GHSA-QQ8V-696H-FHV2

Vulnerability from github – Published: 2026-05-08 15:31 – Updated: 2026-05-20 18:31
VLAI
Details

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

mctp: route: hold key->lock in mctp_flow_prepare_output()

mctp_flow_prepare_output() checks key->dev and may call mctp_dev_set_key(), but it does not hold key->lock while doing so.

mctp_dev_set_key() and mctp_dev_release_key() are annotated with __must_hold(&key->lock), so key->dev access is intended to be serialized by key->lock. The mctp_sendmsg() transmit path reaches mctp_flow_prepare_output() via mctp_local_output() -> mctp_dst_output() without holding key->lock, so the check-and-set sequence is racy.

Example interleaving:

CPU0 CPU1 ---- ---- mctp_flow_prepare_output(key, devA) if (!key->dev) // sees NULL mctp_flow_prepare_output( key, devB) if (!key->dev) // still NULL mctp_dev_set_key(devB, key) mctp_dev_hold(devB) key->dev = devB mctp_dev_set_key(devA, key) mctp_dev_hold(devA) key->dev = devA // overwrites devB

Now both devA and devB references were acquired, but only the final key->dev value is tracked for release. One reference can be lost, causing a resource leak as mctp_dev_release_key() would only decrease the reference on one dev.

Fix by taking key->lock around the key->dev check and mctp_dev_set_key() call.

Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-43455"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-08T15:16:58Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmctp: route: hold key-\u003elock in mctp_flow_prepare_output()\n\nmctp_flow_prepare_output() checks key-\u003edev and may call\nmctp_dev_set_key(), but it does not hold key-\u003elock while doing so.\n\nmctp_dev_set_key() and mctp_dev_release_key() are annotated with\n__must_hold(\u0026key-\u003elock), so key-\u003edev access is intended to be\nserialized by key-\u003elock. The mctp_sendmsg() transmit path reaches\nmctp_flow_prepare_output() via mctp_local_output() -\u003e mctp_dst_output()\nwithout holding key-\u003elock, so the check-and-set sequence is racy.\n\nExample interleaving:\n\n  CPU0                                  CPU1\n  ----                                  ----\n  mctp_flow_prepare_output(key, devA)\n    if (!key-\u003edev)  // sees NULL\n                                        mctp_flow_prepare_output(\n                                            key, devB)\n                                          if (!key-\u003edev)  // still NULL\n                                          mctp_dev_set_key(devB, key)\n                                            mctp_dev_hold(devB)\n                                            key-\u003edev = devB\n    mctp_dev_set_key(devA, key)\n      mctp_dev_hold(devA)\n      key-\u003edev = devA   // overwrites devB\n\nNow both devA and devB references were acquired, but only the final\nkey-\u003edev value is tracked for release. One reference can be lost,\ncausing a resource leak as mctp_dev_release_key() would only decrease\nthe reference on one dev.\n\nFix by taking key-\u003elock around the key-\u003edev check and\nmctp_dev_set_key() call.",
  "id": "GHSA-qq8v-696h-fhv2",
  "modified": "2026-05-20T18:31:30Z",
  "published": "2026-05-08T15:31:29Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-43455"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0695712f3a6f1a48915f95767cfb42077683dcdc"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/47893166bc5611ee9a20de6b8d2933b2320fb772"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7d86aa41c073c4e7eb75fd2e674f1fd8f289728a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/86f5334fcb48a5b611c33364ab52ca684d0f6d91"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8d27d9b260dd19c1b519e1a13de6448f9984e30e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/925a5ffd99cddd7a7e41d5ad120c7a2c6d50260f"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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