Rafael J. Wysocki <[email protected]> 于2022年5月10日周二 23:35写道：
>
> On Tue, May 10, 2022 at 5:28 PM Schspa Shi <[email protected]> wrote:
> >
> > 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 <[email protected]>
> >
> > ---
> >
> > 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) {
>
> You seem to have missed the down_write() before the
>
> cpumask_and(policy->cpus, policy->cpus, cpu_online_mask);
>
> statement.
>
> It needs to be removed, because the semaphore is already being held
> for writing at that point after the changes above.
>
Sorry for that, I have upload a v3 patch to remove this.
> > @@ -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);
> > --
---
BRs
Schspa Shi