Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept

{
  "id": "a714d078a6d63b04d8cbe99d08fa5fb5039c5a87b5462954b642f5acc309daa8",
  "url": "https://osv.dev/vulnerability/CVE-2026-80819",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept rfcomm_sock_recvmsg() completes a deferred setup by calling rfcomm_dlc_accept() without holding any RFCOMM lock: if (test_and_clear_bit(RFCOMM_DEFER_SETUP, &d->flags)) { rfcomm_dlc_accept(d); return 0; } and rfcomm_dlc_accept() dereferences the session on its first line: struct sock *sk = d->session->sock->sk; Every other path that touches d->session runs under rfcomm_mutex: rfcomm_dlc_open(), rfcomm_dlc_close(), rfcomm_dlc_exists(), rfcomm_dlc_send_rpn(), and the RFCOMM thread through rfcomm_process_sessions(). rfcomm_connect_ind() is even documented as \"called under rfcomm_lock()\". This call site is the only one that skips it. The RFCOMM_DEFER_SETUP bit looks like it serialises the accept against teardown, since __rfcomm_dlc_close() returns early when it wins the test_and_clear. But rfcomm_recv_disc() forces the state first: d->state = BT_CLOSED; __rfcomm_dlc_close(d, err); and the early return only covers BT_CONNECT, BT_CONFIG, BT_OPEN and BT_CONNECT2. With the state already BT_CLOSED that switch does not match, the bit is never consulted, and __rfcomm_dlc_close() falls through to rfcomm_dlc_unlink(), which sets d->session = NULL. So a remote DISC on a deferred dlc clears the session while leaving RFCOMM_DEFER_SETUP set. The next recvmsg() then passes the test_and_clear and dereferences a NULL session. No timing window is needed: once the D",
    "evidence": "osv:CVE-2026-80819",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.267",
            "evidence": "/affected/1/ranges"
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            "evidence": "/affected/1/ranges"
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            "evidence": "/affected/1/ranges"
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        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-80819",
      "aliases": [
        "CVE-2026-80819"
      ],
      "affected": [
        {
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      "modified": "2026-10-28T02:30:39.439848228Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/355bfd57ca4ca881c6eb03ca813b440a094b1f44",
        "https://git.kernel.org/stable/c/362726c9c6e56eea4262109183e49868c39ccd3a",
        "https://git.kernel.org/stable/c/43a556b2fd43f2df6dded59c2e26560a27874c24",
        "https://git.kernel.org/stable/c/56f0aa75c7640e46397ef73bea251fcbef9150c0",
        "https://git.kernel.org/stable/c/825b95561d7b7c393df9e7bc295451aaeadc3d18",
        "https://git.kernel.org/stable/c/b405c2f96ae2e37375105881890f7738833b1d62",
        "https://git.kernel.org/stable/c/d4b1a13b1eff2e80925c7368ffdeaaa50cba93df",
        "https://git.kernel.org/stable/c/d8d686dd5662a7c4745e4515f1237a9f3b7df181",
        "https://git.kernel.org/stable/c/eb71d5a1ea8ff2683e394b48ae3cd676037ab4c2",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80819.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-80819",
        "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/2026/80xxx/CVE-2026-80819.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-80819",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 507190,
  "published_at": "2026-09-04T15:13:40.309+00:00"
}