namespace: check a recursive bind mount for mount namespace loops

{
  "id": "3d8cd8baaf898680fee265262d91de5e5dca6f8ec49ca7cd9a170a993d736619",
  "url": "https://osv.dev/vulnerability/CVE-2026-98989",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "namespace: check a recursive bind mount for mount namespace loops",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: namespace: check a recursive bind mount for mount namespace loops do_loopback() refuses to bind mount the file of a mount namespace that is as old as the caller's or older because a mount namespace that holds a mount of its own file, or of an ancestor's, would cause a cycle. But it only checks the dentry the bind mount starts from. With MS_REC everything below it is copied and do_loopback() passes CL_COPY_MNT_NS_FILE so mount namespace files below the source are copied. That's fine for a source in the caller's own mount namespace. Every mount namespace file in there passed the same check when it was bind-mounted. It isn't fine for a source in another mount namespace. may_copy_tree() accepts a bind mount of any nsfs or pidfs file no matter what mount namespace it lives in so that /proc//ns/ and pidfds can be bind mounted. If we create a bind-mount stack of mount namespaces file descriptors the kernel will copy them irrespective of their ancestoral relationship to the mount namespace in question: 151 146 0:7 net:[4026531833] /tmp/nrc/y rw - nsfs nsfs rw 152 151 0:7 mnt:[4026532293] /tmp/nrc/y rw - nsfs nsfs rw Mount 152 is a mount of the mount namespace file of mount namespace 4026532293 inside mount namespace 4026532293. That namespace and every mount in it are leaked... All it takes is a process in an older mount namespace that stacks the file and repeating it leaks without limit: after control: Shmem: 380 kB",
    "evidence": "osv:CVE-2026-98989",
    "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": "unknown",
    "structured": {
      "id": "CVE-2026-98989",
      "aliases": [
        "CVE-2026-98989"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e149ed2b805fefdccf7ccdfc19eca22fdd4514ac"
                },
                {
                  "fixed": "a0ba48256f5dff6f75a45f8ce39fe57f21df1022"
                },
                {
                  "fixed": "37a82f400efa4d263542a5fa41755b21057f1e5d"
                },
                {
                  "fixed": "c640a01a78e42302879006ed7b7d5a9a943ba815"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98989.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "3.19.0"
                },
                {
                  "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-2026-98989.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:29.755205519Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/37a82f400efa4d263542a5fa41755b21057f1e5d",
        "https://git.kernel.org/stable/c/a0ba48256f5dff6f75a45f8ce39fe57f21df1022",
        "https://git.kernel.org/stable/c/c640a01a78e42302879006ed7b7d5a9a943ba815",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98989.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-98989",
        "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-2026-98989.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-98989",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 496801,
  "published_at": "2026-10-23T12:20:08.366+00:00"
}