linux-cve-announce - CVE-2025-68299: afs: Fix delayed allocation of a cell's anonymous key

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Message-ID: <2025121642-CVE-2025-68299-411f@gregkh>
Date: Tue, 16 Dec 2025 16:06:53 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-68299: afs: Fix delayed allocation of a cell's anonymous key

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

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

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

afs: Fix delayed allocation of a cell's anonymous key

The allocation of a cell's anonymous key is done in a background thread
along with other cell setup such as doing a DNS upcall.  In the reported
bug, this is triggered by afs_parse_source() parsing the device name given
to mount() and calling afs_lookup_cell() with the name of the cell.

The normal key lookup then tries to use the key description on the
anonymous authentication key as the reference for request_key() - but it
may not yet be set and so an oops can happen.

This has been made more likely to happen by the fix for dynamic lookup
failure.

Fix this by firstly allocating a reference name and attaching it to the
afs_cell record when the record is created.  It can share the memory
allocation with the cell name (unfortunately it can't just overlap the cell
name by prepending it with "afs@" as the cell name already has a '.'
prepended for other purposes).  This reference name is then passed to
request_key().

Secondly, the anon key is now allocated on demand at the point a key is
requested in afs_request_key() if it is not already allocated.  A mutex is
used to prevent multiple allocation for a cell.

Thirdly, make afs_request_key_rcu() return NULL if the anonymous key isn't
yet allocated (if we need it) and then the caller can return -ECHILD to
drop out of RCU-mode and afs_request_key() can be called.

Note that the anonymous key is kind of necessary to make the key lookup
cache work as that doesn't currently cache a negative lookup, but it's
probably worth some investigation to see if NULL can be used instead.

The Linux kernel CVE team has assigned CVE-2025-68299 to this issue.

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

	Issue introduced in 6.17.9 with commit 7e33b15d5a6578a99ebf189cea34983270ae92dd and fixed in 6.17.11 with commit 5613bde937dfac6725e9c3fc766b9d6b8481e55b

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-2025-68299
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/cell.c
	fs/afs/internal.h
	fs/afs/security.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/5613bde937dfac6725e9c3fc766b9d6b8481e55b
	https://git.kernel.org/stable/c/d27c71257825dced46104eefe42e4d9964bd032e