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=-11.3 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 DD390C433E0 for ; Thu, 23 Jul 2020 12:52:51 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A7F3B20768 for ; Thu, 23 Jul 2020 12:52:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="irCJ5mVu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A7F3B20768 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:56590 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jyaiQ-0005SX-TM for qemu-devel@archiver.kernel.org; Thu, 23 Jul 2020 08:52:50 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41126) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jyagl-0003vH-HY for qemu-devel@nongnu.org; Thu, 23 Jul 2020 08:51:07 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:38375 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jyagj-0007Kq-KA for qemu-devel@nongnu.org; Thu, 23 Jul 2020 08:51:07 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595508664; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=mbl7igg55iL4JVzvE7179tNN557zpiyPlrvNFaVxqfM=; b=irCJ5mVugLDjlp44NQAJU/72CJkXG00/Ceyz20dIOqRPFUwzY25UYM8CIf+QtyQGeyJ6a5 pHfjPTThqJXmegNtOt8R/xY8X2MkGjabu+Cq3Ju9Ezto4ohu2v44KZSXmeL7fzlSsGaQrU nMEOsPOYI5NyEcyR8a8gX1c6divHP10= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-115-gPw5sBQjOjeJyWm-UvN1FQ-1; Thu, 23 Jul 2020 08:50:46 -0400 X-MC-Unique: gPw5sBQjOjeJyWm-UvN1FQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D643D80183C; Thu, 23 Jul 2020 12:50:45 +0000 (UTC) Received: from redhat.com (unknown [10.36.110.60]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2383572E48; Thu, 23 Jul 2020 12:50:38 +0000 (UTC) Date: Thu, 23 Jul 2020 13:50:35 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Stefan Hajnoczi Subject: Re: [PATCH for-5.1 3/3] virtiofsd: probe unshare(CLONE_FS) and print an error Message-ID: <20200723125035.GH2615312@redhat.com> References: <20200722130206.224898-1-stefanha@redhat.com> <20200722130206.224898-4-stefanha@redhat.com> <20200722170328.GU2324845@redhat.com> <20200723124611.GL186372@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: <20200723124611.GL186372@stefanha-x1.localdomain> User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/23 02:26:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: vromanso@redhat.com, Misono Tomohiro , qemu-devel@nongnu.org, virtio-fs@redhat.com, rmohr@redhat.com, "Dr. David Alan Gilbert" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, Jul 23, 2020 at 01:46:11PM +0100, Stefan Hajnoczi wrote: > On Wed, Jul 22, 2020 at 06:03:28PM +0100, Daniel P. Berrangé wrote: > > On Wed, Jul 22, 2020 at 02:02:06PM +0100, Stefan Hajnoczi wrote: > > > An assertion failure is raised during request processing if > > > unshare(CLONE_FS) fails. Implement a probe at startup so the problem can > > > be detected right away. > > > > > > Unfortunately Docker/Moby does not include unshare in the seccomp.json > > > list unless CAP_SYS_ADMIN is given. Other seccomp.json lists always > > > include unshare (e.g. podman is unaffected): > > > https://raw.githubusercontent.com/seccomp/containers-golang/master/seccomp.json > > > > > > Use "docker run --security-opt seccomp=path/to/seccomp.json ..." if the > > > default seccomp.json is missing unshare. > > > > > > Cc: Misono Tomohiro > > > Signed-off-by: Stefan Hajnoczi > > > --- > > > tools/virtiofsd/fuse_virtio.c | 13 +++++++++++++ > > > 1 file changed, 13 insertions(+) > > > > > > diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c > > > index 3b6d16a041..ebeb352514 100644 > > > --- a/tools/virtiofsd/fuse_virtio.c > > > +++ b/tools/virtiofsd/fuse_virtio.c > > > @@ -949,6 +949,19 @@ int virtio_session_mount(struct fuse_session *se) > > > { > > > int ret; > > > > > > + /* > > > + * Test that unshare(CLONE_FS) works. fv_queue_worker() will need it. It's > > > + * an unprivileged system call but some Docker/Moby versions are known to > > > + * reject it via seccomp when CAP_SYS_ADMIN is not given. > > > + */ > > > + ret = unshare(CLONE_FS); > > > + if (ret == -1 && errno == EPERM) { > > > + fuse_log(FUSE_LOG_ERR, "unshare(CLONE_FS) failed with EPERM. If " > > > + "running in a container please check that the container " > > > + "runtime seccomp policy allows unshare.\n"); > > > + return -1; > > > + } > > > + > > > > This describes the unshare() call as a "probe" and a "test", but that's > > misleading IMHO. A "probe" / "test" implies that after it has completed, > > there's no lingering side-effect, which isn't the case here. > > > > This is actively changing the process' namespace environment in the > > success case, and not putting it back how it was originally. > > > > May be this is in fact OK, but if so I think the commit message and > > comment should explain/justify what its fine to have this lingering > > side-effect. > > > > If we want to avoid the side-effect then we need to fork() and run > > unshare() in the child, and use a check of exit status of the child > > to determine the result. > > Thanks for pointing this out. I'll add a comment explaining that > virtiofsd is single-threaded at this point. No other threads share the > file system attributes so the call has no observable side-effects. Also, if we do an unshare() here, do we still need the unshare() later on in the code ? Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|