cpuidle: preventive check in cpuidle_select against crash

PATCH In review gaurav jindal 3 participants 7 messages Dec 26, 2017 – Jan 4, 2018 CPU idle time management framework

Share & tools

gaurav jindal

author

2017-12-26 07:26 UTC #0 lore raw

PATCH 1/1 cpuidle: preventive check in cpuidle_select against crash

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<[email protected]>

---

drivers/cpuidle/cpuidle.c +13 -0

index 68a1682..bf08e3a 100644
@@ -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);
 }

Rafael J. Wysocki

maintainer

2017-12-27 00:42 UTC #1 lore raw

Quoted 3 lines · 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".

How exactly?

gaurav jindal

author

2017-12-27 01:57 UTC #2 lore raw

Quoted 7 lines · Rafael J. Wysocki

Quoted 3 lines · 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".
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.

Rafael J. Wysocki

maintainer

2017-12-27 02:30 UTC #3 lore raw

Quoted 34 lines · gaurav jindal

Quoted 7 lines · Rafael J. Wysocki
Quoted 3 lines · 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".
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;

Quoted 3 lines

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?

gaurav jindal

author

2017-12-29 18:45 UTC #4 lore raw

Quoted 36 lines · Rafael J. Wysocki

Quoted 34 lines · gaurav jindal
Quoted 7 lines · Rafael J. Wysocki
Quoted 3 lines · 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".
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;

Quoted 8 lines

Quoted 3 lines
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.

Rafael J. Wysocki

2018-01-03 11:17 UTC #5 lore raw

Quoted 65 lines · CET gaurav jindal

Quoted 36 lines · Rafael J. Wysocki
Quoted 34 lines · gaurav jindal
Quoted 7 lines · Rafael J. Wysocki
Quoted 3 lines · 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".
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;
Quoted 8 lines
Quoted 3 lines
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

Quoted 8 lines

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

gaurav jindal

author

2018-01-04 18:09 UTC #6 lore raw

Quoted 75 lines · Rafael J. Wysocki

Quoted 65 lines · CET gaurav jindal
Quoted 36 lines · Rafael J. Wysocki
Quoted 34 lines · gaurav jindal
Quoted 7 lines · Rafael J. Wysocki
Quoted 3 lines · 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".
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;
Quoted 8 lines
Quoted 3 lines
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
Quoted 8 lines
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.

Quoted 2 lines

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 :(.

Quoted 3 lines

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

Okay

Quoted 3 lines

Thanks,
Rafael

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

Signed-off-by gaurav jindal<[email protected]>

---

drivers/cpuidle/governor.c +3 -2

index 4e78263..5d359af 100644
@@ -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;