linux-cve-announce - CVE-2025-39840: audit: fix out-of-bounds read in audit_compare_dname

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Message-ID: <2025091902-CVE-2025-39840-bad6@gregkh>
Date: Fri, 19 Sep 2025 17:28:04 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39840: audit: fix out-of-bounds read in audit_compare_dname_path()

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

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

audit: fix out-of-bounds read in audit_compare_dname_path()

When a watch on dir=/ is combined with an fsnotify event for a
single-character name directly under / (e.g., creating /a), an
out-of-bounds read can occur in audit_compare_dname_path().

The helper parent_len() returns 1 for "/". In audit_compare_dname_path(),
when parentlen equals the full path length (1), the code sets p = path + 1
and pathlen = 1 - 1 = 0. The subsequent loop then dereferences
p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.

Fix this by adding a pathlen > 0 check to the while loop condition
to prevent the out-of-bounds access.

[PM: subject tweak, sign-off email fixes]

The Linux kernel CVE team has assigned CVE-2025-39840 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.14 with commit e92eebb0d6116f942ab25dfb1a41905aa59472a8 and fixed in 6.16.6 with commit 9735a9dcc307427e7d6336c54171682f1bac9789
	Issue introduced in 6.14 with commit e92eebb0d6116f942ab25dfb1a41905aa59472a8 and fixed in 6.17-rc5 with commit 4540f1d23e7f387880ce46d11b5cd3f27248bf8d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-39840
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/auditfilter.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/9735a9dcc307427e7d6336c54171682f1bac9789
	https://git.kernel.org/stable/c/4540f1d23e7f387880ce46d11b5cd3f27248bf8d