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Fri, 31 Jul 2020 08:26:39 +0000 (UTC) Date: Fri, 31 Jul 2020 09:26:38 +0100 From: Stefan Hajnoczi To: Roman Mohr Subject: Re: [PATCH v2 3/3] virtiofsd: probe unshare(CLONE_FS) and print an error Message-ID: <20200731082638.GA173083@stefanha-x1.localdomain> References: <20200727190223.422280-1-stefanha@redhat.com> <20200727190223.422280-4-stefanha@redhat.com> <20200728131250.GB78409@redhat.com> <20200729144027.GF52286@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="T4sUOijqQbZv57TR" Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/31 02:46:11 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 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_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-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: , Cc: "vromanso@redhat.com" , Daniel Walsh , "qemu-devel@nongnu.org" , "Dr. David Alan Gilbert" , "virtio-fs@redhat.com" , "misono.tomohiro@fujitsu.com" , "mpatel@redhat.com" , Vivek Goyal Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --T4sUOijqQbZv57TR Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jul 30, 2020 at 06:21:34PM -0400, Daniel Walsh wrote: > On 7/29/20 10:40, Stefan Hajnoczi wrote: > > On Wed, Jul 29, 2020 at 09:59:01AM +0200, Roman Mohr wrote: > >> On Tue, Jul 28, 2020 at 3:13 PM Vivek Goyal wrote: > >> > >>> On Tue, Jul 28, 2020 at 12:00:20PM +0200, Roman Mohr wrote: > >>>> On Tue, Jul 28, 2020 at 3:07 AM misono.tomohiro@fujitsu.com < > >>>> misono.tomohiro@fujitsu.com> wrote: > >>>> > >>>>>> Subject: [PATCH v2 3/3] virtiofsd: probe unshare(CLONE_FS) and pri= nt > >>> an > >>>>> error > >> Yes they can run as root. I can tell you what we plan to do with the > >> containerized virtiofsd: We run it as part of the user-owned pod (a se= t of > >> containers). > >> One of our main goals at the moment is to run VMs in a user-owned pod > >> without additional privileges. > >> So that in case the user (VM-creator/owner) enters the pod or somethin= g > >> breaks out of the VM they are just in the unprivileged container sandb= ox. > >> As part of that we try to get also rid of running containers in the > >> user-context with the root user. > >> > >> One possible scenario which I could think of as being desirable from a > >> kubevirt perspective: > >> We would run the VM in one container and have an unprivileged > >> virtiofsd container in parallel. > >> This container already has its own mount namespace and it is not that > >> critical if something manages to enter this sandbox. > >> > >> But we are not as far yet as getting completely rid of root right now = in > >> kubevirt, so if as a temporary step it needs root, the current propose= d > >> changes would still be very useful for us. > > What is the issue with root in user namespaces? > > > > I remember a few years ago it was seen as a major security issue but > > don't remember if container runtimes were already using user namespaces > > back then. > > > > I guess the goal might be simply to minimize Linux capabilities as much > > as possible? > > > > virtiofsd could nominally run with an arbitrary uid/gid but it still > > needs the Linux capabilities that allow it to change uid/gid and > > override file system permission checks just like the root user. Not sur= e > > if there is any advantage to running with uid 1000 when you still have > > these Linux capabilities. > > > > Stefan >=20 > When you run in a user namespace, virtiofsd would only have > setuid/setgid over the range of UIDs mapped into the user namespace.=A0 S= o > if UID=3D0 on the host is not mapped, then the container can not create > real UID=3D0 files on disk. >=20 > Similarly you can protect the user directories and any content by > running the containers in a really high UID Mapping. Roman, do user namespaces address your concerns about uid 0 in containers? 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