Re: [PATCH 5.10.y] ALSA: pcm: Properly take rwsem lock in ctl_elem_read_user/ctl_elem_write_user to prevent UAF

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On 13. 01. 23 15:26, Takashi Iwai wrote:
From: Clement Lecigne <clecigne@xxxxxxxxxx>

[ 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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx # 5.12 and older
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>

Reviewed-by: Jaroslav Kysela <perex@xxxxxxxx>

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



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