ceph: fix UAF in __kick_flushing_caps() on cf entry freed during unlock

{
  "id": "81a9d8e9445b658054ae9ca9cc818a6f3f865d6a82cd7d2c88eb8c575bd41417",
  "url": "https://osv.dev/vulnerability/CVE-2026-89655",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ceph: fix UAF in __kick_flushing_caps() on cf entry freed during unlock",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ceph: fix UAF in __kick_flushing_caps() on cf entry freed during unlock list_for_each_entry() iterates ci->i_cap_flush_list but drops i_ceph_lock to send cap messages. During the unlock window, handle_cap_flush_ack() can acquire i_ceph_lock, detach cf entries with tid <= flush_tid from the list, release i_ceph_lock, and free them via ceph_free_cap_flush() outside any lock. When the original thread reacquires i_ceph_lock and the for-loop macro advances via cf = list_next_entry(cf, i_list), it dereferences cf->i_list.next on freed memory. The race timeline: __kick_flushing_caps() handle_cap_flush_ack() ----------------------- ----------------------- holds i_ceph_lock <--- iterates to cf (tid=10) prepares FLUSH message drops i_ceph_lock <--- __send_cap() ── FLUSH(tid=10) MDS sends FLUSH_ACK(tid=10) ---> acquires i_ceph_lock cf->tid(10) <= flush_tid(10), detaches cf from i_cap_flush_list drops i_ceph_lock ceph_free_cap_flush(cf) <- frees it! acquires i_ceph_lock <--- for-loop advances: cf = list_next_entry(cf, i_list) -- UAF on freed cf->i_list.next The cf was just sent by __kick_flushing_caps itself via __send_cap(). The MDS may respond with FLUSH_ACK quickly enough that handle_cap_flush_ack() frees cf before __kick_flushing_caps can finish the iteration. Fix by converting to a manual while loop: save the next pointer under i_ceph_lock before dropping it, then use the saved pointer after reacquiring, so the pote",
    "evidence": "osv:CVE-2026-89655",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.270",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.221",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.188",
            "evidence": "/affected/1/ranges"
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            "value": "6.6.157",
            "evidence": "/affected/1/ranges"
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            "value": "6.18.50",
            "evidence": "/affected/1/ranges"
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          {
            "value": "7.2.4",
            "evidence": "/affected/1/ranges"
          }
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        "affected_versions": []
      }
    ],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-89655",
      "aliases": [
        "CVE-2026-89655"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
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              "type": "GIT",
              "events": [
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                  "fixed": "01542430081014d80fc9e70e92d6647432ddb7fc"
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                {
                  "fixed": "23eb34a53a53cb1a6dab1eeee830633207ac158d"
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                {
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89655.json"
          }
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        {
          "ranges": [
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              "type": "ECOSYSTEM",
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                  "introduced": "4.8.0"
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          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89655.json"
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      "modified": "2026-10-28T02:30:22.448701184Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/01542430081014d80fc9e70e92d6647432ddb7fc",
        "https://git.kernel.org/stable/c/091137821e1fc88f37e15201abf055c9494ddc61",
        "https://git.kernel.org/stable/c/19f16f04c2b014a7dd214dc1e42557d8530b16f3",
        "https://git.kernel.org/stable/c/23eb34a53a53cb1a6dab1eeee830633207ac158d",
        "https://git.kernel.org/stable/c/2701431aa3cc8b23efe6890182e7b04f5e76fab5",
        "https://git.kernel.org/stable/c/2dba24dcd5050be4b7b119e6f0b01f62203b5d26",
        "https://git.kernel.org/stable/c/7af4c4f01305b0935adf6d4301b1ec407025485d",
        "https://git.kernel.org/stable/c/fe46746087b5b9c5bb2d022df6c7819218494ced",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89655.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-89655",
        "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/2026/89xxx/CVE-2026-89655.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-89655",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 488820,
  "published_at": "2026-09-11T19:45:44.841+00:00"
}