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

Author: Clement Lecigne

sound/core/control_compat.c

@@ -320,8 +320,11 @@ static int ctl_elem_read_user(struct snd_card *card,
 
 	snd_power_lock(card);
 	err = snd_power_wait(card, SNDRV_CTL_POWER_D0);
-	if (err >= 0)
+	if (err >= 0) {
+		down_read(&card->controls_rwsem);
 		err = snd_ctl_elem_read(card, data);
+		up_read(&card->controls_rwsem);
+	}
 	snd_power_unlock(card);
 	if (err >= 0)
 		err = copy_ctl_value_to_user(userdata, valuep, data,
@@ -349,8 +352,11 @@ static int ctl_elem_write_user(struct snd_ctl_file *file,
 
 	snd_power_lock(card);
 	err = snd_power_wait(card, SNDRV_CTL_POWER_D0);
-	if (err >= 0)
+	if (err >= 0) {
+		down_write(&card->controls_rwsem);
 		err = snd_ctl_elem_write(card, file, data);
+		up_write(&card->controls_rwsem);
+	}
 	snd_power_unlock(card);
 	if (err >= 0)
 		err = copy_ctl_value_to_user(userdata, valuep, data,