linux-cve-announce - CVE-2025-40002: thunderbolt: Fix use-after-free in tb_dp_dprx

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Message-ID: <2025101828-CVE-2025-40002-a9c1@gregkh>
Date: Sat, 18 Oct 2025 10:03:28 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-40002: thunderbolt: Fix use-after-free in tb_dp_dprx_work

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

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

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

thunderbolt: Fix use-after-free in tb_dp_dprx_work

The original code relies on cancel_delayed_work() in tb_dp_dprx_stop(),
which does not ensure that the delayed work item tunnel->dprx_work has
fully completed if it was already running. This leads to use-after-free
scenarios where tb_tunnel is deallocated by tb_tunnel_put(), while
tunnel->dprx_work remains active and attempts to dereference tb_tunnel
in tb_dp_dprx_work().

A typical race condition is illustrated below:

CPU 0                            | CPU 1
tb_dp_tunnel_active()            |
  tb_deactivate_and_free_tunnel()| tb_dp_dprx_start()
    tb_tunnel_deactivate()       |   queue_delayed_work()
      tb_dp_activate()           |
        tb_dp_dprx_stop()        | tb_dp_dprx_work() //delayed worker
          cancel_delayed_work()  |
    tb_tunnel_put(tunnel);       |
                                 |   tunnel = container_of(...); //UAF
                                 |   tunnel-> //UAF

Replacing cancel_delayed_work() with cancel_delayed_work_sync() is
not feasible as it would introduce a deadlock: both tb_dp_dprx_work()
and the cleanup path acquire tb->lock, and cancel_delayed_work_sync()
would wait indefinitely for the work item that cannot proceed.

Instead, implement proper reference counting:
- If cancel_delayed_work() returns true (work is pending), we release
  the reference in the stop function.
- If it returns false (work is executing or already completed), the
  reference is released in delayed work function itself.

This ensures the tb_tunnel remains valid during work item execution
while preventing memory leaks.

This bug was found by static analysis.

The Linux kernel CVE team has assigned CVE-2025-40002 to this issue.


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

	Issue introduced in 6.14 with commit d6d458d42e1e1544a18f37f1d5c840e00d5261b9 and fixed in 6.17.3 with commit c07923f6a8729fc27ee652221a51702ff6654097
	Issue introduced in 6.14 with commit d6d458d42e1e1544a18f37f1d5c840e00d5261b9 and fixed in 6.18-rc1 with commit 67600ccfc4f38ebd331b9332ac94717bfbc87ea7

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-2025-40002
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:
	drivers/thunderbolt/tunnel.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/c07923f6a8729fc27ee652221a51702ff6654097
	https://git.kernel.org/stable/c/67600ccfc4f38ebd331b9332ac94717bfbc87ea7