Re: [PATCH -net] netpoll: fix NULL pointer dereference in netpoll_cleanup

[Joe Perches <joe@perches.com>]

On Wed, 2013-09-18 at 12:15 -0400, David Miller wrote:
> From: Nikolay Aleksandrov <nikolay@redhat.com>
> Date: Tue, 17 Sep 2013 16:12:35 +0200
> 
> > @@ -1284,15 +1284,15 @@ EXPORT_SYMBOL_GPL(__netpoll_free_async);
> >  
> >  void netpoll_cleanup(struct netpoll *np)
> >  {
> > -     if (!np->dev)
> > -             return;
> > -
> >       rtnl_lock();
> > +     if (!np->dev) {
> > +             rtnl_unlock();
> > +             return;
> > +     }
> >       __netpoll_cleanup(np);
> > -     rtnl_unlock();
> > -
> >       dev_put(np->dev);
> >       np->dev = NULL;
> > +     rtnl_unlock();
> >  }
> >  EXPORT_SYMBOL(netpoll_cleanup);
> 
> I know it seems arbitrary, but please do this like:
> 
>         lock();
>         if (condition) {
>                 ...
>         }
>         unlock();
> 
> rather than having multiple return/unlock code paths.
> 
> This style I am suggesting is easier to audit for locking problems.

Another alternative is:

	lock();

	if (!condition)
		goto out;

	...

out:
	unlock();
	return ...;
}