From 8244a3bc27b3efd057da154b8d7e414670d5044f Mon Sep 17 00:00:00 2001

From: Anand K Mistry <amistry@google.com>

Date: Thu, 30 Sep 2021 09:00:07 +1000

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

Git-commit: 8244a3bc27b3efd057da154b8d7e414670d5044f

Patch-mainline: v5.16-rc1

References: bsc#1152472

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."

Signed-off-by: Anand K Mistry <amistry@google.com>

Fixes: 9786b65bc61a ("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: Thomas Zimmermann <tzimmermann@suse.de>

Link: https://patchwork.freedesktop.org/patch/msgid/20210930085932.1.I8043d61cc238e0168e2f4ca5f4783223434aa587@changeid

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>

---

 drivers/gpu/drm/drm_prime.c |    8 +++++---

 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/drm_prime.c

+++ b/drivers/gpu/drm/drm_prime.c

@@ -719,11 +719,13 @@ int drm_gem_prime_mmap(struct drm_gem_ob

 	vma->vm_pgoff += drm_vma_node_start(&obj->vma_node);

 	if (obj->funcs && obj->funcs->mmap) {

+		drm_gem_object_get(obj);

 		ret = obj->funcs->mmap(obj, vma);

-		if (ret)

-			return ret;

+		if (ret) {

+			drm_gem_object_put(obj);

+ 			return ret;

+		}

 		vma->vm_private_data = obj;

-		drm_gem_object_get(obj);

 		return 0;

 	}