Thanks for your reply!
Best regards,
Tuo Li
On Mon, Jul 3, 2023 at 4:10 PM Takashi Iwai <tiwai@xxxxxxx> wrote:
> 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 <bass@xxxxxxxxxxx>
> > Signed-off-by: Tuo Li <islituo@xxxxxxxxx>
>
> 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
> >
>
