linux-kernel - [PATCH v5 3/6] kernfs: Acquire kernfs_rwsem in kernfs_node

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Message-ID: <20250128084226.1499291-4-bigeasy@linutronix.de>
Date: Tue, 28 Jan 2025 09:42:23 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Michal Koutný <mkoutny@...e.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Hillf Danton <hdanton@...a.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Marco Elver <elver@...gle.com>,
	Tejun Heo <tj@...nel.org>,
	tglx@...utronix.de,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH v5 3/6] kernfs: Acquire kernfs_rwsem in kernfs_node_dentry().

kernfs_node_dentry() passes kernfs_node::name to
lookup_positive_unlocked().

Acquire kernfs_root::kernfs_rwsem to ensure the node is not renamed
during the operation.

Acked-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 fs/kernfs/mount.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index b9b16e97bff18..4a0ff08d589ca 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -209,6 +209,7 @@ struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 {
 	struct dentry *dentry;
 	struct kernfs_node *knparent;
+	struct kernfs_root *root;
 
 	BUG_ON(sb->s_op != &kernfs_sops);
 
@@ -218,6 +219,9 @@ struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 	if (!kn->parent)
 		return dentry;
 
+	root = kernfs_root(kn);
+	guard(rwsem_read)(&root->kernfs_rwsem);
+
 	knparent = find_next_ancestor(kn, NULL);
 	if (WARN_ON(!knparent)) {
 		dput(dentry);
-- 
2.47.2