linux-kernel - [PATCH v2] drm/nouveau: Fix potential memory access error in nouveau_debugfs_pstate

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Date:   Mon, 30 Jul 2018 21:05:23 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     nouveau@...ts.freedesktop.org
Cc:     Karol Herbst <karolherbst@...il.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2] drm/nouveau: Fix potential memory access error in nouveau_debugfs_pstate_get()

nouveau_debugfs(drm) will never be NULL, because we're taking the value
of the potentially null device pointer and adding to it so it isn't 0x0.
So, check if drm is NULL instead.

Signed-off-by: Lyude Paul <lyude@...hat.com>
Cc: Karol Herbst <karolherbst@...il.com>
---
Forgot to hit :w before committing, whoops!

 drivers/gpu/drm/nouveau/nouveau_debugfs.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_debugfs.c b/drivers/gpu/drm/nouveau/nouveau_debugfs.c
index 963a4dba8213..8e758c4cb4fd 100644
--- a/drivers/gpu/drm/nouveau/nouveau_debugfs.c
+++ b/drivers/gpu/drm/nouveau/nouveau_debugfs.c
@@ -50,13 +50,15 @@ static int
 nouveau_debugfs_pstate_get(struct seq_file *m, void *data)
 {
 	struct drm_device *drm = m->private;
-	struct nouveau_debugfs *debugfs = nouveau_debugfs(drm);
-	struct nvif_object *ctrl = &debugfs->ctrl;
+	struct nouveau_debugfs *debugfs;
+	struct nvif_object *ctrl;
 	struct nvif_control_pstate_info_v0 info = {};
 	int ret, i;
 
-	if (!debugfs)
+	if (!drm)
 		return -ENODEV;
+	debugfs = nouveau_debugfs(drm);
+	ctrl = &debugfs->ctrl;
 
 	ret = nvif_mthd(ctrl, NVIF_CONTROL_PSTATE_INFO, &info, sizeof(info));
 	if (ret)
-- 
2.17.1