Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753683Ab0BIGqz (ORCPT ); Tue, 9 Feb 2010 01:46:55 -0500 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:55425 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751853Ab0BIGqy (ORCPT ); Tue, 9 Feb 2010 01:46:54 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: Michael Neuling Subject: Re: [PATCH] Restrict initial stack space expansion to rlimit Cc: kosaki.motohiro@jp.fujitsu.com, 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 In-Reply-To: <1273.1265695885@neuling.org> References: <20100208161014.7C6D.A69D9226@jp.fujitsu.com> <1273.1265695885@neuling.org> Message-Id: <20100209154141.03F0.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.50.07 [ja] Date: Tue, 9 Feb 2010 15:46:50 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5660 Lines: 161 > 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) Umm.. It looks correct. but the nested complex if statement seems a bit ugly. Instead, How about following? note: it's untested. =============== From: Michael Neuling Subject: Restrict initial stack space expansion to rlimit 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. [kosaki.motohiro@jp.fujitsu.com: cleanups] Signed-off-by: Michael Neuling Signed-off-by: KOSAKI Motohiro 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. diff --git a/fs/exec.c b/fs/exec.c index 6f7fb0c..325bad4 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -573,6 +573,9 @@ int setup_arg_pages(struct linux_binprm *bprm, 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 */ @@ -629,10 +632,27 @@ int setup_arg_pages(struct linux_binprm *bprm, 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; + if (rlim_stack < stack_size) + 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) -- 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/