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SubjectRe: x86: randomize brk() and RLIMIT_DATA
On Thu, 25 Oct 2007, Arjan van de Ven wrote:

> > Would be neat if randomized brk and setrlimit(RLIMIT_DATA, ...)
> > worked in a predictable way:
> this isn't a valid case afaics; even on "traditional x86" (before we
> changed the address space layout, or even today if you have an unlimited
> stack rlimit) this isn't going to work. applications really shouldn't
> use (s)brk() but malloc(); you have to be able to fall back to mmap
> regardless of what you do.

I tend to agree here with Arjan. However it probably would make no harm to
make at least a little bit consisten behavior of setrlimit(), though it
has a little use in such cases.

Sami, does the patch below work for you?

diff --git a/mm/mmap.c b/mm/mmap.c
index facc1a7..c7ade18 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_data -
+ (mm->start_brk - mm->end_data) > rlim)
goto out;

newbrk = PAGE_ALIGN(brk);
-
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