From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753718AbdK0TfD (ORCPT ); Mon, 27 Nov 2017 14:35:03 -0500 Received: from mail-pl0-f67.google.com ([209.85.160.67]:33263 "EHLO mail-pl0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751830AbdK0TfB (ORCPT ); Mon, 27 Nov 2017 14:35:01 -0500 X-Google-Smtp-Source: AGs4zMZsbUh+Qf/YKSMqX07iNECLDNkbFJdbLfcBshtBLWjbK25CaDfsWA7dhZQRysL6suZTke4+oA== Date: Mon, 27 Nov 2017 11:34:57 -0800 From: Kees Cook To: Andrew Morton Cc: Ben Hutchings , James Morris , Serge Hallyn , Andy Lutomirski , Oleg Nesterov , Jiri Slaby , linux-kernel@vger.kernel.org Subject: [PATCH] exec: Avoid RLIMIT_STACK races with prlimit() Message-ID: <20171127193457.GA11348@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 While the defense-in-depth RLIMIT_STACK limit on setuid processes was protected against races from other threads calling setrlimit(), I missed protecting it against races from external processes calling prlimit(). This adds locking around the change and makes sure that rlim_max is set too. Reported-by: Ben Hutchings Reported-by: Brad Spengler Fixes: 64701dee4178e ("exec: Use sane stack rlimit under secureexec") Cc: stable@vger.kernel.org Cc: James Morris Cc: Serge Hallyn Cc: Andy Lutomirski Cc: Oleg Nesterov Cc: Jiri Slaby Signed-off-by: Kees Cook --- fs/exec.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/exec.c b/fs/exec.c index 1d6243d9f2b6..6be2aa0ab26f 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1340,10 +1340,15 @@ void setup_new_exec(struct linux_binprm * bprm) * avoid bad behavior from the prior rlimits. This has to * happen before arch_pick_mmap_layout(), which examines * RLIMIT_STACK, but after the point of no return to avoid - * needing to clean up the change on failure. + * races from other threads changing the limits. This also + * must be protected from races with prlimit() calls. */ + task_lock(current->group_leader); if (current->signal->rlim[RLIMIT_STACK].rlim_cur > _STK_LIM) current->signal->rlim[RLIMIT_STACK].rlim_cur = _STK_LIM; + if (current->signal->rlim[RLIMIT_STACK].rlim_max > _STK_LIM) + current->signal->rlim[RLIMIT_STACK].rlim_max = _STK_LIM; + task_unlock(current->group_leader); } arch_pick_mmap_layout(current->mm); -- 2.7.4 -- Kees Cook Pixel Security