CVE-2025-21771

/// Technical description

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

sched_ext: Fix incorrect autogroup migration detection

scx_move_task() is called from sched_move_task() and tells the BPF scheduler

that cgroup migration is being committed. sched_move_task() is used by both

cgroup and autogroup migrations and scx_move_task() tried to filter out

autogroup migrations by testing the destination cgroup and PF_EXITING but

this is not enough. In fact, without explicitly tagging the thread which is

doing the cgroup migration, there is no good way to tell apart

scx_move_task() invocations for racing migration to the root cgroup and an

autogroup migration.

This led to scx_move_task() incorrectly ignoring a migration from non-root

cgroup to an autogroup of the root cgroup triggering the following warning:

WARNING: CPU: 7 PID: 1 at kernel/sched/ext.c:3725 scx_cgroup_can_attach+0x196/0x340

...

Call Trace:

<TASK>

cgroup_migrate_execute+0x5b1/0x700

cgroup_attach_task+0x296/0x400

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References