Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753480Ab0BIGL2 (ORCPT ); Tue, 9 Feb 2010 01:11:28 -0500 Received: from ozlabs.org ([203.10.76.45]:42061 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751853Ab0BIGL1 (ORCPT ); Tue, 9 Feb 2010 01:11:27 -0500 From: Michael Neuling To: KOSAKI Motohiro cc: Americo Wang , Anton Blanchard , Andrew Morton , Linus Torvalds , Alexander Viro , Oleg Nesterov , James Morris , Ingo Molnar , linux-fsdevel@vger.kernel.org, stable@kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org, Serge Hallyn , Paul Mackerras , benh@kernel.crashing.org, miltonm@bga.com, aeb@cwi.nl Subject: [PATCH] Restrict initial stack space expansion to rlimit In-reply-to: <20100208161014.7C6D.A69D9226@jp.fujitsu.com> References: <20100208145240.FB58.A69D9226@jp.fujitsu.com> <2375c9f91002072307h4af1ba6dw1b7a598582991dc4@mail.gmail.com> <20100208161014.7C6D.A69D9226@jp.fujitsu.com> Comments: In-reply-to KOSAKI Motohiro message dated "Mon, 08 Feb 2010 16:11:47 +0900." X-Mailer: MH-E 8.2; nmh 1.3; GNU Emacs 23.1.1 Date: Tue, 09 Feb 2010 17:11:25 +1100 Message-ID: <1273.1265695885@neuling.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2916 Lines: 78 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 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 Cc: stable@kernel.org --- Attempts to answer comments from Kosaki Motohiro. Tested on PPC only, hence !CONFIG_STACK_GROWSUP. Someone should probably ACK for an arch with CONFIG_STACK_GROWSUP. As noted, stable needs the same patch, but 2.6.32 doesn't have the rlimit() helper. fs/exec.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) Index: linux-2.6-ozlabs/fs/exec.c =================================================================== --- linux-2.6-ozlabs.orig/fs/exec.c +++ linux-2.6-ozlabs/fs/exec.c @@ -555,6 +555,7 @@ static int shift_arg_pages(struct vm_are } #define EXTRA_STACK_VM_PAGES 20 /* random */ +#define ALIGN_DOWN(addr,size) ((addr)&(~((size)-1))) /* * Finalizes the stack vm_area_struct. The flags and permissions are updated, @@ -570,7 +571,7 @@ int setup_arg_pages(struct linux_binprm struct vm_area_struct *vma = bprm->vma; struct vm_area_struct *prev = NULL; unsigned long vm_flags; - unsigned long stack_base; + unsigned long stack_base, stack_expand, stack_expand_lim, stack_size; #ifdef CONFIG_STACK_GROWSUP /* Limit stack size to 1GB */ @@ -627,10 +628,24 @@ 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; + if (rlimit(RLIMIT_STACK) < stack_size) + stack_expand_lim = 0; /* don't shrick the stack */ + else + /* + * Align this down to a page boundary as expand_stack + * will align it up. + */ + stack_expand_lim = ALIGN_DOWN(rlimit(RLIMIT_STACK) - stack_size, + PAGE_SIZE); + /* 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) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/