Commit 1336b579 authored by Cheng-Yang Chou's avatar Cheng-Yang Chou Committed by Tejun Heo
Browse files

sched_ext: Remove redundant css_put() in scx_cgroup_init() 



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: 81951366 ("sched_ext: Add cgroup support")
Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: default avatarCheng-Yang Chou <yphbchou0911@gmail.com>
Reviewed-by: default avatarAndrea Righi <arighi@nvidia.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 75ad5182

kernel/sched/ext.c

+0 −1
Original line number Diff line number Diff line
@@ -3589,7 +3589,6 @@ static int scx_cgroup_init(struct scx_sched *sch) 
		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;

		}