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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=ham 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 80004C48BE6 for ; Wed, 16 Jun 2021 19:23:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6650161246 for ; Wed, 16 Jun 2021 19:23:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232661AbhFPTZY (ORCPT ); Wed, 16 Jun 2021 15:25:24 -0400 Received: from cloud48395.mywhc.ca ([173.209.37.211]:58004 "EHLO cloud48395.mywhc.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232670AbhFPTZX (ORCPT ); Wed, 16 Jun 2021 15:25:23 -0400 Received: from modemcable064.203-130-66.mc.videotron.ca ([66.130.203.64]:32882 helo=[192.168.1.179]) by cloud48395.mywhc.ca with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1ltb88-0000z6-2x; Wed, 16 Jun 2021 15:23:16 -0400 Message-ID: <4163ed48afbcb1c288b366fe2745205cd66bea3d.camel@trillion01.com> Subject: Re: [PATCH] coredump: Limit what can interrupt coredumps From: Olivier Langlois To: "Eric W. Biederman" , Oleg Nesterov Cc: Linus Torvalds , Linux Kernel Mailing List , linux-fsdevel , io-uring , Alexander Viro , Jens Axboe , "Pavel Begunkov>" Date: Wed, 16 Jun 2021 15:23:14 -0400 In-Reply-To: <87pmwmn5m0.fsf@disp2133> References: <198e912402486f66214146d4eabad8cb3f010a8e.camel@trillion01.com> <87eeda7nqe.fsf@disp2133> <87pmwt6biw.fsf@disp2133> <87czst5yxh.fsf_-_@disp2133> <87y2bh4jg5.fsf@disp2133> <87sg1p4h0g.fsf_-_@disp2133> <20210614141032.GA13677@redhat.com> <87pmwmn5m0.fsf@disp2133> Organization: Trillion01 Inc Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.40.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - cloud48395.mywhc.ca X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - trillion01.com X-Get-Message-Sender-Via: cloud48395.mywhc.ca: authenticated_id: olivier@trillion01.com X-Authenticated-Sender: cloud48395.mywhc.ca: olivier@trillion01.com X-Source: X-Source-Args: X-Source-Dir: Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Tue, 2021-06-15 at 17:08 -0500, Eric W. Biederman wrote: > Oleg Nesterov writes: > > > > --- a/fs/coredump.c > > > +++ b/fs/coredump.c > > > @@ -519,7 +519,7 @@ static bool dump_interrupted(void) > > >          * but then we need to teach dump_write() to restart and > > > clear > > >          * TIF_SIGPENDING. > > >          */ > > > -       return signal_pending(current); > > > +       return fatal_signal_pending(current) || > > > freezing(current); > > >  } > > > > > > Well yes, this is what the comment says. > > > > But note that there is another reason why dump_interrupted() > > returns true > > if signal_pending(), it assumes thagt __dump_emit()- > > >__kernel_write() may > > fail anyway if signal_pending() is true. Say, pipe_write(), or iirc > > nfs, > > perhaps something else... > > > > That is why zap_threads() clears TIF_SIGPENDING. Perhaps it should > > clear > > TIF_NOTIFY_SIGNAL as well and we should change io-uring to not > > abuse the > > dumping threads? > > > > Or perhaps we should change __dump_emit() to clear signal_pending() > > and > > restart __kernel_write() if it fails or returns a short write. > > > > Otherwise the change above doesn't look like a full fix to me. > > Agreed.  The coredump to a pipe will still be short.  That needs > something additional. > > The problem Olivier Langlois reported was > core dumps coming up short because TIF_NOTIFY_SIGNAL was being > set during a core dump. > > We can see this with pipe_write returning -ERESTARTSYS > on a full pipe if signal_pending which includes TIF_NOTIFY_SIGNAL > is true. > Eric, I redid my test but this time instead of dumping directly into a file, I did let the coredump be piped to the systemd coredump module and the coredump generation isn't working as expected when piping. So your code review conclusions are correct.