Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Tue, 10 May 2022 17:34:49 +0200 | Subject | Re: [PATCH v2] cpufreq: fix race on cpufreq online |
| |
On Tue, May 10, 2022 at 5:28 PM Schspa Shi <schspa@gmail.com> 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 <schspa@gmail.com> > > --- > > 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.
> @@ -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); > --
| |