linux-kernel - [PATCH v4 1/6] kernfs: Acquire kernfs_rwsem in kernfs_notify

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Message-ID: <20250124174614.866884-2-bigeasy@linutronix.de>
Date: Fri, 24 Jan 2025 18:46:09 +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>,
	Zefan Li <lizefan.x@...edance.com>,
	tglx@...utronix.de,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH v4 1/6] kernfs: Acquire kernfs_rwsem in kernfs_notify_workfn().

kernfs_notify_workfn() dereferences kernfs_node::name and passes it
later to fsnotify(). If the node is renamed then the previously observed
name pointer becomes invalid.

Acquire kernfs_root::kernfs_rwsem to block renames of the node.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 fs/kernfs/file.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 8502ef68459b9..38033caeaea51 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -911,6 +911,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
 	/* kick fsnotify */
 
 	down_read(&root->kernfs_supers_rwsem);
+	down_read(&root->kernfs_rwsem);
 	list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
 		struct kernfs_node *parent;
 		struct inode *p_inode = NULL;
@@ -948,6 +949,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
 	}
 
 	up_read(&root->kernfs_supers_rwsem);
+	up_read(&root->kernfs_rwsem);
 	kernfs_put(kn);
 	goto repeat;
 }
-- 
2.47.2