linux-kernel - Re: [PATCH v2] drm/amdgpu: Fix a NULL pointer dereference in amdgpu_connector_lcd_native

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Date:   Thu, 2 Dec 2021 12:10:10 -0500
From:   Alex Deucher <alexdeucher@...il.com>
To:     Zhou Qingyang <zhou1615@....edu>
Cc:     Jammy Zhou <Jammy.Zhou@....com>, David Airlie <airlied@...ux.ie>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        "Pan, Xinhui" <Xinhui.Pan@....com>, Kangjie Lu <kjlu@....edu>,
        LKML <linux-kernel@...r.kernel.org>,
        hongao <hongao@...ontech.com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>
Subject: Re: [PATCH v2] drm/amdgpu: Fix a NULL pointer dereference in amdgpu_connector_lcd_native_mode()

Applied.  Thanks!

Alex

On Thu, Dec 2, 2021 at 11:17 AM Zhou Qingyang <zhou1615@....edu> wrote:
>
> In amdgpu_connector_lcd_native_mode(), the return value of
> drm_mode_duplicate() is assigned to mode, and there is a dereference
> of it in amdgpu_connector_lcd_native_mode(), which will lead to a NULL
> pointer dereference on failure of drm_mode_duplicate().
>
> Fix this bug add a check of mode.
>
> This bug was found by a static analyzer. 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.
>
> Builds with CONFIG_DRM_AMDGPU=m show no new warnings, and
> our static analyzer no longer warns about this code.
>
> Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
> Signed-off-by: Zhou Qingyang <zhou1615@....edu>
> ---
> Changes in v2:
>   -  Fix the similar bug in else clause
>
>  drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> index 0de66f59adb8..df1f9b88a53f 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> @@ -387,6 +387,9 @@ amdgpu_connector_lcd_native_mode(struct drm_encoder *encoder)
>             native_mode->vdisplay != 0 &&
>             native_mode->clock != 0) {
>                 mode = drm_mode_duplicate(dev, native_mode);
> +               if (!mode)
> +                       return NULL;
> +
>                 mode->type = DRM_MODE_TYPE_PREFERRED | DRM_MODE_TYPE_DRIVER;
>                 drm_mode_set_name(mode);
>
> @@ -401,6 +404,9 @@ amdgpu_connector_lcd_native_mode(struct drm_encoder *encoder)
>                  * simpler.
>                  */
>                 mode = drm_cvt_mode(dev, native_mode->hdisplay, native_mode->vdisplay, 60, true, false, false);
> +               if (!mode)
> +                       return NULL;
> +
>                 mode->type = DRM_MODE_TYPE_PREFERRED | DRM_MODE_TYPE_DRIVER;
>                 DRM_DEBUG_KMS("Adding cvt approximation of native panel mode %s\n", mode->name);
>         }
> --
> 2.25.1
>