linux-kernel - [PATCH v1 2/2] drm/gem: Check whether object is NULL in drm_gem

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Message-Id: <20221026224640.7542-3-dmitry.osipenko@collabora.com>
Date:   Thu, 27 Oct 2022 01:46:40 +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 v1 2/2] drm/gem: Check whether object is NULL in drm_gem_vunmap()

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_gem_vunmap() functions to handle
the NULL pointers better.

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_gem.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index b8db675e7fb5..ee0a246ff4ac 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -1175,11 +1175,11 @@ EXPORT_SYMBOL(drm_gem_vmap);
 
 void drm_gem_vunmap(struct drm_gem_object *obj, struct iosys_map *map)
 {
-	dma_resv_assert_held(obj->resv);
-
-	if (iosys_map_is_null(map))
+	if (!obj || iosys_map_is_null(map))
 		return;
 
+	dma_resv_assert_held(obj->resv);
+
 	if (obj->funcs->vunmap)
 		obj->funcs->vunmap(obj, map);
 
@@ -1202,6 +1202,9 @@ EXPORT_SYMBOL(drm_gem_vmap_unlocked);
 
 void drm_gem_vunmap_unlocked(struct drm_gem_object *obj, struct iosys_map *map)
 {
+	if (!obj || iosys_map_is_null(map))
+		return;
+
 	dma_resv_lock(obj->resv, NULL);
 	drm_gem_vunmap(obj, map);
 	dma_resv_unlock(obj->resv);
-- 
2.37.3