From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753484Ab0BUGmt (ORCPT ); Sun, 21 Feb 2010 01:42:49 -0500 Received: from ozlabs.org ([203.10.76.45]:52759 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751961Ab0BUGmr (ORCPT ); Sun, 21 Feb 2010 01:42:47 -0500 From: Michael Neuling To: Greg KH cc: linux-kernel@vger.kernel.org, stable@kernel.org, stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, KOSAKI Motohiro , Americo Wang , Anton Blanchard , Oleg Nesterov , James Morris , Ingo Molnar , Serge Hallyn , Benjamin Herrenschmidt Subject: Re: [29/93] fs/exec.c: restrict initial stack space expansion to rlimit In-reply-to: <20100219163238.671588178@kvm.kroah.org> References: <20100219163238.671588178@kvm.kroah.org> Comments: In-reply-to Greg KH message dated "Fri, 19 Feb 2010 08:29:22 -0800." X-Mailer: MH-E 8.2; nmh 1.3; GNU Emacs 23.1.1 Date: Sun, 21 Feb 2010 17:42:44 +1100 Message-ID: <11054.1266734564@neuling.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In message <20100219163238.671588178@kvm.kroah.org> you wrote: > 2.6.32-stable review patch. If anyone has any objections, please let us know . > > ------------------ > > From: Michael Neuling > > commit 803bf5ec259941936262d10ecc84511b76a20921 upstream. > > When reserving stack space for a new process, make sure we're not > attempting to expand the stack by more than rlimit allows. This breaks UML, so you also need to take this also: http://patchwork.kernel.org/patch/79365/ It's in akpm's tree only so far. Mikey > > 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. > > To test, do: > > 'ulimit -s 15; ls' > > before and after the patch is applied. Before it's applied, 'ls' should > be killed. After the patch is applied, 'ls' should no longer be killed. > > A stack limit of 15KB since it's small enough to trigger 20*PAGE_SIZE. > Also 15KB not a multiple of PAGE_SIZE, which is a trickier case to handle > correctly with this code. > > 4K pages should be fine to test with. > > [kosaki.motohiro@jp.fujitsu.com: cleanup] > [akpm@linux-foundation.org: cleanup cleanup] > Signed-off-by: Michael Neuling > Signed-off-by: KOSAKI Motohiro > Cc: Americo Wang > Cc: Anton Blanchard > Cc: Oleg Nesterov > Cc: James Morris > Cc: Ingo Molnar > Cc: Serge Hallyn > Cc: Benjamin Herrenschmidt > Signed-off-by: Andrew Morton > Signed-off-by: Linus Torvalds > Signed-off-by: Greg Kroah-Hartman > > --- > fs/exec.c | 21 +++++++++++++++++++-- > 1 file changed, 19 insertions(+), 2 deletions(-) > > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -572,6 +572,9 @@ 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 */ > @@ -628,10 +631,24 @@ 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) > >