threads/160708: Bypass process stack quota :)

[Michael Pounov]

On Mon, 19 Sep 2011 08:43:27 -0400
John Baldwin <jhb at freebsd.org> wrote:

> On Saturday, September 17, 2011 7:50:08 am Michael Pounov wrote:
> > The following reply was made to PR threads/160708; it has been noted by 
> GNATS.
> > 
> > From: Michael Pounov <misho at elwix.org>
> > To: freebsd-gnats-submit at freebsd.org
> > Cc:  
> > Subject: Re: threads/160708: Bypass process stack quota :)
> > Date: Sat, 17 Sep 2011 14:26:11 +0300
> > 
> >  Hmm, you no so right Peter. 
> >  
> >  	Yes I can move esp pointer in any other address, but please 
> >  start program and see address of allocated memory for every thread. 
> >  All this allocations is made in upper memory called stack. 
> >  	
> >  	Try same alloca() in main program thread and you see how 
> >  system terminate program if you going over stack limit.
> 
> It's not very practical to apply this limit to multithreaded apps.  Would you 
> want it to be a global limit (i.e. all stacks summed together must be <= 
> limit) or a per-thread limit (i.e. each thread's stack must be <= limit).  
> Also, given that RLIMIT_DATA is now obsolete (since malloc() defaults to using 
> MAP_ANON with mmap() rather than sbrk()), using RLIMIT_AS is probably the 
> right thing if you are trying to prevent local DOS.
> 
> -- 
> John Baldwin

My opinion from security viewpoint is all stacks summed together must be <= limit.
Also reasonable solution is each thread's stack must be <= limit.

Problem is not from own software, problem appears from buggy software of customer installed on server. I am not happy with that, when customer able get all resources with user account.
This should be avoided when posible.

-- 
Michael Pounov <misho at elwix.org>