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Fri, 19 Jun 2020 08:39:56 +0000 (UTC) Date: Fri, 19 Jun 2020 09:39:53 +0100 From: "Dr. David Alan Gilbert" To: Chirantan Ekbote Subject: Re: [Virtio-fs] [PATCH 0/2] virtiofsd: drop Linux capabilities(7) Message-ID: <20200619083953.GB2690@work-vm> References: <20200416164907.244868-1-stefanha@redhat.com> <20200618190816.GD3814@redhat.com> <20200618191655.GI2769@work-vm> <20200618192717.GE3814@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.14.0 (2020-05-02) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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=205.139.110.61; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/19 02:45:39 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 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, Vivek Goyal , Miklos Szeredi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Chirantan Ekbote (chirantan@chromium.org) wrote: > On Fri, Jun 19, 2020 at 4:27 AM Vivek Goyal wrote: > > > > On Thu, Jun 18, 2020 at 08:16:55PM +0100, Dr. David Alan Gilbert wrote: > > > * Vivek Goyal (vgoyal@redhat.com) 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. > > > > > > > > overlayfs sets "trusted.overlay.*" and xattrs in trusted domain > > > > need CAP_SYS_ADMIN. > > > > > > Not just that but it needs CAP_SYS_ADMIN in the init namespace[1]. We > have the same problem. Our virtiofs process has CAP_SYS_ADMIN in a > user namespace and it cannot set any trusted or security xattrs. The > security xattrs check is at least namespace aware so you only need > CAP_SYS_ADMIN in the namespace that mounted the fs but that doesn't > help us much. It would have been good if you'd mentioned that; it would have saved Vivek some confusion! > We ended up working around it by prefixing "user.virtiofs." to the > xattr name[2], which has its own problems but there was pretty much no > chance that we would be able to give the fs device CAP_SYS_ADMIN in > the init namespace. What problems did you hit with that? We should standardise the renaming so we make an on-disc format that's compatible. Dave > > [1]: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux/+/5e857ce6eae7ca21b2055cca4885545e29228fe2/fs/xattr.c#116 > [2]: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2243111 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK