namespace: queue a mount only once for mount notifications

{
  "id": "3af0d3613d29a82ff430c23f974bbc760cb93b5704eea85bc75ed004fb21d682",
  "url": "https://osv.dev/vulnerability/CVE-2026-98991",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "namespace: queue a mount only once for mount notifications",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: namespace: queue a mount only once for mount notifications mnt_notify_add() puts a mount on notify_list. It doesn't check whether the mount is on the list already. That's fine as long as every mount is queued at most once per namespace_sem hold. It isn't. propagate_umount() moves a surviving overmount off a stack of mounts that are going away and queues it as moved. shrink_submounts() and mark_mounts_for_expiry() call umount_tree() for several mounts under a single namespace_sem hold. So the second umount_tree() can take down exactly the mount the first one reparented, reparent it once more and so end up queueing it a second time. The second list_add_tail() cuts the mounts queued in between out of the list while the head still points at the last of them. notify_mnt_list() then only visits that one mount and the others are freed after the grace period with notify_list still pointing at them. Every later mount operation on the host walks freed memory: BUG: KASAN: slab-use-after-free in __list_add_valid_or_report Read of size 8 at addr ffff8881003d57e0 by task notify_dq/162 __list_add_valid_or_report+0x15c/0x1a0 mnt_add_to_ns+0x322/0x890 attach_recursive_mnt.isra.0+0xf2a/0x1a00 path_mount+0x139c/0x1d40 This needs a mount with MNT_SHRINKABLE to bind from. That's what finish_automount() creates (submounts of NFS, AFS and CIFS and the tracefs mount below debugfs). Bind mounts inherit the flag. A mount namespace wit",
    "evidence": "osv:CVE-2026-98991",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.18.57",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.2.11",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-98991",
      "aliases": [
        "CVE-2026-98991"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "bf630c40164162ba1d3933c2f5e3397d083e0948"
                },
                {
                  "fixed": "acbe9e4418e2ef7bef1a12e62e0e7d6145a15190"
                },
                {
                  "fixed": "702ff3fe499876e09c45558a05366d21a5bc41ab"
                },
                {
                  "fixed": "bd2feb7796b6585938a4241e7b7c4148a6f7b762"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98991.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.15.0"
                },
                {
                  "fixed": "6.18.57"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.2.11"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98991.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:46.206168372Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/702ff3fe499876e09c45558a05366d21a5bc41ab",
        "https://git.kernel.org/stable/c/acbe9e4418e2ef7bef1a12e62e0e7d6145a15190",
        "https://git.kernel.org/stable/c/bd2feb7796b6585938a4241e7b7c4148a6f7b762",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98991.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-98991",
        "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/2026/98xxx/CVE-2026-98991.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-98991",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 514384,
  "published_at": "2026-10-23T12:20:10.289+00:00"
}