linux-kernel - [PATCH 5.19 004/158] cgroup: Fix race condition at rebind

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Date:   Mon, 29 Aug 2022 12:57:34 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Jing-Ting Wu <jing-ting.wu@...iatek.com>,
        Michal Koutný <mkoutny@...e.com>,
        Mukesh Ojha <quic_mojha@...cinc.com>, Tejun Heo <tj@...nel.org>
Subject: [PATCH 5.19 004/158] cgroup: Fix race condition at rebind_subsystems()

From: Jing-Ting Wu <Jing-Ting.Wu@...iatek.com>

commit 763f4fb76e24959c370cdaa889b2492ba6175580 upstream.

Root cause:
The rebind_subsystems() is no lock held when move css object from A
list to B list,then let B's head be treated as css node at
list_for_each_entry_rcu().

Solution:
Add grace period before invalidating the removed rstat_css_node.

Reported-by: Jing-Ting Wu <jing-ting.wu@...iatek.com>
Suggested-by: Michal Koutný <mkoutny@...e.com>
Signed-off-by: Jing-Ting Wu <jing-ting.wu@...iatek.com>
Tested-by: Jing-Ting Wu <jing-ting.wu@...iatek.com>
Link: https://lore.kernel.org/linux-arm-kernel/d8f0bc5e2fb6ed259f9334c83279b4c011283c41.camel@mediatek.com/T/
Acked-by: Mukesh Ojha <quic_mojha@...cinc.com>
Fixes: a7df69b81aac ("cgroup: rstat: support cgroup1")
Cc: stable@...r.kernel.org # v5.13+
Signed-off-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/cgroup/cgroup.c |    1 +
 1 file changed, 1 insertion(+)

--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1811,6 +1811,7 @@ int rebind_subsystems(struct cgroup_root
 
 		if (ss->css_rstat_flush) {
 			list_del_rcu(&css->rstat_css_node);
+			synchronize_rcu();
 			list_add_rcu(&css->rstat_css_node,
 				     &dcgrp->rstat_css_list);
 		}