CVE-2026-53328

Summary

In the Linux kernel, the following vulnerability has been resolved:

sched_ext: Don't warn on NULL cgrp_moving_from in scx_cgroup_move_task()

A WARN fires when systemd's user manager writes "+cpu +memory +pids" to its own subtree_control while a sched_ext scheduler is loaded:

WARNING: at kernel/sched/ext.c:3227 scx_cgroup_move_task+0xa8/0xb0 scx_cgroup_move_task+0xa8/0xb0 sched_move_task+0x134/0x290 cpu_cgroup_attach+0x39/0x70 cgroup_migrate_execute+0x37d/0x450 cgroup_update_dfl_csses+0x1e3/0x270 cgroup_subtree_control_write+0x3e7/0x440

scx_cgroup_can_attach() arms cgrp_moving_from only when a task's cpu cgroup changes. It can still be NULL when scx_cgroup_move_task() runs, through this sequence:

Step Result

1. cpu enabled on cgroup G cpu css = A
2. cpu toggled off then on for G A killed, B created (same cgroup)
3. an exiting task keeps A alive migration skips it, A now stale
4. +memory migrates G stale A vs current B pulls cpu in
5. cpu attach runs for all tasks hits a live, cpu-unchanged task
6. scx_cgroup_move_task() on it cgrp_moving_from NULL -> WARN

The mismatch is that scx_cgroup_can_attach() keys on cgroup identity while migration drives the move on css identity, so a NULL cgrp_moving_from here is a legitimate css-only migration, not a missing prep.

The call is already gated on cgrp_moving_from, so just drop the warning. ops.cgroup_prep_move() and ops.cgroup_move() stay paired.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/cdff2eb97be147d2ce52ac1327841068781f25dc
• https://git.kernel.org/stable/c/0ffcad63b19a1cadb475c9f405a93607fdcd0d7c
• https://git.kernel.org/stable/c/bc75f5951fac4e49d175c4433fc08fb1ec01172f
• https://git.kernel.org/stable/c/02e545c4297a26dbbc41df81b831e7f605bcd306

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