{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2024-50217",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2024-50217"
  ],
  "published": "2024-11-09T10:15:51Z",
  "summary": "btrfs: fix use-after-free of block device file in __btrfs_free_extra_devids()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix use-after-free of block device file in __btrfs_free_extra_devids()\n\nMounting btrfs from two images (which have the same one fsid and two\ndifferent dev_uuids) in certain executing order may trigger an UAF for\nvariable 'device->bdev_file' in __btrfs_free_extra_devids(). And\nfollowing are the details:\n\n1. Attach image_1 to loop0, attach image_2 to loop1, and scan btrfs\n   devices by ioctl(BTRFS_IOC_SCAN_DEV):\n\n             /  btrfs_device_1 \u2192 loop0\n   fs_device\n             \\  btrfs_device_2 \u2192 loop1\n2. mount /dev/loop0 /mnt\n   btrfs_open_devices\n    btrfs_device_1->bdev_file = btrfs_get_bdev_and_sb(loop0)\n    btrfs_device_2->bdev_file = btrfs_get_bdev_and_sb(loop1)\n   btrfs_fill_super\n    open_ctree\n     fail: btrfs_close_devices // -ENOMEM\n\t    btrfs_close_bdev(btrfs_device_1)\n             fput(btrfs_device_1->bdev_file)\n\t      // btrfs_device_1->bdev_file is freed\n\t    btrfs_close_bdev(btrfs_device_2)\n             fput(btrfs_device_2->bdev_file)\n\n3. mount /dev/loop1 /mnt\n   btrfs_open_devices\n    btrfs_get_bdev_and_sb(&bdev_file)\n     // EIO, btrfs_device_1->bdev_file is not assigned,\n     // which points to a freed memory area\n    btrfs_device_2->bdev_file = btrfs_get_bdev_and_sb(loop1)\n   btrfs_fill_super\n    open_ctree\n     btrfs_free_extra_devids\n      if (btrfs_device_1->bdev_file)\n       fput(btrfs_device_1->bdev_file) // UAF !\n\nFix it by setting 'device->bdev_file' as 'NULL' after closing the\nbtrfs_device in btrfs_close_one_device().",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H"
    }
  ],
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2024-50217"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/47a83f8df39545f3f552bb6a1b6d9c30e37621dd"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/aec8e6bf839101784f3ef037dcdb9432c3f32343"
    }
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  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T11:52:36Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The vulnerability is reached only through local block-device operations \u2014 `mount(2)` of a btrfs volume plus device registration via `BTRFS_IOC_SCAN_DEV`/`device=` \u2014 on a locally attached device or loop-mounted image. No network or remote-peer data is involved.\nAC:L - The attacker fully controls both filesystem images and the order of the two mounts; the first mount's `open_ctree()` failure can be forced deterministically by corrupting the superblock/chunk tree rather than relying on the ENOMEM fault injection in the report, and no race must be won. Heap grooming of the `filp` slab between the two mounts is entirely under attacker control.\nPR:N - The attacker supplies only the malicious images (USB stick, disk image file, or loop-backed file) and needs no account or privilege on the target system; the privileged mount is performed by the victim or by an automounter such as udisks2 on the attacker's behalf.\nUI:R - Exploitation requires the victim (or an automount daemon acting for a logged-in user) to mount the attacker's crafted btrfs images, twice in sequence, since btrfs lacks `FS_USERNS_MOUNT` and cannot be mounted directly by an unprivileged attacker.\nS:U - The corruption and its consequences are confined to the kernel of the same system; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - The stray `fput()` on a freed `struct file` in a `SLAB_TYPESAFE_BY_RCU` cache causes a live file's refcount to be dropped, yielding a reusable use-after-free object that can be leveraged for arbitrary kernel memory disclosure.\nI:H - The same reference-count underflow gives a premature-free UAF on `struct file`, a well-established primitive for heap spraying, arbitrary write, and control-flow hijack leading to privilege escalation.\nA:H - Even without full exploitation the `fput()` on freed memory corrupts the slab and reliably produces a KASAN splat, refcount BUG, or kernel panic, taking the system down."
    }
  }
}