Filter any machine_ip when preparing the NFS settings

When preparing the NFS settings on VirtualBox the guest IP addresses
are pulled from VirtualBox directly and any static addresses are
pulled as well. This can lead to aquiring a host IP and machine IP
but results in a failure of NFS mount because the IPs are not on
the same network. This filters the machine IP result to validate
it is within the host adapter IP range.

plugins/providers/virtualbox/action/prepare_nfs_settings.rb

@@ -1,3 +1,4 @@
+require "ipaddr"
 require "vagrant/action/builtin/mixin_synced_folders"
 
 module VagrantPlugins
@@ -59,6 +60,23 @@ module VagrantPlugins
             end
           end
 
+          if host_ip && !machine_ip.empty?
+            interface = @machine.provider.driver.read_host_only_interfaces.detect do |iface|
+              iface[:ip] == host_ip
+            end
+            host_ipaddr = IPAddr.new("#{host_ip}/#{interface.fetch(:netmask, "0.0.0.0")}")
+
+            case machine_ip
+            when String
+              machine_ip = nil if !host_ipaddr.include?(machine_ip)
+            when Array
+              machine_ip.delete_if do |m_ip|
+                !host_ipaddr.include?(m_ip)
+              end
+              machine_ip = nil if machine_ip.empty?
+            end
+          end
+
           raise Vagrant::Errors::NFSNoHostonlyNetwork if !host_ip || !machine_ip
 
           env[:nfs_host_ip]    = host_ip

test/unit/plugins/providers/virtualbox/action/prepare_nfs_settings_test.rb

@@ -47,6 +47,10 @@ describe VagrantPlugins::ProviderVirtualBox::Action::PrepareNFSSettings do
   end
 
   context "with an nfs synced folder" do
+    let(:host_only_interfaces) {
+      [{name: "vmnet2", ip: "1.2.3.4"}]
+    }
+
     before do
       # We can't be on Windows, because NFS gets disabled on Windows
       Vagrant::Util::Platform.stub(windows?: false)
@@ -58,9 +62,7 @@ describe VagrantPlugins::ProviderVirtualBox::Action::PrepareNFSSettings do
       driver.stub(read_network_interfaces: {
         2 => {type: :hostonly, hostonly: "vmnet2"},
       })
-      driver.stub(read_host_only_interfaces: [
-        {name: "vmnet2", ip: "1.2.3.4"},
-      ])
+      driver.stub(read_host_only_interfaces: host_only_interfaces)
       allow(driver).to receive(:read_guest_ip).with(1).and_return("2.3.4.5")
 
       # override sleep to 0 so test does not take seconds
@@ -68,6 +70,30 @@ describe VagrantPlugins::ProviderVirtualBox::Action::PrepareNFSSettings do
       allow(subject).to receive(:retry_options).and_return(retry_options.merge(sleep: 0))
     end
 
+    context "with host interface netmask defined" do
+      context "with machine IP included within host interface range" do
+        let(:host_only_interfaces) {
+          [{name: "vmnet2", ip: "2.3.4.1", netmask: "255.255.255.0"}]
+        }
+
+        it "sets nfs_host_ip and nfs_machine_ip properly" do
+          subject.call(env)
+
+          expect(env[:nfs_host_ip]).to eq("2.3.4.1")
+          expect(env[:nfs_machine_ip]).to eq("2.3.4.5")
+        end
+      end
+      context "with machine IP included within host interface range" do
+        let(:host_only_interfaces) {
+          [{name: "vmnet2", ip: "1.2.3.4", netmask: "255.255.255.0"}]
+        }
+
+        it "raises an error when the machine IP is not within host interface range" do
+          expect{ subject.call(env) }.to raise_error(Vagrant::Errors::NFSNoHostonlyNetwork)
+        end
+      end
+    end
+
     it "sets nfs_host_ip and nfs_machine_ip properly" do
       subject.call(env)