---
id: CVE-2026-99040
title: 'KEYS: Fix add_key() race with keyring restriction'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  KEYS: Fix add_key() race with keyring restriction

  __key_create_or_update() snapshots keyring->restrict_link before taking
  the destination keyring's semaphore.  keyring…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <
    305f1828b871dd46bf41addeb6f11d2c162dcb25
  - >-
    Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <
    f99399b48e3edd6851fac34cd329bab9f1f33baf
  - >-
    Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <
    11516a0c402a6c1fa52254aa70d8d65fb921e59e
  - >-
    Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <
    da0b595d8e6e2dd798f6e34e09dc51a13b888514
  - >-
    Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <
    dd3ea3fcba7c75493760cdbccd35f029597e8d5e
  - Linux 4.7
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T12:21:59.288Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-99040'
references:
  - url: 'https://git.kernel.org/stable/c/305f1828b871dd46bf41addeb6f11d2c162dcb25'
  - url: 'https://git.kernel.org/stable/c/f99399b48e3edd6851fac34cd329bab9f1f33baf'
  - url: 'https://git.kernel.org/stable/c/11516a0c402a6c1fa52254aa70d8d65fb921e59e'
  - url: 'https://git.kernel.org/stable/c/da0b595d8e6e2dd798f6e34e09dc51a13b888514'
  - url: 'https://git.kernel.org/stable/c/dd3ea3fcba7c75493760cdbccd35f029597e8d5e'
tags:
  - cve.org
ingestedAt: '2026-10-23T13:24:55.529Z'
---

## Overview

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

KEYS: Fix add_key() race with keyring restriction

__key_create_or_update() snapshots keyring->restrict_link before taking
the destination keyring's semaphore.  keyring_restrict() installs a
restriction while holding that semaphore.

This allows a writer to observe no restriction, wait for the keyring
owner to install a reject-all restriction and return successfully, and
then link a key using the stale NULL snapshot.  The writer only needs
write permission on the destination keyring.

Move the restrict_link read after __key_link_lock() and
__key_link_begin().  The read and the subsequent restriction check are
then serialized with restriction installation by keyring->sem.

The race was reproduced on v7.2.8 in 19 executions where restriction
installation returned before the link completed.  All 19 linked the key
despite the reject-all restriction.  With this change, 312 executions
reached the same ordering and every add_key() call failed with -EPERM.

The issue was found by manual concurrency analysis assisted by AI-based
analysis and independently verified with a QEMU reproducer and kernel
instrumentation.

## Affected

- `Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c < 305f1828b871dd46bf41addeb6f11d2c162dcb25`
- `Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c < f99399b48e3edd6851fac34cd329bab9f1f33baf`
- `Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c < 11516a0c402a6c1fa52254aa70d8d65fb921e59e`
- `Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c < da0b595d8e6e2dd798f6e34e09dc51a13b888514`
- `Linux >= 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c < dd3ea3fcba7c75493760cdbccd35f029597e8d5e`
- `Linux 4.7`

## Remediation

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