|Subject:||Re: [Qemu-devel] [RFC Patch 0/3] Accept passed in socket 'fd' open from outside for unix socket|
|Date:||Wed, 15 Jun 2016 01:50:31 +0800|
|User-agent:||Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0|
On 2016年06月14日 22:23, Aaron Conole wrote:
"Daniel P. Berrange" <address@hidden> 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 <address@hidden> 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" <address@hidden> To: "Daniel P. Berrange" <address@hidden> Cc: address@hidden, "amit shah" <address@hidden>, address@hidden, "Wei Xu" <address@hidden>, address@hidden 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, address@hidden wrote:From: Wei Xu <address@hidden> 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.
Michal, Can we fix it with this as a replacement?One of my concerns about the patch is looks there are a few other places in system which need 'fd' like sockets, therefore each needs a new 'fd' parameter in command line, this maybe not a clean and concise way, i think qemu_open() proposed by Eric is better to generally solve these kind of issues, maybe we can consider enhancing it along that direction in the future, what's your opinion?
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