Messages in this thread Patch in this message | | | From | Schspa Shi <> | Subject | [PATCH v2] cpufreq: fix race on cpufreq online | Date | Tue, 10 May 2022 23:28:11 +0800 |
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When cpufreq online failed, policy->cpus are not empty while cpufreq sysfs file available, we may access some data freed.
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);
down_write(&policy->rwsem); ... /* cpufreq nitialization fails in some cases */ if (cpufreq_driver->get && has_target()) { policy->cur = cpufreq_driver->get(policy->cpu); if (!policy->cur) { ret = -EIO; pr_err("%s: ->get() failed\n", __func__); goto out_destroy_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); }
We can fix it by clear the policy->cpus mask. Both show_scaling_cur_freq and show_cpuinfo_cur_freq will return an error by checking this mask, thus avoiding UAF.
Signed-off-by: Schspa Shi <schspa@gmail.com>
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Changelog: v1 -> v2: - Fix bad critical region enlarge which causes uninitialized unlock. --- 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 80f535cc8a75..8edfa840dd74 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1337,12 +1337,12 @@ static int cpufreq_online(unsigned int cpu) down_write(&policy->rwsem); policy->cpu = cpu; policy->governor = NULL; - up_write(&policy->rwsem); } else { new_policy = true; policy = cpufreq_policy_alloc(cpu); if (!policy) return -ENOMEM; + down_write(&policy->rwsem); } if (!new_policy && cpufreq_driver->online) { @@ -1533,7 +1533,7 @@ 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); + cpumask_clear(policy->cpus); out_offline_policy: if (cpufreq_driver->offline) @@ -1542,6 +1542,7 @@ static int cpufreq_online(unsigned int cpu) out_exit_policy: if (cpufreq_driver->exit) cpufreq_driver->exit(policy); + up_write(&policy->rwsem); out_free_policy: cpufreq_policy_free(policy); -- 2.24.3 (Apple Git-128)
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