---
id: CVE-2024-49885
title: 'mm, slub: avoid zeroing kmalloc redzone'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  mm, slub: avoid zeroing kmalloc redzone

  Since commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra
  allocated kmalloc space than requested"), setting orig_size …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 946fa0dbf2d8923a587f7348adf16563d59f1b3d <
    7299868253c0e8ba9bf31f6e5198e8eafa1e700b
  - >-
    Linux >= 946fa0dbf2d8923a587f7348adf16563d59f1b3d <
    7a2e823a19746d54052c625faecf0d2d6c52ee0a
  - >-
    Linux >= 946fa0dbf2d8923a587f7348adf16563d59f1b3d <
    83f0440b2f92227fcce9898118ca7fe7e0d64b1f
  - >-
    Linux >= 946fa0dbf2d8923a587f7348adf16563d59f1b3d <
    59090e479ac78ae18facd4c58eb332562a23020e
  - Linux 6.2
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2024-10-22T13:45:07.682094Z'
published: '2024-10-21'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T12:35:18.866Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2024-49885'
references:
  - url: 'https://git.kernel.org/stable/c/7299868253c0e8ba9bf31f6e5198e8eafa1e700b'
  - url: 'https://git.kernel.org/stable/c/7a2e823a19746d54052c625faecf0d2d6c52ee0a'
  - url: 'https://git.kernel.org/stable/c/83f0440b2f92227fcce9898118ca7fe7e0d64b1f'
  - url: 'https://git.kernel.org/stable/c/59090e479ac78ae18facd4c58eb332562a23020e'
tags:
  - cve.org
epss: 0.00282
epssPercentile: 0.20599
ingestedAt: '2026-10-21T12:48:53.730Z'
---

## Overview

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

mm, slub: avoid zeroing kmalloc redzone

Since commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra
allocated kmalloc space than requested"), setting orig_size treats
the wasted space (object_size - orig_size) as a redzone. However with
init_on_free=1 we clear the full object->size, including the redzone.

Additionally we clear the object metadata, including the stored orig_size,
making it zero, which makes check_object() treat the whole object as a
redzone.

These issues lead to the following BUG report with "slub_debug=FUZ
init_on_free=1":

[    0.000000] =============================================================================
[    0.000000] BUG kmalloc-8 (Not tainted): kmalloc Redzone overwritten
[    0.000000] -----------------------------------------------------------------------------
[    0.000000]
[    0.000000] 0xffff000010032858-0xffff00001003285f @offset=2136. First byte 0x0 instead of 0xcc
[    0.000000] FIX kmalloc-8: Restoring kmalloc Redzone 0xffff000010032858-0xffff00001003285f=0xcc
[    0.000000] Slab 0xfffffdffc0400c80 objects=36 used=23 fp=0xffff000010032a18 flags=0x3fffe0000000200(workingset|node=0|zone=0|lastcpupid=0x1ffff)
[    0.000000] Object 0xffff000010032858 @offset=2136 fp=0xffff0000100328c8
[    0.000000]
[    0.000000] Redzone  ffff000010032850: cc cc cc cc cc cc cc cc                          ........
[    0.000000] Object   ffff000010032858: cc cc cc cc cc cc cc cc                          ........
[    0.000000] Redzone  ffff000010032860: cc cc cc cc cc cc cc cc                          ........
[    0.000000] Padding  ffff0000100328b4: 00 00 00 00 00 00 00 00 00 00 00 00              ............
[    0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.11.0-rc3-next-20240814-00004-g61844c55c3f4 #144
[    0.000000] Hardware name: NXP i.MX95 19X19 board (DT)
[    0.000000] Call trace:
[    0.000000]  dump_backtrace+0x90/0xe8
[    0.000000]  show_stack+0x18/0x24
[    0.000000]  dump_stack_lvl+0x74/0x8c
[    0.000000]  dump_stack+0x18/0x24
[    0.000000]  print_trailer+0x150/0x218
[    0.000000]  check_object+0xe4/0x454
[    0.000000]  free_to_partial_list+0x2f8/0x5ec

To address the issue, use orig_size to clear the used area. And restore
the value of orig_size after clear the remaining area.

When CONFIG_SLUB_DEBUG not defined, (get_orig_size()' directly returns
s->object_size. So when using memset to init the area, the size can simply
be orig_size, as orig_size returns object_size when CONFIG_SLUB_DEBUG not
enabled. And orig_size can never be bigger than object_size.

## Affected

- `Linux >= 946fa0dbf2d8923a587f7348adf16563d59f1b3d < 7299868253c0e8ba9bf31f6e5198e8eafa1e700b`
- `Linux >= 946fa0dbf2d8923a587f7348adf16563d59f1b3d < 7a2e823a19746d54052c625faecf0d2d6c52ee0a`
- `Linux >= 946fa0dbf2d8923a587f7348adf16563d59f1b3d < 83f0440b2f92227fcce9898118ca7fe7e0d64b1f`
- `Linux >= 946fa0dbf2d8923a587f7348adf16563d59f1b3d < 59090e479ac78ae18facd4c58eb332562a23020e`
- `Linux 6.2`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.