CVE-2026-74670: ipvs: stop estimator after disabled calc phase

From: Greg Kroah-Hartman <[email protected]>

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

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

ipvs: stop estimator after disabled calc phase

IPVS estimator kthread 0 starts with zeroed chain and tick limits until
its initial calculation phase completes. If network namespace teardown
clears ipvs->enable during that phase, ip_vs_est_calc_phase() can return
without installing positive limits.

The kthread can then continue into its main loop and drain
est_temp_list with zero chain_max, tick_max and est_max_count values.
Each enqueue consumes one available tick row, but est_count never
reaches the zero est_max_count value. After all rows are consumed, the
row lookup returns IPVS_EST_NTICKS and ip_vs_enqueue_estimator() writes
past the ticks and tick_len arrays.

Exit kthread 0 after the calculation phase if the kthread is stopping or
IPVS has been disabled. That keeps temporary estimators from being
drained after the limits failed to initialize.

Estimator kthreads can now self-exit before teardown or reload stops
kd->task. Keep an extra task reference after creation and release it
with kthread_stop_put(), so kd->task remains valid until the stop paths
consume that reference.

The Linux kernel CVE team has assigned CVE-2026-74670 to this issue.


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

	Issue introduced in 6.2 with commit 705dd34440812735ece298eb5bc153fde9544d42 and fixed in 6.6.152 with commit d5122a2b2601145975d387006e517c56896e310e
	Issue introduced in 6.2 with commit 705dd34440812735ece298eb5bc153fde9544d42 and fixed in 6.12.104 with commit de98dc5ef94b83bbb444c670c253ea02ca0f5e43
	Issue introduced in 6.2 with commit 705dd34440812735ece298eb5bc153fde9544d42 and fixed in 6.18.45 with commit e7f34f29b330265d456943bf0b984dcecfcef9af
	Issue introduced in 6.2 with commit 705dd34440812735ece298eb5bc153fde9544d42 and fixed in 7.1.9 with commit 2335dedc1922dfa889ca1f9f70370924e8e79a08
	Issue introduced in 6.2 with commit 705dd34440812735ece298eb5bc153fde9544d42 and fixed in 7.2 with commit 558f67f1340f803a346ecd14a69c49653111c5f4

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-2026-74670
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:
	net/netfilter/ipvs/ip_vs_est.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/d5122a2b2601145975d387006e517c56896e310e
	https://git.kernel.org/stable/c/de98dc5ef94b83bbb444c670c253ea02ca0f5e43
	https://git.kernel.org/stable/c/e7f34f29b330265d456943bf0b984dcecfcef9af
	https://git.kernel.org/stable/c/2335dedc1922dfa889ca1f9f70370924e8e79a08
	https://git.kernel.org/stable/c/558f67f1340f803a346ecd14a69c49653111c5f4