---
id: CVE-2024-42305
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: check dot and dotdot of dx_root before making dir indexed

  Syzbot reports a issue as follows:
  ============================================
  BUG: unable to handle p…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: check dot and dotdot of dx_root before making dir indexed

  Syzbot reports a issue as follows:
  ============================================
  BUG: unable to handle p…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-125
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 2.6.20, < 4.19.320'
  - 'linux_kernel >= 4.20, < 5.4.282'
  - 'linux_kernel >= 5.5, < 5.10.224'
  - 'linux_kernel >= 5.11, < 5.15.165'
  - 'linux_kernel >= 5.16, < 6.1.103'
  - 'linux_kernel >= 6.2, < 6.6.44'
  - 'linux_kernel >= 6.7, < 6.10.3'
  - linux_kernel = 2.6.19
patched:
  - linux_kernel 6.10.3
published: '2024-08-17'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T01:18:46.367'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2024-42305'
references:
  - url: 'https://git.kernel.org/stable/c/19e13b4d7f0303186fcc891aba8d0de7c8fdbda8'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/42d420517072028fb0eb852c358056b7717ba5aa'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/50ea741def587a64e08879ce6c6a30131f7111e7'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8afe06ed3be7a874b3cd82ef5f8959aca8d6429a'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9d241b7a39af192d1bb422714a458982c7cc67a2'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/abb411ac991810c0bcbe51c2e76d2502bf611b5c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b80575ffa98b5bb3a5d4d392bfe4c2e03e9557db'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/cdd345321699042ece4a9d2e70754d2397d378c5'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://lists.debian.org/debian-lts-announce/2024/10/msg00003.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-265688.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00226
epssPercentile: 0.13256
ingestedAt: '2026-10-15T03:30:12.733Z'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2024-09-10T16:10:19.161352Z'
---

## Overview

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

ext4: check dot and dotdot of dx_root before making dir indexed

Syzbot reports a issue as follows:
============================================
BUG: unable to handle page fault for address: ffffed11022e24fe
PGD 23ffee067 P4D 23ffee067 PUD 0
Oops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 0 PID: 5079 Comm: syz-executor306 Not tainted 6.10.0-rc5-g55027e689933 #0
Call Trace:
 <TASK>
 make_indexed_dir+0xdaf/0x13c0 fs/ext4/namei.c:2341
 ext4_add_entry+0x222a/0x25d0 fs/ext4/namei.c:2451
 ext4_rename fs/ext4/namei.c:3936 [inline]
 ext4_rename2+0x26e5/0x4370 fs/ext4/namei.c:4214
[...]
============================================

The immediate cause of this problem is that there is only one valid dentry
for the block to be split during do_split, so split==0 results in out of
bounds accesses to the map triggering the issue.

    do_split
      unsigned split
      dx_make_map
       count = 1
      split = count/2 = 0;
      continued = hash2 == map[split - 1].hash;
       ---> map[4294967295]

The maximum length of a filename is 255 and the minimum block size is 1024,
so it is always guaranteed that the number of entries is greater than or
equal to 2 when do_split() is called.

But syzbot's crafted image has no dot and dotdot in dir, and the dentry
distribution in dirblock is as follows:

  bus     dentry1          hole           dentry2           free
|xx--|xx-------------|...............|xx-------------|...............|
0   12 (8+248)=256  268     256     524 (8+256)=264 788     236     1024

So when renaming dentry1 increases its name_len length by 1, neither hole
nor free is sufficient to hold the new dentry, and make_indexed_dir() is
called.

In make_indexed_dir() it is assumed that the first two entries of the
dirblock must be dot and dotdot, so bus and dentry1 are left in dx_root
because they are treated as dot and dotdot, and only dentry2 is moved
to the new leaf block. That's why count is equal to 1.

Therefore add the ext4_check_dx_root() helper function to add more sanity
checks to dot and dotdot before starting the conversion to avoid the above
issue.

## Affected

- `linux_kernel >= 2.6.20, < 4.19.320`
- `linux_kernel >= 4.20, < 5.4.282`
- `linux_kernel >= 5.5, < 5.10.224`
- `linux_kernel >= 5.11, < 5.15.165`
- `linux_kernel >= 5.16, < 6.1.103`
- `linux_kernel >= 6.2, < 6.6.44`
- `linux_kernel >= 6.7, < 6.10.3`
- `linux_kernel = 2.6.19`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.10.3`