[libvirt] [PATCH 6/9] network: setup bridge devices for promiscLinks='no'

[Laine Stump]

When the bridge device for a network has promiscLinks='no', the intent
is to setup the bridge to opportunistically turn off promiscuous mode
and/or flood mode for as many ports/links on the bridge as possible,
thus improving performance and security. The setup for the bridge
itself is:

1) set the "vlan_filtering" property of the bridge device to 1.  2) If
the bridge has a "Dummy" tap device used to set a fixed MAC address on
the bridge, turn off learning and unicast_flood on this tap (this is
needed even though this tap is never IFF_UP, because the kernel
ignores the IFF_UP flag of other devices when using their settings to
automatically decide whether or not to turn off promiscuous mode for
any attached device).

This is done both for libvirt-created/managed bridges, and for bridges
that are created by the host system config.

There is no attempt to turn vlan_filtering off when destroying the
network because in the case of a libvirt-created bridge, the bridge is
about to be destroyed anyway, and in the case of a system bridge, if
the other devices attached to the bridge could operate properly before
destroying libvirt's network object, they will continue to operate
properly (this is similar to the way that libvirt will enable
ip_forwarding whenever a routed/natted network is started, but will
never attempt to disable it if they are stopped).
---
 src/network/bridge_driver.c | 53 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/src/network/bridge_driver.c b/src/network/bridge_driver.c
index bc8da79..f2564c3 100644
--- a/src/network/bridge_driver.c
+++ b/src/network/bridge_driver.c
@@ -1893,6 +1893,28 @@ networkAddAddrToBridge(virNetworkObjPtr network,
     return 0;
 }
 
+
+static int
+networkStartHandlePromiscLinks(virNetworkObjPtr network, const char *macTapIfName)
+{
+    const char *brname = network->def->bridge;
+
+    /* promiscuous mode won't be turned off unless vlan filtering is enabled. */
+    if (brname &&
+        network->def->promiscLinks == VIR_TRISTATE_BOOL_NO) {
+        if (virNetDevBridgeSetVlanFiltering(brname, true) < 0)
+            return -1;
+        if (macTapIfName) {
+            if (virNetDevBridgePortSetLearning(brname, macTapIfName, false) < 0)
+                return -1;
+            if (virNetDevBridgePortSetUnicastFlood(brname, macTapIfName, false) < 0)
+                return -1;
+        }
+    }
+    return 0;
+}
+
+
 /* add an IP (static) route to a bridge */
 static int
 networkAddRouteToBridge(virNetworkObjPtr network,
@@ -2019,6 +2041,9 @@ networkStartNetworkVirtual(virNetworkObjPtr network)
             goto err2;
     }
 
+    if (networkStartHandlePromiscLinks(network, macTapIfName) < 0)
+        goto err2;
+
     /* Bring up the bridge interface */
     if (virNetDevSetOnline(network->def->bridge, 1) < 0)
         goto err2;
@@ -2163,6 +2188,27 @@ static int networkShutdownNetworkVirtual(virNetworkObjPtr network)
 }
 
 
+static int
+networkStartNetworkBridge(virNetworkObjPtr network)
+{
+    /* put anything here that needs to be done each time a network of
+     * type BRIDGE, is started. On failure, undo anything you've done,
+     * and return -1. On success return 0.
+     */
+    return networkStartHandlePromiscLinks(network, NULL);
+}
+
+static
+int networkShutdownNetworkBridge(virNetworkObjPtr network ATTRIBUTE_UNUSED)
+{
+    /* put anything here that needs to be done each time a network of
+     * type BRIDGE is shutdown. On failure, undo anything you've done,
+     * and return -1. On success return 0.
+     */
+    return 0;
+}
+
+
 /* networkCreateInterfacePool:
  * @netdef: the original NetDef from the network
  *
@@ -2326,6 +2372,10 @@ networkStartNetwork(virNetworkObjPtr network)
         break;
 
     case VIR_NETWORK_FORWARD_BRIDGE:
+       if (networkStartNetworkBridge(network) < 0)
+          goto cleanup;
+       break;
+
     case VIR_NETWORK_FORWARD_PRIVATE:
     case VIR_NETWORK_FORWARD_VEPA:
     case VIR_NETWORK_FORWARD_PASSTHROUGH:
@@ -2392,6 +2442,9 @@ static int networkShutdownNetwork(virNetworkObjPtr network)
         break;
 
     case VIR_NETWORK_FORWARD_BRIDGE:
+        ret = networkShutdownNetworkBridge(network);
+        break;
+
     case VIR_NETWORK_FORWARD_PRIVATE:
     case VIR_NETWORK_FORWARD_VEPA:
     case VIR_NETWORK_FORWARD_PASSTHROUGH:
-- 
1.9.3