ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc

{
  "id": "e21c7f65d09ec639342074c467418197daf18bc4bb387dc05f84384c7b41f3f9",
  "url": "https://osv.dev/vulnerability/CVE-2026-31610",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix mechToken leak when SPNEGO decode fails after token alloc The kernel ASN.1 BER decoder calls action callbacks incrementally as it walks the input. When ksmbd_decode_negTokenInit() reaches the mechToken [2] OCTET STRING element, ksmbd_neg_token_alloc() allocates conn->mechToken immediately via kmemdup_nul(). If a later element in the same blob is malformed, then the decoder will return nonzero after the allocation is already live. This could happen if mechListMIC [3] overrunse the enclosing SEQUENCE. decode_negotiation_token() then sets conn->use_spnego = false because both the negTokenInit and negTokenTarg grammars failed. The cleanup at the bottom of smb2_sess_setup() is gated on use_spnego: if (conn->use_spnego && conn->mechToken) { kfree(conn->mechToken); conn->mechToken = NULL; } so the kfree is skipped, causing the mechToken to never be freed. This codepath is reachable pre-authentication, so untrusted clients can cause slow memory leaks on a server without even being properly authenticated. Fix this up by not checking check for use_spnego, as it's not required, so the memory will always be properly freed. At the same time, always free the memory in ksmbd_conn_free() incase some other failure path forgot to free it.",
    "evidence": "osv:CVE-2026-31610",
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    "severity": "unknown",
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      "aliases": [
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      "modified": "2026-10-28T02:30:49.600923652Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/269c800a7a7e363459291885b35f7bc72e231ed6",
        "https://git.kernel.org/stable/c/6c8c44e6553b9f072f62d9875e567766eb293162",
        "https://git.kernel.org/stable/c/745a535461bbb90a56d9357573c9f97a5c12abe1",
        "https://git.kernel.org/stable/c/ad0057fb91218914d6c98268718ceb9d59b388e1",
        "https://git.kernel.org/stable/c/ae9cdb29efed20ffdee9ff3b0bb72fb369c353da",
        "https://git.kernel.org/stable/c/bd4a7fb04f06f419b0e93d8b52fe32067eb312d1",
        "https://git.kernel.org/stable/c/dd53414e301beb915fe672dc4c4a51bafb917604",
        "https://git.kernel.org/stable/c/dd577cb55588ec3fbc66af3621280306601c4192",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31610.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31610",
        "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/2026/31xxx/CVE-2026-31610.json"
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      {
        "value": "CVE-2026-31610",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 517801,
  "published_at": "2026-04-24T14:42:31.471+00:00"
}