(#8697) Introduce extra_args setting for ssh configs

Prior to this commit, there was no way to add additional ssh arguments
within a Vagrantfile for a given vagrant machine. This commit introduces
a new option extra_args that allows users to pass in a single argument
or an array of flags that will be added onto the ssh command.

lib/vagrant/machine.rb

@@ -442,6 +442,7 @@ module Vagrant
       info[:username] ||= @config.ssh.default.username
       info[:compression] ||= @config.ssh.default.compression
       info[:dsa_authentication] ||= @config.ssh.default.dsa_authentication
+      info[:extra_args] ||= @config.ssh.default.extra_args
 
       # We set overrides if they are set. These take precedence over
       # provider-returned data.
@@ -453,6 +454,7 @@ module Vagrant
       info[:dsa_authentication] = @config.ssh.dsa_authentication
       info[:username] = @config.ssh.username if @config.ssh.username
       info[:password] = @config.ssh.password if @config.ssh.password
+      info[:extra_args] = @config.ssh.extra_args if @config.ssh.extra_args
 
       # We also set some fields that are purely controlled by Varant
       info[:forward_agent] = @config.ssh.forward_agent

lib/vagrant/util/ssh.rb

@@ -167,6 +167,12 @@ module Vagrant
         #
         # Without having extra_args be last, the user loses this ability
         command_options += ["-o", "ForwardAgent=yes"] if ssh_info[:forward_agent]
+
+        # Note about :extra_args
+        #   ssh_info[:extra_args] comes from a machines ssh config in a Vagrantfile,
+        #   where as opts[:extra_args] comes from running the ssh command
+        command_options += Array(ssh_info[:extra_args]) if ssh_info[:extra_args]
+
         command_options.concat(opts[:extra_args]) if opts[:extra_args]
 
         # Build up the host string for connecting

plugins/kernel_v2/config/ssh_connect.rb

@@ -11,6 +11,7 @@ module VagrantPlugins
       attr_accessor :paranoid
       attr_accessor :compression
       attr_accessor :dsa_authentication
+      attr_accessor :extra_args
 
       def initialize
         @host             = UNSET_VALUE
@@ -23,6 +24,7 @@ module VagrantPlugins
         @paranoid         = UNSET_VALUE
         @compression      = UNSET_VALUE
         @dsa_authentication = UNSET_VALUE
+        @extra_args       = UNSET_VALUE
       end
 
       def finalize!
@@ -36,6 +38,7 @@ module VagrantPlugins
         @paranoid         = false if @paranoid == UNSET_VALUE
         @compression      = true if @compression == UNSET_VALUE
         @dsa_authentication = true if @dsa_authentication == UNSET_VALUE
+        @extra_args       = nil if @extra_args == UNSET_VALUE
 
         if @private_key_path && !@private_key_path.is_a?(Array)
           @private_key_path = [@private_key_path]

test/unit/vagrant/machine_test.rb

@@ -793,6 +793,17 @@ describe Vagrant::Machine do
         it "paranoid should be default" do
           expect(instance.ssh_info[:paranoid]).to be(false)
         end
+        it "extra_args should be nil" do
+          expect(instance.ssh_info[:extra_args]).to be(nil)
+        end
+        it "extra_args should be set" do
+          instance.config.ssh.extra_args = ["-L", "127.1.2.7:8008:127.1.2.7:8008"]
+          expect(instance.ssh_info[:extra_args]).to eq(["-L", "127.1.2.7:8008:127.1.2.7:8008"])
+        end
+        it "extra_args should be set as an array" do
+          instance.config.ssh.extra_args = "-6"
+          expect(instance.ssh_info[:extra_args]).to eq("-6")
+        end
         it "keys_only should be overridden" do
           instance.config.ssh.keys_only = false
           expect(instance.ssh_info[:keys_only]).to be(false)

test/unit/vagrant/util/ssh_test.rb

@@ -162,6 +162,42 @@ describe Vagrant::Util::SSH do
       end
     end
 
+    context "when extra_args is provided as an array" do
+      let(:ssh_info) {{
+        host: "localhost",
+        port: 2222,
+        username: "vagrant",
+        private_key_path: [temporary_file],
+        extra_args: ["-L", "8008:localhost:80"]
+      }}
+
+      it "enables agent forwarding options" do
+        allow(Vagrant::Util::SafeExec).to receive(:exec).and_return(nil)
+
+        expect(described_class.exec(ssh_info)).to eq(nil)
+        expect(Vagrant::Util::SafeExec).to have_received(:exec)
+          .with("ssh", "vagrant@localhost", "-p", "2222", "-o", "LogLevel=FATAL", "-o", "StrictHostKeyChecking=no", "-o", "UserKnownHostsFile=/dev/null", "-o", "IdentityFile=#{ssh_info[:private_key_path][0]}", "-L", "8008:localhost:80")
+      end
+    end
+
+    context "when extra_args is provided as a string" do
+      let(:ssh_info) {{
+        host: "localhost",
+        port: 2222,
+        username: "vagrant",
+        private_key_path: [temporary_file],
+        extra_args: "-6"
+      }}
+
+      it "enables agent forwarding options" do
+        allow(Vagrant::Util::SafeExec).to receive(:exec).and_return(nil)
+
+        expect(described_class.exec(ssh_info)).to eq(nil)
+        expect(Vagrant::Util::SafeExec).to have_received(:exec)
+          .with("ssh", "vagrant@localhost", "-p", "2222", "-o", "LogLevel=FATAL", "-o", "StrictHostKeyChecking=no", "-o", "UserKnownHostsFile=/dev/null", "-o", "IdentityFile=#{ssh_info[:private_key_path][0]}", "-6")
+      end
+    end
+
     context "with subprocess enabled" do
       let(:ssh_info) {{
         host: "localhost",

website/source/docs/vagrantfile/ssh_settings.html.md

@@ -157,3 +157,10 @@ default to `true` and `Compression=yes` will be enabled with ssh.
 `config.ssh.dsa_authentication` - If `false`, this setting  will not include
 `DSAAuthentication` when ssh'ing into a machine. If this is not set, it will
 default to `true` and `DSAAuthentication=yes` will be used with ssh.
+
+`config.ssh.extra_args` - This settings value is passed directly into the
+ssh executable. This allows you to pass any arbitrary commands to do things such
+as reverse tunneling down into the ssh program. These options can either be
+single flags set as strings such as `"-6"` for IPV6 or an array of arguments
+such as `["-L", "8008:localhost:80"]` for enabling a tunnel from host port 8008
+to port 80 on guest.