CVE-2025-21654

/// Technical description

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

ovl: support encoding fid from inode with no alias

Dmitry Safonov reported that a WARN_ON() assertion can be trigered by

userspace when calling inotify_show_fdinfo() for an overlayfs watched

inode, whose dentry aliases were discarded with drop_caches.

The WARN_ON() assertion in inotify_show_fdinfo() was removed, because

it is possible for encoding file handle to fail for other reason, but

the impact of failing to encode an overlayfs file handle goes beyond

this assertion.

As shown in the LTP test case mentioned in the link below, failure to

encode an overlayfs file handle from a non-aliased inode also leads to

failure to report an fid with FAN_DELETE_SELF fanotify events.

As Dmitry notes in his analyzis of the problem, ovl_encode_fh() fails

if it cannot find an alias for the inode, but this failure can be fixed.

ovl_encode_fh() seldom uses the alias and in the case of non-decodable

file handles, as is often the ca

/// 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