On Thu, 25 Oct 2007, Sami Farin 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?
> Thanks, Jiri, now RLIMIT_DATA works as expected. Using only RLIMIT_AS to
> limit processes' memory usage is not very easy. It includes also
> libraries mapped read-only, I have to check/modify the limits when I
> update/add libraries,...
This patch is [RFC] as I am not sure whether it is worth it (see Arjan's
comment above).
From: Jiri Kosina <[email protected]>
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 <[email protected]>
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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