linux-cve-announce - CVE-2022-50344: ext4: fix null-ptr-deref in ext4_write

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Message-ID: <2025091639-CVE-2022-50344-8893@gregkh>
Date: Tue, 16 Sep 2025 18:11:40 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2022-50344: ext4: fix null-ptr-deref in ext4_write_info

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

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

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

ext4: fix null-ptr-deref in ext4_write_info

I caught a null-ptr-deref bug as follows:
==================================================================
KASAN: null-ptr-deref in range [0x0000000000000068-0x000000000000006f]
CPU: 1 PID: 1589 Comm: umount Not tainted 5.10.0-02219-dirty #339
RIP: 0010:ext4_write_info+0x53/0x1b0
[...]
Call Trace:
 dquot_writeback_dquots+0x341/0x9a0
 ext4_sync_fs+0x19e/0x800
 __sync_filesystem+0x83/0x100
 sync_filesystem+0x89/0xf0
 generic_shutdown_super+0x79/0x3e0
 kill_block_super+0xa1/0x110
 deactivate_locked_super+0xac/0x130
 deactivate_super+0xb6/0xd0
 cleanup_mnt+0x289/0x400
 __cleanup_mnt+0x16/0x20
 task_work_run+0x11c/0x1c0
 exit_to_user_mode_prepare+0x203/0x210
 syscall_exit_to_user_mode+0x5b/0x3a0
 do_syscall_64+0x59/0x70
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
 ==================================================================

Above issue may happen as follows:
-------------------------------------
exit_to_user_mode_prepare
 task_work_run
  __cleanup_mnt
   cleanup_mnt
    deactivate_super
     deactivate_locked_super
      kill_block_super
       generic_shutdown_super
        shrink_dcache_for_umount
         dentry = sb->s_root
         sb->s_root = NULL              <--- Here set NULL
        sync_filesystem
         __sync_filesystem
          sb->s_op->sync_fs > ext4_sync_fs
           dquot_writeback_dquots
            sb->dq_op->write_info > ext4_write_info
             ext4_journal_start(d_inode(sb->s_root), EXT4_HT_QUOTA, 2)
              d_inode(sb->s_root)
               s_root->d_inode          <--- Null pointer dereference

To solve this problem, we use ext4_journal_start_sb directly
to avoid s_root being used.

The Linux kernel CVE team has assigned CVE-2022-50344 to this issue.


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

	Fixed in 4.9.331 with commit dc451578446afd03c0c21913993c08898a691435
	Fixed in 4.14.296 with commit f4b5ff0b794aa94afac7269c494550ca2f66511b
	Fixed in 4.19.262 with commit 947264e00c46de19a016fd81218118c708fed2f3
	Fixed in 5.4.220 with commit 3638aa1c7d87c0ca0aef23cf58cae2c48e7daca4
	Fixed in 5.10.150 with commit f34ab95162763cd7352f46df169296eec28b688d
	Fixed in 5.15.75 with commit 533c60a0b97cee5daab376933f486207e6680fb7
	Fixed in 5.19.17 with commit 4a657319cfabd6199fd0b7b65bbebf6ded7a11c1
	Fixed in 6.0.3 with commit bb420e8afc854d2a1caaa23a0c129839acfb7888
	Fixed in 6.1 with commit f9c1f248607d5546075d3f731e7607d5571f2b60

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-2022-50344
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/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/dc451578446afd03c0c21913993c08898a691435
	https://git.kernel.org/stable/c/f4b5ff0b794aa94afac7269c494550ca2f66511b
	https://git.kernel.org/stable/c/947264e00c46de19a016fd81218118c708fed2f3
	https://git.kernel.org/stable/c/3638aa1c7d87c0ca0aef23cf58cae2c48e7daca4
	https://git.kernel.org/stable/c/f34ab95162763cd7352f46df169296eec28b688d
	https://git.kernel.org/stable/c/533c60a0b97cee5daab376933f486207e6680fb7
	https://git.kernel.org/stable/c/4a657319cfabd6199fd0b7b65bbebf6ded7a11c1
	https://git.kernel.org/stable/c/bb420e8afc854d2a1caaa23a0c129839acfb7888
	https://git.kernel.org/stable/c/f9c1f248607d5546075d3f731e7607d5571f2b60