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 AE1B1C433EF for ; Mon, 21 Mar 2022 16:03:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350625AbiCUQFT (ORCPT ); Mon, 21 Mar 2022 12:05:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40992 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346093AbiCUQFS (ORCPT ); Mon, 21 Mar 2022 12:05:18 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 1314B1B7B6 for ; Mon, 21 Mar 2022 09:03:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647878632; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=DJyMtVQ5+0AfNUolDd6Lt5IE2lynsgQekcoq9taq1eE=; b=IOvk/7E/Q5EY/4Ty3aXlbsCfpdRBwSHglMVr7BngFFma4b0kkWfFgVd7uvcKrH7uB6ifYZ VJpy5p5IdKXhLyw9oN3FcAHwwG7eq2VEhKeSKIHtlJfznjm/FNnHLRQld3DCmoigIhQyqF E0cM42Zbtn83cR4Xa2nusKVCLiNxM1s= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-279-tqlhcQEaOwuiuk4cCIL_Kg-1; Mon, 21 Mar 2022 12:03:51 -0400 X-MC-Unique: tqlhcQEaOwuiuk4cCIL_Kg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6ABC8811E84; Mon, 21 Mar 2022 16:03:50 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6BC0C2166B40; Mon, 21 Mar 2022 16:03:49 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <000000000000778f1005dab1558e@google.com> To: Jann Horn Cc: dhowells@redhat.com, syzbot , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk Subject: Re: [syzbot] possible deadlock in pipe_write MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1037988.1647878628.1@warthog.procyon.org.uk> Date: Mon, 21 Mar 2022 16:03:48 +0000 Message-ID: <1037989.1647878628@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jann Horn wrote: > The syz reproducer is: > > #{"threaded":true,"procs":1,"slowdown":1,"sandbox":"","close_fds":false} > pipe(&(0x7f0000000240)={0xffffffffffffffff, 0xffffffffffffffff}) > pipe2(&(0x7f00000001c0)={0xffffffffffffffff, 0xffffffffffffffff}, 0x80) > splice(r0, 0x0, r2, 0x0, 0x1ff, 0x0) > vmsplice(r1, &(0x7f00000006c0)=[{&(0x7f0000000080)="b5", 0x1}], 0x1, 0x0) > > That 0x80 is O_NOTIFICATION_PIPE (==O_EXCL). > > It looks like the bug is that when you try to splice between a normal > pipe and a notification pipe, get_pipe_info(..., true) fails, so > splice() falls back to treating the notification pipe like a normal > pipe - so we end up in iter_file_splice_write(), which first locks the > input pipe, then calls vfs_iter_write(), which locks the output pipe. > > I think this probably (?) can't actually lead to deadlocks, since > you'd need another way to nest locking a normal pipe into locking a > watch_queue pipe, but the lockdep annotations don't make that clear. Is this then a bug/feature in iter_file_splice_write() rather than in the watch queue code, per se? David