From: Sebastian Andrzej Siewior bigeasy@linutronix.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@kernel.org Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Link: https://lore.kernel.org/r/20250213145023.2820193-5-bigeasy@linutronix.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.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 2c74b24fc22aa..6ddab75a68dd2 100644 --- a/fs/kernfs/dir.c +++ b/fs/kernfs/dir.c @@ -1846,10 +1846,10 @@ 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;