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CriticalFix available

NFSD: restart ssc_expire_umount walk after dropping nfsd_ssc_lock

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: NFSD: restart ssc_expire_umount walk after dropping nfsd_ssc_lock nfsd4_ssc_expire_umount() walks nn->nfsd_ssc_mount_list with list_for_each_entry_safe(ni, tmp, ...). For each expired entry it sets nsui_busy = true, drops nfsd_ssc_lock to run mntput() on the source vfsmount, then reacquires the lock to list_del + kfree the entry and continue iterating via the macro's saved tmp pointer. The nsui_busy flag protects the current ni from concurrent nfsd4_ssc_setup_dul() finders during the lock-drop window, but it does not pin tmp. Another nfsd RPC thread that fails its source- server mount and reaches nfsd4_ssc_cancel_dul() will, during that same window, take nfsd_ssc_lock, list_del + kfree its own ssc_umount item, and release the lock. If that item is the saved tmp of the expire walk, the next iteration dereferences a freed nfsd4_ssc_umount_item. Restart the walk from the head after the mntput() unlock window so no saved next pointer survives the lock-drop. The list is bounded by the number of active inter-server source mounts (typically small) and the expire delayed-work runs periodically rather than per-IO, so the restart is cheap.

Products
Kernel
Affected versions
Not specified
Fixed versions
5.10.270, 5.15.221, 6.1.188, 6.12.109, 6.18.50, 6.6.157, 7.2.4
CVEs
CVE-2026-89712
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 20:49 UTC · Revision 1

Source evidence

NFSD: restart ssc_expire_umount walk after dropping nfsd_ssc_lock

core-osv · Original source

Published 11 Sept 2026, 19:46 UTC

In the Linux kernel, the following vulnerability has been resolved: NFSD: restart ssc_expire_umount walk after dropping nfsd_ssc_lock nfsd4_ssc_expire_umount() walks nn->nfsd_ssc_mount_list with list_for_each_entry_safe(ni, tmp, ...). For each expired entry it sets nsui_busy = true, drops nfsd_ssc_lock to run mntput() on the source vfsmount, then reacquires the lock to list_del + kfree the entry and continue iterating via the macro's saved tmp pointer. The nsui_busy flag protects the current ni from concurrent nfsd4_ssc_setup_dul() finders during the lock-drop window, but it does not pin tmp. Another nfsd RPC thread that fails its source- server mount and reaches nfsd4_ssc_cancel_dul() will, during that same window, take nfsd_ssc_lock, list_del + kfree its own ssc_umount item, and release the lock. If that item is the saved tmp of the expire walk, the next iteration dereferences a freed nfsd4_ssc_umount_item. Restart the walk from the head after the mntput() unlock window so no saved next pointer survives the lock-drop. The list is bounded by the number of active inter-server source mounts (typically small) and the expire delayed-work runs periodically rather than per-IO, so the restart is cheap.

osv:CVE-2026-89712

Kernel

Fixed versions: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, 6.18.50, 7.2.4

Complete source record
{
  "id": "5248611272a01af158514487b7103e992e4d88d96f2e9a1648915c76f8ab10f9",
  "url": "https://osv.dev/vulnerability/CVE-2026-89712",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "NFSD: restart ssc_expire_umount walk after dropping nfsd_ssc_lock",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: NFSD: restart ssc_expire_umount walk after dropping nfsd_ssc_lock nfsd4_ssc_expire_umount() walks nn->nfsd_ssc_mount_list with list_for_each_entry_safe(ni, tmp, ...). For each expired entry it sets nsui_busy = true, drops nfsd_ssc_lock to run mntput() on the source vfsmount, then reacquires the lock to list_del + kfree the entry and continue iterating via the macro's saved tmp pointer. The nsui_busy flag protects the current ni from concurrent nfsd4_ssc_setup_dul() finders during the lock-drop window, but it does not pin tmp. Another nfsd RPC thread that fails its source- server mount and reaches nfsd4_ssc_cancel_dul() will, during that same window, take nfsd_ssc_lock, list_del + kfree its own ssc_umount item, and release the lock. If that item is the saved tmp of the expire walk, the next iteration dereferences a freed nfsd4_ssc_umount_item. Restart the walk from the head after the mntput() unlock window so no saved next pointer survives the lock-drop. The list is bounded by the number of active inter-server source mounts (typically small) and the expire delayed-work runs periodically rather than per-IO, so the restart is cheap.",
    "evidence": "osv:CVE-2026-89712",
    "products": [
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        "affected_versions": []
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    "severity": "critical",
    "structured": {
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      "aliases": [
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      "metrics": [
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              "events": [
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            "v5.10.226",
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            "v5.10.224",
            "v5.10.223",
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        {
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          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-89712.json"
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        }
      ],
      "modified": "2026-10-28T02:30:39.413119356Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/036c1b182f4da65363e79ec0ac276edc6b7296e5",
        "https://git.kernel.org/stable/c/2b59029b8f24a99b5d844af2da3950d39d36eeea",
        "https://git.kernel.org/stable/c/4ed8d2317aef21cc2a9e5a55d6b59860b4b151a8",
        "https://git.kernel.org/stable/c/60680ae7243b22de3d09be990d8e23bcfc4af837",
        "https://git.kernel.org/stable/c/659ee3da073164e1e6e40dfcbc26eeed85845f93",
        "https://git.kernel.org/stable/c/7377fa964b8aaf47cb04e5efcc4c82d15e8c2ce9",
        "https://git.kernel.org/stable/c/77de363d9a1c8cd35f20482782c612cda085791a",
        "https://git.kernel.org/stable/c/d9e151fea5ed706c1284adacabd869b0be745db2",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89712.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-89712",
        "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-2026-89712.json"
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    "related_cves": [
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    "security_relevant": true,
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  "source_id": "core-osv",
  "document_id": 506871,
  "published_at": "2026-09-11T19:46:27.018+00:00"
}