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Date: Tue, 9 Feb 2010 13:25:29 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Michael Neuling <mikey@...ling.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Americo Wang <xiyou.wangcong@...il.com>,
Anton Blanchard <anton@...ba.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Oleg Nesterov <oleg@...hat.com>,
James Morris <jmorris@...ei.org>, Ingo Molnar <mingo@...e.hu>,
linux-fsdevel@...r.kernel.org, stable@...nel.org,
linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
Serge Hallyn <serue@...ibm.com>,
Paul Mackerras <paulus@...ba.org>, benh@...nel.crashing.org,
miltonm@....com, aeb@....nl, linux-parisc@...r.kernel.org
Subject: Re: [PATCH] Restrict initial stack space expansion to rlimit
On Tue, 09 Feb 2010 19:59:27 +1100
Michael Neuling <mikey@...ling.org> wrote:
> > > + /* Initial stack must not cause stack overflow. */
> > > + if (stack_expand > stack_expand_lim)
> > > + stack_expand = stack_expand_lim;
> > > #ifdef CONFIG_STACK_GROWSUP
> > > - stack_base = vma->vm_end + EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> > > + stack_base = vma->vm_end + stack_expand;
> > > #else
> > > - stack_base = vma->vm_start - EXTRA_STACK_VM_PAGES * PAGE_SIZE;
> > > + stack_base = vma->vm_start - stack_expand;
> > > #endif
> > > ret = expand_stack(vma, stack_base);
> > > if (ret)
> >
> > Umm.. It looks correct. but the nested complex if statement seems a bit ugly.
> > Instead, How about following?
>
> I don't like the duplicated code in the #ifdef/else but I can live with it.
cleanup the cleanup:
--- a/fs/exec.c~fs-execc-restrict-initial-stack-space-expansion-to-rlimit-cleanup-cleanup
+++ a/fs/exec.c
@@ -637,20 +637,17 @@ int setup_arg_pages(struct linux_binprm
* will align it up.
*/
rlim_stack = rlimit(RLIMIT_STACK) & PAGE_MASK;
- if (rlim_stack < stack_size)
- rlim_stack = stack_size;
+ rlim_stack = min(rlim_stack, stack_size);
#ifdef CONFIG_STACK_GROWSUP
- if (stack_size + stack_expand > rlim_stack) {
+ if (stack_size + stack_expand > rlim_stack)
stack_base = vma->vm_start + rlim_stack;
- } else {
+ else
stack_base = vma->vm_end + stack_expand;
- }
#else
- if (stack_size + stack_expand > rlim_stack) {
+ if (stack_size + stack_expand > rlim_stack)
stack_base = vma->vm_end - rlim_stack;
- } else {
+ else
stack_base = vma->vm_start - stack_expand;
- }
#endif
ret = expand_stack(vma, stack_base);
if (ret)
_
> > note: it's untested.
>
> Works for me on ppc64 with 4k and 64k pages. Thanks!
>
> I'd still like someone with a CONFIG_STACK_GROWSUP arch to test/ACK it
> as well.
There's only one CONFIG_GROWSUP arch - parisc.
Guys, here's the rolled-up patch. Could someone please test it on
parisc?
err, I'm not sure what one needs to do to test it, actually.
Presumably it involves setting an unusual `ulimit -s'. Can someone
please suggest a test plan?
From: Michael Neuling <mikey@...ling.org>
When reserving stack space for a new process, make sure we're not
attempting to expand the stack by more than rlimit allows.
This fixes a bug caused by b6a2fea39318e43fee84fa7b0b90d68bed92d2ba ("mm:
variable length argument support") and unmasked by
fc63cf237078c86214abcb2ee9926d8ad289da9b ("exec: setup_arg_pages() fails
to return errors").
This bug means that when limiting the stack to less the 20*PAGE_SIZE (eg.
80K on 4K pages or 'ulimit -s 79') all processes will be killed before
they start. This is particularly bad with 64K pages, where a ulimit below
1280K will kill every process.
Signed-off-by: Michael Neuling <mikey@...ling.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Americo Wang <xiyou.wangcong@...il.com>
Cc: Anton Blanchard <anton@...ba.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: James Morris <jmorris@...ei.org>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Serge Hallyn <serue@...ibm.com>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: <stable@...nel.org>
fs/exec.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff -puN fs/exec.c~fs-execc-restrict-initial-stack-space-expansion-to-rlimit fs/exec.c
--- a/fs/exec.c~fs-execc-restrict-initial-stack-space-expansion-to-rlimit
+++ a/fs/exec.c
@@ -571,6 +571,9 @@ int setup_arg_pages(struct linux_binprm
struct vm_area_struct *prev = NULL;
unsigned long vm_flags;
unsigned long stack_base;
+ unsigned long stack_size;
+ unsigned long stack_expand;
+ unsigned long rlim_stack;
#ifdef CONFIG_STACK_GROWSUP
/* Limit stack size to 1GB */
@@ -627,10 +630,24 @@ int setup_arg_pages(struct linux_binprm
goto out_unlock;
}
+ stack_expand = EXTRA_STACK_VM_PAGES * PAGE_SIZE;
+ stack_size = vma->vm_end - vma->vm_start;
+ /*
+ * Align this down to a page boundary as expand_stack
+ * will align it up.
+ */
+ rlim_stack = rlimit(RLIMIT_STACK) & PAGE_MASK;
+ rlim_stack = min(rlim_stack, stack_size);
#ifdef CONFIG_STACK_GROWSUP
- stack_base = vma->vm_end + EXTRA_STACK_VM_PAGES * PAGE_SIZE;
+ if (stack_size + stack_expand > rlim_stack)
+ stack_base = vma->vm_start + rlim_stack;
+ else
+ stack_base = vma->vm_end + stack_expand;
#else
- stack_base = vma->vm_start - EXTRA_STACK_VM_PAGES * PAGE_SIZE;
+ if (stack_size + stack_expand > rlim_stack)
+ stack_base = vma->vm_end - rlim_stack;
+ else
+ stack_base = vma->vm_start - stack_expand;
#endif
ret = expand_stack(vma, stack_base);
if (ret)
_
--
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