linux-cve-announce - CVE-2025-40258: mptcp: fix race condition in mptcp_schedule

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Message-ID: <2025120433-CVE-2025-40258-d10d@gregkh>
Date: Thu,  4 Dec 2025 16:57:39 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40258: mptcp: fix race condition in mptcp_schedule_work()

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

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

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

mptcp: fix race condition in mptcp_schedule_work()

syzbot reported use-after-free in mptcp_schedule_work() [1]

Issue here is that mptcp_schedule_work() schedules a work,
then gets a refcount on sk->sk_refcnt if the work was scheduled.
This refcount will be released by mptcp_worker().

[A] if (schedule_work(...)) {
[B]     sock_hold(sk);
        return true;
    }

Problem is that mptcp_worker() can run immediately and complete before [B]

We need instead :

    sock_hold(sk);
    if (schedule_work(...))
        return true;
    sock_put(sk);

[1]
refcount_t: addition on 0; use-after-free.
 WARNING: CPU: 1 PID: 29 at lib/refcount.c:25 refcount_warn_saturate+0xfa/0x1d0 lib/refcount.c:25
Call Trace:
 <TASK>
 __refcount_add include/linux/refcount.h:-1 [inline]
  __refcount_inc include/linux/refcount.h:366 [inline]
  refcount_inc include/linux/refcount.h:383 [inline]
  sock_hold include/net/sock.h:816 [inline]
  mptcp_schedule_work+0x164/0x1a0 net/mptcp/protocol.c:943
  mptcp_tout_timer+0x21/0xa0 net/mptcp/protocol.c:2316
  call_timer_fn+0x17e/0x5f0 kernel/time/timer.c:1747
  expire_timers kernel/time/timer.c:1798 [inline]
  __run_timers kernel/time/timer.c:2372 [inline]
  __run_timer_base+0x648/0x970 kernel/time/timer.c:2384
  run_timer_base kernel/time/timer.c:2393 [inline]
  run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2403
  handle_softirqs+0x22f/0x710 kernel/softirq.c:622
  __do_softirq kernel/softirq.c:656 [inline]
  run_ktimerd+0xcf/0x190 kernel/softirq.c:1138
  smpboot_thread_fn+0x542/0xa60 kernel/smpboot.c:160
  kthread+0x711/0x8a0 kernel/kthread.c:463
  ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The Linux kernel CVE team has assigned CVE-2025-40258 to this issue.

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

	Issue introduced in 5.7 with commit 3b1d6210a9577369103330b0d802b0bf74b65e7f and fixed in 6.6.118 with commit 8f9ba1a99a89feef9b5867c15a0141a97e893309
	Issue introduced in 5.7 with commit 3b1d6210a9577369103330b0d802b0bf74b65e7f and fixed in 6.12.60 with commit ac28dfddedf6f209190950fc71bcff65ec4ab47b
	Issue introduced in 5.7 with commit 3b1d6210a9577369103330b0d802b0bf74b65e7f and fixed in 6.17.10 with commit 3fc7723ed01d1130d4bf7063c50e0af60ecccbb4
	Issue introduced in 5.7 with commit 3b1d6210a9577369103330b0d802b0bf74b65e7f and fixed in 6.18 with commit 035bca3f017ee9dea3a5a756e77a6f7138cc6eea

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-2025-40258
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:
	net/mptcp/protocol.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/8f9ba1a99a89feef9b5867c15a0141a97e893309
	https://git.kernel.org/stable/c/ac28dfddedf6f209190950fc71bcff65ec4ab47b
	https://git.kernel.org/stable/c/3fc7723ed01d1130d4bf7063c50e0af60ecccbb4
	https://git.kernel.org/stable/c/035bca3f017ee9dea3a5a756e77a6f7138cc6eea