linux-kernel - [PATCH 5.15 230/667] cpufreq: Fix possible race in cpufreq online error path

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Date:   Tue,  7 Jun 2022 18:58:15 +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, Schspa Shi <schspa@...il.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 230/667] cpufreq: Fix possible race in cpufreq online error path

From: Schspa Shi <schspa@...il.com>

[ Upstream commit f346e96267cd76175d6c201b40f770c0116a8a04 ]

When cpufreq online fails, the policy->cpus mask is not cleared and
policy->rwsem is released too early, so the driver can be invoked
via the cpuinfo_cur_freq sysfs attribute while its ->offline() or
->exit() callbacks are being run.

Take policy->clk as an example:

static int cpufreq_online(unsigned int cpu)
{
  ...
  // policy->cpus != 0 at this time
  down_write(&policy->rwsem);
  ret = cpufreq_add_dev_interface(policy);
  up_write(&policy->rwsem);

  return 0;

out_destroy_policy:
	for_each_cpu(j, policy->real_cpus)
		remove_cpu_dev_symlink(policy, get_cpu_device(j));
    up_write(&policy->rwsem);
...
out_exit_policy:
  if (cpufreq_driver->exit)
    cpufreq_driver->exit(policy);
      clk_put(policy->clk);
      // policy->clk is a wild pointer
...
                                    ^
                                    |
                            Another process access
                            __cpufreq_get
                              cpufreq_verify_current_freq
                                cpufreq_generic_get
                                  // acces wild pointer of policy->clk;
                                    |
                                    |
out_offline_policy:                 |
  cpufreq_policy_free(policy);      |
    // deleted here, and will wait for no body reference
    cpufreq_policy_put_kobj(policy);
}

Address this by modifying cpufreq_online() to release policy->rwsem
in the error path after the driver callbacks have run and to clear
policy->cpus before releasing the semaphore.

Fixes: 7106e02baed4 ("cpufreq: release policy->rwsem on error")
Signed-off-by: Schspa Shi <schspa@...il.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/cpufreq/cpufreq.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index cddf7e13c232..502245710ee0 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1528,8 +1528,6 @@ static int cpufreq_online(unsigned int cpu)
 	for_each_cpu(j, policy->real_cpus)
 		remove_cpu_dev_symlink(policy, get_cpu_device(j));
 
-	up_write(&policy->rwsem);
-
 out_offline_policy:
 	if (cpufreq_driver->offline)
 		cpufreq_driver->offline(policy);
@@ -1538,6 +1536,9 @@ static int cpufreq_online(unsigned int cpu)
 	if (cpufreq_driver->exit)
 		cpufreq_driver->exit(policy);
 
+	cpumask_clear(policy->cpus);
+	up_write(&policy->rwsem);
+
 out_free_policy:
 	cpufreq_policy_free(policy);
 	return ret;
-- 
2.35.1