[PATCH 6.18 106/333] sched_ext: Remove redundant css_put() in scx_cgroup_init()

Greg Kroah-Hartman
2026-03-17T17:14:59Z

From: Cheng-Yang Chou <yphbchou0911@gmail.com>

commit 1336b579f6079fb8520be03624fcd9ba443c930b upstream.

The iterator css_for_each_descendant_pre() walks the cgroup hierarchy
under cgroup_lock(). It does not increment the reference counts on
yielded css structs.

According to the cgroup documentation, css_put() should only be used
to release a reference obtained via css_get() or css_tryget_online().
Since the iterator does not use either of these to acquire a reference,
calling css_put() in the error path of scx_cgroup_init() causes a
refcount underflow.

Remove the unbalanced css_put() to prevent a potential Use-After-Free
(UAF) vulnerability.

Fixes: 819513666966 ("sched_ext: Add cgroup support")
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/sched/ext.c | 1 -
1 file changed, 1 deletion(-)

--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3450,7 +3450,6 @@ static int scx_cgroup_init(struct scx_sc
ret = SCX_CALL_OP_RET(sch, SCX_KF_UNLOCKED, cgroup_init, NULL,
css->cgroup, &args);
if (ret) {
- css_put(css);
scx_error(sch, "ops.cgroup_init() failed (%d)", ret);
return ret;
}