CVE-2026-97902 (GCVE-0-2026-97902)
Vulnerability from cvelistv5
Published
2026-09-25 10:22
Modified
2026-10-19 09:10
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: fs: don't return -EINVAL for successful nested thaw Commit 7366f8b6fc6a ("fs: handle freezing from multiple devices") replaced the freeze_holders bitmask with per-holder counters to allow nested freezes. In the bitmask version, a thaw that released a shared hold while another holder remained returned 0. Since the rework, thaw_super_locked() drops the freeze reference via freeze_dec() but then returns -EINVAL when other freezers remain, misinforming the caller: the thaw did succeed, the superblock just stays frozen for the remaining holders. This breaks bdev-initiated freezing. When a filesystem is frozen with FIFREEZE and additionally frozen via bdev_freeze() -- which nests by design, see fs_bdev_freeze() -- the subsequent bdev_thaw() receives -EINVAL from the holder op although its freeze reference was dropped, and therefore keeps bd_fsfreeze_count elevated. Then device-mapper's unlock_fs() ignores bdev_thaw()'s return value, so nothing rebalances the count. After the user's FITHAW and umount, the block device can never be mounted again: dm-1: Can't mount, blockdev is frozen There is no way for userspace to drop the leaked count; only destroying the block device (or a reboot) recovers the device. Reproducer (any kernel since v6.8): dmsetup create dut --table "0 $(blockdev --getsz "$DEV") linear $DEV 0" mkfs.ext4 /dev/mapper/dut mount /dev/mapper/dut /mnt fsfreeze --freeze /mnt # freeze_ucount == 1 dmsetup suspend dut # bd_fsfreeze_count == 1, ucount == 2 dmsetup resume dut # ucount 2 -> 1, but thaw_super() # returns -EINVAL, so bdev_thaw() # keeps bd_fsfreeze_count at 1 fsfreeze --unfreeze /mnt # filesystem thaws fine umount /mnt mount /dev/mapper/dut /mnt # EBUSY, forever The same happens with fsfreeze held across an LVM snapshot of the origin volume. fs_bdev_thaw()'s documentation already describes the intended semantics: "If this function returns zero it doesn't mean that the filesystem is unfrozen as it may have been frozen multiple times". Restore them by returning 0 when a nested thaw drops its hold while other freezers remain. Thawing without holding a freeze still fails with -EINVAL as may_unfreeze() rejects that case before the reference count is touched.
References
Impacted products
Vendor Product Version
Linux Linux Version: 7366f8b6fc6aa21c4199cb5d337b023df69745b0
Version: 7366f8b6fc6aa21c4199cb5d337b023df69745b0
Version: 7366f8b6fc6aa21c4199cb5d337b023df69745b0
Version: 7366f8b6fc6aa21c4199cb5d337b023df69745b0
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{
  "containers": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/super.c"
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              "version": "0",
              "versionType": "semver"
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              "lessThanOrEqual": "6.12.*",
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              "version": "6.12.111",
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              "version": "6.18.53",
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              "version": "7.2.7",
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                  "vulnerable": true
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfs: don\u0027t return -EINVAL for successful nested thaw\n\nCommit 7366f8b6fc6a (\"fs: handle freezing from multiple devices\")\nreplaced the freeze_holders bitmask with per-holder counters to allow\nnested freezes. In the bitmask version, a thaw that released a shared\nhold while another holder remained returned 0. Since the rework,\nthaw_super_locked() drops the freeze reference via freeze_dec() but\nthen returns -EINVAL when other freezers remain, misinforming the\ncaller: the thaw did succeed, the superblock just stays frozen for the\nremaining holders.\n\nThis breaks bdev-initiated freezing. When a filesystem is frozen with\nFIFREEZE and additionally frozen via bdev_freeze() -- which nests by\ndesign, see fs_bdev_freeze() -- the subsequent bdev_thaw() receives\n-EINVAL from the holder op although its freeze reference was dropped,\nand therefore keeps bd_fsfreeze_count elevated. Then device-mapper\u0027s\nunlock_fs() ignores bdev_thaw()\u0027s return value, so nothing rebalances\nthe count. After the user\u0027s FITHAW and umount, the block device can\nnever be mounted again:\n\n    dm-1: Can\u0027t mount, blockdev is frozen\n\nThere is no way for userspace to drop the leaked count; only\ndestroying the block device (or a reboot) recovers the device.\n\nReproducer (any kernel since v6.8):\n\n    dmsetup create dut --table \"0 $(blockdev --getsz \"$DEV\") linear $DEV 0\"\n    mkfs.ext4 /dev/mapper/dut\n    mount /dev/mapper/dut /mnt\n    fsfreeze --freeze /mnt      # freeze_ucount == 1\n    dmsetup suspend dut         # bd_fsfreeze_count == 1, ucount == 2\n    dmsetup resume dut          # ucount 2 -\u003e 1, but thaw_super()\n                                # returns -EINVAL, so bdev_thaw()\n                                # keeps bd_fsfreeze_count at 1\n    fsfreeze --unfreeze /mnt    # filesystem thaws fine\n    umount /mnt\n    mount /dev/mapper/dut /mnt  # EBUSY, forever\n\nThe same happens with fsfreeze held across an LVM snapshot of the\norigin volume.\n\nfs_bdev_thaw()\u0027s documentation already describes the intended\nsemantics: \"If this function returns zero it doesn\u0027t mean that the\nfilesystem is unfrozen as it may have been frozen multiple times\".\nRestore them by returning 0 when a nested thaw drops its hold while\nother freezers remain. Thawing without holding a freeze still fails\nwith -EINVAL as may_unfreeze() rejects that case before the reference\ncount is touched."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:10:28.572Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/111339816138f042a59778322f941edc26903484"
        },
        {
          "url": "https://git.kernel.org/stable/c/76e478499913dc1f368aebe85b28b7d1265985ff"
        },
        {
          "url": "https://git.kernel.org/stable/c/ff2a694f6613d54ebd77ba72583d4d94446f55bd"
        },
        {
          "url": "https://git.kernel.org/stable/c/fe967191e5851ea79818c5fe4e781c3882139218"
        }
      ],
      "title": "fs: don\u0027t return -EINVAL for successful nested thaw",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-97902",
    "datePublished": "2026-09-25T10:22:29.259Z",
    "dateReserved": "2026-09-25T10:18:58.200Z",
    "dateUpdated": "2026-10-19T09:10:28.572Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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