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Mon, 13 Jul 2020 13:39:36 +0000 (UTC) Received: by horse.redhat.com (Postfix, from userid 10451) id 9767A2237D7; Mon, 13 Jul 2020 09:39:35 -0400 (EDT) Date: Mon, 13 Jul 2020 09:39:35 -0400 From: Vivek Goyal To: Chirantan Ekbote Subject: Re: [Virtio-fs] [PATCH 0/2] virtiofsd: drop Linux capabilities(7) Message-ID: <20200713133935.GA271133@redhat.com> References: <20200416164907.244868-1-stefanha@redhat.com> <20200618190816.GD3814@redhat.com> <20200618191655.GI2769@work-vm> <20200618192717.GE3814@redhat.com> <20200619191540.GI3154@redhat.com> <20200625125508.GB149340@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=vgoyal@redhat.com 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 = 2020/07/13 03:20:22 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-list , Miklos Szeredi , "Dr. David Alan Gilbert" , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 13, 2020 at 05:54:19PM +0900, Chirantan Ekbote wrote: > On Thu, Jun 25, 2020 at 9:55 PM Vivek Goyal wrote: > > > > On Thu, Jun 25, 2020 at 12:19:39PM +0900, Chirantan Ekbote wrote: > > [..] > > > > Chirantan, > > > > > > > > So you ended up renaming all "trusted", "security" and "system" xattrs? > > > > Only "user" xattrs are complete passthrough? > > > > > > > > > > No, we only rename "security" xattrs (except for selinux). > > > > > > > > > > > IOW, security.selinux will be renamed to user.virtiofs.security.selinux > > > > on host? > > > > > > > > > > We don't relabel security.selinux because it only requires CAP_FOWNER > > > in the process's user namespace and it also does its own MAC-based > > > checks. Also we have some tools that label files beforehand so it > > > seemed easier to leave them unchanged. > > > > If we rename selinux xattr also, then we can support selinux both in > > guest and host and they both can have their own independent policies. > > > > This works as long as you don't need to support setfscreatecon, which > exists to guarantee that an inode is atomically created with the > correct selinux context. It's kind of possible for files with > O_TMPFILE + fsetxattr + linkat but there is no equivalent for > directories. You're basically forced to create the directory and then > set the xattr and while it's possible to prevent other threads in the > server from seeing the unfinished directories with a rwlock or similar > there is no protection against power loss. If the machine loses power > after the directory is created but before the selinux xattr is set > then that directory will have the wrong selinux context and the guest > would need to run restorecon at boot to assign the correct label. Overlayfs has this notion of work directory where they create directory (and file if O_TMPFILE is not supported), and then rename it to correct place. I am wondering if we could do something similar. If server is given a work directory where. A. Create new directory B. set selinux lables C. rename directory That way if machine crashes after step A or step B, that directory never becomes visible to guest and no relabeling is required. Thanks Vivek