---
id: CVE-2025-40205
title: 'btrfs: avoid potential out-of-bounds in btrfs_encode_fh()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  btrfs: avoid potential out-of-bounds in btrfs_encode_fh()

  The function btrfs_encode_fh() does not properly account for the three
  cases it handles.

  Before writing to t…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 <
    60de2f55d2aca53e81b4ef2a67d7cc9e1eb677db
  - >-
    Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 <
    742b44342204e5dfe3926433823623c1a0c581df
  - >-
    Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 <
    d3a9a8e1275eb9b87f006b5562a287aea3f6885f
  - >-
    Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 <
    d91f6626133698362bba08fbc04bd72c466806d3
  - >-
    Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 <
    0276c8582488022f057b4cec21975a5edf079f47
  - >-
    Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 <
    361d67276eb8ec6be8f27f4ad6c6090459438fee
  - >-
    Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 <
    43143776b0a7604d873d1a6f3e552a00aa930224
  - >-
    Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 <
    dff4f9ff5d7f289e4545cc936362e01ed3252742
  - Linux 2.6.29
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-15T21:58:09.178444Z'
published: '2025-11-12'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T22:02:40.845Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-40205'
references:
  - url: 'https://git.kernel.org/stable/c/60de2f55d2aca53e81b4ef2a67d7cc9e1eb677db'
  - url: 'https://git.kernel.org/stable/c/742b44342204e5dfe3926433823623c1a0c581df'
  - url: 'https://git.kernel.org/stable/c/d3a9a8e1275eb9b87f006b5562a287aea3f6885f'
  - url: 'https://git.kernel.org/stable/c/d91f6626133698362bba08fbc04bd72c466806d3'
  - url: 'https://git.kernel.org/stable/c/0276c8582488022f057b4cec21975a5edf079f47'
  - url: 'https://git.kernel.org/stable/c/361d67276eb8ec6be8f27f4ad6c6090459438fee'
  - url: 'https://git.kernel.org/stable/c/43143776b0a7604d873d1a6f3e552a00aa930224'
  - url: 'https://git.kernel.org/stable/c/dff4f9ff5d7f289e4545cc936362e01ed3252742'
tags:
  - cve.org
epss: 0.00153
epssPercentile: 0.03998
ingestedAt: '2026-10-15T22:48:25.552Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

btrfs: avoid potential out-of-bounds in btrfs_encode_fh()

The function btrfs_encode_fh() does not properly account for the three
cases it handles.

Before writing to the file handle (fh), the function only returns to the
user BTRFS_FID_SIZE_NON_CONNECTABLE (5 dwords, 20 bytes) or
BTRFS_FID_SIZE_CONNECTABLE (8 dwords, 32 bytes).

However, when a parent exists and the root ID of the parent and the
inode are different, the function writes BTRFS_FID_SIZE_CONNECTABLE_ROOT
(10 dwords, 40 bytes).

If *max_len is not large enough, this write goes out of bounds because
BTRFS_FID_SIZE_CONNECTABLE_ROOT is greater than
BTRFS_FID_SIZE_CONNECTABLE originally returned.

This results in an 8-byte out-of-bounds write at
fid->parent_root_objectid = parent_root_id.

A previous attempt to fix this issue was made but was lost.

https://lore.kernel.org/all/4CADAEEC020000780001B32C@vpn.id2.novell.com/

Although this issue does not seem to be easily triggerable, it is a
potential memory corruption bug that should be fixed. This patch
resolves the issue by ensuring the function returns the appropriate size
for all three cases and validates that *max_len is large enough before
writing any data.

## Affected

- `Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 60de2f55d2aca53e81b4ef2a67d7cc9e1eb677db`
- `Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 742b44342204e5dfe3926433823623c1a0c581df`
- `Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < d3a9a8e1275eb9b87f006b5562a287aea3f6885f`
- `Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < d91f6626133698362bba08fbc04bd72c466806d3`
- `Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 0276c8582488022f057b4cec21975a5edf079f47`
- `Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 361d67276eb8ec6be8f27f4ad6c6090459438fee`
- `Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < 43143776b0a7604d873d1a6f3e552a00aa930224`
- `Linux >= be6e8dc0ba84029997075a1ec77b4ddb863cbe15 < dff4f9ff5d7f289e4545cc936362e01ed3252742`
- `Linux 2.6.29`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.