linux-kernel - Re: [PATCH] kobject_set_name

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Date:	Fri, 26 Jun 2009 16:00:04 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Sergey Senozhatsky <sergey.senozhatsky@...l.by>
Cc:	Greg KH <gregkh@...e.de>, Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kobject_set_name_vargs memory leak

Sergey Senozhatsky <sergey.senozhatsky@...l.by> writes:

> On (06/26/09 07:49), Greg KH wrote:
>> Date: Fri, 26 Jun 2009 07:49:49 -0700
>> From: Greg KH <gregkh@...e.de>
>> To: Sergey Senozhatsky <sergey.senozhatsky@...l.by>
>> Cc: Kay Sievers <kay.sievers@...y.org>,
>> 	"Eric W. Biederman" <ebiederm@...ssion.com>,
>> 	linux-kernel@...r.kernel.org
>> Subject: Re: [PATCH] kobject_set_name_vargs memory leak
>> User-Agent: Mutt/1.5.19 (2009-01-05)
>> 
>> On Fri, Jun 26, 2009 at 05:36:52PM +0300, Sergey Senozhatsky wrote:
>> > Hello.
>> > I suppose this patch fixes memory leak in kobject.c
>> > Correct me if I'm wrong.
>> > Thanks.
>> > -----------
>> > 
>> > Fix memory leak when kobject_set_name_vargs returns -ENOMEM.
>> > 
>> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...l.by>
>> > ---
>> > diff --git a/lib/kobject.c b/lib/kobject.c
>> > index b512b74..922cd8c 100644
>> > --- a/lib/kobject.c
>> > +++ b/lib/kobject.c
>> > @@ -222,8 +222,10 @@ int kobject_set_name_vargs(struct kobject *kobj, const char *fmt,
>> >  		return 0;
>> >  
>> >  	kobj->name = kvasprintf(GFP_KERNEL, fmt, vargs);
>> > -	if (!kobj->name)
>> > +	if (!kobj->name) {
>> > +		kfree(old_name);
>> >  		return -ENOMEM;
>> > +	}
>> 
>> We've been through this before (search lkml archives).  If kvasprintf
>> fails, then we don't want to free old_name, as the caller might want to
>> do something with it.
>> 
> Hello Greg,
>
> int kobject_set_name_vargs.... {
> 	const char *old_name = kobj->name;
>
> old_name is local variable.
>
> In the following lines we overwrite kobject->name.
>
> 	kobj->name = kvasprintf(GFP_KERNEL, fmt, vargs);
> 	if (!kobj->name)
> 		return -ENOMEM;
>
> It's not clear to me how we can do anything (including kfree) with old_name after 'return -ENOMEM'.

My feel is that if we fail we should restore kobject->name to old_name.

That should also prevent the leak without getting us into trouble elsewhere.

Eric

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