Re: [PATCH] [RFC] brk randomization: compute RLIMIT_DATA properly (was Re: x86: randomize brk() and RLIMIT_DATA)

[Hugh Dickins <hugh@veritas.com>]

On Fri, 26 Oct 2007, Jiri Kosina wrote:
> On Fri, 26 Oct 2007, Hugh Dickins wrote:
> 
> > > -	if (rlim < RLIM_INFINITY && brk - mm->start_data > rlim)
> > > +	if (rlim < RLIM_INFINITY && brk - mm->start_data -
> > > +			(mm->start_brk - mm->end_data) > rlim)
> > I find the order in that test mysterious.
> 
> I agree that the order you proposed is easier to understand on the first 
> sight.
> 
> 
> From: Jiri Kosina <jkosina@suse.cz>
> 
> brk randomization: compute RLIMIT_DATA properly
> 
> In cases of heap area placed at randomly-generated offset from
> mm->end_data (arch_randomize_brk()), we need to subtract the value of the
> offset for setrlimit(RLIMIT_DATA) to work properly -- otherwise we count
> the unoccupied memory between mm->end_data and mm->start_brk as occupied.
> 
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Acked-by: Hugh Dickins <hugh@veritas.com>

> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index facc1a7..673ac7d 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -251,7 +251,8 @@ asmlinkage unsigned long sys_brk(unsigned long brk)
>  	 * not page aligned -Ram Gupta
>  	 */
>  	rlim = current->signal->rlim[RLIMIT_DATA].rlim_cur;
> -	if (rlim < RLIM_INFINITY && brk - mm->start_data > rlim)
> +	if (rlim < RLIM_INFINITY && (brk - mm->start_brk) +
> +			(mm->end_data - mm->start_data) > rlim)
>  		goto out;
>  
>  	newbrk = PAGE_ALIGN(brk);