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ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF

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[ Note: this is a fix that works around the bug equivalently as the
  two upstream commits:
   1fa4445f9a ("ALSA: control - introduce snd_ctl_notify_one() helper")
   56b88b5056 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Clement Lecigne 2023-01-13 13:07:45 +01:00 committed by Greg Kroah-Hartman
parent 755193f252
commit 5b2ea7e913
1 changed files with 4 additions and 0 deletions
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4
sound/core/control_compat.c
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@ -319,7 +319,9 @@ static int ctl_elem_read_user(struct snd_card *card,
err = snd_power_wait(card, SNDRV_CTL_POWER_D0);
if (err < 0)
goto error;
down_read(&card->controls_rwsem);
err = snd_ctl_elem_read(card, data);
up_read(&card->controls_rwsem);
if (err < 0)
goto error;
err = copy_ctl_value_to_user(userdata, valuep, data, type, count);
@ -347,7 +349,9 @@ static int ctl_elem_write_user(struct snd_ctl_file *file,
err = snd_power_wait(card, SNDRV_CTL_POWER_D0);
if (err < 0)
goto error;
down_write(&card->controls_rwsem);
err = snd_ctl_elem_write(card, file, data);
up_write(&card->controls_rwsem);
if (err < 0)
goto error;
err = copy_ctl_value_to_user(userdata, valuep, data, type, count);