linux-cve-announce - CVE-2025-68240: nilfs2: avoid having an active sc

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Message-ID: <2025121632-CVE-2025-68240-03ff@gregkh>
Date: Tue, 16 Dec 2025 15:21:32 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-68240: nilfs2: avoid having an active sc_timer before freeing sci

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

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

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

nilfs2: avoid having an active sc_timer before freeing sci

Because kthread_stop did not stop sc_task properly and returned -EINTR,
the sc_timer was not properly closed, ultimately causing the problem [1]
reported by syzbot when freeing sci due to the sc_timer not being closed.

Because the thread sc_task main function nilfs_segctor_thread() returns 0
when it succeeds, when the return value of kthread_stop() is not 0 in
nilfs_segctor_destroy(), we believe that it has not properly closed
sc_timer.

We use timer_shutdown_sync() to sync wait for sc_timer to shutdown, and
set the value of sc_task to NULL under the protection of lock
sc_state_lock, so as to avoid the issue caused by sc_timer not being
properly shutdowned.

[1]
ODEBUG: free active (active state 0) object: 00000000dacb411a object type: timer_list hint: nilfs_construction_timeout
Call trace:
 nilfs_segctor_destroy fs/nilfs2/segment.c:2811 [inline]
 nilfs_detach_log_writer+0x668/0x8cc fs/nilfs2/segment.c:2877
 nilfs_put_super+0x4c/0x12c fs/nilfs2/super.c:509

The Linux kernel CVE team has assigned CVE-2025-68240 to this issue.


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

	Issue introduced in 6.12 with commit 3f66cc261ccb54a8e4d8d5aa51c389c19453b00c and fixed in 6.12.59 with commit 36049e81dc7f077e0e24d5b9688a7458beacef8f
	Issue introduced in 6.12 with commit 3f66cc261ccb54a8e4d8d5aa51c389c19453b00c and fixed in 6.17.9 with commit 2f65799e2a736d556d306440c4e1e8906736117a
	Issue introduced in 6.12 with commit 3f66cc261ccb54a8e4d8d5aa51c389c19453b00c and fixed in 6.18 with commit 9a6b60cb147d53968753a34805211d2e5e08c027

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-2025-68240
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:
	fs/nilfs2/segment.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/36049e81dc7f077e0e24d5b9688a7458beacef8f
	https://git.kernel.org/stable/c/2f65799e2a736d556d306440c4e1e8906736117a
	https://git.kernel.org/stable/c/9a6b60cb147d53968753a34805211d2e5e08c027