CVE-2026-89685: nfsd: fix clock domain mismatch in clients_still_reclaiming()

CVE-2026-89685: nfsd: fix clock domain mismatch in clients_still_reclaiming()

[Greg Kroah-Hartman]

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

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

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

nfsd: fix clock domain mismatch in clients_still_reclaiming()

clients_still_reclaiming() computes a deadline from nn->boot_time
(CLOCK_REALTIME, ~1.7 billion) but compares it against
ktime_get_boottime_seconds() (CLOCK_BOOTTIME, seconds since boot).
The comparison is always false — it would take ~54 years of uptime
for BOOTTIME to exceed the REALTIME-derived deadline.

This means any client can hold the server in grace indefinitely by
sending CLAIM_PREVIOUS OPEN requests, blocking all non-reclaim
operations for all other clients.

Add boot_time_bt (CLOCK_BOOTTIME) alongside the existing boot_time
and use it for the deadline computation. boot_time (CLOCK_REALTIME)
is preserved for its cl_boot clientid-nonce role.

The Linux kernel CVE team has assigned CVE-2026-89685 to this issue.


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

	Issue introduced in 5.6 with commit 20b7d86f29d39e8ae19bb29c24ffee70dc385ddf and fixed in 6.18.51 with commit f9cec313efb2fd18d962aad738a4892bce806016
	Issue introduced in 5.6 with commit 20b7d86f29d39e8ae19bb29c24ffee70dc385ddf and fixed in 7.2.4 with commit 9843649196221152b6e5d138a3ce859bdaae1d96
	Issue introduced in 5.6 with commit 20b7d86f29d39e8ae19bb29c24ffee70dc385ddf and fixed in 7.3-rc1 with commit 09ea3eb9a518565f5bca386e81b993ed8825f5e8

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-2026-89685
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/nfsd/netns.h
	fs/nfsd/nfs4state.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/f9cec313efb2fd18d962aad738a4892bce806016
	https://git.kernel.org/stable/c/9843649196221152b6e5d138a3ce859bdaae1d96
	https://git.kernel.org/stable/c/09ea3eb9a518565f5bca386e81b993ed8825f5e8