Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20220124165732.56587-1-zhou1615@umn.edu>
In-Reply-To: <20220124165732.56587-1-zhou1615@umn.edu>
From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Mon, 24 Jan 2022 14:59:22 -0500
Message-ID: <CADnq5_P9cnxi27FM6cU1sf1FjkV2sZdHjJciuuDd9ZZ92qyxeg@mail.gmail.com>
Subject: Re: [PATCH] drm/amd/display: Fix a NULL pointer dereference in amdgpu_dm_connector_add_common_modes()
To:     Zhou Qingyang <zhou1615@umn.edu>
Cc:     Wayne Lin <Wayne.Lin@amd.com>, Leo Li <sunpeng.li@amd.com>,
        Kangjie Lu <kjlu@umn.edu>,
        Qingqing Zhuo <qingqing.zhuo@amd.com>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>,
        Roman Li <Roman.Li@amd.com>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
        Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>,
        David Airlie <airlied@linux.ie>,
        Aurabindo Pillai <aurabindo.pillai@amd.com>,
        Tony Cheng <Tony.Cheng@amd.com>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>, Jude Shih <shenshih@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Nikola Cornij <nikola.cornij@amd.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Applied.  Thanks!

Alex

On Mon, Jan 24, 2022 at 12:05 PM Zhou Qingyang <zhou1615@umn.edu> wrote:
>
> In amdgpu_dm_connector_add_common_modes(), amdgpu_dm_create_common_mode()
> is assigned to mode and is passed to drm_mode_probed_add() directly after
> that. drm_mode_probed_add() passes &mode->head to list_add_tail(), and
> there is a dereference of it in list_add_tail() without recoveries, which
> could lead to NULL pointer dereference on failure of
> amdgpu_dm_create_common_mode().
>
> Fix this by adding a NULL check of mode.
>
> This bug was found by a static analyzer.
>
> Builds with 'make allyesconfig' show no new warnings,
> and our static analyzer no longer warns about this code.
>
> Fixes: e7b07ceef2a6 ("drm/amd/display: Merge amdgpu_dm_types and amdgpu_dm")
> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> ---
> The analysis employs differential checking to identify inconsistent
> security operations (e.g., checks or kfrees) between two code paths
> and confirms that the inconsistent operations are not recovered in the
> current function or the callers, so they constitute bugs.
>
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
>
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 7f9773f8dab6..9ad94186b146 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -8143,6 +8143,9 @@ static void amdgpu_dm_connector_add_common_modes(struct drm_encoder *encoder,
>                 mode = amdgpu_dm_create_common_mode(encoder,
>                                 common_modes[i].name, common_modes[i].w,
>                                 common_modes[i].h);
> +               if (!mode)
> +                       continue;
> +
>                 drm_mode_probed_add(connector, mode);
>                 amdgpu_dm_connector->num_modes++;
>         }
> --
> 2.25.1
>