From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC PATCH 2/2] tun: fix LSM/SELinux labeling of tun/tap devices Date: Tue, 4 Dec 2012 17:24:20 +0200 Message-ID: <20121204152420.GJ7499@redhat.com> References: <20121129215724.30020.69464.stgit@sifl> <50BC7BCE.7000502@redhat.com> <2549856.XZ72FtkyJK@sifl> <7659411.O2Or69Bf6n@jason-thinkpad-t430s> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Paul Moore , netdev@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov To: Jason Wang Return-path: Content-Disposition: inline In-Reply-To: <7659411.O2Or69Bf6n@jason-thinkpad-t430s> Sender: linux-security-module-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Dec 04, 2012 at 09:24:43PM +0800, Jason Wang wrote: > On Monday, December 03, 2012 11:22:29 AM Paul Moore wrote: > > On Monday, December 03, 2012 06:15:42 PM Jason Wang wrote: > > > On 11/30/2012 06:06 AM, Paul Moore wrote: > > > > This patch corrects some problems with LSM/SELinux that were introduced > > > > with the multiqueue patchset. The problem stems from the fact that the > > > > multiqueue work changed the relationship between the tun device and its > > > > associated socket; before the socket persisted for the life of the > > > > device, however after the multiqueue changes the socket only persisted > > > > for the life of the userspace connection (fd open). For non-persistent > > > > devices this is not an issue, but for persistent devices this can cause > > > > the tun device to lose its SELinux label. > > > > > > > > We correct this problem by adding an opaque LSM security blob to the > > > > tun device struct which allows us to have the LSM security state, e.g. > > > > SELinux labeling information, persist for the lifetime of the tun > > > > device. > > > > ... > > > > > > -static int selinux_tun_dev_attach(struct sock *sk) > > > > +static int selinux_tun_dev_attach(struct sock *sk, void *security) > > > > > > > > { > > > > > > > > + struct tun_security_struct *tunsec = security; > > > > > > > > struct sk_security_struct *sksec = sk->sk_security; > > > > u32 sid = current_sid(); > > > > int err; > > > > > > > > + /* we don't currently perform any NetLabel based labeling here ... > > > > > > > > err = avc_has_perm(sid, sksec->sid, SECCLASS_TUN_SOCKET, > > > > > > > > TUN_SOCKET__RELABELFROM, NULL); > > > > > > > > if (err) > > > > > > > > return err; > > > > > > > > - err = avc_has_perm(sid, sid, SECCLASS_TUN_SOCKET, > > > > + err = avc_has_perm(sid, tunsec->sid, SECCLASS_TUN_SOCKET, > > > > > > > > TUN_SOCKET__RELABELTO, NULL); > > > > > > > > if (err) > > > > > > > > return err; > > > > > > > > - sksec->sid = sid; > > > > + sksec->sid = tunsec->sid; > > > > + sksec->sclass = SECCLASS_TUN_SOCKET; > > > > > > I'm not sure whether this is correct, looks like we need to differ between > > > TUNSETQUEUE and TUNSETIFF. When userspace call TUNSETIFF for persistent > > > device, looks like we need change the sid of tunsec like in the past. > > > > It may be that I'm misunderstanding TUNSETQUEUE and/or TUNSETIFF. Can you > > elaborate as to why they should be different? > > If I understand correctly, before multiqueue patchset, TUNSETIFF is used to: > > 1) Create the tun/tap network device > 2) For persistent device, re-attach the fd to the network device / socket. In > this case, we call selinux_tun_dev_attch() to relabel the socket sid (in fact > also the device's since the socket were persistent also) to the sid of process > that calls TUNSETIFF. > > So, after the changes of multiqueue, we need try to preserve those policy. The > interesting part is the introducing of TUNSETQUEUE, it's used to attach more > file descriptors/sockets to a tun/tap device after at least one file descriptor > were attached to the tun/tap device through TUNSETIFF. So I think maybe we > need differ those two ioctls. This patch looks fine for TUNSETQUEUE, but for > TUNSETIFF, we need relabel the tunsec to the process that calling TUNSETIFF > for persistent device? Basically, it looks like currently once you get a tun fd, you can attach it to any device even if normally selinux would prevent you from accessing it. If we reuse selinux_tun_dev_attach, we won't need to change selinux policy, with a new capability we will need to change it to allow libvirt to do TUNSETQUEUE. > > btw. Current code does allow calling TUNSETQUEUE to a persistent tun/tap > device with no file attached. It should be a bug and need to be fixed. Is this a problem? You can always attach set queue detach and it would be hard to prevent this ... > > > > One thing that I think we probably should change is the relabelto/from > > permissions in the function above (selinux_tun_dev_attach()); in the case > > where the socket does not yet have a label, e.g. 'sksec->sid == 0', we > > should probably skip the relabel permissions since we want to assign the > > TUN device label regardless in this case. > > I'm not familiar with the selinux, have a quick glance of the code, looks like > the label has been initialized to SECINITSID_KERNEL in > selinux_socket_post_create(). > > Thanks