linux-kernel - Re: [PATCH] ASoC: soc-core: Add missing NULL check

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Date:   Fri, 9 Mar 2018 10:45:16 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Takashi Iwai <tiwai@...e.com>, Pavel Machek <pavel@....cz>,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        moderated for non-subscribers <alsa-devel@...a-project.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: soc-core: Add missing NULL check

On Fri, Mar 9, 2018 at 4:50 AM, Mark Brown <broonie@...nel.org> wrote:
> On Thu, Mar 08, 2018 at 12:06:53PM -0800, Kees Cook wrote:
>
>> If a codec is not attached to the sound soc, a NULL deref is possible as a
>> regular user in /sys.
>
> I can't parse this, sorry.  What is the "sound soc"?

SoC's sound component? I'm not sure either. :) I was just sending the
patch that I mentioned from the thread where Pavel mentioned this
Oops.

Pavel, can you isolate the specific file that is causing the oops?
(Maybe this patch should be a WARN() instead of silent return 0, since
we still don't want to crash, but it should be considered a bug...)

>
>> +++ b/sound/soc/soc-core.c
>> @@ -137,6 +137,9 @@ static ssize_t soc_codec_reg_show(struct snd_soc_codec *codec, char *buf,
>>       size_t total = 0;
>>       loff_t p = 0;
>>
>> +     if (!codec || !codec->driver)
>> +             return 0;
>> +
>
> How are we managing to create a sysfs file for a CODEC which doesn't
> have a CODEC struct associated with it?  That is obviously nonsensical
> and suggests we've got some more serious problem going on here - if
> there's no CODEC those sysfs attributes simply shouldn't be there.

No idea! Hopefully Pavel has more details...

-Kees

-- 
Kees Cook
Pixel Security