From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 842D26B0279 for ; Wed, 21 Jun 2017 20:17:23 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id r70so1266551pfb.7 for ; Wed, 21 Jun 2017 17:17:23 -0700 (PDT) Received: from mail-pg0-x231.google.com (mail-pg0-x231.google.com. [2607:f8b0:400e:c05::231]) by mx.google.com with ESMTPS id y12si14199722pfi.21.2017.06.21.17.17.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 21 Jun 2017 17:17:22 -0700 (PDT) Received: by mail-pg0-x231.google.com with SMTP id f127so622427pgc.0 for ; Wed, 21 Jun 2017 17:17:22 -0700 (PDT) Date: Wed, 21 Jun 2017 17:17:20 -0700 From: Kees Cook Subject: [PATCH] exec: Account for argv/envp pointers Message-ID: <20170622001720.GA32173@beast> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Alexander Viro , Qualys Security Advisory , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com When limiting the argv/envp strings during exec to 1/4 of the stack limit, the storage of the pointers to the strings was not included. This means that an exec with huge numbers of tiny strings could eat 1/4 of the stack limit in strings and then additional space would be later used by the pointers to the strings. For example, on 32-bit with a 8MB stack rlimit, an exec with 1677721 single-byte strings would consume less than 2MB of stack, the max (8MB / 4) amount allowed, but the pointers to the strings would consume the remaining additional stack space (1677721 * 4 == 6710884). The result (1677721 + 6710884 == 8388605) would exhaust stack space entirely. Controlling this stack exhaustion could result in pathological behavior in setuid binaries (CVE-2017-1000365). Fixes: b6a2fea39318 ("mm: variable length argument support") Cc: stable@vger.kernel.org Signed-off-by: Kees Cook --- fs/exec.c | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 72934df68471..8079ca70cfda 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -220,8 +220,18 @@ 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 + * must account for them as well. + */ + ptr_size = (bprm->argc + bprm->envc) * sizeof(void *); + if (ptr_size > ULONG_MAX - size) + goto fail; + size += ptr_size; + acct_arg_size(bprm, size / PAGE_SIZE); /* @@ -239,13 +249,15 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos, * to work from. */ rlim = current->signal->rlim; - if (size > ACCESS_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) { - put_page(page); - return NULL; - } + if (size > READ_ONCE(rlim[RLIMIT_STACK].rlim_cur) / 4) + goto fail; } return page; + +fail: + put_page(page); + return NULL; } static void put_arg_page(struct page *page) -- 2.7.4 -- Kees Cook Pixel Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org