linux-kernel - [PATCH] kernfs: fix potential null pointer dereference

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Message-Id: <20190705134730.20833-1-rocking@whu.edu.cn>
Date:   Fri,  5 Jul 2019 21:47:30 +0800
From:   Peng Wang <rocking@....edu.cn>
To:     gregkh@...uxfoundation.org, tj@...nel.org
Cc:     linux-kernel@...r.kernel.org, Peng Wang <rocking@....edu.cn>
Subject: [PATCH] kernfs: fix potential null pointer dereference

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

Signed-off-by: Peng Wang <rocking@....edu.cn>
---
 fs/kernfs/dir.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index a387534c9577..ea3fc972c48b 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -430,7 +430,7 @@ 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);
+	struct kernfs_root *root;
 	int v;
 
 	if (unlikely(!kn))
@@ -442,6 +442,7 @@ void kernfs_put_active(struct kernfs_node *kn)
 	if (likely(v != KN_DEACTIVATED_BIAS))
 		return;
 
+	root = kernfs_root(kn);
 	wake_up_all(&root->deactivate_waitq);
 }
 
-- 
2.19.1