From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 43CE1C3F2CE for ; Tue, 17 Mar 2020 08:57:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 20B3D2073C for ; Tue, 17 Mar 2020 08:57:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726130AbgCQI5u (ORCPT ); Tue, 17 Mar 2020 04:57:50 -0400 Received: from relay.sw.ru ([185.231.240.75]:60238 "EHLO relay.sw.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725730AbgCQI5t (ORCPT ); Tue, 17 Mar 2020 04:57:49 -0400 Received: from [192.168.15.225] by relay.sw.ru with esmtp (Exim 4.92.3) (envelope-from ) id 1jE81u-0003Hm-6F; Tue, 17 Mar 2020 11:56:54 +0300 Subject: Re: [PATCH v3 5/5] exec: Add a exec_update_mutex to replace cred_guard_mutex To: Bernd Edlinger , "Eric W. Biederman" Cc: Christian Brauner , Kees Cook , Jann Horn , Jonathan Corbet , Alexander Viro , Andrew Morton , Alexey Dobriyan , Thomas Gleixner , Oleg Nesterov , Frederic Weisbecker , Andrei Vagin , Ingo Molnar , "Peter Zijlstra (Intel)" , Yuyang Du , David Hildenbrand , Sebastian Andrzej Siewior , Anshuman Khandual , David Howells , James Morris , Greg Kroah-Hartman , Shakeel Butt , Jason Gunthorpe , Christian Kellner , Andrea Arcangeli , Aleksa Sarai , "Dmitry V. Levin" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "stable@vger.kernel.org" , "linux-api@vger.kernel.org" References: <87a74xi4kz.fsf@x220.int.ebiederm.org> <87r1y8dqqz.fsf@x220.int.ebiederm.org> <87tv32cxmf.fsf_-_@x220.int.ebiederm.org> <87v9ne5y4y.fsf_-_@x220.int.ebiederm.org> <87zhcq4jdj.fsf_-_@x220.int.ebiederm.org> <87d09hn4kt.fsf@x220.int.ebiederm.org> <87lfo5lju6.fsf@x220.int.ebiederm.org> <6002ac56-025a-d50f-e89d-1bf42a072323@virtuozzo.com> From: Kirill Tkhai Message-ID: <532ce6a3-f0df-e3e4-6966-473c608246e1@virtuozzo.com> Date: Tue, 17 Mar 2020 11:56:53 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14.03.2020 12:11, Bernd Edlinger wrote: > The cred_guard_mutex is problematic. The cred_guard_mutex is held > over the userspace accesses as the arguments from userspace are read. > The cred_guard_mutex is held of PTRACE_EVENT_EXIT as the the other > threads are killed. The cred_guard_mutex is held over > "put_user(0, tsk->clear_child_tid)" in exit_mm(). > > Any of those can result in deadlock, as the cred_guard_mutex is held > over a possible indefinite userspace waits for userspace. > > Add exec_update_mutex that is only held over exec updating process > with the new contents of exec, so that code that needs not to be > confused by exec changing the mm and the cred in ways that can not > happen during ordinary execution of a process. > > The plan is to switch the users of cred_guard_mutex to > exec_udpate_mutex one by one. This lets us move forward while still > being careful and not introducing any regressions. > > Link: https://lore.kernel.org/lkml/20160921152946.GA24210@dhcp22.suse.cz/ > Link: https://lore.kernel.org/lkml/AM6PR03MB5170B06F3A2B75EFB98D071AE4E60@AM6PR03MB5170.eurprd03.prod.outlook.com/ > Link: https://lore.kernel.org/linux-fsdevel/20161102181806.GB1112@redhat.com/ > Link: https://lore.kernel.org/lkml/20160923095031.GA14923@redhat.com/ > Link: https://lore.kernel.org/lkml/20170213141452.GA30203@redhat.com/ > Ref: 45c1a159b85b ("Add PTRACE_O_TRACEVFORKDONE and PTRACE_O_TRACEEXIT facilities.") > Ref: 456f17cd1a28 ("[PATCH] user-vm-unlock-2.5.31-A2") > Signed-off-by: "Eric W. Biederman" > Signed-off-by: Bernd Edlinger > --- > fs/exec.c | 17 ++++++++++++++--- > include/linux/binfmts.h | 8 +++++++- > include/linux/sched/signal.h | 9 ++++++++- > init/init_task.c | 1 + > kernel/fork.c | 1 + > 5 files changed, 31 insertions(+), 5 deletions(-) > > v3: this update fixes lock-order and adds an explicit data member in linux_binprm > > diff --git a/fs/exec.c b/fs/exec.c > index d820a72..11974a1 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -1014,12 +1014,17 @@ static int exec_mmap(struct mm_struct *mm) > { > struct task_struct *tsk; > struct mm_struct *old_mm, *active_mm; > + int ret; > > /* Notify parent that we're no longer interested in the old VM */ > tsk = current; > old_mm = current->mm; > exec_mm_release(tsk, old_mm); > > + ret = mutex_lock_killable(&tsk->signal->exec_update_mutex); > + if (ret) > + return ret; > + > if (old_mm) { > sync_mm_rss(old_mm); > /* > @@ -1031,9 +1036,11 @@ static int exec_mmap(struct mm_struct *mm) > down_read(&old_mm->mmap_sem); > if (unlikely(old_mm->core_state)) { > up_read(&old_mm->mmap_sem); > + mutex_unlock(&tsk->signal->exec_update_mutex); > return -EINTR; > } > } > + > task_lock(tsk); > active_mm = tsk->active_mm; > membarrier_exec_mmap(mm); > @@ -1288,11 +1295,12 @@ int flush_old_exec(struct linux_binprm * bprm) > goto out; > > /* > - * After clearing bprm->mm (to mark that current is using the > - * prepared mm now), we have nothing left of the original > + * After setting bprm->called_exec_mmap (to mark that current is > + * using the prepared mm now), we have nothing left of the original > * process. If anything from here on returns an error, the check > * in search_binary_handler() will SEGV current. > */ > + bprm->called_exec_mmap = 1; The two below is non-breaking pair: exec_mmap(bprm->mm); bprm->called_exec_mmap = 1; Why not move this into exec_mmap(), so nobody definitely inserts something between them? > bprm->mm = NULL; > > #ifdef CONFIG_POSIX_TIMERS > @@ -1438,6 +1446,8 @@ static void free_bprm(struct linux_binprm *bprm) > { > free_arg_pages(bprm); > if (bprm->cred) { > + if (bprm->called_exec_mmap) > + mutex_unlock(¤t->signal->exec_update_mutex); > mutex_unlock(¤t->signal->cred_guard_mutex); > abort_creds(bprm->cred); > } > @@ -1487,6 +1497,7 @@ void install_exec_creds(struct linux_binprm *bprm) > * credentials; any time after this it may be unlocked. > */ > security_bprm_committed_creds(bprm); > + mutex_unlock(¤t->signal->exec_update_mutex); > mutex_unlock(¤t->signal->cred_guard_mutex); > } > EXPORT_SYMBOL(install_exec_creds); > @@ -1678,7 +1689,7 @@ int search_binary_handler(struct linux_binprm *bprm) > > read_lock(&binfmt_lock); > put_binfmt(fmt); > - if (retval < 0 && !bprm->mm) { > + if (retval < 0 && bprm->called_exec_mmap) { > /* we got to flush_old_exec() and failed after it */ > read_unlock(&binfmt_lock); > force_sigsegv(SIGSEGV); > diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h > index b40fc63..a345d9f 100644 > --- a/include/linux/binfmts.h > +++ b/include/linux/binfmts.h > @@ -44,7 +44,13 @@ struct linux_binprm { > * exec has happened. Used to sanitize execution environment > * and to set AT_SECURE auxv for glibc. > */ > - secureexec:1; > + secureexec:1, > + /* > + * Set by flush_old_exec, when exec_mmap has been called. > + * This is past the point of no return, when the > + * exec_update_mutex has been taken. > + */ > + called_exec_mmap:1; > #ifdef __alpha__ > unsigned int taso:1; > #endif > diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h > index 8805025..a29df79 100644 > --- a/include/linux/sched/signal.h > +++ b/include/linux/sched/signal.h > @@ -224,7 +224,14 @@ struct signal_struct { > > struct mutex cred_guard_mutex; /* guard against foreign influences on > * credential calculations > - * (notably. ptrace) */ > + * (notably. ptrace) > + * Deprecated do not use in new code. > + * Use exec_update_mutex instead. > + */ > + struct mutex exec_update_mutex; /* Held while task_struct is being > + * updated during exec, and may have > + * inconsistent permissions. > + */ > } __randomize_layout; > > /* > diff --git a/init/init_task.c b/init/init_task.c > index 9e5cbe5..bd403ed 100644 > --- a/init/init_task.c > +++ b/init/init_task.c > @@ -26,6 +26,7 @@ > .multiprocess = HLIST_HEAD_INIT, > .rlim = INIT_RLIMITS, > .cred_guard_mutex = __MUTEX_INITIALIZER(init_signals.cred_guard_mutex), > + .exec_update_mutex = __MUTEX_INITIALIZER(init_signals.exec_update_mutex), > #ifdef CONFIG_POSIX_TIMERS > .posix_timers = LIST_HEAD_INIT(init_signals.posix_timers), > .cputimer = { > diff --git a/kernel/fork.c b/kernel/fork.c > index 8642530..036b692 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1594,6 +1594,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk) > sig->oom_score_adj_min = current->signal->oom_score_adj_min; > > mutex_init(&sig->cred_guard_mutex); > + mutex_init(&sig->exec_update_mutex); > > return 0; > } >