[PATCH] mm/slub: release kobject if kobject_init_and_add failed in sysfs_slab_add

[PATCH] mm/slub: release kobject if kobject_init_and_add failed in sysfs_slab_add

[Xin Hao]

In kobject_init_and_add() function, the refcount is setted by calling
kobject_init() function, regardless of whether the return value is zero
or not, therefore, we must call kobject_del(&s->kobj) to prevent memory
of s->kobj is leaked.

Signed-off-by: Xin Hao <xhao@linux.alibaba.com>
---
 mm/slub.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index b1281b8654bd..63b0a8a3a71f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5981,19 +5981,18 @@ static int sysfs_slab_add(struct kmem_cache *s)
 
 	err = sysfs_create_group(&s->kobj, &slab_attr_group);
 	if (err)
-		goto out_del_kobj;
+		goto out;
 
 	if (!unmergeable) {
 		/* Setup first alias */
 		sysfs_slab_alias(s, s->name);
 	}
+	return err;
 out:
 	if (!unmergeable)
 		kfree(name);
-	return err;
-out_del_kobj:
 	kobject_del(&s->kobj);
-	goto out;
+	return err;
 }
 
 void sysfs_slab_unlink(struct kmem_cache *s)
-- 
2.31.0

Re: [PATCH] mm/slub: release kobject if kobject_init_and_add failed in sysfs_slab_add

[Hyeonggon Yoo]

On Thu, Aug 11, 2022 at 10:52:58AM +0800, Xin Hao wrote:
> In kobject_init_and_add() function, the refcount is setted by calling
> kobject_init() function, regardless of whether the return value is zero
> or not, therefore, we must call kobject_del(&s->kobj) to prevent memory

Hello and thanks!

Should kobject_del() be called when kobject_add() failed?

its comments says:

 597  * kobject_del() - Unlink kobject from hierarchy.
 598  * @kobj: object.
 599  *
 600  * This is the function that should be called to delete an object
 601  * successfully added via kobject_add().

AFAIK kobject_put() is proper function to call when
kobject_init_and_add() failed as stated in its comment:

 417 /**
 418  * kobject_init_and_add() - Initialize a kobject structure and add it to
 419  *                          the kobject hierarchy.
 420  * @kobj: pointer to the kobject to initialize
 421  * @ktype: pointer to the ktype for this kobject.
 422  * @parent: pointer to the parent of this kobject.
 423  * @fmt: the name of the kobject.
 424  *
 425  * This function combines the call to kobject_init() and kobject_add().
 426  *
 427  * If this function returns an error, kobject_put() must be called to
 428  * properly clean up the memory associated with the object.  This is the
 429  * same type of error handling after a call to kobject_add() and kobject
 430  * lifetime rules are the same here.

> of s->kobj is leaked.
> 
> Signed-off-by: Xin Hao <xhao@linux.alibaba.com>
> ---
>  mm/slub.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index b1281b8654bd..63b0a8a3a71f 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5981,19 +5981,18 @@ static int sysfs_slab_add(struct kmem_cache *s)
>  
>  	err = sysfs_create_group(&s->kobj, &slab_attr_group);
>  	if (err)
> -		goto out_del_kobj;
> +		goto out;
>  
>  	if (!unmergeable) {
>  		/* Setup first alias */
>  		sysfs_slab_alias(s, s->name);
>  	}
> +	return err;
>  out:
>  	if (!unmergeable)
>  		kfree(name);
> -	return err;
> -out_del_kobj:
>  	kobject_del(&s->kobj);
> -	goto out;
> +	return err;
>  }
>  
>  void sysfs_slab_unlink(struct kmem_cache *s)
> -- 
> 2.31.0

Re: [PATCH] mm/slub: release kobject if kobject_init_and_add failed in sysfs_slab_add

[haoxin]

在 2022/8/11 上午11:31, Hyeonggon Yoo 写道:
> On Thu, Aug 11, 2022 at 10:52:58AM +0800, Xin Hao wrote:
>> In kobject_init_and_add() function, the refcount is setted by calling
>> kobject_init() function, regardless of whether the return value is zero
>> or not, therefore, we must call kobject_del(&s->kobj) to prevent memory
> Hello and thanks!
>
> Should kobject_del() be called when kobject_add() failed?

Yes,  I'm afraid think so， you can see the comment about kobject_add()

* Return: If this function returns an error, kobject_put() must be
  *         called to properly clean up the memory associated with the
  *         object.  Under no instance should the kobject that is passed
  *         to this function be directly freed with a call to kfree(),
  *         that can leak memory.
  *
  *         If this function returns success, kobject_put() must also be 
called
  *         in order to properly clean up the memory associated with the 
object.
  *
  *         In short, once this function is called, kobject_put() MUST 
be called
  *         when the use of the object is finished in order to properly free
  *         everything.
  */
int kobject_add(struct kobject *kobj, struct kobject *parent,
                 const char *fmt, ...)

>
> its comments says:
>
>   597  * kobject_del() - Unlink kobject from hierarchy.
>   598  * @kobj: object.
>   599  *
>   600  * This is the function that should be called to delete an object
>   601  * successfully added via kobject_add().
>
> AFAIK kobject_put() is proper function to call when
> kobject_init_and_add() failed as stated in its comment:
>
>   417 /**
>   418  * kobject_init_and_add() - Initialize a kobject structure and add it to
>   419  *                          the kobject hierarchy.
>   420  * @kobj: pointer to the kobject to initialize
>   421  * @ktype: pointer to the ktype for this kobject.
>   422  * @parent: pointer to the parent of this kobject.
>   423  * @fmt: the name of the kobject.
>   424  *
>   425  * This function combines the call to kobject_init() and kobject_add().
>   426  *
>   427  * If this function returns an error, kobject_put() must be called to
>   428  * properly clean up the memory associated with the object.  This is the
>   429  * same type of error handling after a call to kobject_add() and kobject
>   430  * lifetime rules are the same here.
>
>> of s->kobj is leaked.
>>
>> Signed-off-by: Xin Hao <xhao@linux.alibaba.com>
>> ---
>>   mm/slub.c | 7 +++----
>>   1 file changed, 3 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index b1281b8654bd..63b0a8a3a71f 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -5981,19 +5981,18 @@ static int sysfs_slab_add(struct kmem_cache *s)
>>   
>>   	err = sysfs_create_group(&s->kobj, &slab_attr_group);
>>   	if (err)
>> -		goto out_del_kobj;
>> +		goto out;
>>   
>>   	if (!unmergeable) {
>>   		/* Setup first alias */
>>   		sysfs_slab_alias(s, s->name);
>>   	}
>> +	return err;
>>   out:
>>   	if (!unmergeable)
>>   		kfree(name);
>> -	return err;
>> -out_del_kobj:
>>   	kobject_del(&s->kobj);
Maybe there use kobject_put will be better.
>> -	goto out;
>> +	return err;
>>   }
>>   
>>   void sysfs_slab_unlink(struct kmem_cache *s)
>> -- 
>> 2.31.0