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Fencer Vulns
medium 5.5

CVE-2025-21654 json

ovl: support encoding fid from inode with no alias

published 2025-01-19 21 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-2603

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 10%
public exploits
0
none known

Summary

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 case with fanotify fid info, ovl_encode_fh() never needs to use the alias to encode a file handle.

Defer finding an alias until it is actually needed so ovl_encode_fh() will not fail in the common case of FAN_DELETE_SELF fanotify events.

Patch / fix

  • Linux Linux 6.6.74, 6.12.10, 6.13
  • linux Debian 14, Debian 13 6.12.10-1

debian advisories DEBIAN-CVE-2025-21654

  • linux Ubuntu 24.04 LTS 6.8.0-60.63
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1029.31
  • linux-gcp Ubuntu 24.04 LTS 6.8.0-1030.32
  • linux-gke Ubuntu 24.04 LTS 6.8.0-1025.29
  • linux-ibm Ubuntu 24.04 LTS 6.8.0-1026.26
  • linux-azure Ubuntu 24.04 LTS 6.8.0-1029.34
  • linux-gkeop Ubuntu 24.04 LTS 6.8.0-1012.14
  • linux-raspi Ubuntu 24.04 LTS 6.8.0-1028.32

ubuntu advisories UBUNTU-CVE-2025-21654

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-21654 updated cvss 5.5

kernel: ovl: support encoding fid from inode with no alias

  • Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.20% chance of exploitation in the next 30 days, higher than 10% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.