Commit 880df131 authored Nov 04, 2019 by Tejun Heo

kernfs: kernfs_find_and_get_node_by_ino() should only look up activated nodes



kernfs node can be created in two separate steps - allocation and
activation.  This is used to make kernfs nodes visible only after the
internal states attached to the node are fully initialized.
kernfs_find_and_get_node_by_id() currently allows lookups of nodes
which aren't activated yet and thus can expose nodes are which are
still being prepped by kernfs users.

Fix it by disallowing lookups of nodes which aren't activated yet.

kernfs_find_and_get_node_by_ino()

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>

parent b680b081

fs/kernfs/dir.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -714,7 +714,13 @@ struct kernfs_node kernfs_find_and_get_node_by_ino(struct kernfs_root root,
		if (!kn)
		goto err_unlock;

		if (unlikely(!atomic_inc_not_zero(&kn->count)))
		/*
		* ACTIVATED is protected with kernfs_mutex but it was clear when
		* @kn was added to idr and we just wanna see it set. No need to
		* grab kernfs_mutex.
		*/
		if (unlikely(!(kn->flags & KERNFS_ACTIVATED) \|\|
		!atomic_inc_not_zero(&kn->count)))
		goto err_unlock;

		spin_unlock(&kernfs_idr_lock);

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