linux-kernel - [PATCH AUTOSEL 6.12 336/486] kernfs: Acquire kernfs_rwsem in kernfs_node

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Message-Id: <20250505223922.2682012-336-sashal@kernel.org>
Date: Mon,  5 May 2025 18:36:52 -0400
From: Sasha Levin <sashal@...nel.org>
To: linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Tejun Heo <tj@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 6.12 336/486] kernfs: Acquire kernfs_rwsem in kernfs_node_dentry().

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

[ Upstream commit 5b2fabf7fe8f745ff214ff003e6067b64f172271 ]

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>
Link: https://lore.kernel.org/r/20250213145023.2820193-4-bigeasy@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/kernfs/mount.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index 1358c21837f1a..0f6379ae258d1 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -207,6 +207,7 @@ 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);
 
@@ -216,6 +217,9 @@ 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);
-- 
2.39.5