linux-kernel - Re: [PATCH] [v2] ASoC: cros_ec_codec: fix uninitialized memory read

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Message-ID: <CAK8P3a1t-JhJ73ikf=FZQn1L0AbT3e=e7zJGkOMvCXky6apj+w@mail.gmail.com>
Date:   Fri, 4 Dec 2020 10:11:50 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Tzung-Bi Shih <tzungbi@...gle.com>
Cc:     Cheng-Yi Chiang <cychiang@...omium.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Benson Leung <bleung@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Arnd Bergmann <arnd@...db.de>,
        Guenter Roeck <groeck@...omium.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ardb@...nel.org>,
        Eric Biggers <ebiggers@...gle.com>,
        Yu-Hsuan Hsu <yuhsuan@...omium.org>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        ALSA development <alsa-devel@...a-project.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [v2] ASoC: cros_ec_codec: fix uninitialized memory read

On Fri, Dec 4, 2020 at 9:57 AM Tzung-Bi Shih <tzungbi@...gle.com> wrote:
>
> On Fri, Dec 4, 2020 at 4:36 PM Arnd Bergmann <arnd@...nel.org> wrote:
> > diff --git a/sound/soc/codecs/cros_ec_codec.c b/sound/soc/codecs/cros_ec_codec.c
> > index 58894bf47514..6ec673573c70 100644
> > --- a/sound/soc/codecs/cros_ec_codec.c
> > +++ b/sound/soc/codecs/cros_ec_codec.c
> > @@ -348,7 +348,7 @@ static int i2s_rx_event(struct snd_soc_dapm_widget *w,
> >         }
> >
> >         return send_ec_host_command(priv->ec_device, EC_CMD_EC_CODEC_I2S_RX,
> > -                                   (uint8_t *)&p, sizeof(p), NULL, 0);
> > +                                   &p.cmd, sizeof(p.cmd), NULL, 0);
> >  }
>
> I would prefer your v1.
>
> Reasons:
> 1. The change is not just kernel related.
> There is a EC (embedded controller) firmware to collaborate with the
> code.  The firmware doesn't know the kernel only copies the first byte
> of the packet (at least for now).  See
> https://chromium.googlesource.com/chromiumos/platform/ec/+/refs/heads/master/common/audio_codec_i2s_rx.c#120.
>
> 2. We don't copy partial packets in a EC host command.
> IMHO, it is also not a big deal if copying a few unused bytes in the packet.

Ok, so if the EC does access the uninitialized data, then it is indeed
better to initialize it to zero as I first thought.

      Arnd