GHSA-XFXP-JQFR-M4G5

Vulnerability from github – Published: 2026-10-23 15:31 – Updated: 2026-10-23 15:31
VLAI
Details

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.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-99040"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-23T13:17:27Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nKEYS: Fix add_key() race with keyring restriction\n\n__key_create_or_update() snapshots keyring-\u003erestrict_link before taking\nthe destination keyring\u0027s semaphore.  keyring_restrict() installs a\nrestriction while holding that semaphore.\n\nThis allows a writer to observe no restriction, wait for the keyring\nowner to install a reject-all restriction and return successfully, and\nthen link a key using the stale NULL snapshot.  The writer only needs\nwrite permission on the destination keyring.\n\nMove the restrict_link read after __key_link_lock() and\n__key_link_begin().  The read and the subsequent restriction check are\nthen serialized with restriction installation by keyring-\u003esem.\n\nThe race was reproduced on v7.2.8 in 19 executions where restriction\ninstallation returned before the link completed.  All 19 linked the key\ndespite the reject-all restriction.  With this change, 312 executions\nreached the same ordering and every add_key() call failed with -EPERM.\n\nThe issue was found by manual concurrency analysis assisted by AI-based\nanalysis and independently verified with a QEMU reproducer and kernel\ninstrumentation.",
  "id": "GHSA-xfxp-jqfr-m4g5",
  "modified": "2026-10-23T15:31:36Z",
  "published": "2026-10-23T15:31:35Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99040"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/11516a0c402a6c1fa52254aa70d8d65fb921e59e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/305f1828b871dd46bf41addeb6f11d2c162dcb25"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/da0b595d8e6e2dd798f6e34e09dc51a13b888514"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/dd3ea3fcba7c75493760cdbccd35f029597e8d5e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f99399b48e3edd6851fac34cd329bab9f1f33baf"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}



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