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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- sound/core/control_compat.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/sound/core/control_compat.c +++ b/sound/core/control_compat.c @@ -306,7 +306,9 @@ static int ctl_elem_read_user(struct snd 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); @@ -334,7 +336,9 @@ static int ctl_elem_write_user(struct sn 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);