Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   zys.zljxml@gmail.com
To:     tj@kernel.org, gregkh@linuxfoundation.org, viro@zeniv.linux.org.uk
Cc:     linux-kernel@vger.kernel.org, katrinzhou <katrinzhou@tencent.com>
Subject: [PATCH] kernfs: fix potential NULL dereference in __kernfs_remove
Date:   Thu, 30 Jun 2022 12:00:47 +0800
Message-Id: <20220630040047.3241781-1-zys.zljxml@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: katrinzhou <katrinzhou@tencent.com>

When lockdep is enabled, lockdep_assert_held_write would
cause potential NULL pointer dereference.

Fix the folloeing smatch warnings:

fs/kernfs/dir.c:1353 __kernfs_remove() warn: variable dereferenced before check 'kn' (see line 1346)

Signed-off-by: katrinzhou <katrinzhou@tencent.com>
---
 fs/kernfs/dir.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 6eca72cfa1f2..1cc88ba6de90 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1343,14 +1343,17 @@ static void __kernfs_remove(struct kernfs_node *kn)
 {
 	struct kernfs_node *pos;
 
+	/* Short-circuit if non-root @kn has already finished removal. */
+	if (!kn)
+		return;
+
 	lockdep_assert_held_write(&kernfs_root(kn)->kernfs_rwsem);
 
 	/*
-	 * Short-circuit if non-root @kn has already finished removal.
 	 * This is for kernfs_remove_self() which plays with active ref
 	 * after removal.
 	 */
-	if (!kn || (kn->parent && RB_EMPTY_NODE(&kn->rb)))
+	if (kn->parent && RB_EMPTY_NODE(&kn->rb))
 		return;
 
 	pr_debug("kernfs %s: removing\n", kn->name);
-- 
2.27.0