[PATCH 5.18 335/879] cpufreq: Fix possible race in cpufreq online error path

Greg Kroah-Hartman
2022-06-07T22:36:34Z

From: Schspa Shi <schspa@gmail.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@gmail.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.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 fbaa8e6c7d23..233e8af48848 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1534,8 +1534,6 @@ 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);
@@ -1544,6 +1542,9 @@ 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