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Subject[PATCH] ALSA: hda: fix a possible null-pointer dereference due to data race in snd_hdac_regmap_sync()
Date
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().

Reported-by: BassCheck <bass@buaa.edu.cn>
Signed-off-by: Tuo Li <islituo@gmail.com>
---
sound/hda/hdac_regmap.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/sound/hda/hdac_regmap.c b/sound/hda/hdac_regmap.c
index fe3587547cfe..39610a15bcc9 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);
--
2.34.1
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