[PATCH v2 1/4] drm: NULL pointer dereference [null-pointer-deref] (CWE 476) problem

[Joe Moriarty]

On 2/19/2018 6:57 AM, Daniel Vetter wrote:
> On Mon, Feb 12, 2018 at 02:51:41PM -0500, Joe Moriarty wrote:
>> The Parfait (version 2.1.0) static code analysis tool found the
>> following NULL pointer dereference problem.
>>
>> - drivers/gpu/drm/drm_drv.c
>> Any calls to drm_minor_get_slot() could result in the return of a NULL
>> pointer when an invalid DRM device type is encountered.  2 helper
>> functions where added for pointer manipulation (drm_minor_get_slot()
>> and drm_minor_set_minor()) along with checks for valid pointers for
>> struct drm_device variables throughout this module.
>>
>> Signed-off-by: Joe Moriarty <joe.moriarty at oracle.com>
>> Reviewed-by: Steven Sistare <steven.sistare at oracle.com>
> 
> We do not ask for an invalid minor (userspace can't do that, it would be a
> kernel bug). BUG_ON for the invalid case instead of all these changes
> acceptable to shut up your checker?
> -Daniel
>
Daniel,

I did the following and the static checker liked it:

	default:
-		return NULL;
+		BUG();
	}

I will make the change in the patch and resubmit.

Joe

>> ---
>>   drivers/gpu/drm/drm_drv.c | 38 ++++++++++++++++++++++++++++++++++----
>>   1 file changed, 34 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
>> index 9acc1e157813..dee6a4470e2c 100644
>> --- a/drivers/gpu/drm/drm_drv.c
>> +++ b/drivers/gpu/drm/drm_drv.c
>> @@ -99,10 +99,36 @@ static struct drm_minor **drm_minor_get_slot(struct drm_device *dev,
>>   	case DRM_MINOR_CONTROL:
>>   		return &dev->control;
>>   	default:
>> +		DRM_ERROR("Error in %s: Invalid dev, type = %d\n",
>> +			  __func__, type);
>>   		return NULL;
>>   	}
>>   }
>>   
>> +static inline int drm_minor_set_minor(struct drm_device *dev,
>> +				      unsigned int type,
>> +				      struct drm_minor *minor)
>> +{
>> +	struct drm_minor **slot = drm_minor_get_slot(dev, type);
>> +	int retval = -ENODEV;
>> +
>> +	if (slot) {
>> +		retval = 0;
>> +		*slot = minor;
>> +	}
>> +	return retval;
>> +}
>> +
>> +static inline struct drm_minor *drm_minor_get_minor(struct drm_device *dev,
>> +						    unsigned int type)
>> +{
>> +	struct drm_minor **slot = drm_minor_get_slot(dev, type);
>> +
>> +	if (slot)
>> +		return *slot;
>> +	return NULL;
>> +}
>> +
>>   static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
>>   {
>>   	struct drm_minor *minor;
>> @@ -137,8 +163,9 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
>>   		goto err_index;
>>   	}
>>   
>> -	*drm_minor_get_slot(dev, type) = minor;
>> -	return 0;
>> +	r = drm_minor_set_minor(dev, type, minor);
>> +	if (r == 0)
>> +		return r;
>>   
>>   err_index:
>>   	spin_lock_irqsave(&drm_minor_lock, flags);
>> @@ -155,6 +182,9 @@ static void drm_minor_free(struct drm_device *dev, unsigned int type)
>>   	unsigned long flags;
>>   
>>   	slot = drm_minor_get_slot(dev, type);
>> +	if (!slot)
>> +		return;
>> +
>>   	minor = *slot;
>>   	if (!minor)
>>   		return;
>> @@ -177,7 +207,7 @@ static int drm_minor_register(struct drm_device *dev, unsigned int type)
>>   
>>   	DRM_DEBUG("\n");
>>   
>> -	minor = *drm_minor_get_slot(dev, type);
>> +	minor = drm_minor_get_minor(dev, type);
>>   	if (!minor)
>>   		return 0;
>>   
>> @@ -209,7 +239,7 @@ static void drm_minor_unregister(struct drm_device *dev, unsigned int type)
>>   	struct drm_minor *minor;
>>   	unsigned long flags;
>>   
>> -	minor = *drm_minor_get_slot(dev, type);
>> +	minor = drm_minor_get_minor(dev, type);
>>   	if (!minor || !device_is_registered(minor->kdev))
>>   		return;
>>   
>> -- 
>> 2.15.0
>>
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