Is fork() hook ever possible?

[Andrey Chernov]

On Tue, Sep 16, 2008 at 06:27:07PM +0200, Max Laier wrote:
> On Tuesday 16 September 2008 16:03:20 Andrey Chernov wrote:
> > I need some sort of fork() hook to detect that pid is changed to re-stir
> > ar4random() after that (in the child), simple flag variable with
> > child's pid is needed.
> >
> > Currently OpenBSD does almost that checking getpid() every time
> > arc4random() called, but it is very slow way to use getpid() syscall
> > repeatedly, about 12-15 times slower than just arc4random() without
> > getpid().
> >
> > Any ideas?
> 
> I guess the goal here is not to leak the state of the seed to the child, 
> right?
> 
> Wouldn't it be easier to do something like this in libc's fork():
> 
>   arc4random_stir();		/* create a new seed for the child */
>   fork_syscall();
>   if (parent)
>      arc4random_stir();	/* create a new seed for the parent */
> 
> This should solve the problem and doesn't require any handling in arc4random.  
> Of course, programs that call the fork syscall directly won't benefit, but 
> then again ... they are using the syscall directly and should know what they 
> are doing, right?

Calling arc4random_stir() inside fork() will slow down fork() and is not 
acceptable because of it.

-- 
http://ache.pp.ru/