[PATCH] [v2] ASoC: cros_ec_codec: fix uninitialized memory read

[Arnd Bergmann]

On Fri, Dec 4, 2020 at 9:57 AM Tzung-Bi Shih <tzungbi at google.com> wrote:
>
> On Fri, Dec 4, 2020 at 4:36 PM Arnd Bergmann <arnd at kernel.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