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@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20250213145023.2820193-4-bigeasy@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index b9b16e97bff18960da9cd9824f80e05742264a94..4a0ff08d589ca12b925495ab7e9596b4a84f8e9f 100644 (file)
--- 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);