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    Subject[PATCH 4.9 038/157] drm/amdgpu: Fix a NULL pointer dereference in amdgpu_connector_lcd_native_mode()
    Date
    From: Zhou Qingyang <zhou1615@umn.edu>

    [ Upstream commit b220110e4cd442156f36e1d9b4914bb9e87b0d00 ]

    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@umn.edu>
    Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 eb79d0d3d34f1..7264169d5f2a7 100644
    --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
    +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
    @@ -404,6 +404,9 @@ 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);

    @@ -418,6 +421,9 @@ 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);
    }
    --
    2.34.1


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