[PATCH v3] drm/nouveau: Fix potential memory access error in debugfs_pstate_get/set()

[Lyude Paul]

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@xxxxxxxxxx>
Cc: Karol Herbst <karolherbst@xxxxxxxxx>
---
Changes since v2:
 - Also fix nouveau_debugfs_pstate_set()

 drivers/gpu/drm/nouveau/nouveau_debugfs.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_debugfs.c b/drivers/gpu/drm/nouveau/nouveau_debugfs.c
index 963a4dba8213..b7440b542cb2 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)
@@ -121,14 +123,16 @@ nouveau_debugfs_pstate_set(struct file *file, const char __user *ubuf,
 {
 	struct seq_file *m = file->private_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_user_v0 args = { .pwrsrc = -EINVAL };
 	char buf[32] = {}, *tmp, *cur = buf;
 	long value, ret;
 
-	if (!debugfs)
+	if (!drm)
 		return -ENODEV;
+	debugfs = nouveau_debugfs(drm);
+	ctrl = &debugfs->ctrl;
 
 	if (len >= sizeof(buf))
 		return -EINVAL;
-- 
2.17.1