Revert "drm/gem-dma: Use dma_buf from GEM object instance"

In the Linux kernel, the following vulnerability has been resolved: Revert "drm/gem-dma: Use dma_buf from GEM object instance" This reverts commit e8afa1557f4f963c9a511bd2c6074a941c308685. The dma_buf field in struct drm_gem_object is not stable over the object instance's lifetime. The field becomes NULL when user space releases the final GEM handle on the buffer object. This resulted in a NULL-pointer deref. Workarounds in commit 5307dce878d4 ("drm/gem: Acquire references on GEM handles for framebuffers") and commit f6bfc9afc751 ("drm/framebuffer: Acquire internal references on GEM handles") only solved the problem partially. They especially don't work for buffer objects without a DRM framebuffer associated. Hence, this revert to going back to using .import_attach->dmabuf. v3: - cc stable

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Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于dma_buf字段不稳定，可能导致空指针取消引用。

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