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@linutronix.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

Hello,

On Fri, Jan 24, 2025 at 06:46:09PM +0100, Sebastian Andrzej Siewior wrote:
> @@ -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;

Maybe match the locking and unlocking order so that what's locked last is
unlocked first? Other than that,

 Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun