From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753025AbbG1RPo (ORCPT ); Tue, 28 Jul 2015 13:15:44 -0400 Received: from smtp.outflux.net ([198.145.64.163]:39953 "EHLO smtp.outflux.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752343AbbG1RPn (ORCPT ); Tue, 28 Jul 2015 13:15:43 -0400 Date: Tue, 28 Jul 2015 10:15:00 -0700 From: Kees Cook To: "Eric W. Biederman" Cc: Oleg Nesterov , David Howells , linux-kernel@vger.kernel.org, Andrew Morton , Peter Zijlstra , Ingo Molnar , "Kirill A. Shutemov" , Rik van Riel , Vladimir Davydov , Ricky Zhou , Julien Tinnes Subject: [PATCH] user_ns: use correct check for single-threadedness Message-ID: <20150728171500.GA2871@www.outflux.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-HELO: www.outflux.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ricky Zhou Checking mm_users > 1 does not mean a process is multithreaded. For example, reading /proc/PID/maps temporarily increments mm_users, allowing other processes to (accidentally) interfere with unshare() calls. This fixes observed failures of unshare(CLONE_NEWUSER) incorrectly returning EINVAL if another processes happened to be simultaneously reading the maps file. Signed-off-by: Ricky Zhou Signed-off-by: Kees Cook Cc: stable@vger.kernel.org --- kernel/fork.c | 4 ++-- kernel/user_namespace.c | 3 ++- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index dbd9b8d7b7cc..7d138f152dcd 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -75,6 +75,7 @@ #include #include #include +#include #include #include @@ -1876,8 +1877,7 @@ static int check_unshare_flags(unsigned long unshare_flags) * needs to unshare vm. */ if (unshare_flags & (CLONE_THREAD | CLONE_SIGHAND | CLONE_VM)) { - /* FIXME: get_task_mm() increments ->mm_users */ - if (atomic_read(¤t->mm->mm_users) > 1) + if (!current_is_single_threaded()) return -EINVAL; } diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index 4109f8320684..7e0e021e4304 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -22,6 +22,7 @@ #include #include #include +#include static struct kmem_cache *user_ns_cachep __read_mostly; static DEFINE_MUTEX(userns_state_mutex); @@ -977,7 +978,7 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns) return -EINVAL; /* Threaded processes may not enter a different user namespace */ - if (atomic_read(¤t->mm->mm_users) > 1) + if (!current_is_single_threaded()) return -EINVAL; if (current->fs->users != 1) -- 1.9.1 -- Kees Cook Chrome OS Security