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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FB81C433EF for ; Mon, 11 Jul 2022 21:38:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230306AbiGKVhv (ORCPT ); Mon, 11 Jul 2022 17:37:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51266 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230399AbiGKVhs (ORCPT ); Mon, 11 Jul 2022 17:37:48 -0400 Received: from out03.mta.xmission.com (out03.mta.xmission.com [166.70.13.233]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E810032BB2; Mon, 11 Jul 2022 14:37:46 -0700 (PDT) Received: from in01.mta.xmission.com ([166.70.13.51]:56004) by out03.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1oB169-00Fyyi-KE; Mon, 11 Jul 2022 15:37:45 -0600 Received: from ip68-227-174-4.om.om.cox.net ([68.227.174.4]:45020 helo=email.froward.int.ebiederm.org.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1oB168-00GwFM-AH; Mon, 11 Jul 2022 15:37:45 -0600 From: "Eric W. Biederman" To: Tycho Andersen Cc: Miklos Szeredi , Christian Brauner , fuse-devel , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: Date: Mon, 11 Jul 2022 16:37:12 -0500 In-Reply-To: (Tycho Andersen's message of "Mon, 11 Jul 2022 14:25:21 -0600") Message-ID: <877d4jbabb.fsf@email.froward.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1oB168-00GwFM-AH;;;mid=<877d4jbabb.fsf@email.froward.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.174.4;;;frm=ebiederm@xmission.com;;;spf=softfail X-XM-AID: U2FsdGVkX1+BNhhz/q5rz9OSWYm2QD2VMDoDaU2rMNc= X-SA-Exim-Connect-IP: 68.227.174.4 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: strange interaction between fuse + pidns X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Tycho Andersen writes: > Hi all, > > On Mon, Jul 11, 2022 at 03:59:15PM +0200, Miklos Szeredi wrote: >> On Mon, 11 Jul 2022 at 12:35, Miklos Szeredi wrote: >> > >> > Can you try the attached untested patch? >> >> Updated patch to avoid use after free on req->args. >> >> Still mostly untested. > > Thanks, when I applied your patch, I still ended up with tasks stuck > waiting with a SIGKILL pending. So I looked into that and came up with > the patch below. With both your patch and mine, my testcase exits > cleanly. > > Eric (or Christian, or anyone), can you comment on the patch below? I > have no idea what this will break. Maybe instead a better approach is > some additional special case in __send_signal_locked()? > > Tycho > > From b7ea26adcf3546be5745063cc86658acb5ed37e9 Mon Sep 17 00:00:00 2001 > From: Tycho Andersen > Date: Mon, 11 Jul 2022 11:26:58 -0600 > Subject: [PATCH] sched: __fatal_signal_pending() should also check shared > signals > > The wait_* code uses signal_pending_state() to test whether a thread has > been interrupted, which ultimately uses __fatal_signal_pending() to detect > if there is a fatal signal. > > When a pid ns dies, in zap_pid_ns_processes() it does: > > group_send_sig_info(SIGKILL, SEND_SIG_PRIV, task, PIDTYPE_MAX); > > for all the tasks in the pid ns. That calls through: > > group_send_sig_info() -> > do_send_sig_info() -> > send_signal_locked() -> > __send_signal_locked() > > which does: > > pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending; > > which puts sigkill in the set of shared signals, but not the individual > pending ones. If tasks are stuck in a killable wait (e.g. a fuse flush > operation), they won't see this shared signal, and will hang forever, since > TIF_SIGPENDING is set, but the fatal signal can't be detected. Hmm. That is perplexing. __send_signal_locked calls complete_signal. Then if any of the tasks of the process can receive the signal, complete_signal will loop through all of the tasks of the process and set the per thread SIGKILL. Pretty much by definition tasks can always receive SIGKILL. Is complete_signal not being able to do that? The patch below really should not be necessary, and I have pending work that if I can push over the finish line won't even make sense. As it is currently an abuse to use the per thread SIGKILL to indicate that a fatal signal has been short circuit delivered. That abuse as well as being unclean tends to confuse people reading the code. Eric > Signed-off-by: Tycho Andersen > --- > include/linux/sched/signal.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h > index cafbe03eed01..a033ccb0a729 100644 > --- a/include/linux/sched/signal.h > +++ b/include/linux/sched/signal.h > @@ -402,7 +402,8 @@ static inline int signal_pending(struct task_struct *p) > > static inline int __fatal_signal_pending(struct task_struct *p) > { > - return unlikely(sigismember(&p->pending.signal, SIGKILL)); > + return unlikely(sigismember(&p->pending.signal, SIGKILL) || > + sigismember(&p->signal->shared_pending.signal, SIGKILL)); > } > > static inline int fatal_signal_pending(struct task_struct *p) > > base-commit: 32346491ddf24599decca06190ebca03ff9de7f8