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SubjectRe: [PATCH 5.10.y] ALSA: pcm: Properly take rwsem lock in ctl_elem_read_user/ctl_elem_write_user to prevent UAF
From
On 13. 01. 23 15:26, Takashi Iwai wrote:
> From: Clement Lecigne <clecigne@google.com>
>
> [ Note: this is a fix that works around the bug equivalently as the
> two upstream commits:
> 1fa4445f9adf ("ALSA: control - introduce snd_ctl_notify_one() helper")
> 56b88b50565c ("ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF")
> but in a simpler way to fit with older stable trees -- tiwai ]
>
> Add missing locking in ctl_elem_read_user/ctl_elem_write_user which can be
> easily triggered and turned into an use-after-free.
>
> Example code paths with SNDRV_CTL_IOCTL_ELEM_READ:
>
> 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 (compat):
> 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.
>
> Signed-off-by: Clement Lecigne <clecigne@google.com>
> Cc: stable@kernel.org # 5.12 and older
> Signed-off-by: Takashi Iwai <tiwai@suse.de>

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

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

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