From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753275AbbG1Uzn (ORCPT ); Tue, 28 Jul 2015 16:55:43 -0400 Received: from mail-vn0-f47.google.com ([209.85.216.47]:35301 "EHLO mail-vn0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752040AbbG1Uzl (ORCPT ); Tue, 28 Jul 2015 16:55:41 -0400 MIME-Version: 1.0 In-Reply-To: <87d1zcm9iz.fsf@x220.int.ebiederm.org> References: <20150728171500.GA2871@www.outflux.net> <87d1zcm9iz.fsf@x220.int.ebiederm.org> Date: Tue, 28 Jul 2015 13:55:40 -0700 Message-ID: Subject: Re: [PATCH] user_ns: use correct check for single-threadedness From: Ricky Zhou To: "Eric W. Biederman" Cc: Kees Cook , Oleg Nesterov , David Howells , linux-kernel@vger.kernel.org, Andrew Morton , Peter Zijlstra , Ingo Molnar , "Kirill A. Shutemov" , Rik van Riel , Vladimir Davydov , Julien Tinnes Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (apologies for the dup, forgot to reply all) userns_install in user_namespace.c (affects setns of a user namespace): cde1975bc242f3e1072bde623ef378e547b73f91. The check in check_unshare_flags is a little more complex. The incorrect check was added in cf2e340f4249b781b3d2beb41e891d08581f0e10 but I don't think it would have triggered under any supported combination of flags at that point. >>From 50804fe3737ca6a5942fdc2057a18a8141d00141 until 6e556ce209b09528dbf1931cbfd5d323e1345926, the bug affected unshare(CLONE_NEWPID). >>From b2e0d98705e60e45bbb3c0032c48824ad7ae0704 onward, unshare(CLONE_NEWUSER) is affected. Thanks, Ricky On Tue, Jul 28, 2015 at 11:17 AM, Eric W. Biederman wrote: > Kees Cook writes: > >> 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 > > This looks like a good fix. Any chance you can drudge up the commit where > this hack came in so that Greg & Company know how far to back port this? > >> --- >> 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