From: Takashi Iwai <tiwai@suse.de>
To: Tuo Li <islituo@gmail.com>
Cc: perex@perex.cz, tiwai@suse.com, alsa-devel@alsa-project.org,
linux-kernel@vger.kernel.org, baijiaju1990@outlook.com,
BassCheck <bass@buaa.edu.cn>
Subject: Re: [PATCH] ALSA: hda: fix a possible null-pointer dereference due to data race in snd_hdac_regmap_sync()
Date: Mon, 03 Jul 2023 10:10:34 +0200 [thread overview]
Message-ID: <87a5wd76v9.wl-tiwai@suse.de> (raw)
In-Reply-To: <20230703031016.1184711-1-islituo@gmail.com>
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@buaa.edu.cn>
> Signed-off-by: Tuo Li <islituo@gmail.com>
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
>
prev parent reply other threads:[~2023-07-03 8:10 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-03 3:10 [PATCH] ALSA: hda: fix a possible null-pointer dereference due to data race in snd_hdac_regmap_sync() Tuo Li
2023-07-03 8:10 ` Takashi Iwai [this message]
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