not currently in
> process, the user could stop it via snd_timer_stop1() without delete it
> from the ack_list. Then the user could free the timer instance and when
> it was actually processed UAF occurred.
> 
> This issue could be reproduced via testcase snd_timer01 in ltp - running
> several instances of that testcase at the same time.
> 
> What I actually met was that the ack_list of the timer broken and the
> kernel went into deadloop with irqoff. That could be detected by
> hardlockup detector on board or when we run it on qemu, we could use gdb
> to dump the ack_list when the console has no response.
> 
> To fix this issue, we delete the timer instance from ack_list and
> active_list unconditionally in snd_timer_stop1().
> 
> Signed-off-by: Wang Wensheng <wangwensheng4 at huawei.com>
> Suggested-by: Takashi Iwai <tiwai at suse.de>

Thanks, applied now.


Takashi