linux-kernel - [PATCH AUTOSEL 6.6 209/294] kernfs: Acquire kernfs_rwsem in kernfs_get_parent

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Message-Id: <20250505225634.2688578-209-sashal@kernel.org>
Date: Mon,  5 May 2025 18:55:09 -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 6.6 209/294] kernfs: Acquire kernfs_rwsem in kernfs_get_parent_dentry().

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

[ Upstream commit 122ab92dee80582c39740609a627198dd5b6b595 ]

kernfs_get_parent_dentry() passes kernfs_node::parent to
kernfs_get_inode().

Acquire kernfs_root::kernfs_rwsem to ensure kernfs_node::parent isn't
replaced 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/20250213145023.2820193-3-bigeasy@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/kernfs/mount.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index c4bf26142eec9..5fda25dbbd256 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -147,7 +147,9 @@ static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
 static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
 {
 	struct kernfs_node *kn = kernfs_dentry_node(child);
+	struct kernfs_root *root = kernfs_root(kn);
 
+	guard(rwsem_read)(&root->kernfs_rwsem);
 	return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
 }
 
-- 
2.39.5