"Daniel P. Berrange" <berra...@redhat.com> writes: > On Tue, Jun 14, 2016 at 04:03:43PM +0800, Wei Xu wrote: >> On 2016年06月09日 05:48, Aaron Conole wrote: >> > Flavio Leitner <f...@redhat.com> writes: >> > >> > > Adding Aaron who is fixing exactly that on the OVS side. >> > > >> > > Aaron, please see the last question in the bottom of this email. >> > > >> > > On Wed, Jun 08, 2016 at 06:07:29AM -0400, Amnon Ilan wrote: >> > > > >> > > > >> > > > ----- Original Message ----- >> > > > > From: "Michal Privoznik" <mpriv...@redhat.com> >> > > > > To: "Daniel P. Berrange" <berra...@redhat.com> >> > > > > Cc: qemu-devel@nongnu.org, "amit shah" <amit.s...@redhat.com>, >> > > > > jasow...@redhat.com, "Wei Xu" <w...@redhat.com>, >> > > > > arm...@redhat.com >> > > > > Sent: Thursday, June 2, 2016 2:38:53 PM >> > > > > Subject: Re: [Qemu-devel] [RFC Patch 0/3] Accept passed in socket >> > > > > 'fd' open from outside for unix socket >> > > > > >> > > > > On 02.06.2016 10:29, Daniel P. Berrange wrote: >> > > > > > On Thu, Jun 02, 2016 at 09:41:56AM +0200, Michal Privoznik wrote: >> > > > > > > On 01.06.2016 18:16, Wei Xu wrote: >> > > > > > > > On 2016年06月01日 00:44, Daniel P. Berrange wrote: >> > > > > > > > > On Wed, Jun 01, 2016 at 12:30:44AM +0800, w...@redhat.com >> > > > > > > > > wrote: >> > > > > > > > > > From: Wei Xu <w...@redhat.com> >> > > > > > > > > > >> > > > > > > > > > Recently I'm working on a fd passing issue, >> > > > > > > > > > selinux forbids qemu to >> > > > > > > > > > create a unix socket for a chardev when managing >> > > > > > > > > > VMs with libvirt, >> > > > > > > > > > because qemu don't have sufficient permissions in >> > > > > > > > > > this case, and >> > > > > > > > > > proposal from libvirt team is opening the 'fd' in >> > > > > > > > > > libvirt and merely >> > > > > > > > > > passing it to qemu. >> > > > > > > > > >> > > > > > > > > This sounds like a bug in libvirt, or selinux, or a mistaken >> > > > > > > > > configuration >> > > > > > > > > of the guest. It is entirely possible for QEMU to >> > > > > > > > > create a unix socket >> > > > > > > > > - not >> > > > > > > > > least because that is exactly what QEMU uses for its QMP >> > > > > > > > > monitor >> > > > > > > > > backend. >> > > > > > > > > Looking at your example command line, I think the >> > > > > > > > > issue is simply that >> > > > > > > > > you >> > > > > > > > > should be putting the sockets in a different location. ie at >> > > > > > > > > /var/lib/libvirt/qemu/$guest-vhost-user1.sock where QEMU has >> > > > > > > > > permission to >> > > > > > > > > create sockets already. >> > > > > > > > ah.. adjusting permission or file location can solve >> > > > > > > > this problem, i'm >> > > > > > > > guessing maybe this is a more security concern, the >> > > > > > > > socket is used as a >> > > > > > > > network interface for a vm, similar as the qcow image >> > > > > > > > file, thus should >> > > > > > > > prevent it to be arbitrarily accessed. >> > > > > > > > >> > > > > > > > Michael, do you have any comment on this? >> > > > > > > >> > > > > > > I haven't seen the patches. But in libvirt we allow users to >> > > > > > > create a >> > > > > > > vhostuser interface and even specify where the socket should be >> > > > > > > placed: >> > > > > > > >> > > > > > > <interface type='vhostuser'> >> > > > > > > <mac address='52:54:00:ee:96:6c'/> >> > > > > > > <source type='unix' path='/tmp/vhost1.sock' >> > > > > > > mode='server'/> >> > > > > > > <model type='virtio'/> >> > > > > > > </interface> >> > > > > > > >> > > > > > > The following cmd line is generated by libvirt then: >> > > > > > > >> > > > > > > -chardev socket,id=charnet1,path=/tmp/vhost1.sock,server \ >> > > > > > > -netdev type=vhost-user,id=hostnet1,chardev=charnet1 \ >> > > > > > > -device >> > > > > > > virtio-net-pci,netdev=hostnet1,id=net1,mac=52:54:00:ee:96:6c,bus=pci.0,\ >> > > > > > > >> > > > > > > Now, if we accept only /var/run/openvwitch path in >> > > > > > > /interface/source/@path (or whatever path to OVS is), we don't >> > > > > > > need this >> > > > > > > and have users manually label the dir (unless already labeled). >> > > > > > > But >> > > > > > > since we accept just any path in there, we should make sure that >> > > > > > > qemu is >> > > > > > > then able to create the socket. One possible fix would be to >> > > > > > > allow qemu >> > > > > > > create sockets just anywhere in the system. This, however, >> > > > > > > brings huge >> > > > > > > security risks and it's not acceptable IMO. The other option >> > > > > > > would be >> > > > > > > that libvirt would create the socket, and pass its FD to qemu >> > > > > > > (since >> > > > > > > libvirt already is allowed to create sockets anywhere). >> > > > > > >> > > > > > There are plenty of other places where we allow arbitrary paths in >> > > > > > the >> > > > > > XML, but which have restrictions imposed by the security drivers. >> > > > > > Not >> > > > > > least the <channel> devices which have the exact same scenario as >> > > > > > this >> > > > > > network device, and require use of /var/lib/libvirt/qemu >> > > > > > as the directory >> > > > > > for the sockets. We certainly do not want to allow QEMU to >> > > > > > create sockets >> > > > > > anywhere. >> > > > > > >> > > > > > I don't think we want to grant QEMU svirtt permission to create >> > > > > > sockets >> > > > > > in the /var/run/openvswitch directory either really.IMHO, >> > > > > > users of vhost >> > > > > > user should really be using /var/lib/libvirt/qemu, as is used for >> > > > > > all >> > > > > > other UNIX sockets we create wrt other devices. >> > > > > >> > > > > Okay. I can live with that; but in that case we should document it >> > > > > somewhere, that we guarantee only paths under /var/lib/libvirt/ to be >> > > > > accessible and for the rest we do our best but maybe require sys >> > > > > admin >> > > > > intervention (e.g. to label the whole tree for a non-standard >> > > > > location). >> > > > >> > > > Does OVS has some limit for it's sockets to be only in >> > > > /var/run/openvswitch ? >> > >> > As of a recent commit, it can only be in /var/run/openvswitch or a >> > subdirectory therein (found in the openvswitch database). >> Aaron, thanks for your reply. >> >> Just a question about the usage of openvswitch, in this user case when >> launching a vhostuser/dpdk via libvirt, qemu works as server mode for socket >> under /var/run/openvswitch, but per my previous test, ovs/dpdk always works >> as server mode, which means ovs will creates the socket and listening for >> connection, thus qemu works as client mode, does ovs/dpdk support working in >> client mode? which means it's qemu's duty to create the socket? and ovs will >> connect to it on demanding? > > Oh, I was assuming that QEMU would be working in server mode - no wonder > we have somewhat different views :-) > > If OVS is running the UNIX socket server, and QEMU is purely the client, > then that means the solution would be slightly different. In particular > libvirt would *not* do any SELinux relabelling. Instead you would have > to get an addition to the SELinux policy, to allow svirt_t type to connect > to the SELinux type associated with the openvswitch socket.
I agree, this is a good MAC solution. > For file permissions, if the OVS socket is owned by a particular UNIX > group, you could potentially add the 'qemu' user account to that group > to grant access. I actually would propose making a new vhost group, and adding the qemu user account and openvswitch user accounts to that group. That way reduces pollution into other aspects of each process' function. -Aaron > > Regards, > Daniel
