Features/HelperNetworking: Difference between revisions

Latest revision as of 14:55, 11 October 2016

Summary

Introduce infrastructure to allow QEMU network backends to be implemented outside of QEMU in a generic way.

Owner

Name: Anthony Liguori
Email: anthony@codemonkey.ws
Name: Corey Bryant
Email: coreyb@linux.vnet.ibm.com
Name: Richa Marwaha
Email: rmarwah@linux.vnet.ibm.com

Detailed Summary

Infrastructure is introduced to enable a network helper to be executed by QEMU. This also allows third parties to implement user-visible network backends without having to introduce them into QEMU itself.

A default network helper is introduced that implements the same functionality as the common qemu-ifup script. It creates a tap file descriptor, attaches it to a bridge, and passes it back to QEMU. This helper runs with higher privileges and allows QEMU to be invoked as a non-privileged user. (The helper runs as setuid root and privileges are immediately dropped to cap_net_admin.)

The default network helper uses it's own ACL mechanism for access control. Administrators can restrict the bridges that an unprivileged user can put a guest on. A future network helper could be developed to support PolicyKit for access control.

Setup

The setuid attribute needs to be turned on for the default network helper:

   sudo chmod u+s /usr/local/libexec/qemu-bridge-helper

If invoking QEMU as a non-privileged user, make sure the user has necessary permissions (ie. access to image file).

ACLs must be implemented for the default network helper. The ACL mechanism that is enforced by qemu-bridge-helper is a fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'. All users are blacklisted by default, and deny takes precedence over allow.

The minimum required to run the default helper with the default bridge br0 is:

/etc/qemu/bridge.conf root:qemu 0640

  allow br0

Execution

The following examples run Qemu with the default network helper and default bridge br0:

   qemu linux.img -netdev bridge,id=hn0 -device virtio-net-pci,netdev=hn0,id=nic1

   qemu linux.img -netdev tap,helper=/usr/local/libexec/qemu-bridge-helper,id=hn0 -device virtio-net-pci,netdev=hn0,id=nic1

Status

Patches are upstream in QEMU 1.1.
Latest version of patches: http://lists.gnu.org/archive/html/qemu-devel/2012-01/msg03562.html

@@ Line 2: / Line 2: @@
 == Summary ==
-Introduce infrastructure to allowed QEMU network backends to be implemented outside of QEMU in a generic way.
+Introduce infrastructure to allow QEMU network backends to be implemented outside of QEMU in a generic way.
 == Owner ==
@@ Line 13: / Line 13: @@
 == Detailed Summary ==
-A network helper (and supporting infrastructure) is introduced that can be invoked to create appropriate file descriptors and pass them back to QEMU.  This helper runs with higher privilegs, allowing QEMU to attach a tap device to a bridge, while being invoked as a non-privileged user.  This also allows third parties to implement user-visible network backends without having to introduce them into QEMU itself.  The helper that is provided could just as easily be run by libvirt, and the open fd passed to QEMU over the -net tap,fd= option.
+Infrastructure is introduced to enable a network helper to be executed by QEMU.  This also allows third parties to implement user-visible network backends without having to introduce them into QEMU itself.
-== Network Helper ==
+A default network helper is introduced that implements the same functionality as the common qemu-ifup script.  It creates a tap file descriptor, attaches it to a bridge, and passes it back to QEMU.  This helper runs with higher privileges and allows QEMU to be invoked as a non-privileged user.  (The helper runs as setuid root and privileges are immediately dropped to cap_net_admin.)
-With the help of qemu_network_helper,  an unprivileged user can configure the TAP interface which connects to a bridge. The helper can be invoked by using the br{bridge name} and helper{executable to configure the bridge} options in -net tap or by using -net bridge option which by default invokes br and helper options. The default helper implements the most common qemu-ifup script that can be safely given cap_net_admin.
-Currently helper uses it's own ACL mechanism for access control as default,but future network helpers could be developed, for example, to support PolicyKit for access control.
+The default network helper uses it's own ACL mechanism for access control.  Administrators can restrict the bridges that an unprivileged user can put a guest on.  A future network helper could be developed to support PolicyKit for access control.
-== Examples ==
+== Setup ==
-The following examples run Qemu with the default network helper, attaching a tap device to the default br0 bridge:
+The setuid attribute needs to be turned on for the default network helper:
-     qemu linux.img -net bridge -net nic,model=virtio
+     sudo chmod u+s /usr/local/libexec/qemu-bridge-helper
-    qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper -net nic,model=virtio
+If invoking QEMU as a non-privileged user, make sure the user has necessary permissions (ie. access to image file).
+ACLs must be implemented for the default network helper.  The ACL mechanism that is enforced by qemu-bridge-helper is a fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'.  All users are blacklisted by default, and deny takes precedence over allow.
+The minimum required to run the default helper with the default bridge br0 is:
+/etc/qemu/bridge.conf root:qemu 0640
+   allow br0
+== Execution ==
+The following examples run Qemu with the default network helper and default bridge br0:
      qemu linux.img -netdev bridge,id=hn0 -device virtio-net-pci,netdev=hn0,id=nic1
@@ Line 32: / Line 42: @@
 == Status ==
+* Patches are upstream in QEMU 1.1.
+* Latest version of patches: http://lists.gnu.org/archive/html/qemu-devel/2012-01/msg03562.html
-* http://www.mail-archive.com/qemu-devel@nongnu.org/msg90423.html
+[[Category:Completed feature pages]]