CVE-2026-89646 (GCVE-0-2026-89646)
Vulnerability from cvelistv5
Published
2026-09-11 19:45
Modified
2026-10-19 08:50
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ceph: fix leaked inode reference on writeback abort at umount ceph_dirty_folio() takes a wrbuffer claim on each newly dirtied folio: it bumps i_wrbuffer_ref (taking an ihold() on the 0->1 transition) and attaches the snap_context to folio->private. That claim is released only by ceph_put_wrbuffer_cap_refs(), which for a submitted write runs from writepages_finish(). In ceph_submit_write(), if ceph_inc_osd_stopping_blocker() fails -- which happens during umount -- the request is aborted before submission: the already-collected folios are only redirtied and unlocked, so writepages_finish() never runs and the claim is leaked. redirty_page_for_writepage() -> folio_redirty_for_writepage() -> filemap_dirty_folio() sets PG_dirty directly and does not go through ->dirty_folio, so ceph_dirty_folio() is not re-entered to rebalance it. Because every subsequent writeback also fails the osd_stopping_blocker, i_wrbuffer_ref never returns to 0, the ihold() is never dropped, and the inode cannot be evicted: VFS: Busy inodes after unmount of ceph kernel BUG at fs/super.c:650! Release the orphaned claim in the abort path before redirtying, via ceph_undo_wrbuffer_claim(): detach the snap_context, drop the wrbuffer reference (letting i_wrbuffer_ref reach 0 and iput() the inode), and drop the snap_context reference -- i.e. do what writepages_finish() would have done for these never-submitted folios. Only the locked_pages entries are undone; folios still in the fbatch were never dirty-cleared by this call (folio_clear_dirty_for_io() is the ownership-transfer point, and a successful move NULLs the fbatch slot), so they hold no claim this call owns.
References
Impacted products
Vendor Product Version
Linux Linux Version: fd7449d937e7fb3144770592927cf452bf66dbd3
Version: fd7449d937e7fb3144770592927cf452bf66dbd3
Version: fd7449d937e7fb3144770592927cf452bf66dbd3
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/ceph/addr.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "ec32015a955c5d326c5e26610edfdcccd52f2314",
              "status": "affected",
              "version": "fd7449d937e7fb3144770592927cf452bf66dbd3",
              "versionType": "git"
            },
            {
              "lessThan": "ac7a5a5385762df458d10cccc086a4e079be7409",
              "status": "affected",
              "version": "fd7449d937e7fb3144770592927cf452bf66dbd3",
              "versionType": "git"
            },
            {
              "lessThan": "c25aee9c630fb86f98d79eccb75765067079b972",
              "status": "affected",
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              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/ceph/addr.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "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
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.4",
                  "versionStartIncluding": "6.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "6.15",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix leaked inode reference on writeback abort at umount\n\nceph_dirty_folio() takes a wrbuffer claim on each newly dirtied folio: it\nbumps i_wrbuffer_ref (taking an ihold() on the 0-\u003e1 transition) and\nattaches the snap_context to folio-\u003eprivate.  That claim is released only\nby ceph_put_wrbuffer_cap_refs(), which for a submitted write runs from\nwritepages_finish().\n\nIn ceph_submit_write(), if ceph_inc_osd_stopping_blocker() fails -- which\nhappens during umount -- the request is aborted before submission: the\nalready-collected folios are only redirtied and unlocked, so\nwritepages_finish() never runs and the claim is leaked.\nredirty_page_for_writepage() -\u003e folio_redirty_for_writepage() -\u003e\nfilemap_dirty_folio() sets PG_dirty directly and does not go through\n-\u003edirty_folio, so ceph_dirty_folio() is not re-entered to rebalance it.\nBecause every subsequent writeback also fails the osd_stopping_blocker,\ni_wrbuffer_ref never returns to 0, the ihold() is never dropped, and the\ninode cannot be evicted:\n\n  VFS: Busy inodes after unmount of ceph\n  kernel BUG at fs/super.c:650!\n\nRelease the orphaned claim in the abort path before redirtying, via\nceph_undo_wrbuffer_claim(): detach the snap_context, drop the wrbuffer\nreference (letting i_wrbuffer_ref reach 0 and iput() the inode), and drop\nthe snap_context reference -- i.e. do what writepages_finish() would have\ndone for these never-submitted folios.\n\nOnly the locked_pages entries are undone; folios still in the fbatch were\nnever dirty-cleared by this call (folio_clear_dirty_for_io() is the\nownership-transfer point, and a successful move NULLs the fbatch slot), so\nthey hold no claim this call owns."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The leak is in ceph_submit_write() from ceph_writepages_start() during local VFS writeback on umount (ceph_kill_sb \u2192 sync_filesystem \u2192 do_writepages), not MDS/OSD message handlers. fs/ceph is a kernel client with no network-facing server listener.\nAC:L - Dirtying pages then unmounting drives both sides: ceph_kill_sb waits at most mount_timeout (default 60s) or a killable signal, then sets STOPPING_FLUSHING while writepages_start still holds a blocker and locked folios, so the abort is reached reliably without an uncontrolled race.\nPR:L - An unprivileged user with write access to an already-mounted CephFS can dirty pages; container/pod teardown, autofs, or systemd performs the umount. CephFS lacks FS_USERNS_MOUNT, but the attacker does not need CAP_SYS_ADMIN themselves.\nUI:N - The attacker dirties files and can trigger or wait for unmount via pod exit, autofs idle unmount, or their own umount; no separate victim action such as opening a file or mounting the filesystem is required.\nS:U - The leaked inode references and subsequent superblock teardown affect only the host kernel\u0027s VFS/Ceph client state within the same security authority; this is not a VM escape, IOMMU bypass, or sandbox escape.\nC:H - The leaked ihold pins inodes through generic_shutdown_super so the superblock and ceph_fs_client are destroyed while those inodes remain. Later writeback or iput on the leftover mapping is a use-after-free of the freed superblock, scored High per UAF guidance.\nI:H - Inodes that survive umount retain address_spaces and pointers into destroyed ceph_fs_client/mdsc state. Subsequent iput_final/writeback operate on freed objects and poisoned i_op/s_op, a UAF write and control-flow primitive scored High.\nA:H - Unmount reports \"VFS: Busy inodes after unmount of ceph\" and hits CHECK_DATA_CORRUPTION in generic_shutdown_super (BUG() with CONFIG_BUG_ON_DATA_CORRUPTION), and VFS_PTR_POISON on surviving inodes guarantees a later oops or panic."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:50:17.976Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/ec32015a955c5d326c5e26610edfdcccd52f2314"
        },
        {
          "url": "https://git.kernel.org/stable/c/ac7a5a5385762df458d10cccc086a4e079be7409"
        },
        {
          "url": "https://git.kernel.org/stable/c/c25aee9c630fb86f98d79eccb75765067079b972"
        }
      ],
      "title": "ceph: fix leaked inode reference on writeback abort at umount",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89646",
    "datePublished": "2026-09-11T19:45:37.767Z",
    "dateReserved": "2026-09-11T19:38:34.741Z",
    "dateUpdated": "2026-10-19T08:50:17.976Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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