Don't free shmem object if it has pages that are in use at the time of
the GEM's freeing if DRM driver doesn't manage GEM/pages lifetime properly.
This prevents memory corruption due to the use-after-free bug in exchange
to leaking GEM.
Signed-off-by: Dmitry Osipenko <dmitry.osipe...@collabora.com>
---
drivers/gpu/drm/drm_gem_shmem_helper.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c
b/drivers/gpu/drm/drm_gem_shmem_helper.c
index e6e6e693ab95..0d95d723b90d 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -205,9 +205,15 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem)
if (obj->import_attach)
drm_prime_gem_destroy(obj, shmem->sgt);
- drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count));
- drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count));
- drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_pin_count));
+ /*
+ * Prevent memory corruption caused by the use-after-free bug in a
+ * case where shmem user erroneously holds reference to pages while
+ * GEM is freed by leaking the GEM.
+ */
+ if (drm_WARN_ON(obj->dev, refcount_read(&shmem->vmap_use_count)) ||
+ drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_use_count)) ||
+ drm_WARN_ON(obj->dev, refcount_read(&shmem->pages_pin_count)))
+ return;
drm_gem_object_release(obj);
kfree(shmem);
--
2.43.0
