9p: fix access mode flags being ORed instead of replaced

{
  "id": "2454bedac7523e1430138e94cc3eacf4b07abce4283d81b77399e31742f94fd9",
  "url": "https://osv.dev/vulnerability/CVE-2026-52906",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "9p: fix access mode flags being ORed instead of replaced",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: 9p: fix access mode flags being ORed instead of replaced Since commit 1f3e4142c0eb (\"9p: convert to the new mount API\"), v9fs_apply_options() applies parsed mount flags with |= onto flags already set by v9fs_session_init(). For 9P2000.L, session_init sets V9FS_ACCESS_CLIENT as the default, so when the user mounts with \"access=user\", both bits end up set. Access mode checks compare against exact values, so having both bits set matches neither mode. This causes v9fs_fid_lookup() to fall through to the default switch case, using INVALID_UID (nobody/65534) instead of current_fsuid() for all fid lookups. Root is then unable to chown or perform other privileged operations. Fix by clearing the access mask before applying the user's choice.",
    "evidence": "osv:CVE-2026-52906",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.0.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-52906",
      "aliases": [
        "CVE-2026-52906"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "1f3e4142c0eb178089ea0cbc97506a061470ad27"
                },
                {
                  "fixed": "b8f037e87a083291190204b959cda417aaf01058"
                },
                {
                  "fixed": "da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52906.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
                },
                {
                  "fixed": "7.0.4"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-52906.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:51.546428974Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/b8f037e87a083291190204b959cda417aaf01058",
        "https://git.kernel.org/stable/c/da2346a48a5a1fed86c3fe3d73c0b60e7b3027c9",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/52xxx/CVE-2026-52906.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-52906",
        "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/2026/52xxx/CVE-2026-52906.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-52906",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 520087,
  "published_at": "2026-06-09T12:36:03.521+00:00"
}