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 E949BC433B4 for ; Sun, 4 Apr 2021 17:05:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AA47661365 for ; Sun, 4 Apr 2021 17:05:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230210AbhDDRFZ (ORCPT ); Sun, 4 Apr 2021 13:05:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:60100 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229861AbhDDRFY (ORCPT ); Sun, 4 Apr 2021 13:05:24 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CDBC96128B; Sun, 4 Apr 2021 17:05:16 +0000 (UTC) Date: Sun, 4 Apr 2021 19:05:13 +0200 From: Christian Brauner To: Al Viro 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: <20210404170513.mfl5liccdaxjnpls@wittgenstein> References: <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=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Sun, Apr 04, 2021 at 04:44:06PM +0000, Al Viro wrote: > 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? Yeah, I have at least namei.o https://drive.google.com/file/d/1AvO1St0YltIrA86DXjp1Xg3ojtS9owGh/view?usp=sharing Christian