2023-07-03 03:22:05

by Tuo Li

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

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 <[email protected]>
Signed-off-by: Tuo Li <[email protected]>
---
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

2023-07-03 08:25:49

by Takashi Iwai

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

On Mon, 03 Jul 2023 05:10:16 +0200,
Tuo Li wrote:
>
> 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 <[email protected]>
> Signed-off-by: Tuo Li <[email protected]>

Practically seen, it's pretty harmless, as the flag is set at the very
beginning of the codec driver probe, while snd_hdac_regmap_sync() is
used only in the runtime PM resume that must not happen during the
probe. IOW, codec->regmap_lock itself isn't really meant to
protectthe change of codec->regmap flag.

OTOH, your change makes things more consistent, so I applied the patch
now.


Thanks!

Takashi


> ---
> 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
>