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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 08F2CC433B4 for ; Sun, 4 Apr 2021 16:44:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C152261364 for ; Sun, 4 Apr 2021 16:44:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230039AbhDDQoO (ORCPT ); Sun, 4 Apr 2021 12:44:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42198 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229861AbhDDQoO (ORCPT ); Sun, 4 Apr 2021 12:44:14 -0400 Received: from zeniv-ca.linux.org.uk (zeniv-ca.linux.org.uk [IPv6:2607:5300:60:148a::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0374C061756; Sun, 4 Apr 2021 09:44:09 -0700 (PDT) Received: from viro by zeniv-ca.linux.org.uk with local (Exim 4.94 #2 (Red Hat Linux)) id 1lT5r4-002V2g-3Z; Sun, 04 Apr 2021 16:44:06 +0000 Date: Sun, 4 Apr 2021 16:44:06 +0000 From: Al Viro To: Christian Brauner Cc: Jens Axboe , syzbot , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, io-uring@vger.kernel.org Subject: Re: [syzbot] WARNING in mntput_no_expire (2) Message-ID: References: <0000000000003a565e05bee596f2@google.com> <20210401154515.k24qdd2lzhtneu47@wittgenstein> <90e7e339-eaec-adb2-cfed-6dc058a117a3@kernel.dk> <20210401174613.vymhhrfsemypougv@wittgenstein> <20210401175919.jpiylhfrlb4xb67u@wittgenstein> <20210404113445.xo6ntgfpxigcb3x6@wittgenstein> <20210404164040.vtxdcfzgliuzghwk@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210404164040.vtxdcfzgliuzghwk@wittgenstein> Sender: Al Viro Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Sun, Apr 04, 2021 at 06:40:40PM +0200, Christian Brauner wrote: > > Very interesting. What happens if you call loop() twice? And now I wonder > > whether it's root or cwd, actually... Hmm... > > > > How about this: > > fd = open("/proc/self/mountinfo", 0); > > mkdir("./newroot/foo", 0777); > > mount("./newroot/foo", "./newroot/foo", 0, MS_BIND, NULL); > > chroot("./newroot"); > > chdir("/foo"); > > while (1) { > > static char buf[4096]; > > int n = read(fd, buf, 4096); > > if (n <= 0) > > break; > > write(1, buf, n); > > } > > close(fd); > > drop_caps(); > > loop(); > > as the end of namespace_sandbox_proc(), instead of > > chroot("./newroot"); > > chdir("/"); > > drop_caps(); > > loop(); > > sequence we have there? > > Uhum, well then we oops properly with a null-deref. Cute... Could you dump namei.o (ideally - with namei.s) from your build someplace public?