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Thu, 23 Jul 2020 15:36:48 +0000 (UTC) Date: Thu, 23 Jul 2020 16:36:47 +0100 From: Stefan Hajnoczi To: Vivek Goyal Subject: Re: [Virtio-fs] [PATCH for-5.1 2/3] virtiofsd: add container-friendly -o chroot sandboxing option Message-ID: <20200723153647.GB300121@stefanha-x1.localdomain> References: <20200722130206.224898-1-stefanha@redhat.com> <20200722130206.224898-3-stefanha@redhat.com> <20200722175820.GL2660@work-vm> <20200723122850.GI186372@stefanha-x1.localdomain> <20200723134733.GA5885@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200723134733.GA5885@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="QTprm0S8XgL7H0Dt" Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.120; envelope-from=stefanha@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/23 06:04:25 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: virtio-fs@redhat.com, qemu-devel@nongnu.org, vromanso@redhat.com, "Dr. David Alan Gilbert" , rmohr@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --QTprm0S8XgL7H0Dt Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jul 23, 2020 at 09:47:33AM -0400, Vivek Goyal wrote: > On Thu, Jul 23, 2020 at 01:28:50PM +0100, Stefan Hajnoczi wrote: > > On Wed, Jul 22, 2020 at 06:58:20PM +0100, Dr. David Alan Gilbert wrote: > > > * Stefan Hajnoczi (stefanha@redhat.com) wrote: > > > > virtiofsd cannot run in an unprivileged container because CAP_SYS_A= DMIN > > > > is required to create namespaces. > > > >=20 > > > > Introduce a weaker sandbox that is sufficient in container environm= ents > > > > because the container runtime already sets up namespaces. Use chroo= t to > > > > restrict path traversal to the shared directory. > > > >=20 > > > > virtiofsd loses the following: > > > >=20 > > > > 1. Mount namespace. The process chroots to the shared directory but > > > > leaves the mounts in place. Seccomp rejects mount(2)/umount(2) > > > > syscalls. > > >=20 > > > OK, I'm guessing the behaviour of what happens if the host adds anoth= er > > > mount afterwards might be different? > >=20 > > Running inside a container with -o chroot: > > - The container has its own mount namespace and it is therefore not > > affected, modulo shared subtrees (see mount(8)). >=20 > How does virtiofsd inside container gets the directory it wants to > export to guest? I am assuming that its probably a volume mount > inside container. If yes, volume mounts can set propagation > properties say "slave" and that means mounts done later will > propagate inside container in that volume (and hopefully be > visible inside guest once submount patches are upstream). Yes, the shared directory is a volume mount and propagation works as expected: $ docker run -v path/to/shared-dir:/shared-dir:slave \ =09 -v /tmp/socket-dir:/var/run \ =09 virtiofsd When I mount things in path/to/shared-dir on the host they appear in /shared-dir inside the guest. When I omit the "slave" option (the default is "private") then the mount does not propagate. The following Dockerfile was used: $ cp ~/src/qemu/virtiofsd . # copy the executable $ cat >Dockerfile FROM fedora:32 COPY --chown=3D0:0 virtiofsd /usr/bin/virtiofsd RUN dnf update -qy && dnf install -qy libseccomp liburing zlib glib2 nett= le gnutls libcap-ng VOLUME ["/shared-dir", "/var/run"] CMD ["/usr/bin/virtiofsd", "--socket-path=3D/var/run/virtiofsd.sock", "-o= ", "source=3D/shared-dir", "-o", "cache=3Dauto", "-o", "no_posix_lock", "-o= ", "xattr", "-o", "chroot"] Stefan --QTprm0S8XgL7H0Dt Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl8Zro8ACgkQnKSrs4Gr c8iWkggAtGpbfo1cQOxcG92FgjYSVkpMbpQGp+Mlmr1zpPbb/3jfk9KnX8ONeV5M YqCPm0tkPdX0Ufjkzano+Q3X1udYRCk3AShn7CfwhrkcWixQzzdk0QzO24pJDOjX tL1msD+tMuljJf4X6lqAxFnTVWegUPcGGtRH4kk+ebNoPwccWdO6f1P9y50Q5ChB POu4IFzY92ykUhJSB1EkyUKiQiqa467jU8twOkhaHjcw2ydGAs4Q6LAWSCgB0z+S QWgBhS/4VcMxipfOQC3kj1Zlhlax6Jp8QnokO95MHyIATVk0FS93K8o/g6CkbzNb TMoVWMMIHn1F4oMmVvpoF6JvWO0CfQ== =paOA -----END PGP SIGNATURE----- --QTprm0S8XgL7H0Dt--