This is a note to let you know that I've just added the patch titled ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: alsa-pcm-move-rwsem-lock-inside-snd_ctl_elem_read-to-prevent-uaf.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 56b88b50565cd8b946a2d00b0c83927b7ebb055e Mon Sep 17 00:00:00 2001 From: Clement Lecigne <clecigne@xxxxxxxxxx> Date: Fri, 13 Jan 2023 13:07:45 +0100 Subject: ALSA: pcm: Move rwsem lock inside snd_ctl_elem_read to prevent UAF 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> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- sound/core/control_compat.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/sound/core/control_compat.c +++ b/sound/core/control_compat.c @@ -319,7 +319,9 @@ 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); @@ -347,7 +349,9 @@ 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); Patches currently in stable-queue which might be from clecigne@xxxxxxxxxx are queue-4.19/alsa-pcm-move-rwsem-lock-inside-snd_ctl_elem_read-to-prevent-uaf.patch