[PATCH 1/1] kernfs: fix potential null pointer dereference

[Kai-Heng Feng]

From: Peng Wang <rocking at whu.edu.cn>

BugLink: https://bugs.launchpad.net/bugs/1874221

Get root safely after kn is ensureed to be not null.

Signed-off-by: Peng Wang <rocking at whu.edu.cn>
Acked-by: Tejun Heo <tj at kernel.org>
Link: https://lore.kernel.org/r/20190708151611.13242-1-rocking@whu.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
(cherry picked from commit 2fd60da46da76948b8cc561ae8cc902209686253)
Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
---
 fs/kernfs/dir.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index a5a65de50318..c7b31e1f095b 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -430,7 +430,6 @@ struct kernfs_node *kernfs_get_active(struct kernfs_node *kn)
  */
 void kernfs_put_active(struct kernfs_node *kn)
 {
-	struct kernfs_root *root = kernfs_root(kn);
 	int v;
 
 	if (unlikely(!kn))
@@ -442,7 +441,7 @@ void kernfs_put_active(struct kernfs_node *kn)
 	if (likely(v != KN_DEACTIVATED_BIAS))
 		return;
 
-	wake_up_all(&root->deactivate_waitq);
+	wake_up_all(&kernfs_root(kn)->deactivate_waitq);
 }
 
 /**
-- 
2.17.1