ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF
[ 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.
Bug: 265303544
Signed-off-by: Clement Lecigne <clecigne@google.com>
Cc: stable@vger.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>
Change-Id: I09e6834ccdacb1e35b4dfa20d94e82a0e4afac7e
diff --git a/sound/core/control_compat.c b/sound/core/control_compat.c
index 3fc2166..00d826b 100644
--- a/sound/core/control_compat.c
+++ b/sound/core/control_compat.c
@@ -319,7 +319,9 @@
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 @@
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);
