linux-cve-announce - CVE-2025-21646: afs: Fix the maximum cell name length

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Message-ID: <2025011945-CVE-2025-21646-8f6e@gregkh>
Date: Sun, 19 Jan 2025 11:17:55 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21646: afs: Fix the maximum cell name length

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

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

afs: Fix the maximum cell name length

The kafs filesystem limits the maximum length of a cell to 256 bytes, but a
problem occurs if someone actually does that: kafs tries to create a
directory under /proc/net/afs/ with the name of the cell, but that fails
with a warning:

        WARNING: CPU: 0 PID: 9 at fs/proc/generic.c:405

because procfs limits the maximum filename length to 255.

However, the DNS limits the maximum lookup length and, by extension, the
maximum cell name, to 255 less two (length count and trailing NUL).

Fix this by limiting the maximum acceptable cellname length to 253.  This
also allows us to be sure we can create the "/afs/.<cell>/" mountpoint too.

Further, split the YFS VL record cell name maximum to be the 256 allowed by
the protocol and ignore the record retrieved by YFSVL.GetCellName if it
exceeds 253.

The Linux kernel CVE team has assigned CVE-2025-21646 to this issue.


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

	Issue introduced in 5.8 with commit c3e9f888263bb4df11cbd623ceced02081cb2f9f and fixed in 6.1.125 with commit aabe47cf5ac5e1db2ae0635f189d836f67024904
	Issue introduced in 5.8 with commit c3e9f888263bb4df11cbd623ceced02081cb2f9f and fixed in 6.6.72 with commit 7673030efe0f8ca1056d3849d61784c6caa052af
	Issue introduced in 5.8 with commit c3e9f888263bb4df11cbd623ceced02081cb2f9f and fixed in 6.12.10 with commit 7922b1f058fe24a93730511dd0ae2e1630920096
	Issue introduced in 5.8 with commit c3e9f888263bb4df11cbd623ceced02081cb2f9f and fixed in 6.13-rc7 with commit 8fd56ad6e7c90ac2bddb0741c6b248c8c5d56ac8

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-2025-21646
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:
	fs/afs/afs.h
	fs/afs/afs_vl.h
	fs/afs/vl_alias.c
	fs/afs/vlclient.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/aabe47cf5ac5e1db2ae0635f189d836f67024904
	https://git.kernel.org/stable/c/7673030efe0f8ca1056d3849d61784c6caa052af
	https://git.kernel.org/stable/c/7922b1f058fe24a93730511dd0ae2e1630920096
	https://git.kernel.org/stable/c/8fd56ad6e7c90ac2bddb0741c6b248c8c5d56ac8