linux-cve-announce - CVE-2022-50177: rcutorture: Fix ksoftirqd boosting timing and iteration

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Message-ID: <2025061831-CVE-2022-50177-1d63@gregkh>
Date: Wed, 18 Jun 2025 13:04:02 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2022-50177: rcutorture: Fix ksoftirqd boosting timing and iteration

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

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

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

rcutorture: Fix ksoftirqd boosting timing and iteration

The RCU priority boosting can fail in two situations:

1) If (nr_cpus= > maxcpus=), which means if the total number of CPUs
is higher than those brought online at boot, then torture_onoff() may
later bring up CPUs that weren't online on boot. Now since rcutorture
initialization only boosts the ksoftirqds of the CPUs that have been
set online on boot, the CPUs later set online by torture_onoff won't
benefit from the boost, making RCU priority boosting fail.

2) The ksoftirqd kthreads are boosted after the creation of
rcu_torture_boost() kthreads, which opens a window large enough for these
rcu_torture_boost() kthreads to wait (despite running at FIFO priority)
for ksoftirqds that are still running at SCHED_NORMAL priority.

The issues can trigger for example with:

	./kvm.sh --configs TREE01 --kconfig "CONFIG_RCU_BOOST=y"

	[   34.968561] rcu-torture: !!!
	[   34.968627] ------------[ cut here ]------------
	[   35.014054] WARNING: CPU: 4 PID: 114 at kernel/rcu/rcutorture.c:1979 rcu_torture_stats_print+0x5ad/0x610
	[   35.052043] Modules linked in:
	[   35.069138] CPU: 4 PID: 114 Comm: rcu_torture_sta Not tainted 5.18.0-rc1 #1
	[   35.096424] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014
	[   35.154570] RIP: 0010:rcu_torture_stats_print+0x5ad/0x610
	[   35.198527] Code: 63 1b 02 00 74 02 0f 0b 48 83 3d 35 63 1b 02 00 74 02 0f 0b 48 83 3d 21 63 1b 02 00 74 02 0f 0b 48 83 3d 0d 63 1b 02 00 74 02 <0f> 0b 83 eb 01 0f 8e ba fc ff ff 0f 0b e9 b3 fc ff f82
	[   37.251049] RSP: 0000:ffffa92a0050bdf8 EFLAGS: 00010202
	[   37.277320] rcu: De-offloading 8
	[   37.290367] RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000001
	[   37.290387] RDX: 0000000000000000 RSI: 00000000ffffbfff RDI: 00000000ffffffff
	[   37.290398] RBP: 000000000000007b R08: 0000000000000000 R09: c0000000ffffbfff
	[   37.290407] R10: 000000000000002a R11: ffffa92a0050bc18 R12: ffffa92a0050be20
	[   37.290417] R13: ffffa92a0050be78 R14: 0000000000000000 R15: 000000000001bea0
	[   37.290427] FS:  0000000000000000(0000) GS:ffff96045eb00000(0000) knlGS:0000000000000000
	[   37.290448] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
	[   37.290460] CR2: 0000000000000000 CR3: 000000001dc0c000 CR4: 00000000000006e0
	[   37.290470] Call Trace:
	[   37.295049]  <TASK>
	[   37.295065]  ? preempt_count_add+0x63/0x90
	[   37.295095]  ? _raw_spin_lock_irqsave+0x12/0x40
	[   37.295125]  ? rcu_torture_stats_print+0x610/0x610
	[   37.295143]  rcu_torture_stats+0x29/0x70
	[   37.295160]  kthread+0xe3/0x110
	[   37.295176]  ? kthread_complete_and_exit+0x20/0x20
	[   37.295193]  ret_from_fork+0x22/0x30
	[   37.295218]  </TASK>

Fix this with boosting the ksoftirqds kthreads from the boosting
hotplug callback itself and before the boosting kthreads are created.

The Linux kernel CVE team has assigned CVE-2022-50177 to this issue.


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

	Issue introduced in 5.14 with commit ea6d962e80b61996aeacb443661cc3adcb605315 and fixed in 5.15.61 with commit 621595f771a6bd458ffbc40679e222ba5d0a7a1e
	Issue introduced in 5.14 with commit ea6d962e80b61996aeacb443661cc3adcb605315 and fixed in 5.18.18 with commit 8e84693621f53bf894af9905a6531e0530402145
	Issue introduced in 5.14 with commit ea6d962e80b61996aeacb443661cc3adcb605315 and fixed in 5.19.2 with commit 7e7472c62c6ded322afd9d5ac8bb20a08e7c5674
	Issue introduced in 5.14 with commit ea6d962e80b61996aeacb443661cc3adcb605315 and fixed in 6.0 with commit 3002153a91a9732a6d1d0bb95138593c7da15743

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-2022-50177
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/rcu/rcutorture.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/621595f771a6bd458ffbc40679e222ba5d0a7a1e
	https://git.kernel.org/stable/c/8e84693621f53bf894af9905a6531e0530402145
	https://git.kernel.org/stable/c/7e7472c62c6ded322afd9d5ac8bb20a08e7c5674
	https://git.kernel.org/stable/c/3002153a91a9732a6d1d0bb95138593c7da15743