CVE-2026-23371

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

sched/deadline: Fix missing ENQUEUE_REPLENISH during PI de-boosting

Running stress-ng --schedpolicy 0 on an RT kernel on a big machine

might lead to the following WARNINGs (edited).

sched: DL de-boosted task PID 22725: REPLENISH flag missing

WARNING: CPU: 93 PID: 0 at kernel/sched/deadline.c:239 dequeue_task_dl+0x15c/0x1f8

... (running_bw underflow)

Call trace:

dequeue_task_dl+0x15c/0x1f8 (P)

dequeue_task+0x80/0x168

deactivate_task+0x24/0x50

push_dl_task+0x264/0x2e0

dl_task_timer+0x1b0/0x228

__hrtimer_run_queues+0x188/0x378

hrtimer_interrupt+0xfc/0x260

...

The problem is that when a SCHED_DEADLINE task (lock holder) is

changed to a lower priority class via sched_setscheduler(), it may

fail to properly inherit the parameters of potential DEADLINE donors

if it didn't already inherit them in the past (shorter deadline than

donor's at that time). This might lead to bandwidth accounting

corruption, as enqueue_task_dl() won't recognize the lock holder as

boosted.

The scenario occurs when:

1. A DEADLINE task (donor) blocks on a PI mutex held by another

DEADLINE task (holder), but the holder doesn't inherit parameters

(e.g., it already has a shorter deadline)

2. sched_setscheduler() changes the holder from DEADLINE to a lower

class while still holding the mutex

3. The holder should now inherit DEADLINE parameters from the donor

and be enqueued with ENQUEUE_REPLENISH, but this doesn't happen

Fix the issue by introducing __setscheduler_dl_pi(), which detects when

a DEADLINE (proper or boosted) task gets setscheduled to a lower

priority class. In case, the function makes the task inherit DEADLINE

parameters of the donoer (pi_se) and sets ENQUEUE_REPLENISH flag to

ensure proper bandwidth accounting during the next enqueue operation.