From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751854AbdGGS5d (ORCPT ); Fri, 7 Jul 2017 14:57:33 -0400 Received: from mail-pg0-f42.google.com ([74.125.83.42]:32858 "EHLO mail-pg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750848AbdGGS5b (ORCPT ); Fri, 7 Jul 2017 14:57:31 -0400 Date: Fri, 7 Jul 2017 11:57:29 -0700 From: Kees Cook To: Linus Torvalds Cc: Andy Lutomirski , "Eric W. Biederman" , Michal Hocko , Ben Hutchings , Hugh Dickins , Oleg Nesterov , "Jason A. Donenfeld" , Rik van Riel , linux-kernel@vger.kernel.org Subject: [PATCH] exec: Limit arg stack to at most _STK_LIM / 4 * 3 Message-ID: <20170707185729.GA70967@beast> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org To avoid pathological stack usage or the need to special-case setuid execs, just limit all arg stack usage to at most _STK_LIM / 4 * 3 (6MB). Signed-off-by: Kees Cook --- fs/exec.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 904199086490..ddca2cf15f71 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -221,7 +221,6 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, if (write) { unsigned long size = bprm->vma->vm_end - bprm->vma->vm_start; unsigned long ptr_size; - struct rlimit *rlim; /* * Since the stack will hold pointers to the strings, we @@ -250,14 +249,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, return page; /* - * Limit to 1/4-th the stack size for the argv+env strings. + * Limit to 1/4 of the max stack size or 3/4 of _STK_LIM + * (whichever is smaller) for the argv+env strings. * This ensures that: * - the remaining binfmt code will not run out of stack space, * - the program will have a reasonable amount of stack left * to work from. */ - rlim = current->signal->rlim; - if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) + if (size > min_t(unsigned long, rlimit(RLIMIT_STACK) / 4, + _STK_LIM / 4 * 3)) goto fail; } -- 2.7.4 -- Kees Cook Pixel Security