[PATCH] md: fix the problem that the pointer may be double free

[zhangyue]

int driver/md/md.c, if the function autorun_array() is called,
the problem of double free may occur.

in function autorun_array(), when the function do_md_run() returns an
error, the function do_md_stop() will be called.

The function do_md_run() called function md_run(), but in function
md_run(), the pointer mddev->private may be freed.

The function do_md_stop() called the function __md_stop(), but in
function __md_stop(), the pointer mddev->private also will be freed
without judging null.

At this time, the pointer mddev->private will be double free, so it
needs to be judged null or not.

Signed-off-by: zhangyue <zhangyue1@xxxxxxxxxx>
---
 drivers/md/md.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index f16f190546ef..07c9071578d4 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -6307,7 +6307,8 @@ static void __md_stop(struct mddev *mddev)
 	spin_lock(&mddev->lock);
 	mddev->pers = NULL;
 	spin_unlock(&mddev->lock);
-	pers->free(mddev, mddev->private);
+	if (mddev->private)
+		pers->free(mddev, mddev->private);
 	mddev->private = NULL;
 	if (pers->sync_request && mddev->to_remove == NULL)
 		mddev->to_remove = &md_redundancy_group;
-- 
2.30.0