On Mon, 26 Apr 2021 at 13:44, Lv Yunlong lyl2019@mail.ustc.edu.cn wrote:
Our code analyzer reported a double free bug.
In gen8_preallocate_top_level_pdp, pde and pde->pt.base are allocated via alloc_pd(vm) with one reference. If pin_pt_dma() failed, pde->pt.base is freed by i915_gem_object_put() with a reference dropped. Then free_pd calls free_px() defined in intel_ppgtt.c, which calls i915_gem_object_put() to put pde->pt.base again.
As pde->pt.base is protected by refcount, so the second put will not free pde->pt.base actually. But, maybe it is better to remove the first put?
Fixes: 82adf901138cc ("drm/i915/gt: Shrink i915_page_directory's slab bucket") Signed-off-by: Lv Yunlong lyl2019@mail.ustc.edu.cn
Yes, it looks like this fixes a potential use-after-free. Thanks for the patch, Reviewed-by: Matthew Auld matthew.auld@intel.com
Pushed to drm-intel-gt-next.