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From:   Alexey Minnekhanov <alexeymin@postmarketos.org>
To:     Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        linux-arm-msm@vger.kernel.org (open list:DRM DRIVER FOR MSM ADRENO GPU),
        dri-devel@lists.freedesktop.org (open list:DRM DRIVER FOR MSM ADRENO
        GPU),
        freedreno@lists.freedesktop.org (open list:DRM DRIVER FOR MSM ADRENO
        GPU), linux-kernel@vger.kernel.org (open list)
Cc:     ~postmarketos/upstreaming@lists.sr.ht,
        Alexey Minnekhanov <alexeymin@postmarketos.org>
Subject: [PATCH] drm/msm: Init mm_list before accessing it for use_vram path
Date:   Tue, 18 May 2021 13:26:24 +0300
Message-Id: <20210518102624.1193955-1-alexeymin@postmarketos.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Fix NULL pointer dereference caused by update_inactive()
trying to list_del() an uninitialized mm_list who's
prev/next pointers are NULL.

Signed-off-by: Alexey Minnekhanov <alexeymin@postmarketos.org>
---
 drivers/gpu/drm/msm/msm_gem.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index b199942266a26..b8c873fc63a78 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -1227,6 +1227,13 @@ static struct drm_gem_object *_msm_gem_new(struct drm_device *dev,
 
 		to_msm_bo(obj)->vram_node = &vma->node;
 
+		/* Call chain get_pages() -> update_inactive() tries to
+		 * access msm_obj->mm_list, but it is not initialized yet.
+		 * To avoid NULL pointer dereference error, initialize
+		 * mm_list to be empty.
+		 */
+		INIT_LIST_HEAD(&msm_obj->mm_list);
+
 		msm_gem_lock(obj);
 		pages = get_pages(obj);
 		msm_gem_unlock(obj);
-- 
2.26.3