From: Clement Lecigne <[email protected]>
[ 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 <[email protected]>
Cc: [email protected] # 5.12 and older
Signed-off-by: Takashi Iwai <[email protected]>
---
Greg, this is a patch for the last ALSA PCM UCM fix for the older
stable trees. Please take this to 5.10.y and older stable trees.
Thanks!
sound/core/control_compat.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/sound/core/control_compat.c b/sound/core/control_compat.c
index 97467f6a32a1..980ab3580f1b 100644
--- a/sound/core/control_compat.c
+++ b/sound/core/control_compat.c
@@ -304,7 +304,9 @@ 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);
@@ -332,7 +334,9 @@ 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);
--
2.35.3
On 13. 01. 23 15:26, Takashi Iwai wrote:
> From: Clement Lecigne <[email protected]>
>
> [ 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 <[email protected]>
> Cc: [email protected] # 5.12 and older
> Signed-off-by: Takashi Iwai <[email protected]>
Reviewed-by: Jaroslav Kysela <[email protected]>
--
Jaroslav Kysela <[email protected]>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.
On Fri, Jan 13, 2023 at 03:26:39PM +0100, Takashi Iwai wrote:
> From: Clement Lecigne <[email protected]>
>
> [ 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 ]
Thanks for the backport, now queued up.
greg k-h