From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH] Restrict initial stack space expansion to rlimit Date: Tue, 9 Feb 2010 13:25:29 -0800 Message-ID: <20100209132529.bfc455b7.akpm@linux-foundation.org> References: <20100208161014.7C6D.A69D9226@jp.fujitsu.com> <1273.1265695885@neuling.org> <20100209154141.03F0.A69D9226@jp.fujitsu.com> <11046.1265705967@neuling.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, aeb@cwi.nl, Oleg Nesterov , miltonm@bga.com, James Morris , linuxppc-dev@ozlabs.org, Paul Mackerras , Anton Blanchard , KOSAKI Motohiro , Serge Hallyn , linux-fsdevel@vger.kernel.org, Americo Wang , Ingo Molnar , Linus Torvalds , stable@kernel.org, Alexander Viro To: Michael Neuling Return-path: In-Reply-To: <11046.1265705967@neuling.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org List-Id: linux-fsdevel.vger.kernel.org On Tue, 09 Feb 2010 19:59:27 +1100 Michael Neuling 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 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 Cc: KOSAKI Motohiro Cc: Americo Wang Cc: Anton Blanchard Cc: Oleg Nesterov Cc: James Morris Cc: Ingo Molnar Cc: Serge Hallyn Cc: Benjamin Herrenschmidt Cc: 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) _