CVE-2021-47200 Information

Description

In the Linux kernel the following vulnerability has been resolved:

drm/prime: Fix use after free in mmap with drm_gem_ttm_mmap

drm_gem_ttm_mmap() drops a reference to the gem object on success. If the gem object’s refcount == 1 on entry to drm_gem_prime_mmap() that drop will free the gem object and the subsequent drm_gem_object_get() will be a UAF. Fix by grabbing a reference before calling the mmap helper.

This issue was forseen when the reference dropping was adding in commit 9786b65bc61ac (\drm/ttm: fix mmap refcounting): \For that to work properly the drm_gem_object_get() call in drm_gem_ttm_mmap() must be moved so it happens before calling obj->funcs->mmap() otherwise the gem refcount would go down to zero.\

Reference

https://git.kernel.org/stable/c/4f8e469a2384dfa4047145b0093126462cbb6dc0 https://git.kernel.org/stable/c/8244a3bc27b3efd057da154b8d7e414670d5044f