Patch "ALSA: hda: fix a possible null-pointer dereference due to data race in snd_hdac_regmap_sync()" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ALSA: hda: fix a possible null-pointer dereference due to data race in snd_hdac_regmap_sync()

to the 5.15-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-hda-fix-a-possible-null-pointer-dereference-due.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 1d80e074cc1fc342fbe378d8fcb6b06773d07b0e
Author: Tuo Li <islituo@xxxxxxxxx>
Date:   Mon Jul 3 11:10:16 2023 +0800

    ALSA: hda: fix a possible null-pointer dereference due to data race in snd_hdac_regmap_sync()
    
    [ Upstream commit 1f4a08fed450db87fbb5ff5105354158bdbe1a22 ]
    
    The variable codec->regmap is often protected by the lock
    codec->regmap_lock when is accessed. However, it is accessed without
    holding the lock when is accessed in snd_hdac_regmap_sync():
    
      if (codec->regmap)
    
    In my opinion, this may be a harmful race, because if codec->regmap is
    set to NULL right after the condition is checked, a null-pointer
    dereference can occur in the called function regcache_sync():
    
      map->lock(map->lock_arg); --> Line 360 in drivers/base/regmap/regcache.c
    
    To fix this possible null-pointer dereference caused by data race, the
    mutex_lock coverage is extended to protect the if statement as well as the
    function call to regcache_sync().
    
    [ Note: the lack of the regmap_lock itself is harmless for the current
      codec driver implementations, as snd_hdac_regmap_sync() is only for
      PM runtime resume that is prohibited during the codec probe.
      But the change makes the whole code more consistent, so it's merged
      as is -- tiwai ]
    
    Reported-by: BassCheck <bass@xxxxxxxxxxx>
    Signed-off-by: Tuo Li <islituo@xxxxxxxxx>
    Link: https://lore.kernel.org/r/20230703031016.1184711-1-islituo@xxxxxxxxx
    Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/sound/hda/hdac_regmap.c b/sound/hda/hdac_regmap.c
index fe3587547cfec..39610a15bcc98 100644
--- a/sound/hda/hdac_regmap.c
+++ b/sound/hda/hdac_regmap.c
@@ -597,10 +597,9 @@ EXPORT_SYMBOL_GPL(snd_hdac_regmap_update_raw_once);
  */
 void snd_hdac_regmap_sync(struct hdac_device *codec)
 {
-	if (codec->regmap) {
-		mutex_lock(&codec->regmap_lock);
+	mutex_lock(&codec->regmap_lock);
+	if (codec->regmap)
 		regcache_sync(codec->regmap);
-		mutex_unlock(&codec->regmap_lock);
-	}
+	mutex_unlock(&codec->regmap_lock);
 }
 EXPORT_SYMBOL_GPL(snd_hdac_regmap_sync);