linux-kernel - Re: [PATCH] Reserve N process to root

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Message-ID: <20071010011523.7d6cca12@0xff.cl>
Date:	Wed, 10 Oct 2007 01:15:23 -0400
From:	Gustavo Chain <g@...f.cl>
To:	unlisted-recipients:; (no To-header on input)
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Reserve N process to root

El Wed, 10 Oct 2007 11:19:27 +0930
David Newall <david@...idnewall.com> escribió:

> Gustavo Chain wrote:
> > I think it's necessary to reserve some pids to the super user.
> > 5 must be sufficient.
> 
> Why?  (Sorry if I missed something.)

To prevent a posible DoS ?

> 
> Shouldn't you test for error return before the pid is allocated?  
> Otherwise, I think, you have to free it.  Thus:
> >  long do_fork(unsigned long clone_flags,
> >               int __user *parent_tidptr,
> >               int __user *child_tidptr)
> >  {
> > +#define RESERVED_PIDS   5      /* danged if I know why */
> > +
> > +       if (!capable(CAP_SYS_ADMIN) && nr_threads >= max_threads -
> > RESERVED_PIDS)
> > +               return -EAGAIN;
> > +
> >
> >         struct task_struct *p;
> >         int trace = 0;
> >         struct pid *pid = alloc_pid();
> >         long nr;
> >  
> >         if (!pid)
> >                 return -EAGAIN;
> >         nr = pid->nr;
> >   
> 
> (While I'm being picky, I don't like braces around a simple return,
> and neither, I note, does the style guide.)
> -
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-- 
Gustavo Chaín Dumit
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