linux-kernel - [PATCH v2 2/2] drm/client: Prevent NULL dereference in drm_client_buffer

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Date:   Sun, 30 Oct 2022 18:44:12 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Christian König <christian.koenig@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, noralf@...nnes.org,
        Dan Carpenter <dan.carpenter@...cle.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] drm/client: Prevent NULL dereference in drm_client_buffer_delete()

The drm_gem_vunmap() will crash with a NULL dereference if the passed
object pointer is NULL. It wasn't a problem before we added the locking
support to drm_gem_vunmap function because the mapping argument was always
NULL together with the object. Make drm_client_buffer_delete() to check
whether GEM is NULL before trying to unmap the GEM, it will happen on
framebuffer creation error.

Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Link: https://lore.kernel.org/dri-devel/Y1kFEGxT8MVlf32V@kili/
Fixes: 79e2cf2e7a19 ("drm/gem: Take reservation lock for vmap/vunmap operations")
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
---
 drivers/gpu/drm/drm_client.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c
index 38e1be991caa..fd67efe37c63 100644
--- a/drivers/gpu/drm/drm_client.c
+++ b/drivers/gpu/drm/drm_client.c
@@ -235,10 +235,10 @@ static void drm_client_buffer_delete(struct drm_client_buffer *buffer)
 {
 	struct drm_device *dev = buffer->client->dev;
 
-	drm_gem_vunmap_unlocked(buffer->gem, &buffer->map);
-
-	if (buffer->gem)
+	if (buffer->gem) {
+		drm_gem_vunmap_unlocked(buffer->gem, &buffer->map);
 		drm_gem_object_put(buffer->gem);
+	}
 
 	if (buffer->handle)
 		drm_mode_destroy_dumb(dev, buffer->handle, buffer->client->file);
-- 
2.37.3