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Fri, 19 Jun 2020 15:57:37 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 328B6220390; Fri, 19 Jun 2020 11:57:37 -0400 (EDT) Date: Fri, 19 Jun 2020 11:57:37 -0400 From: Vivek Goyal To: Miklos Szeredi Subject: Re: [Virtio-fs] [PATCH 0/2] virtiofsd: drop Linux capabilities(7) Message-ID: <20200619155737.GA12225@redhat.com> References: <20200416164907.244868-1-stefanha@redhat.com> <20200618190816.GD3814@redhat.com> <20200619142508.GB3154@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.120; envelope-from=vgoyal@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/19 05:19:18 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_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN 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-list , qemu-devel@nongnu.org, Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Jun 19, 2020 at 05:26:37PM +0200, Miklos Szeredi wrote: > On Fri, Jun 19, 2020 at 4:25 PM Vivek Goyal wrote: > > > > On Fri, Jun 19, 2020 at 04:16:30PM +0200, Miklos Szeredi wrote: > > > On Thu, Jun 18, 2020 at 9:08 PM Vivek Goyal wrote: > > > > > > > > On Thu, Apr 16, 2020 at 05:49:05PM +0100, Stefan Hajnoczi wrote: > > > > > virtiofsd doesn't need of all Linux capabilities(7) available to root. Keep a > > > > > whitelisted set of capabilities that we require. This improves security in > > > > > case virtiofsd is compromised by making it hard for an attacker to gain further > > > > > access to the system. > > > > > > > > Hi Stefan, > > > > > > > > I just noticed that this patch set breaks overlayfs on top of virtiofs. > > > > > > How so? Virtiofs isn't mounting overlayfs, is it? Only the mounter > > > requires CAP_SYS_ADMIN, not the accessor. > > > > virtiofsd needs CAP_SYS_ADMIN, otherwise fsetxattr(trusted.overlay.opaque) > > fails in lo_setxattr(). > > > > This is triggered when we mount overlayfs on top of virtiofs and overlayfs > > tries to set OVL_XATTR_OPAQUE on upper to check if trusted xattrs are > > supported or not. > > Ah, right. > > Plan is to use "user.*" xattr for unprivileged overlay. This would be > a good way to eliminate this attack surface in the overlay on virtiofs > case as well. So unpriviliged overlay is one which is mounted from inside a user namespace. But in this case we might be mounting it from init_user_ns of guest. So from overlayfs perspective this will still be treated as priviliged overlay instance and it will use trusted xattrs, IIUC? Thanks Vivek > > Other ways to minimize risk is to separate operations requiring > CAP_SYS_ADMIN into a separate process, preferably a separate > executable, that communicates with virtiofsd using a pipe and contains > the minimum amount of code. > > Thanks, > Miklos >