6.15-stable review patch. If anyone has any objections, please let me know.
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From: Thomas Zimmermann tzimmermann@suse.de
commit 2712ca878b688682ac2ce02aefc413fc76019cd9 upstream.
This reverts commit cce16fcd7446dcff7480cd9d2b6417075ed81065.
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
Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Reviewed-by: Simona Vetter simona.vetter@ffwll.ch Acked-by: Christian König christian.koenig@amd.com Acked-by: Zack Rusin zack.rusin@broadcom.com Cc: stable@vger.kernel.org # v6.15+ Link: https://lore.kernel.org/r/20250715155934.150656-6-tzimmermann@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/drm_gem_framebuffer_helper.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
--- a/drivers/gpu/drm/drm_gem_framebuffer_helper.c +++ b/drivers/gpu/drm/drm_gem_framebuffer_helper.c @@ -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( 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( */ 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 d 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; }