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Message-Id: <20250505225634.2688578-208-sashal@kernel.org>
Date: Mon, 5 May 2025 18:55:08 -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 6.6 208/294] kernfs: Don't re-lock kernfs_root::kernfs_rwsem in kernfs_fop_readdir().
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
[ Upstream commit 9aab10a0249eab4ec77c6a5e4f66442610c12a09 ]
The readdir operation iterates over all entries and invokes dir_emit()
for every entry passing kernfs_node::name as argument.
Since the name argument can change, and become invalid, the
kernfs_root::kernfs_rwsem lock should not be dropped to prevent renames
during the operation.
The lock drop around dir_emit() has been initially introduced in commit
1e5289c97bba2 ("sysfs: Cache the last sysfs_dirent to improve readdir scalability v2")
to avoid holding a global lock during a page fault. The lock drop is
wrong since the support of renames and not a big burden since the lock
is no longer global.
Don't re-acquire kernfs_root::kernfs_rwsem while copying the name to the
userpace buffer.
Acked-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Link: https://lore.kernel.org/r/20250213145023.2820193-5-bigeasy@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
fs/kernfs/dir.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index b068ed32d7b32..60ea525dd205f 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1868,10 +1868,10 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
file->private_data = pos;
kernfs_get(pos);
- up_read(&root->kernfs_rwsem);
- if (!dir_emit(ctx, name, len, ino, type))
+ if (!dir_emit(ctx, name, len, ino, type)) {
+ up_read(&root->kernfs_rwsem);
return 0;
- down_read(&root->kernfs_rwsem);
+ }
}
up_read(&root->kernfs_rwsem);
file->private_data = NULL;
--
2.39.5
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