drm/i915/gvt: fix dropping obj reference twice

The reference count of obj will be decremented twice if error occurs
in dma_buf_fd(). Additionally, attempting to read the reference count of
obj after dropping reference may lead to a use after free bug. Here, we
drop obj's reference until it is not used.

Fixes: e546e281d33d ("drm/i915/gvt: Dmabuf support for GVT-g")
Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

diff --git a/drivers/gpu/drm/i915/gvt/dmabuf.c b/drivers/gpu/drm/i915/gvt/dmabuf.c
index 13044c0..4bfaefd 100644 (file)
--- a/drivers/gpu/drm/i915/gvt/dmabuf.c
+++ b/drivers/gpu/drm/i915/gvt/dmabuf.c
@@ -498,8 +498,6 @@ int intel_vgpu_get_dmabuf(struct intel_vgpu *vgpu, unsigned int dmabuf_id)
                goto out_free_gem;
        }
 
-       i915_gem_object_put(obj);
-
        ret = dma_buf_fd(dmabuf, DRM_CLOEXEC | DRM_RDWR);
        if (ret < 0) {
                gvt_vgpu_err("create dma-buf fd failed ret:%d\n", ret);
@@ -524,6 +522,8 @@ int intel_vgpu_get_dmabuf(struct intel_vgpu *vgpu, unsigned int dmabuf_id)
                    file_count(dmabuf->file),
                    kref_read(&obj->base.refcount));
 
+       i915_gem_object_put(obj);
+
        return dmabuf_fd;
 
 out_free_dmabuf: