linux-kernel - [PATCH] drm/mm: prevent a potential null-pointer dereference

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Message-ID: <20200910023858.43759-1-jingxiangfeng@huawei.com>
Date:   Thu, 10 Sep 2020 10:38:58 +0800
From:   Jing Xiangfeng <jingxiangfeng@...wei.com>
To:     <maarten.lankhorst@...ux.intel.com>, <mripard@...nel.org>,
        <tzimmermann@...e.de>, <airlied@...ux.ie>, <daniel@...ll.ch>,
        <nirmoy.das@....com>, <christian.koenig@....com>
CC:     <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <jingxiangfeng@...wei.com>
Subject: [PATCH] drm/mm: prevent a potential null-pointer dereference

The macro 'DECLARE_NEXT_HOLE_ADDR' may hit a potential null-pointer
dereference. So use 'entry' after checking it.

Fixes: 5fad79fd66ff ("drm/mm: cleanup and improve next_hole_*_addr()")
Signed-off-by: Jing Xiangfeng <jingxiangfeng@...wei.com>
---
 drivers/gpu/drm/drm_mm.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index a4a04d246135..6fcf70f71962 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -392,11 +392,14 @@ first_hole(struct drm_mm *mm,
 #define DECLARE_NEXT_HOLE_ADDR(name, first, last)			\
 static struct drm_mm_node *name(struct drm_mm_node *entry, u64 size)	\
 {									\
-	struct rb_node *parent, *node = &entry->rb_hole_addr;		\
+	struct rb_node *parent, *node;					\
 									\
-	if (!entry || RB_EMPTY_NODE(node))				\
+	if (!entry)							\
 		return NULL;						\
 									\
+	node = &entry->rb_hole_addr;					\
+	if (RB_EMPTY_NODE(node))					\
+		return NULL;						\
 	if (usable_hole_addr(node->first, size)) {			\
 		node = node->first;					\
 		while (usable_hole_addr(node->last, size))		\
-- 
2.17.1