CVE-2025-40205

Technical Description

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/[email protected]/

Although this issue does not seem to

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References