Commit 2712ca87 authored by Thomas Zimmermann's avatar Thomas Zimmermann
Browse files

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



This reverts commit cce16fcd.

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 5307dce8 ("drm/gem: Acquire references on
GEM handles for framebuffers") and commit f6bfc9af ("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

Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: default avatarSimona Vetter <simona.vetter@ffwll.ch>
Acked-by: default avatarChristian König <christian.koenig@amd.com>
Acked-by: default avatarZack Rusin <zack.rusin@broadcom.com>
Cc: <stable@vger.kernel.org> # v6.15+
Link: https://lore.kernel.org/r/20250715155934.150656-6-tzimmermann@suse.de
parent fb4ef4a5

drivers/gpu/drm/drm_gem_framebuffer_helper.c

+6 −2
Original line number Diff line number Diff line
@@ -419,6 +419,7 @@ EXPORT_SYMBOL(drm_gem_fb_vunmap); 
static void __drm_gem_fb_end_cpu_access(struct drm_framebuffer *fb, enum dma_data_direction dir,

					unsigned int num_planes)

{

	struct dma_buf_attachment *import_attach;

	struct drm_gem_object *obj;

	int ret;
@@ -427,9 +428,10 @@ static void __drm_gem_fb_end_cpu_access(struct drm_framebuffer *fb, enum dma_dat 
		obj = drm_gem_fb_get_obj(fb, num_planes);

		if (!obj)

			continue;

		import_attach = obj->import_attach;

		if (!drm_gem_is_imported(obj))

			continue;

		ret = dma_buf_end_cpu_access(obj->dma_buf, dir);

		ret = dma_buf_end_cpu_access(import_attach->dmabuf, dir);

		if (ret)

			drm_err(fb->dev, "dma_buf_end_cpu_access(%u, %d) failed: %d\n",

				ret, num_planes, dir);
@@ -452,6 +454,7 @@ static void __drm_gem_fb_end_cpu_access(struct drm_framebuffer *fb, enum dma_dat 
 */

int drm_gem_fb_begin_cpu_access(struct drm_framebuffer *fb, enum dma_data_direction dir)

{

	struct dma_buf_attachment *import_attach;

	struct drm_gem_object *obj;

	unsigned int i;

	int ret;
@@ -462,9 +465,10 @@ int drm_gem_fb_begin_cpu_access(struct drm_framebuffer *fb, enum dma_data_direct 
			ret = -EINVAL;

			goto err___drm_gem_fb_end_cpu_access;

		}

		import_attach = obj->import_attach;

		if (!drm_gem_is_imported(obj))

			continue;

		ret = dma_buf_begin_cpu_access(obj->dma_buf, dir);

		ret = dma_buf_begin_cpu_access(import_attach->dmabuf, dir);

		if (ret)

			goto err___drm_gem_fb_end_cpu_access;

	}