cve/published/2022/CVE-2022-49540.mbox

From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: <linux-cve-announce@vger.kernel.org>
Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org>
Subject: CVE-2022-49540: rcu-tasks: Fix race in schedule and flush work

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

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

rcu-tasks: Fix race in schedule and flush work

While booting secondary CPUs, cpus_read_[lock/unlock] is not keeping
online cpumask stable. The transient online mask results in below
calltrace.

[    0.324121] CPU1: Booted secondary processor 0x0000000001 [0x410fd083]
[    0.346652] Detected PIPT I-cache on CPU2
[    0.347212] CPU2: Booted secondary processor 0x0000000002 [0x410fd083]
[    0.377255] Detected PIPT I-cache on CPU3
[    0.377823] CPU3: Booted secondary processor 0x0000000003 [0x410fd083]
[    0.379040] ------------[ cut here ]------------
[    0.383662] WARNING: CPU: 0 PID: 10 at kernel/workqueue.c:3084 __flush_work+0x12c/0x138
[    0.384850] Modules linked in:
[    0.385403] CPU: 0 PID: 10 Comm: rcu_tasks_rude_ Not tainted 5.17.0-rc3-v8+ #13
[    0.386473] Hardware name: Raspberry Pi 4 Model B Rev 1.4 (DT)
[    0.387289] pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[    0.388308] pc : __flush_work+0x12c/0x138
[    0.388970] lr : __flush_work+0x80/0x138
[    0.389620] sp : ffffffc00aaf3c60
[    0.390139] x29: ffffffc00aaf3d20 x28: ffffffc009c16af0 x27: ffffff80f761df48
[    0.391316] x26: 0000000000000004 x25: 0000000000000003 x24: 0000000000000100
[    0.392493] x23: ffffffffffffffff x22: ffffffc009c16b10 x21: ffffffc009c16b28
[    0.393668] x20: ffffffc009e53861 x19: ffffff80f77fbf40 x18: 00000000d744fcc9
[    0.394842] x17: 000000000000000b x16: 00000000000001c2 x15: ffffffc009e57550
[    0.396016] x14: 0000000000000000 x13: ffffffffffffffff x12: 0000000100000000
[    0.397190] x11: 0000000000000462 x10: ffffff8040258008 x9 : 0000000100000000
[    0.398364] x8 : 0000000000000000 x7 : ffffffc0093c8bf4 x6 : 0000000000000000
[    0.399538] x5 : 0000000000000000 x4 : ffffffc00a976e40 x3 : ffffffc00810444c
[    0.400711] x2 : 0000000000000004 x1 : 0000000000000000 x0 : 0000000000000000
[    0.401886] Call trace:
[    0.402309]  __flush_work+0x12c/0x138
[    0.402941]  schedule_on_each_cpu+0x228/0x278
[    0.403693]  rcu_tasks_rude_wait_gp+0x130/0x144
[    0.404502]  rcu_tasks_kthread+0x220/0x254
[    0.405264]  kthread+0x174/0x1ac
[    0.405837]  ret_from_fork+0x10/0x20
[    0.406456] irq event stamp: 102
[    0.406966] hardirqs last  enabled at (101): [<ffffffc0093c8468>] _raw_spin_unlock_irq+0x78/0xb4
[    0.408304] hardirqs last disabled at (102): [<ffffffc0093b8270>] el1_dbg+0x24/0x5c
[    0.409410] softirqs last  enabled at (54): [<ffffffc0081b80c8>] local_bh_enable+0xc/0x2c
[    0.410645] softirqs last disabled at (50): [<ffffffc0081b809c>] local_bh_disable+0xc/0x2c
[    0.411890] ---[ end trace 0000000000000000 ]---
[    0.413000] smp: Brought up 1 node, 4 CPUs
[    0.413762] SMP: Total of 4 processors activated.
[    0.414566] CPU features: detected: 32-bit EL0 Support
[    0.415414] CPU features: detected: 32-bit EL1 Support
[    0.416278] CPU features: detected: CRC32 instructions
[    0.447021] Callback from call_rcu_tasks_rude() invoked.
[    0.506693] Callback from call_rcu_tasks() invoked.

This commit therefore fixes this issue by applying a single-CPU
optimization to the RCU Tasks Rude grace-period process.  The key point
here is that the purpose of this RCU flavor is to force a schedule on
each online CPU since some past event.  But the rcu_tasks_rude_wait_gp()
function runs in the context of the RCU Tasks Rude's grace-period kthread,
so there must already have been a context switch on the current CPU since
the call to either synchronize_rcu_tasks_rude() or call_rcu_tasks_rude().
So if there is only a single CPU online, RCU Tasks Rude's grace-period
kthread does not need to anything at all.

It turns out that the rcu_tasks_rude_wait_gp() function's call to
schedule_on_each_cpu() causes problems during early boot.  During that
time, there is only one online CPU, namely the boot CPU.  Therefore,
applying this single-CPU optimization fixes early-boot instances of
this problem.

The Linux kernel CVE team has assigned CVE-2022-49540 to this issue.


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

	Fixed in 5.10.121 with commit 1c6c3f2336642fb3074593911f5176565f47ec41
	Fixed in 5.15.46 with commit ba722d061bc4b54802d701fc63fc2fd988934603
	Fixed in 5.17.14 with commit 230bf5878af6038dfb63d9184272a58475236580
	Fixed in 5.18.3 with commit 8f49a8758b5cd541bd7aa9a0d0d11c7426141c0e
	Fixed in 5.19 with commit f75fd4b9221d93177c50dcfde671b2e907f53e86

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-2022-49540
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/tasks.h


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/1c6c3f2336642fb3074593911f5176565f47ec41
	https://git.kernel.org/stable/c/ba722d061bc4b54802d701fc63fc2fd988934603
	https://git.kernel.org/stable/c/230bf5878af6038dfb63d9184272a58475236580
	https://git.kernel.org/stable/c/8f49a8758b5cd541bd7aa9a0d0d11c7426141c0e
	https://git.kernel.org/stable/c/f75fd4b9221d93177c50dcfde671b2e907f53e86