CVE-2026-89692 (GCVE-0-2026-89692)
Vulnerability from cvelistv5
Published
2026-09-11 19:46
Modified
2026-10-19 08:51
Severity ?
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: clear CALLBACK_RUNNING on failed delegation recall queue nfsd_break_one_deleg() sets NFSD4_CALLBACK_RUNNING via test_and_set_bit at entry to serialize recall work, then calls nfsd4_run_cb() to queue the recall. When the queue attempt fails the refcount bump is undone, but the RUNNING bit is left set. The only site that clears the bit is nfsd41_destroy_cb() (fs/nfsd/nfs4callback.c), which runs from the workqueue and is therefore unreachable when nothing was queued. The bit becomes a permanent latch on dp->dl_recall.cb_flags: every subsequent break_lease() on the same delegation hits the early-return guard in nfsd_break_one_deleg() and silently skips the recall, so the delegation is never broken and the conflicting open or lock stalls. Fix by clearing NFSD4_CALLBACK_RUNNING on the !queued branch alongside the refcount_dec.
References
Impacted products
Vendor Product Version
Linux Linux Version: 1054e8ffc5c492f341bdf1888b882f1d163dd3d8
Version: 1054e8ffc5c492f341bdf1888b882f1d163dd3d8
Version: 1054e8ffc5c492f341bdf1888b882f1d163dd3d8
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfsd/nfs4state.c"
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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          ],
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          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.15"
            },
            {
              "lessThan": "6.15",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.50",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.50",
                  "versionStartIncluding": "6.15",
                  "vulnerable": true
                },
                {
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                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: clear CALLBACK_RUNNING on failed delegation recall queue\n\nnfsd_break_one_deleg() sets NFSD4_CALLBACK_RUNNING via test_and_set_bit\nat entry to serialize recall work, then calls nfsd4_run_cb() to queue\nthe recall.  When the queue attempt fails the refcount bump is undone,\nbut the RUNNING bit is left set.  The only site that clears the bit is\nnfsd41_destroy_cb() (fs/nfsd/nfs4callback.c), which runs from the\nworkqueue and is therefore unreachable when nothing was queued.\n\nThe bit becomes a permanent latch on dp-\u003edl_recall.cb_flags: every\nsubsequent break_lease() on the same delegation hits the early-return\nguard in nfsd_break_one_deleg() and silently skips the recall, so the\ndelegation is never broken and the conflicting open or lock stalls.\n\nFix by clearing NFSD4_CALLBACK_RUNNING on the !queued branch alongside\nthe refcount_dec."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - nfsd_break_one_deleg() runs in in-kernel nfsd (fs/nfsd/nfs4state.c) and is reached over TCP/2049 via svc_process to nfsd_dispatch to nfsd4_proc_compound: a remote NFSv4 OPEN grants a delegation, then a conflicting OPEN hits nfsd_file_acquire/nfsd_open_break_lease to __break_lease to nfsd_break_deleg_cb().\nAC:L - The attacker drives both sides with two NFSv4 clients: one holds the delegation while the other sends conflicting OPEN/LOCK/SETATTR to invoke nfsd_break_one_deleg(), and can DESTROY_CLIENTID or flap the backchannel so queue_work() fails; the sequence is retryable and needs no uninfluenced memory layout.\nPR:N - Default AUTH_SYS/AUTH_NULL nfsd exports do not cryptographically verify RPC credentials; any host allowed by the export can EXCHANGE_ID/SETCLIENTID, OPEN to receive a delegation, and issue a conflicting OPEN with no local Linux account or capability.\nUI:N - The attacking NFS clients send the OPEN, conflicting OPEN, and optional DESTROY_CLIENTID RPCs themselves; no victim user on the NFS server must mount a filesystem, open a file, or otherwise interact at attack time.\nS:U - The latched NFSD4_CALLBACK_RUNNING bit and stalled lease-break live in kernel nfsd/VFS state on the NFS server; this is not a VM, IOMMU, or sandbox boundary crossing.\nC:N - The bug only leaves NFSD4_CALLBACK_RUNNING set so later recalls are skipped; it does not read attacker-inaccessible kernel memory, leak pointers, or return extra data to the client.\nI:N - There is no use-after-free, out-of-bounds write, or other memory corruption, and conflicting writers are blocked rather than committing unauthorized file changes, so integrity is unaffected.\nA:H - When nfsd4_run_cb() fails, RUNNING stays set, later break_lease() skips CB_RECALL, nfsd4_cb_recall_prepare never queues the delegation on del_recall_lru, and fl_break_time is zeroed so VFS will not expire the lease; conflicting opens/locks then stall or retry NFS4ERR_JUKEBOX indefinitely, denying the file and NFS service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:51:05.555Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/b137930ee52e3ef38915a3511d4c070463b63a32"
        },
        {
          "url": "https://git.kernel.org/stable/c/cb2d0c4d1b3d301d042ed61365eaa8cb0141a254"
        },
        {
          "url": "https://git.kernel.org/stable/c/b036727d334b1b7cd4c1f1fba3b59ba93a6bbe96"
        }
      ],
      "title": "nfsd: clear CALLBACK_RUNNING on failed delegation recall queue",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89692",
    "datePublished": "2026-09-11T19:46:12.040Z",
    "dateReserved": "2026-09-11T19:38:34.749Z",
    "dateUpdated": "2026-10-19T08:51:05.555Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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