CVE-2025-40049

/// Technical description

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

Squashfs: fix uninit-value in squashfs_get_parent

Syzkaller reports a "KMSAN: uninit-value in squashfs_get_parent" bug.

This is caused by open_by_handle_at() being called with a file handle

containing an invalid parent inode number. In particular the inode number

is that of a symbolic link, rather than a directory.

Squashfs_get_parent() gets called with that symbolic link inode, and

accesses the parent member field.

unsigned int parent_ino = squashfs_i(inode)->parent;

Because non-directory inodes in Squashfs do not have a parent value, this

is uninitialised, and this causes an uninitialised value access.

The fix is to initialise parent with the invalid inode 0, which will cause

an EINVAL error to be returned.

Regular inodes used to share the parent field with the block_list_start

field. This is removed in this commit to enable the parent field to

contain the invalid inode number 0.

/// 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