---
id: CVE-2026-98788
title: 'futex: Fix private hash use-after-free on resize'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  futex: Fix private hash use-after-free on resize

  poll_state_synchronize_rcu(mm->futex.phash.batches) is used by
  futex_ref_drop() to check that a grace period has passe…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 56180dd20c19e5b0fa34822997a9ac66b517e7b3 <
    5d5dc18b3a9ac011619b7d3af4514bf9e9b6a6af
  - >-
    Linux >= 56180dd20c19e5b0fa34822997a9ac66b517e7b3 <
    f35e3b5784221654f9cdbd6222275a7fa203f6c3
  - Linux 6.17
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:48:24.833Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98788'
references:
  - url: 'https://git.kernel.org/stable/c/5d5dc18b3a9ac011619b7d3af4514bf9e9b6a6af'
  - url: 'https://git.kernel.org/stable/c/f35e3b5784221654f9cdbd6222275a7fa203f6c3'
tags:
  - cve.org
ingestedAt: '2026-10-18T16:47:32.487Z'
---

## Overview

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

futex: Fix private hash use-after-free on resize

poll_state_synchronize_rcu(mm->futex.phash.batches) is used by
futex_ref_drop() to check that a grace period has passed since the
current hash was published. This relies on batches referencing a grace
period which started after the hash pointer was assigned.

__futex_pivot_hash() sets mmph->batches before it replaces mmph->hash:

    scoped_guard(rcu) {
            mmph->batches = get_state_synchronize_rcu();
            rcu_assign_pointer(mmph->hash, new);
    }

The scoped_guard(rcu) doesn't stop new grace periods from starting, and
if one starts between those two assignments, futex_ref_drop() can move
forward while a reader still holds a pointer to the old hash.

Fix things by setting mmph->batches after assigning mmph->hash.  The
scoped_guard(rcu) isn't needed, so let's drop that as well.

## Affected

- `Linux >= 56180dd20c19e5b0fa34822997a9ac66b517e7b3 < 5d5dc18b3a9ac011619b7d3af4514bf9e9b6a6af`
- `Linux >= 56180dd20c19e5b0fa34822997a9ac66b517e7b3 < f35e3b5784221654f9cdbd6222275a7fa203f6c3`
- `Linux 6.17`

## Remediation

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