[PATCH] ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF

[Jaroslav Kysela]

On 13. 01. 23 13:07, Takashi Iwai wrote:
> From: Clement Lecigne <clecigne at google.com>
> 
> Takes rwsem lock inside snd_ctl_elem_read instead of snd_ctl_elem_read_user
> like it was done for write in commit 1fa4445f9adf1 ("ALSA: control - introduce
> snd_ctl_notify_one() helper"). Doing this way we are also fixing the following
> locking issue happening in the compat path which can be easily triggered and
> turned into an use-after-free.
> 
> 64-bits:
> snd_ctl_ioctl
>    snd_ctl_elem_read_user
>      [takes controls_rwsem]
>      snd_ctl_elem_read [lock properly held, all good]
>      [drops controls_rwsem]
> 
> 32-bits:
> snd_ctl_ioctl_compat
>    snd_ctl_elem_write_read_compat
>      ctl_elem_write_read
>        snd_ctl_elem_read [missing lock, not good]
> 
> CVE-2023-0266 was assigned for this issue.
> 
> Cc: stable at kernel.org # 5.13+
> Signed-off-by: Clement Lecigne <clecigne at google.com>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>

Reviewed-by: Jaroslav Kysela <perex at perex.cz>

-- 
Jaroslav Kysela <perex at perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.