[PATCH] network: allow for forward dev to be a transient interface

[Laine Stump <laine@xxxxxxxxxx>]

A user reported that if they set <forward mode='nat|route' dev='blah'>
starting the network would fail if the device 'blah' didn't already
exist.

This is caused by using "iif" and "oif" in nftables rules to check for
the forwarding device - these two commands work by saving the named
interface's ifindex (an unsigned integer) when the rule is added, and
comparing it to the ifindex associated with the packet's path at
runtime. This works great if the interface both 1) exists when the
rule is added, and 2) is never deleted and re-created after the rule
is added (since it would end up with a different ifindex).

When checking for the network's bridge device, it is okay for us to
use "iif" and "oif", because the bridge device is created before the
firewall rules are added, and will continue to exist until just after
the firewall rules are deleted when the network is shutdown.

But since the forward device might be deleted/re-added during the
lifetime of the network's firewall rules, we must instead us "oifname"
and "iifname" - these are much less efficient than "Xif" because they
do a string compare of the interface's name rather than just comparing
two integers (ifindex), but they don't require the interface to exist
when the rule is added, and they can properly cope with the named
interface being deleted and re-added later.

Fixes: a4f38f6ffe6a9edc001d18890ccfc3f38e72fb94
Signed-off-by: Laine Stump <laine@xxxxxxxxxx>
---
 src/network/network_nftables.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/network/network_nftables.c b/src/network/network_nftables.c
index 59ab231a06..268d1f12ca 100644
--- a/src/network/network_nftables.c
+++ b/src/network/network_nftables.c
@@ -362,7 +362,7 @@ nftablesAddForwardAllowOut(virFirewall *fw,
                               "iif", iface, NULL);
 
     if (physdev && physdev[0])
-        virFirewallCmdAddArgList(fw, fwCmd, "oif", physdev, NULL);
+        virFirewallCmdAddArgList(fw, fwCmd, "oifname", physdev, NULL);
 
     virFirewallCmdAddArgList(fw, fwCmd, "counter", "accept", NULL);
 
@@ -398,7 +398,7 @@ nftablesAddForwardAllowRelatedIn(virFirewall *fw,
                               VIR_NFTABLES_FWD_IN_CHAIN, NULL);
 
     if (physdev && physdev[0])
-        virFirewallCmdAddArgList(fw, fwCmd, "iif", physdev, NULL);
+        virFirewallCmdAddArgList(fw, fwCmd, "iifname", physdev, NULL);
 
     virFirewallCmdAddArgList(fw, fwCmd, "oif", iface,
                              layerStr, "daddr", networkstr,
@@ -437,7 +437,7 @@ nftablesAddForwardAllowIn(virFirewall *fw,
                              layerStr, "daddr", networkstr, NULL);
 
     if (physdev && physdev[0])
-        virFirewallCmdAddArgList(fw, fwCmd, "iif", physdev, NULL);
+        virFirewallCmdAddArgList(fw, fwCmd, "iifname", physdev, NULL);
 
     virFirewallCmdAddArgList(fw, fwCmd, "oif", iface,
                               "counter", "accept", NULL);
@@ -566,7 +566,7 @@ nftablesAddForwardMasquerade(virFirewall *fw,
                              layerStr, "daddr", "!=", networkstr, NULL);
 
     if (physdev && physdev[0])
-        virFirewallCmdAddArgList(fw, fwCmd, "oif", physdev, NULL);
+        virFirewallCmdAddArgList(fw, fwCmd, "oifname", physdev, NULL);
 
     if (protocol && protocol[0]) {
         if (port->start == 0 && port->end == 0) {
@@ -634,7 +634,7 @@ nftablesAddDontMasquerade(virFirewall *fw,
                               VIR_NFTABLES_NAT_POSTROUTE_CHAIN, NULL);
 
     if (physdev && physdev[0])
-        virFirewallCmdAddArgList(fw, fwCmd, "oif", physdev, NULL);
+        virFirewallCmdAddArgList(fw, fwCmd, "oifname", physdev, NULL);
 
     virFirewallCmdAddArgList(fw, fwCmd,
                              layerStr, "saddr", networkstr,
-- 
2.45.1