linux-kernel - Re: [PATCH 1/1] drm/gma500: mdfld: avoid possible null pointer dereference

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Message-ID: <CAMeQTsaHPFw_JuCDhe2k64NuEHSeu4X5qmPFFfsF_YR-OJL2yg@mail.gmail.com>
Date:	Wed, 18 May 2016 22:51:49 +0200
From:	Patrik Jakobsson <patrik.r.jakobsson@...il.com>
To:	Heinrich Schuchardt <xypron.glpk@....de>
Cc:	David Airlie <airlied@...ux.ie>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] drm/gma500: mdfld: avoid possible null pointer dereference

On Wed, May 18, 2016 at 10:31 PM, Heinrich Schuchardt
<xypron.glpk@....de> wrote:
> Only dereference sender after checking if sender is NULL.

Hi Heinrich

I think we had a patch that did something similar a while ago. Don't
remember what happened to it. We do check for !sender right before
calling this function (at only one call-site) so it cannot be NULL at
this point. I would be ok with your change if you also remove the
extra checks in mdfld_dsi_read_mcs(). That way we don't double check
and we check at the point where it actually matters.

Thanks
Patrik

>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@....de>
> ---
>  drivers/gpu/drm/gma500/mdfld_dsi_pkg_sender.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/gma500/mdfld_dsi_pkg_sender.c b/drivers/gpu/drm/gma500/mdfld_dsi_pkg_sender.c
> index 1616af2..c50534c 100644
> --- a/drivers/gpu/drm/gma500/mdfld_dsi_pkg_sender.c
> +++ b/drivers/gpu/drm/gma500/mdfld_dsi_pkg_sender.c
> @@ -520,7 +520,7 @@ static int __read_panel_data(struct mdfld_dsi_pkg_sender *sender, u8 data_type,
>                         u8 *data, u16 len, u32 *data_out, u16 len_out, bool hs)
>  {
>         unsigned long flags;
> -       struct drm_device *dev = sender->dev;
> +       struct drm_device *dev;
>         int i;
>         u32 gen_data_reg;
>         int retry = MDFLD_DSI_READ_MAX_COUNT;
> @@ -530,6 +530,8 @@ static int __read_panel_data(struct mdfld_dsi_pkg_sender *sender, u8 data_type,
>                 return -EINVAL;
>         }
>
> +       dev = sender->dev;
> +
>         /**
>          * do reading.
>          * 0) send out generic read request
> --
> 2.1.4
>