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Fri, 24 Jul 2020 12:22:53 +0000 (UTC) Date: Fri, 24 Jul 2020 13:22:52 +0100 From: Stefan Hajnoczi To: "Dr. David Alan Gilbert" Subject: Re: [PATCH for-5.1 2/3] virtiofsd: add container-friendly -o chroot sandboxing option Message-ID: <20200724122252.GA333683@stefanha-x1.localdomain> References: <20200722130206.224898-1-stefanha@redhat.com> <20200722130206.224898-3-stefanha@redhat.com> <20200722190318.GM2660@work-vm> <20200723123229.GK186372@stefanha-x1.localdomain> <20200723175538.GW2621@work-vm> MIME-Version: 1.0 In-Reply-To: <20200723175538.GW2621@work-vm> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="OXfL5xGRrasGEqWY" 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 = 2020/07/24 08:23:04 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, rmohr@redhat.com, qemu-devel@nongnu.org, vromanso@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --OXfL5xGRrasGEqWY Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Jul 23, 2020 at 06:55:38PM +0100, Dr. David Alan Gilbert wrote: > * Stefan Hajnoczi (stefanha@redhat.com) wrote: > > On Wed, Jul 22, 2020 at 08:03:18PM +0100, Dr. David Alan Gilbert wrote: > > > * Stefan Hajnoczi (stefanha@redhat.com) wrote: > > > > + /* > > > > + * Make the shared directory the file system root so that FUSE= _OPEN > > > > + * (lo_open()) cannot escape the shared directory by opening a= symlink. > > > > + * > > > > + * It's still possible to escape the chroot via lo->proc_self_= fd but that > > > > + * requires gaining control of the process first. > > > > + */ > > > > + if (chroot(lo->source) !=3D 0) { > > > > + fuse_log(FUSE_LOG_ERR, "chroot(\"%s\"): %m\n", lo->source)= ; > > > > + exit(1); > > > > + } > > >=20 > > > I'm seeing suggestions that you should drop CAP_SYS_CHROOT after > > > chroot'ing to stop an old escape (where you create another jail insid= e > > > the jail and the kernel then lets you walk outside of the old one). > >=20 > > That's already the case: > >=20 > > 1. setup_seccomp() blocks further chroot(2) calls. > > 2. setup_capabilities() drops CAP_SYS_CHROOT. >=20 > Ah yes; could you add a comment if you respin; it's not obvious that > the capability to chroot allows you to break out of an existing chroot > you're in. Sure. Stefan --OXfL5xGRrasGEqWY Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAl8a0pwACgkQnKSrs4Gr c8gtjAf+N3a6aSnhKxco1M3LCLZ/NcE9w+b0cAGpoxUawTBFfxYCHoT569DSsB5M qBhQsAw6JWm6FvmnsSlrND2m6bIvARP5k3OOZzwyv7jrfCkoWG/q53ULaWCtYsOr NFrGoqrDKicuwZa8YwJOERT+yJv/wIpWPJ585UIU8F5NtQ4LirYz2W71YfxkU519 czYfiAoY42QJSmrCjEi18SJCfD6gS7cbY5yOKAWq2y5zK8mGJe2j91WXa4N/DssH 79C2XlmEWpAvQUbXBsO5oYpuxNzRgWBiNruP5PkltPtOtIHOV0nbTnbOvR8aHj9N vNUXY8FWOmZTE4VXa2zvuOCphT6gWg== =3N0O -----END PGP SIGNATURE----- --OXfL5xGRrasGEqWY--