CVE-2021-47200

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> drm/prime: Fix use after free in mmap with drm_gem_ttm_mmap<br /> <br /> drm_gem_ttm_mmap() drops a reference to the gem object on success. If<br /> the gem object&amp;#39;s refcount == 1 on entry to drm_gem_prime_mmap(), that<br /> drop will free the gem object, and the subsequent drm_gem_object_get()<br /> will be a UAF. Fix by grabbing a reference before calling the mmap<br /> helper.<br /> <br /> This issue was forseen when the reference dropping was adding in<br /> commit 9786b65bc61ac ("drm/ttm: fix mmap refcounting"):<br /> "For that to work properly the drm_gem_object_get() call in<br /> drm_gem_ttm_mmap() must be moved so it happens before calling<br /> obj-&gt;funcs-&gt;mmap(), otherwise the gem refcount would go down<br /> to zero."