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

{
  "id": "7c8addc8e100ac69156a89db49fdbe3a2a31d54ed0deeaf510e1d8d712afc405",
  "url": "https://osv.dev/vulnerability/CVE-2026-43455",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "mctp: route: hold key->lock in mctp_flow_prepare_output()",
    "summary": "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.",
    "evidence": "osv:CVE-2026-43455",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.1.167",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.130",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.78",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.19",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.9",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-43455",
      "aliases": [
        "CVE-2026-43455"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                  "introduced": "67737c457281dd199ceb9e31b6ba7efd3bfe566d"
                },
                {
                  "fixed": "47893166bc5611ee9a20de6b8d2933b2320fb772"
                },
                {
                  "fixed": "86f5334fcb48a5b611c33364ab52ca684d0f6d91"
                },
                {
                  "fixed": "0695712f3a6f1a48915f95767cfb42077683dcdc"
                },
                {
                  "fixed": "925a5ffd99cddd7a7e41d5ad120c7a2c6d50260f"
                },
                {
                  "fixed": "8d27d9b260dd19c1b519e1a13de6448f9984e30e"
                },
                {
                  "fixed": "7d86aa41c073c4e7eb75fd2e674f1fd8f289728a"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43455.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
                },
                {
                  "fixed": "6.1.167"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.130"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.78"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.19"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "6.19.9"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43455.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:53.122472673Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0695712f3a6f1a48915f95767cfb42077683dcdc",
        "https://git.kernel.org/stable/c/47893166bc5611ee9a20de6b8d2933b2320fb772",
        "https://git.kernel.org/stable/c/7d86aa41c073c4e7eb75fd2e674f1fd8f289728a",
        "https://git.kernel.org/stable/c/86f5334fcb48a5b611c33364ab52ca684d0f6d91",
        "https://git.kernel.org/stable/c/8d27d9b260dd19c1b519e1a13de6448f9984e30e",
        "https://git.kernel.org/stable/c/925a5ffd99cddd7a7e41d5ad120c7a2c6d50260f",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43455.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-43455",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43455.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-43455",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 521538,
  "published_at": "2026-05-08T14:22:19.375+00:00"
}