Re: [PATCH] Reserve N process to root

[David Newall <david@davidnewall.com>]

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.)