Commit 8244a3bc authored by Anand K Mistry's avatar Anand K Mistry Committed by Thomas Zimmermann

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 9786b65b ("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."
Signed-off-by: default avatarAnand K Mistry <amistry@google.com>
Fixes: 9786b65b ("drm/ttm: fix mmap refcounting")
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v5.5+
Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210930085932.1.I8043d61cc238e0168e2f4ca5f4783223434aa587@changeid
parent 8c0fd126
...@@ -719,11 +719,13 @@ int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma) ...@@ -719,11 +719,13 @@ int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
if (obj->funcs && obj->funcs->mmap) { if (obj->funcs && obj->funcs->mmap) {
vma->vm_ops = obj->funcs->vm_ops; vma->vm_ops = obj->funcs->vm_ops;
drm_gem_object_get(obj);
ret = obj->funcs->mmap(obj, vma); ret = obj->funcs->mmap(obj, vma);
if (ret) if (ret) {
drm_gem_object_put(obj);
return ret; return ret;
}
vma->vm_private_data = obj; vma->vm_private_data = obj;
drm_gem_object_get(obj);
return 0; return 0;
} }
......
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