Subject: CVE-2024-47689: f2fs: fix to don't set SB_RDONLY in f2fs_handle_critical_error()

From: Greg Kroah-Hartman <[email-masked]>

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

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

f2fs: fix to don't set SB_RDONLY in f2fs_handle_critical_error()

syzbot reports a f2fs bug as below:

------------[ cut here ]------------
WARNING: CPU: 1 PID: 58 at kernel/rcu/sync.c:177 rcu_sync_dtor+0xcd/0x180 kernel/rcu/sync.c:177
CPU: 1 UID: 0 PID: 58 Comm: kworker/1:2 Not tainted 6.10.0-syzkaller-12562-g1722389b0d86 #0
Workqueue: events destroy_super_work
RIP: 0010:rcu_sync_dtor+0xcd/0x180 kernel/rcu/sync.c:177
Call Trace:
 percpu_free_rwsem+0x41/0x80 kernel/locking/percpu-rwsem.c:42
 destroy_super_work+0xec/0x130 fs/super.c:282
 process_one_work kernel/workqueue.c:3231 [inline]
 process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
 worker_thread+0x86d/0xd40 kernel/workqueue.c:3390
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

As Christian Brauner pointed out [1]: the root cause is f2fs sets
SB_RDONLY flag in internal function, rather than setting the flag
covered w/ sb->s_umount semaphore via remount procedure, then below
race condition causes this bug:

- freeze_super()
 - sb_wait_write(sb, SB_FREEZE_WRITE)
 - sb_wait_write(sb, SB_FREEZE_PAGEFAULT)
 - sb_wait_write(sb, SB_FREEZE_FS)
					- f2fs_handle_critical_error
					 - sb->s_flags |= SB_RDONLY
- thaw_super
 - thaw_super_locked
  - sb_rdonly() is true, so it skips
    sb_freeze_unlock(sb, SB_FREEZE_FS)
  - deactivate_locked_super

Since f2fs has almost the same logic as ext4 [2] when handling critical
error in filesystem if it mounts w/ errors=remount-ro option:
- set CP_ERROR_FLAG flag which indicates filesystem is stopped
- record errors to superblock
- set SB_RDONLY falg
Once we set CP_ERROR_FLAG flag, all writable interfaces can detect the
flag and stop any further updates on filesystem. So, it is safe to not
set SB_RDONLY flag, let's remove the logic and keep in line w/ ext4 [3].

[1] https://lore.kernel.org/all/20240729-himbeeren-funknetz-96e62f9c7aee@brauner
[2] https://lore.kernel.org/all/20240729132721.hxih6ehigadqf7wx@quack3
[3] https://lore.kernel.org/linux-ext4/[email-masked]

The Linux kernel CVE team has assigned CVE-2024-47689 to this issue.

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

	Issue introduced in 6.5 with commit b62e71be2110 and fixed in 6.6.54 with commit 649ec8b30df1
	Issue introduced in 6.5 with commit b62e71be2110 and fixed in 6.10.13 with commit de43021c7299
	Issue introduced in 6.5 with commit b62e71be2110 and fixed in 6.11.2 with commit 1f63f405c1a1
	Issue introduced in 6.5 with commit b62e71be2110 and fixed in 6.12-rc1 with commit 930c6ab93492
	Issue introduced in 6.4.4 with commit ed1d478bf838

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-2024-47689
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/super.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/649ec8b30df113042588bd3d3cd4e98bcb1091e0
	https://git.kernel.org/stable/c/de43021c72993877a8f86f9fddfa0687609da5a4
	https://git.kernel.org/stable/c/1f63f405c1a1a64b9c310388aad7055fb86b245c
	https://git.kernel.org/stable/c/930c6ab93492c4b15436524e704950b364b2930c