drm/mediatek: Add 0 size check to mtk_drm_gem_obj

Add a check to mtk_drm_gem_init if we attempt to allocate a GEM object
of 0 bytes. Currently, no such check exists and the kernel will panic if
a userspace application attempts to allocate a 0x0 GBM buffer.

Tested by attempting to allocate a 0x0 GBM buffer on an MT8188 and
verifying that we now return EINVAL.

Fixes: 119f517 ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")
Signed-off-by: Justin Green <greenjustin@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240307180051.4104425-1-greenjustin@chromium.org/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

drivers/gpu/drm/mediatek/mtk_drm_gem.c

@@ -38,6 +38,9 @@ static struct mtk_drm_gem_obj *mtk_drm_gem_init(struct drm_device *dev,
 
 	size = round_up(size, PAGE_SIZE);
 
+	if (size == 0)
+		return ERR_PTR(-EINVAL);
+
 	mtk_gem_obj = kzalloc(sizeof(*mtk_gem_obj), GFP_KERNEL);
 	if (!mtk_gem_obj)
 		return ERR_PTR(-ENOMEM);