[v2] cpufreq: fix race on cpufreq online

[PATCH v2] cpufreq: fix race on cpufreq online

Posted by Schspa Shi 3 years, 12 months ago

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) {
@@ -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)

Re: [PATCH v2] cpufreq: fix race on cpufreq online

Posted by Rafael J. Wysocki 3 years, 12 months ago

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);
> --

Re: [PATCH v2] cpufreq: fix race on cpufreq online

Posted by Schspa Shi 3 years, 12 months ago

Rafael J. Wysocki <rafael@kernel.org> 于2022年5月10日周二 23:35写道：
>
> 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.
>

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