linux-cve-announce - CVE-2024-56686: ext4: fix race in buffer

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Message-ID: <2024122833-CVE-2024-56686-b432@gregkh>
Date: Sat, 28 Dec 2024 10:45:38 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-56686: ext4: fix race in buffer_head read fault injection

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

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

ext4: fix race in buffer_head read fault injection

When I enabled ext4 debug for fault injection testing, I encountered the
following warning:

  EXT4-fs error (device sda): ext4_read_inode_bitmap:201: comm fsstress:
         Cannot read inode bitmap - block_group = 8, inode_bitmap = 1051
  WARNING: CPU: 0 PID: 511 at fs/buffer.c:1181 mark_buffer_dirty+0x1b3/0x1d0

The root cause of the issue lies in the improper implementation of ext4's
buffer_head read fault injection. The actual completion of buffer_head
read and the buffer_head fault injection are not atomic, which can lead
to the uptodate flag being cleared on normally used buffer_heads in race
conditions.

[CPU0]           [CPU1]         [CPU2]
ext4_read_inode_bitmap
  ext4_read_bh()
  <bh read complete>
                 ext4_read_inode_bitmap
                   if (buffer_uptodate(bh))
                     return bh
                               jbd2_journal_commit_transaction
                                 __jbd2_journal_refile_buffer
                                   __jbd2_journal_unfile_buffer
                                     __jbd2_journal_temp_unlink_buffer
  ext4_simulate_fail_bh()
    clear_buffer_uptodate
                                      mark_buffer_dirty
                                        <report warning>
                                        WARN_ON_ONCE(!buffer_uptodate(bh))

The best approach would be to perform fault injection in the IO completion
callback function, rather than after IO completion. However, the IO
completion callback function cannot get the fault injection code in sb.

Fix it by passing the result of fault injection into the bh read function,
we simulate faults within the bh read function itself. This requires adding
an extra parameter to the bh read functions that need fault injection.

The Linux kernel CVE team has assigned CVE-2024-56686 to this issue.


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

	Issue introduced in 5.6 with commit 46f870d690fecc792a66730dcbbf0aa109f5f9ab and fixed in 6.6.64 with commit 77035e4d27e15f87ea55929c8bb8fb1970129e2f
	Issue introduced in 5.6 with commit 46f870d690fecc792a66730dcbbf0aa109f5f9ab and fixed in 6.11.11 with commit 25a5acf88fed59e060405bbb48098f4a3a2c2adc
	Issue introduced in 5.6 with commit 46f870d690fecc792a66730dcbbf0aa109f5f9ab and fixed in 6.12.2 with commit 61832ee7fa2fbd569d129379e795038abfb0d128
	Issue introduced in 5.6 with commit 46f870d690fecc792a66730dcbbf0aa109f5f9ab and fixed in 6.13-rc1 with commit 2f3d93e210b9c2866c8b3662adae427d5bf511ec

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-2024-56686
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/ext4/balloc.c
	fs/ext4/ext4.h
	fs/ext4/extents.c
	fs/ext4/ialloc.c
	fs/ext4/indirect.c
	fs/ext4/inode.c
	fs/ext4/mmp.c
	fs/ext4/move_extent.c
	fs/ext4/resize.c
	fs/ext4/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/77035e4d27e15f87ea55929c8bb8fb1970129e2f
	https://git.kernel.org/stable/c/25a5acf88fed59e060405bbb48098f4a3a2c2adc
	https://git.kernel.org/stable/c/61832ee7fa2fbd569d129379e795038abfb0d128
	https://git.kernel.org/stable/c/2f3d93e210b9c2866c8b3662adae427d5bf511ec