linux-cve-announce - CVE-2022-50620: f2fs: fix to invalidate dcc->f2fs_issue

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Message-ID: <2025120852-CVE-2022-50620-bf1f@gregkh>
Date: Mon,  8 Dec 2025 10:16:57 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2022-50620: f2fs: fix to invalidate dcc->f2fs_issue_discard in error path

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

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

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

f2fs: fix to invalidate dcc->f2fs_issue_discard in error path

Syzbot reports a NULL pointer dereference issue as below:

 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 get_task_struct include/linux/sched/task.h:110 [inline]
 kthread_stop+0x34/0x1c0 kernel/kthread.c:703
 f2fs_stop_discard_thread+0x3c/0x5c fs/f2fs/segment.c:1638
 kill_f2fs_super+0x5c/0x194 fs/f2fs/super.c:4522
 deactivate_locked_super+0x70/0xe8 fs/super.c:332
 deactivate_super+0xd0/0xd4 fs/super.c:363
 cleanup_mnt+0x1f8/0x234 fs/namespace.c:1186
 __cleanup_mnt+0x20/0x30 fs/namespace.c:1193
 task_work_run+0xc4/0x14c kernel/task_work.c:177
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0x26c/0xbe0 kernel/exit.c:795
 do_group_exit+0x60/0xe8 kernel/exit.c:925
 __do_sys_exit_group kernel/exit.c:936 [inline]
 __se_sys_exit_group kernel/exit.c:934 [inline]
 __wake_up_parent+0x0/0x40 kernel/exit.c:934
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
 el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
 el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

The root cause of this issue is in error path of f2fs_start_discard_thread(),
it missed to invalidate dcc->f2fs_issue_discard, later kthread_stop() may
access invalid pointer.

The Linux kernel CVE team has assigned CVE-2022-50620 to this issue.


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

	Issue introduced in 5.15 with commit 4d67490498acb4ffcef5ba7bc44990d46e66a44c and fixed in 5.15.86 with commit 865bb7b5a7deeb0e5afbd82381d52d38825dc64d
	Issue introduced in 5.15 with commit 4d67490498acb4ffcef5ba7bc44990d46e66a44c and fixed in 6.0.16 with commit a3e517a6ba695d683ee63615e1ea6e6b4c7d2732
	Issue introduced in 5.15 with commit 4d67490498acb4ffcef5ba7bc44990d46e66a44c and fixed in 6.1.2 with commit ae6c960a82c52c3bda5adc82d90643d6c12d308e
	Issue introduced in 5.15 with commit 4d67490498acb4ffcef5ba7bc44990d46e66a44c and fixed in 6.2 with commit 91586ce0d39a05f88795aa8814fb99b1387236b3

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-2022-50620
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/f2fs/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/865bb7b5a7deeb0e5afbd82381d52d38825dc64d
	https://git.kernel.org/stable/c/a3e517a6ba695d683ee63615e1ea6e6b4c7d2732
	https://git.kernel.org/stable/c/ae6c960a82c52c3bda5adc82d90643d6c12d308e
	https://git.kernel.org/stable/c/91586ce0d39a05f88795aa8814fb99b1387236b3