[PATCH]cpuidle: preventive check in cpuidle_select against crash

[PATCH]cpuidle: preventive check in cpuidle_select against crash

[gaurav jindal]

When selecting the idle state using cpuidle_select, there is no
check on cpuidle_curr_governor. In cpuidle_switch_governor,
cpuidle_currr_governor can be set to NULL to specify "disabled".

Since cpuidle_select cannot return negative value, it has to return 0
in case of error. Printing logs and returning can help in debugging and
preventing possible kernel crash scenarios.

Signed-off-by: Gaurav Jindal<gauravjindal1104@gmail.com>

---

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 68a1682..bf08e3a 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -268,6 +268,19 @@ int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
  */
 int cpuidle_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
+
+	/* Since negative return is not allowed
+	 * we have to return 0 even if the
+	 * framework cannot select the idle state
+	 */
+	if (!cpuidle_curr_governor) {
+		pr_err("idle governor is disabled\n");
+		return 0;
+	}
+	if (!cpuidle_curr_governor->select) {
+		pr_err("idle governor select is NULL\n");
+		return 0;
+	}
 	return cpuidle_curr_governor->select(drv, dev);
 }

Re: [PATCH]cpuidle: preventive check in cpuidle_select against crash

[Rafael J. Wysocki]

On Tue, Dec 26, 2017 at 8:26 AM, gaurav jindal
<gauravjindal1104@gmail.com> wrote:
> When selecting the idle state using cpuidle_select, there is no
> check on cpuidle_curr_governor. In cpuidle_switch_governor,
> cpuidle_currr_governor can be set to NULL to specify "disabled".

How exactly?

Re: [PATCH]cpuidle: preventive check in cpuidle_select against crash

[gaurav jindal]

On Wed, Dec 27, 2017 at 01:42:58AM +0100, Rafael J. Wysocki wrote:
> On Tue, Dec 26, 2017 at 8:26 AM, gaurav jindal
> <gauravjindal1104@gmail.com> wrote:
> > When selecting the idle state using cpuidle_select, there is no
> > check on cpuidle_curr_governor. In cpuidle_switch_governor,
> > cpuidle_currr_governor can be set to NULL to specify "disabled".
> 
> How exactly?

In cpuidle_switch_governor:
 
/**
 * cpuidle_switch_governor - changes the governor
 * @gov: the new target governor
 *
 * NOTE: "gov" can be NULL to specify disabled
 * Must be called with cpuidle_lock acquired.
 */
int cpuidle_switch_governor(struct cpuidle_governor *gov)
{
	struct cpuidle_device *dev;

	if (gov == cpuidle_curr_governor)
		return 0;

	cpuidle_uninstall_idle_handler();

	if (cpuidle_curr_governor) {
		list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
			cpuidle_disable_device(dev);
	}

	cpuidle_curr_governor = gov;

This allows to set the cpuidle_switch_governor as NULL. Although there is no
current code flow leading here, but it has a potential for bug in future. So
may be better to have prevention.

Re: [PATCH]cpuidle: preventive check in cpuidle_select against crash

[Rafael J. Wysocki]

On Wed, Dec 27, 2017 at 2:57 AM, gaurav jindal
<gauravjindal1104@gmail.com> wrote:
> On Wed, Dec 27, 2017 at 01:42:58AM +0100, Rafael J. Wysocki wrote:
>> On Tue, Dec 26, 2017 at 8:26 AM, gaurav jindal
>> <gauravjindal1104@gmail.com> wrote:
>> > When selecting the idle state using cpuidle_select, there is no
>> > check on cpuidle_curr_governor. In cpuidle_switch_governor,
>> > cpuidle_currr_governor can be set to NULL to specify "disabled".
>>
>> How exactly?
>
> In cpuidle_switch_governor:
>
> /**
>  * cpuidle_switch_governor - changes the governor
>  * @gov: the new target governor
>  *
>  * NOTE: "gov" can be NULL to specify disabled
>  * Must be called with cpuidle_lock acquired.
>  */
> int cpuidle_switch_governor(struct cpuidle_governor *gov)
> {
>         struct cpuidle_device *dev;
>
>         if (gov == cpuidle_curr_governor)
>                 return 0;
>
>         cpuidle_uninstall_idle_handler();
>
>         if (cpuidle_curr_governor) {
>                 list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
>                         cpuidle_disable_device(dev);
>         }
>
>         cpuidle_curr_governor = gov;
>
> This allows to set the cpuidle_switch_governor as NULL. Although there is no
> current code flow leading here, but it has a potential for bug in future. So
> may be better to have prevention.

Or maybe not.

Why don't you make cpuidle_switch_governor() check the argument
against NULL instead?

Re: [PATCH]cpuidle: preventive check in cpuidle_select against crash

[gaurav jindal]

On Wed, Dec 27, 2017 at 03:30:02AM +0100, Rafael J. Wysocki wrote:
> On Wed, Dec 27, 2017 at 2:57 AM, gaurav jindal
> <gauravjindal1104@gmail.com> wrote:
> > On Wed, Dec 27, 2017 at 01:42:58AM +0100, Rafael J. Wysocki wrote:
> >> On Tue, Dec 26, 2017 at 8:26 AM, gaurav jindal
> >> <gauravjindal1104@gmail.com> wrote:
> >> > When selecting the idle state using cpuidle_select, there is no
> >> > check on cpuidle_curr_governor. In cpuidle_switch_governor,
> >> > cpuidle_currr_governor can be set to NULL to specify "disabled".
> >>
> >> How exactly?
> >
> > In cpuidle_switch_governor:
> >
> > /**
> >  * cpuidle_switch_governor - changes the governor
> >  * @gov: the new target governor
> >  *
> >  * NOTE: "gov" can be NULL to specify disabled
> >  * Must be called with cpuidle_lock acquired.
> >  */
> > int cpuidle_switch_governor(struct cpuidle_governor *gov)
> > {
> >         struct cpuidle_device *dev;
> >
> >         if (gov == cpuidle_curr_governor)
> >                 return 0;
> >
> >         cpuidle_uninstall_idle_handler();
> >
> >         if (cpuidle_curr_governor) {
> >                 list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
> >                         cpuidle_disable_device(dev);
> >         }
> >
> >         cpuidle_curr_governor = gov;
> >
> > This allows to set the cpuidle_switch_governor as NULL. Although there is no
> > current code flow leading here, but it has a potential for bug in future. So
> > may be better to have prevention.
> 
> Or maybe not.
> 
> Why don't you make cpuidle_switch_governor() check the argument
> against NULL instead?

If we check gov (argument passed in  cpuidle_switch_governor())against
NULL in cpuidle_switch_governor, can be a problem in a case where it 
is called as
cpuidle_switch_governor(NULL);

If cpuidle_curr_governor is not NULL, first the device is disabled.

if (cpuidle_curr_governor) {
	list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
	cpuidle_disable_device(dev);
}

after this cpuidle_curr_governor is set to gov, which is NULL in this case.

cpuidle_curr_governor = gov;
/* if is not updated by inserting a check, it will have an oudated value*/

Now, if gov is not NULL (which it is in this case), cpuidle device is enabled

if (gov) {
	list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
	cpuidle_enable_device(dev);
	cpuidle_install_idle_handler();
	printk(KERN_INFO "cpuidle: using governor %s\n", gov->name);
}
If we check for gov against NULL in this function, it will produce
dangling pointers and resource leaks.

Re: [PATCH]cpuidle: preventive check in cpuidle_select against crash

[Rafael J. Wysocki]

On Friday, December 29, 2017 7:45:22 PM CET gaurav jindal wrote:
> On Wed, Dec 27, 2017 at 03:30:02AM +0100, Rafael J. Wysocki wrote:
> > On Wed, Dec 27, 2017 at 2:57 AM, gaurav jindal
> > <gauravjindal1104@gmail.com> wrote:
> > > On Wed, Dec 27, 2017 at 01:42:58AM +0100, Rafael J. Wysocki wrote:
> > >> On Tue, Dec 26, 2017 at 8:26 AM, gaurav jindal
> > >> <gauravjindal1104@gmail.com> wrote:
> > >> > When selecting the idle state using cpuidle_select, there is no
> > >> > check on cpuidle_curr_governor. In cpuidle_switch_governor,
> > >> > cpuidle_currr_governor can be set to NULL to specify "disabled".
> > >>
> > >> How exactly?
> > >
> > > In cpuidle_switch_governor:
> > >
> > > /**
> > >  * cpuidle_switch_governor - changes the governor
> > >  * @gov: the new target governor
> > >  *
> > >  * NOTE: "gov" can be NULL to specify disabled
> > >  * Must be called with cpuidle_lock acquired.
> > >  */
> > > int cpuidle_switch_governor(struct cpuidle_governor *gov)
> > > {
> > >         struct cpuidle_device *dev;
> > >
> > >         if (gov == cpuidle_curr_governor)
> > >                 return 0;
> > >
> > >         cpuidle_uninstall_idle_handler();
> > >
> > >         if (cpuidle_curr_governor) {
> > >                 list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
> > >                         cpuidle_disable_device(dev);
> > >         }
> > >
> > >         cpuidle_curr_governor = gov;
> > >
> > > This allows to set the cpuidle_switch_governor as NULL. Although there is no
> > > current code flow leading here, but it has a potential for bug in future. So
> > > may be better to have prevention.
> > 
> > Or maybe not.
> > 
> > Why don't you make cpuidle_switch_governor() check the argument
> > against NULL instead?
> 
> If we check gov (argument passed in  cpuidle_switch_governor())against
> NULL in cpuidle_switch_governor, can be a problem in a case where it 
> is called as
> cpuidle_switch_governor(NULL);
> 
> If cpuidle_curr_governor is not NULL, first the device is disabled.
> 
> if (cpuidle_curr_governor) {
> 	list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
> 	cpuidle_disable_device(dev);
> }
> 
> after this cpuidle_curr_governor is set to gov, which is NULL in this case.
> 
> cpuidle_curr_governor = gov;
> /* if is not updated by inserting a check, it will have an oudated value*/
> 
> Now, if gov is not NULL (which it is in this case), cpuidle device is enabled
> 
> if (gov) {
> 	list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
> 	cpuidle_enable_device(dev);
> 	cpuidle_install_idle_handler();
> 	printk(KERN_INFO "cpuidle: using governor %s\n", gov->name);
> }
> If we check for gov against NULL in this function, it will produce
> dangling pointers and resource leaks.

I didn't recommend you to introduce bugs.

Just return -EINVAL if gov is NULL before checking if gov is equal to
cpuidle_curr_governor.

Thanks,
Rafael

Re: [PATCH]cpuidle: preventive check in cpuidle_select against crash

[gaurav jindal]

On Wed, Jan 03, 2018 at 12:16:26PM +0100, Rafael J. Wysocki wrote:
> On Friday, December 29, 2017 7:45:22 PM CET gaurav jindal wrote:
> > On Wed, Dec 27, 2017 at 03:30:02AM +0100, Rafael J. Wysocki wrote:
> > > On Wed, Dec 27, 2017 at 2:57 AM, gaurav jindal
> > > <gauravjindal1104@gmail.com> wrote:
> > > > On Wed, Dec 27, 2017 at 01:42:58AM +0100, Rafael J. Wysocki wrote:
> > > >> On Tue, Dec 26, 2017 at 8:26 AM, gaurav jindal
> > > >> <gauravjindal1104@gmail.com> wrote:
> > > >> > When selecting the idle state using cpuidle_select, there is no
> > > >> > check on cpuidle_curr_governor. In cpuidle_switch_governor,
> > > >> > cpuidle_currr_governor can be set to NULL to specify "disabled".
> > > >>
> > > >> How exactly?
> > > >
> > > > In cpuidle_switch_governor:
> > > >
> > > > /**
> > > >  * cpuidle_switch_governor - changes the governor
> > > >  * @gov: the new target governor
> > > >  *
> > > >  * NOTE: "gov" can be NULL to specify disabled
> > > >  * Must be called with cpuidle_lock acquired.
> > > >  */
> > > > int cpuidle_switch_governor(struct cpuidle_governor *gov)
> > > > {
> > > >         struct cpuidle_device *dev;
> > > >
> > > >         if (gov == cpuidle_curr_governor)
> > > >                 return 0;
> > > >
> > > >         cpuidle_uninstall_idle_handler();
> > > >
> > > >         if (cpuidle_curr_governor) {
> > > >                 list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
> > > >                         cpuidle_disable_device(dev);
> > > >         }
> > > >
> > > >         cpuidle_curr_governor = gov;
> > > >
> > > > This allows to set the cpuidle_switch_governor as NULL. Although there is no
> > > > current code flow leading here, but it has a potential for bug in future. So
> > > > may be better to have prevention.
> > > 
> > > Or maybe not.
> > > 
> > > Why don't you make cpuidle_switch_governor() check the argument
> > > against NULL instead?
> > 
> > If we check gov (argument passed in  cpuidle_switch_governor())against
> > NULL in cpuidle_switch_governor, can be a problem in a case where it 
> > is called as
> > cpuidle_switch_governor(NULL);
> > 
> > If cpuidle_curr_governor is not NULL, first the device is disabled.
> > 
> > if (cpuidle_curr_governor) {
> > 	list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
> > 	cpuidle_disable_device(dev);
> > }
> > 
> > after this cpuidle_curr_governor is set to gov, which is NULL in this case.
> > 
> > cpuidle_curr_governor = gov;
> > /* if is not updated by inserting a check, it will have an oudated value*/
> > 
> > Now, if gov is not NULL (which it is in this case), cpuidle device is enabled
> > 
> > if (gov) {
> > 	list_for_each_entry(dev, &cpuidle_detected_devices, device_list)
> > 	cpuidle_enable_device(dev);
> > 	cpuidle_install_idle_handler();
> > 	printk(KERN_INFO "cpuidle: using governor %s\n", gov->name);
> > }
> > If we check for gov against NULL in this function, it will produce
> > dangling pointers and resource leaks.
> 
> I didn't recommend you to introduce bugs.
> 
I did not intend to do so. I am really sorry it got expressed in that way :(.
> Just return -EINVAL if gov is NULL before checking if gov is equal to
> cpuidle_curr_governor.
> 
Okay 
> Thanks,
> Rafael
> 

this patch checks if the new governor is NULL before updating the
cupidle_curr_governor.

Signed-off-by: gaurav jindal<gauravjindal1104@gmail.com>

---

diff --git a/drivers/cpuidle/governor.c b/drivers/cpuidle/governor.c
index 4e78263..5d359af 100644
--- a/drivers/cpuidle/governor.c
+++ b/drivers/cpuidle/governor.c
@@ -36,14 +36,15 @@ static struct cpuidle_governor * __cpuidle_find_governor(const char *str)
 /**
  * cpuidle_switch_governor - changes the governor
  * @gov: the new target governor
- *
- * NOTE: "gov" can be NULL to specify disabled
  * Must be called with cpuidle_lock acquired.
  */
 int cpuidle_switch_governor(struct cpuidle_governor *gov)
 {
 	struct cpuidle_device *dev;
 
+	if (!gov)
+		return -EINVAL;
+
 	if (gov == cpuidle_curr_governor)
 		return 0;