linux-cve-announce - CVE-2025-22123: f2fs: fix to avoid accessing uninitialized curseg

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Message-ID: <2025041628-CVE-2025-22123-5ca9@gregkh>
Date: Wed, 16 Apr 2025 16:13:34 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-22123: f2fs: fix to avoid accessing uninitialized curseg

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

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

f2fs: fix to avoid accessing uninitialized curseg

syzbot reports a f2fs bug as below:

F2FS-fs (loop3): Stopped filesystem due to reason: 7
kworker/u8:7: attempt to access beyond end of device
BUG: unable to handle page fault for address: ffffed1604ea3dfa
RIP: 0010:get_ckpt_valid_blocks fs/f2fs/segment.h:361 [inline]
RIP: 0010:has_curseg_enough_space fs/f2fs/segment.h:570 [inline]
RIP: 0010:__get_secs_required fs/f2fs/segment.h:620 [inline]
RIP: 0010:has_not_enough_free_secs fs/f2fs/segment.h:633 [inline]
RIP: 0010:has_enough_free_secs+0x575/0x1660 fs/f2fs/segment.h:649
 <TASK>
 f2fs_is_checkpoint_ready fs/f2fs/segment.h:671 [inline]
 f2fs_write_inode+0x425/0x540 fs/f2fs/inode.c:791
 write_inode fs/fs-writeback.c:1525 [inline]
 __writeback_single_inode+0x708/0x10d0 fs/fs-writeback.c:1745
 writeback_sb_inodes+0x820/0x1360 fs/fs-writeback.c:1976
 wb_writeback+0x413/0xb80 fs/fs-writeback.c:2156
 wb_do_writeback fs/fs-writeback.c:2303 [inline]
 wb_workfn+0x410/0x1080 fs/fs-writeback.c:2343
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3317
 worker_thread+0x870/0xd30 kernel/workqueue.c:3398
 kthread+0x7a9/0x920 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Commit 8b10d3653735 ("f2fs: introduce FAULT_NO_SEGMENT") allows to trigger
no free segment fault in allocator, then it will update curseg->segno to
NULL_SEGNO, though, CP_ERROR_FLAG has been set, f2fs_write_inode() missed
to check the flag, and access invalid curseg->segno directly in below call
path, then resulting in panic:

- f2fs_write_inode
 - f2fs_is_checkpoint_ready
  - has_enough_free_secs
   - has_not_enough_free_secs
    - __get_secs_required
     - has_curseg_enough_space
      - get_ckpt_valid_blocks
      : access invalid curseg->segno

To avoid this issue, let's:
- check CP_ERROR_FLAG flag in prior to f2fs_is_checkpoint_ready() in
f2fs_write_inode().
- in has_curseg_enough_space(), save curseg->segno into a temp variable,
and verify its validation before use.

The Linux kernel CVE team has assigned CVE-2025-22123 to this issue.


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

	Issue introduced in 6.9 with commit 8b10d3653735e117bc1954ade80d75ad7b46b801 and fixed in 6.14.2 with commit 7f90e5d423cd2d4c74b2abb527872f335108637f
	Issue introduced in 6.9 with commit 8b10d3653735e117bc1954ade80d75ad7b46b801 and fixed in 6.15-rc1 with commit 986c50f6bca109c6cf362b4e2babcb85aba958f6

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-2025-22123
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/inode.c
	fs/f2fs/segment.h


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/7f90e5d423cd2d4c74b2abb527872f335108637f
	https://git.kernel.org/stable/c/986c50f6bca109c6cf362b4e2babcb85aba958f6