[PATCH 5.10 512/575] drm/nouveau/svm: Fix refcount leak bug and missing check against null bug

[Greg Kroah-Hartman]

From: Chenyuan Mi <cymi20@xxxxxxxxxxxx>

[ Upstream commit 6bb8c2d51811eb5e6504f49efe3b089d026009d2 ]

The reference counting issue happens in one exception handling path of
nouveau_svmm_bind(). When cli->svm.svmm is null, the function forgets
to decrease the refcount of mm increased by get_task_mm(), causing a
refcount leak.

Fix this issue by using mmput() to decrease the refcount in the
exception handling path.

Also, the function forgets to do check against null when get mm
by get_task_mm().

Fix this issue by adding null check after get mm by get_task_mm().

Signed-off-by: Chenyuan Mi <cymi20@xxxxxxxxxxxx>
Signed-off-by: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>
Signed-off-by: Xin Tan <tanxin.ctf@xxxxxxxxx>
Fixes: 822cab6150d3 ("drm/nouveau/svm: check for SVM initialized before migrating")
Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx>
Reviewed-by: Ben Skeggs <bskeggs@xxxxxxxxxx>
Reviewed-by: Karol Herbst <kherbst@xxxxxxxxxx>
Signed-off-by: Karol Herbst <kherbst@xxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20210907122633.16665-1-cymi20@xxxxxxxxxxxx
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/14
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/gpu/drm/nouveau/nouveau_svm.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
index 1c3f890377d2c..f67700c028c75 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -156,10 +156,14 @@ nouveau_svmm_bind(struct drm_device *dev, void *data,
 	 */
 
 	mm = get_task_mm(current);
+	if (!mm) {
+		return -EINVAL;
+	}
 	mmap_read_lock(mm);
 
 	if (!cli->svm.svmm) {
 		mmap_read_unlock(mm);
+		mmput(mm);
 		return -EINVAL;
 	}
 
-- 
2.33.0