Message-ID: <470C2FA7.5030207@davidnewall.com>
Date: Wed, 10 Oct 2007 11:19:27 +0930
From: David Newall <david@davidnewall.com>
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To: Gustavo Chain <g@0xff.cl>
CC: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Reserve N process to root
References: <20071009194820.6c8d6e8d@0xff.cl>
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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.)

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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