[PATCH] drm: hold gem reference until object is no longer accessed

[Steve Cohen]

BUG: KASAN: use-after-free in drm_gem_open_ioctl

There is potential for use-after-free here if the GEM object
handle is closed between the idr lookup and retrieving the size
from the object since a local reference is not being held at that
point. Hold the local reference while the object can still be
accessed to resolve this.

Signed-off-by: Steve Cohen <cohens at codeaurora.org>
---
 drivers/gpu/drm/drm_gem.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 7bf628e..4b2891c 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -898,14 +898,15 @@ drm_gem_open_ioctl(struct drm_device *dev, void *data,
 
 	/* drm_gem_handle_create_tail unlocks dev->object_name_lock. */
 	ret = drm_gem_handle_create_tail(file_priv, obj, &handle);
-	drm_gem_object_put_unlocked(obj);
 	if (ret)
-		return ret;
+		goto out;
 
 	args->handle = handle;
 	args->size = obj->size;
 
-	return 0;
+out:
+	drm_gem_object_put_unlocked(obj);
+	return ret;
 }
 
 /**
-- 
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