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From:   Dmitry Osipenko <dmitry.osipenko@collabora.com>
To:     David Airlie <airlied@gmail.com>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
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        Thomas Zimmermann <tzimmermann@suse.de>,
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Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        kernel@collabora.com, virtualization@lists.linux-foundation.org
Subject: [PATCH v18 22/26] drm/shmem-helper: Don't free refcounted GEM
Date:   Mon, 30 Oct 2023 02:02:01 +0300
Message-ID: <20231029230205.93277-23-dmitry.osipenko@collabora.com>
In-Reply-To: <20231029230205.93277-1-dmitry.osipenko@collabora.com>
References: <20231029230205.93277-1-dmitry.osipenko@collabora.com>
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Don't free refcounted shmem object to prevent use-after-free bug that
is worse than a memory leak.

Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 6dd087f19ea3..4253c367dc07 100644
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -203,9 +203,10 @@ 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));
+	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);
-- 
2.41.0