linux-cve-announce - CVE-2025-39780: sched/ext: Fix invalid task state transitions on class switch

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Message-ID: <2025091149-CVE-2025-39780-a1da@gregkh>
Date: Thu, 11 Sep 2025 18:56:58 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39780: sched/ext: Fix invalid task state transitions on class switch

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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

sched/ext: Fix invalid task state transitions on class switch

When enabling a sched_ext scheduler, we may trigger invalid task state
transitions, resulting in warnings like the following (which can be
easily reproduced by running the hotplug selftest in a loop):

 sched_ext: Invalid task state transition 0 -> 3 for fish[770]
 WARNING: CPU: 18 PID: 787 at kernel/sched/ext.c:3862 scx_set_task_state+0x7c/0xc0
 ...
 RIP: 0010:scx_set_task_state+0x7c/0xc0
 ...
 Call Trace:
  <TASK>
  scx_enable_task+0x11f/0x2e0
  switching_to_scx+0x24/0x110
  scx_enable.isra.0+0xd14/0x13d0
  bpf_struct_ops_link_create+0x136/0x1a0
  __sys_bpf+0x1edd/0x2c30
  __x64_sys_bpf+0x21/0x30
  do_syscall_64+0xbb/0x370
  entry_SYSCALL_64_after_hwframe+0x77/0x7f

This happens because we skip initialization for tasks that are already
dead (with their usage counter set to zero), but we don't exclude them
during the scheduling class transition phase.

Fix this by also skipping dead tasks during class swiching, preventing
invalid task state transitions.

The Linux kernel CVE team has assigned CVE-2025-39780 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.12 with commit a8532fac7b5d27b8d62008a89593dccb6f9786ef and fixed in 6.12.44 with commit 786f6314604b34c3e7de5f733f4e08e35c448a50
	Issue introduced in 6.12 with commit a8532fac7b5d27b8d62008a89593dccb6f9786ef and fixed in 6.16.4 with commit 6a32cbe95029ebe21cc08349fd7ef2a3d32d2043
	Issue introduced in 6.12 with commit a8532fac7b5d27b8d62008a89593dccb6f9786ef and fixed in 6.17-rc3 with commit ddf7233fcab6c247379d0928d46cc316ee122229

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-39780
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	kernel/sched/ext.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/786f6314604b34c3e7de5f733f4e08e35c448a50
	https://git.kernel.org/stable/c/6a32cbe95029ebe21cc08349fd7ef2a3d32d2043
	https://git.kernel.org/stable/c/ddf7233fcab6c247379d0928d46cc316ee122229