Host resource: use bash over netcat in Linux (#2607)

* Add support to use bash in host resource

Netcat's presence is widely regarded as a security issue, and thus not
always available. This solution first tries to use bash builtins and
timeout (from coreutils), so is less likely to require installing
additional packages.

* Darwin UDP support in host resource
* Host: use netcat first if available

Signed-off-by: João Vale <jpvale@gmail.com>

lib/resources/host.rb

@@ -55,13 +55,13 @@ module Inspec::Resources
         @protocol = params.fetch(:protocol, 'icmp')
       end
 
-      return skip_resource 'Invalid protocol: only `tcp` and `icmp` protocols are support for the `host` resource.' unless
-        %w{icmp tcp}.include?(@protocol)
-
       @host_provider = nil
       if inspec.os.linux?
         @host_provider = LinuxHostProvider.new(inspec)
       elsif inspec.os.windows?
+        return skip_resource 'Invalid protocol: only `tcp` and `icmp` protocols are support for the `host` resource on your OS.' unless
+          %w{icmp tcp}.include?(@protocol)
+
         @host_provider = WindowsHostProvider.new(inspec)
       elsif inspec.os.darwin?
         @host_provider = DarwinHostProvider.new(inspec)
@@ -147,6 +147,69 @@ module Inspec::Resources
   end
 
   class UnixHostProvider < HostProvider
+    def initialize(inspec)
+      super
+
+      @has_nc = inspec.command('nc').exist?
+      @has_ncat = inspec.command('ncat').exist?
+      @has_net_redirections = inspec.command("strings `which bash` | grep -qE '/dev/(tcp|udp)/'").exit_status == 0
+    end
+
+    def missing_requirements(protocol)
+      missing = []
+
+      if %w{tcp udp}.include?(protocol) && !@has_nc && !@has_ncat
+        if @has_net_redirections
+          missing << "#{timeout} (part of coreutils) or netcat must be installed" unless inspec.command(timeout).exist?
+        else
+          missing << 'netcat must be installed'
+        end
+      end
+
+      missing
+    end
+
+    def ping(hostname, port, protocol)
+      if %w{tcp udp}.include?(protocol)
+        if @has_nc || @has_ncat
+          resp = inspec.command(netcat_check_command(hostname, port, protocol))
+        else
+          resp = inspec.command("#{timeout} 1 bash -c \"< /dev/#{protocol}/#{hostname}/#{port}\"")
+        end
+      else
+        # fall back to ping, but we can only test ICMP packages with ping
+        resp = inspec.command("ping -w 1 -c 1 #{hostname}")
+      end
+
+      {
+        success: resp.exit_status.to_i.zero?,
+        connection: resp.stderr,
+        socket: resp.stdout,
+      }
+    end
+
+    def netcat_check_command(hostname, port, protocol)
+      if @has_nc
+        base_cmd = 'nc'
+      elsif @has_ncat
+        base_cmd = 'ncat'
+      else
+        return
+      end
+
+      if protocol == 'udp'
+        extra_flags = '-u'
+      else
+        extra_flags = ''
+      end
+
+      "echo | #{base_cmd} -v -w 1 #{extra_flags} #{hostname} #{port}"
+    end
+
+    def timeout
+      'timeout'
+    end
+
     def resolve_with_dig(hostname)
       addresses = []
 
@@ -191,28 +254,8 @@ module Inspec::Resources
   end
 
   class DarwinHostProvider < UnixHostProvider
-    def missing_requirements(protocol)
+    def timeout
-      missing = []
+      'gtimeout'
-
-      if protocol == 'tcp'
-        missing << 'netcat must be installed' unless inspec.command('nc').exist?
-      end
-
-      missing
-    end
-
-    def ping(hostname, port, protocol)
-      if protocol == 'tcp'
-        resp = inspec.command("nc -vz -G 1 #{hostname} #{port}")
-      else
-        resp = inspec.command("ping -W 1 -c 1 #{hostname}")
-      end
-
-      {
-        success: resp.exit_status.to_i.zero?,
-        connection: resp.stderr,
-        socket: resp.stdout,
-      }
     end
 
     def resolve(hostname)
@@ -221,43 +264,6 @@ module Inspec::Resources
   end
 
   class LinuxHostProvider < UnixHostProvider
-    def missing_requirements(protocol)
-      missing = []
-
-      if protocol == 'tcp' && (!inspec.command('nc').exist? && !inspec.command('ncat').exist?)
-        missing << 'netcat must be installed'
-      end
-
-      missing
-    end
-
-    def ping(hostname, port, protocol)
-      if protocol == 'tcp'
-        resp = inspec.command(tcp_check_command(hostname, port))
-      else
-        # fall back to ping, but we can only test ICMP packages with ping
-        resp = inspec.command("ping -w 1 -c 1 #{hostname}")
-      end
-
-      {
-        success: resp.exit_status.to_i.zero?,
-        connection: resp.stderr,
-        socket: resp.stdout,
-      }
-    end
-
-    def tcp_check_command(hostname, port)
-      if inspec.command('nc').exist?
-        base_cmd = 'nc'
-      elsif inspec.command('ncat').exist?
-        base_cmd = 'ncat'
-      else
-        return
-      end
-
-      "echo | #{base_cmd} -v -w 1 #{hostname} #{port}"
-    end
-
     def resolve(hostname)
       resolve_with_getent(hostname)
     end

test/helper.rb

@@ -415,13 +415,22 @@ class MockLoader
       "modprobe --showconfig" => cmd.call('modprobe-config'),
       # get-process cmdlet for processes resource
       '$Proc = Get-Process -IncludeUserName | Where-Object {$_.Path -ne $null } | Select-Object PriorityClass,Id,CPU,PM,VirtualMemorySize,NPM,SessionId,Responding,StartTime,TotalProcessorTime,UserName,Path | ConvertTo-Csv -NoTypeInformation;$Proc.Replace("""","").Replace("`r`n","`n")' => cmd.call('get-process_processes'),
-      # host resource: check to see if netcat is installed
+      # host resource: TCP/UDP reachability check on linux
-      %{bash -c 'type "nc"'} => cmd.call('type-nc'),
+      %{bash -c 'type "nc"'} => empty.call,
-      'type "nc"' => cmd.call('type-nc'),
+      %{bash -c 'type "ncat"'} => empty.call,
-      # host resource: netcat for TCP reachability check on linux
+      %{bash -c 'type "timeout"'} => empty.call,
-      'echo | nc -v -w 1 example.com 1234' => cmd.call('nc-example-com'),
+      %{strings `which bash` | grep -qE '/dev/(tcp|udp)/'} => empty.call,
+      %{echo | nc -v -w 1 -u example.com 1234} => empty.call,
+      %{echo | nc -v -w 1  example.com 1234} => empty.call,
+      'timeout 1 bash -c "< /dev/tcp/example.com/1234"' => empty.call,
+      'timeout 1 bash -c "< /dev/udp/example.com/1234"' => empty.call,
       # host resource: netcat for TCP reachability check on darwin
-      'nc -vz -G 1 example.com 1234' => cmd.call('nc-example-com'),
+      'type "nc"' => empty.call,
+      'type "ncat"' => empty.call,
+      'type "gtimeout"' => empty.call,
+      'nc -vz -G 1 example.com 1234' => empty.call,
+      'gtimeout 1 bash -c "< /dev/tcp/example.com/1234"' => empty.call,
+      'gtimeout 1 bash -c "< /dev/udp/example.com/1234"' => empty.call,
       # host resource: test-netconnection for reachability check on windows
       'Test-NetConnection -ComputerName microsoft.com -WarningAction SilentlyContinue -RemotePort 1234| Select-Object -Property ComputerName, TcpTestSucceeded, PingSucceeded | ConvertTo-Json' => cmd.call('Test-NetConnection'),
       # postgres tests

test/unit/resources/host_test.rb

@@ -55,6 +55,14 @@ describe 'Inspec::Resources::Host' do
     _(resource.to_s).must_equal 'Host example.com port 1234 proto tcp'
   end
 
+  it 'check host udp on ubuntu' do
+    resource = MockLoader.new(:ubuntu1404).load_resource('host', 'example.com', port: 1234, protocol: 'udp')
+    _(resource.resolvable?).must_equal true
+    _(resource.reachable?).must_equal true
+    _(resource.ipaddress).must_equal ["12.34.56.78", "2606:2800:220:1:248:1893:25c8:1946"]
+    _(resource.to_s).must_equal 'Host example.com port 1234 proto udp'
+  end
+
   it 'check host tcp on centos 7' do
     resource = MockLoader.new(:centos7).load_resource('host', 'example.com', port: 1234, protocol: 'tcp')
     _(resource.resolvable?).must_equal true
@@ -63,6 +71,14 @@ describe 'Inspec::Resources::Host' do
     _(resource.to_s).must_equal 'Host example.com port 1234 proto tcp'
   end
 
+  it 'check host udp on centos 7' do
+    resource = MockLoader.new(:centos7).load_resource('host', 'example.com', port: 1234, protocol: 'udp')
+    _(resource.resolvable?).must_equal true
+    _(resource.reachable?).must_equal true
+    _(resource.ipaddress).must_equal ["12.34.56.78", "2606:2800:220:1:248:1893:25c8:1946"]
+    _(resource.to_s).must_equal 'Host example.com port 1234 proto udp'
+  end
+
   it 'check host tcp on darwin' do
     resource = MockLoader.new(:osx104).load_resource('host', 'example.com', port: 1234, protocol: 'tcp')
     _(resource.resolvable?).must_equal true
@@ -71,6 +87,14 @@ describe 'Inspec::Resources::Host' do
     _(resource.to_s).must_equal 'Host example.com port 1234 proto tcp'
   end
 
+  it 'check host udp on darwin' do
+    resource = MockLoader.new(:osx104).load_resource('host', 'example.com', port: 1234, protocol: 'udp')
+    _(resource.resolvable?).must_equal true
+    _(resource.reachable?).must_equal true
+    _(resource.ipaddress).must_equal ["12.34.56.78", "2606:2800:220:1:248:1893:25c8:1946"]
+    _(resource.to_s).must_equal 'Host example.com port 1234 proto udp'
+  end
+
   it 'check host tcp on windows' do
     resource = MockLoader.new(:windows).load_resource('host', 'microsoft.com', port: 1234, protocol: 'tcp')
     _(resource.resolvable?).must_equal true
@@ -89,12 +113,31 @@ describe 'Inspec::Resources::Host' do
 end
 
 describe Inspec::Resources::UnixHostProvider do
-  describe '#resolve_with_dig' do
   let(:provider)        { Inspec::Resources::UnixHostProvider.new(inspec) }
   let(:inspec)          { mock('inspec-backend') }
+  let(:nc_command)      { mock('nc-command') }
+  let(:ncat_command)    { mock('ncat-command') }
+  let(:timeout_command) { mock("timeout-command") }
+  let(:strings_command) { mock("strings-command") }
+
+  before do
+    inspec.stubs(:command).with('nc').returns(nc_command)
+    inspec.stubs(:command).with('ncat').returns(ncat_command)
+    inspec.stubs(:command).with('timeout').returns(timeout_command)
+    inspec.stubs(:command).with('gtimeout').returns(timeout_command)
+    inspec.stubs(:command).with("strings `which bash` | grep -qE '/dev/(tcp|udp)/'").returns(strings_command)
+  end
+
+  describe '#resolve_with_dig' do
     let(:v4_command) { mock('v4_command') }
     let(:v6_command) { mock('v6_command') }
 
+    before do
+      strings_command.stubs(:exit_status).returns(0)
+      nc_command.stubs(:exist?).returns(false)
+      ncat_command.stubs(:exist?).returns(false)
+    end
+
     it 'returns an array of IP addresses' do
       ipv4_command_output = <<-EOL
 a.cname.goes.here
@@ -169,16 +212,20 @@ EOL
   end
 
   describe '#resolve_with_getent' do
+    before do
+      strings_command.stubs(:exit_status).returns(0)
+      nc_command.stubs(:exist?).returns(false)
+      ncat_command.stubs(:exist?).returns(false)
+    end
+
     it 'returns an array of IP addresses when successful' do
       command_output = "123.123.123.123 STREAM testdomain.com\n2607:f8b0:4004:805::200e     STREAM\n"
       command = mock('getent_command')
       command.stubs(:stdout).returns(command_output)
       command.stubs(:exit_status).returns(0)
 
-      inspec = mock('inspec')
       inspec.stubs(:command).with('getent ahosts testdomain.com').returns(command)
 
-      provider = Inspec::Resources::UnixHostProvider.new(inspec)
       provider.resolve_with_getent('testdomain.com').must_equal(['123.123.123.123', '2607:f8b0:4004:805::200e'])
     end
 
@@ -186,84 +233,132 @@ EOL
       command = mock('getent_command')
       command.stubs(:exit_status).returns(1)
 
-      inspec = mock('inspec')
       inspec.stubs(:command).with('getent ahosts testdomain.com').returns(command)
 
-      provider = Inspec::Resources::UnixHostProvider.new(inspec)
       provider.resolve_with_getent('testdomain.com').must_be_nil
     end
   end
-end
 
-describe Inspec::Resources::LinuxHostProvider do
+
-  let(:provider)     { Inspec::Resources::LinuxHostProvider.new(inspec) }
+  describe "#ping" do
-  let(:inspec)       { mock('inspec-backend') }
+    let(:command_response) { mock('response') }
-  let(:nc_command)   { mock('nc-command') }
-  let(:ncat_command) { mock('ncat-command') }
 
     before do
-    provider.stubs(:inspec).returns(inspec)
+      strings_command.stubs(:exit_status).returns(0)
-  end
-
-  describe '#missing_requirements' do
-    it "returns an empty array if nc is installed but ncat is not installed" do
-      inspec.stubs(:command).with('nc').returns(nc_command)
-      nc_command.stubs(:exist?).returns(true)
-      inspec.stubs(:command).with('ncat').returns(ncat_command)
       ncat_command.stubs(:exist?).returns(false)
 
+      command_response.stubs(:exit_status).returns('0')
+      command_response.stubs(:stdout).returns('foo')
+      command_response.stubs(:stderr).returns('bar')
+    end
+
+    it "calls netcat if available" do
+      nc_command.stubs(:exist?).returns(true)
+      inspec.expects(:command).with('echo | nc -v -w 1  example.com 1234').returns(command_response)
+
+      provider.ping('example.com', '1234', 'tcp')
+    end
+
+    it "uses bash if netcat not available" do
+      nc_command.stubs(:exist?).returns(false)
+      inspec.expects(:command).with('timeout 1 bash -c "< /dev/tcp/example.com/1234"').returns(command_response)
+
+      provider.ping('example.com', '1234', 'tcp')
+    end
+
+    it "uses bash if netcat not available on Darwin" do
+      nc_command.stubs(:exist?).returns(false)
+      inspec.expects(:command).with('gtimeout 1 bash -c "< /dev/tcp/example.com/1234"').returns(command_response)
+
+      darwin_provider = Inspec::Resources::DarwinHostProvider.new(inspec)
+      darwin_provider.ping('example.com', '1234', 'tcp')
+    end
+  end
+
+
+  describe '#missing_requirements' do
+    describe 'bash with net redirects and no netcat' do
+      before do
+        strings_command.stubs(:exit_status).returns(0)
+        nc_command.stubs(:exist?).returns(false)
+        ncat_command.stubs(:exist?).returns(false)
+      end
+
+      it "returns an empty array if timeout is available" do
+        timeout_command.stubs(:exist?).returns(true)
+        provider.missing_requirements('tcp').must_equal([])
+      end
+
+      it "returns a missing requirement when timeout is missing" do
+        timeout_command.stubs(:exist?).returns(false)
+        provider.missing_requirements('tcp').must_equal(['timeout (part of coreutils) or netcat must be installed'])
+      end
+    end
+
+    describe 'bash without net redirects' do
+      before do
+        strings_command.stubs(:exit_status).returns(1)
+      end
+
+      it "returns an empty array if nc is installed but ncat is not installed" do
+        nc_command.stubs(:exist?).returns(true)
+        ncat_command.stubs(:exist?).returns(false)
         provider.missing_requirements('tcp').must_equal([])
       end
 
       it "returns an empty array if nc is not installed but ncat is installed" do
-      inspec.stubs(:command).with('nc').returns(nc_command)
         nc_command.stubs(:exist?).returns(false)
-      inspec.stubs(:command).with('ncat').returns(ncat_command)
         ncat_command.stubs(:exist?).returns(true)
-
         provider.missing_requirements('tcp').must_equal([])
       end
 
       it "returns an empty array if both nc and ncat are installed" do
-      inspec.stubs(:command).with('nc').returns(nc_command)
         nc_command.stubs(:exist?).returns(true)
-      inspec.stubs(:command).with('ncat').returns(ncat_command)
         ncat_command.stubs(:exist?).returns(true)
-
         provider.missing_requirements('tcp').must_equal([])
       end
 
       it "returns a missing requirement when neither nc nor ncat are installed" do
-      inspec.stubs(:command).with('nc').returns(nc_command)
         nc_command.stubs(:exist?).returns(false)
-      inspec.stubs(:command).with('ncat').returns(ncat_command)
         ncat_command.stubs(:exist?).returns(false)
-
         provider.missing_requirements('tcp').must_equal(['netcat must be installed'])
       end
     end
-
-  describe '#tcp_check_command' do
-    it 'returns an nc command when nc exists' do
-      inspec.expects(:command).with('nc').returns(nc_command)
-      nc_command.expects(:exist?).returns(true)
-      provider.tcp_check_command('foo', 1234).must_equal 'echo | nc -v -w 1 foo 1234'
   end
 
-    it 'returns an ncat command when nc does not exist but ncat exists' do
+  describe '#netcat_check_command' do
-      inspec.expects(:command).with('nc').returns(nc_command)
+    before do
-      inspec.expects(:command).with('ncat').returns(ncat_command)
+      strings_command.stubs(:exit_status).returns(1)
+    end
+
+    it 'returns an nc command when nc exists tcp' do
+      nc_command.expects(:exist?).returns(true)
+      ncat_command.expects(:exist?).returns(false)
+      provider.netcat_check_command('foo', 1234, 'tcp').must_equal 'echo | nc -v -w 1  foo 1234'
+    end
+
+    it 'returns an nc command when nc exists udp' do
+      nc_command.expects(:exist?).returns(true)
+      ncat_command.expects(:exist?).returns(false)
+      provider.netcat_check_command('foo', 1234, 'udp').must_equal 'echo | nc -v -w 1 -u foo 1234'
+    end
+
+    it 'returns an ncat command when nc does not exist but ncat exists tcp' do
       nc_command.expects(:exist?).returns(false)
       ncat_command.expects(:exist?).returns(true)
-      provider.tcp_check_command('foo', 1234).must_equal 'echo | ncat -v -w 1 foo 1234'
+      provider.netcat_check_command('foo', 1234, 'tcp').must_equal 'echo | ncat -v -w 1  foo 1234'
+    end
+
+    it 'returns an ncat command when nc does not exist but ncat exists udp' do
+      nc_command.expects(:exist?).returns(false)
+      ncat_command.expects(:exist?).returns(true)
+      provider.netcat_check_command('foo', 1234, 'udp').must_equal 'echo | ncat -v -w 1 -u foo 1234'
     end
 
     it 'returns nil if neither nc or ncat exist' do
-      inspec.expects(:command).with('nc').returns(nc_command)
-      inspec.expects(:command).with('ncat').returns(ncat_command)
       nc_command.expects(:exist?).returns(false)
       ncat_command.expects(:exist?).returns(false)
-      provider.tcp_check_command('foo', 1234).must_be_nil
+      provider.netcat_check_command('foo', 1234, 'tcp').must_be_nil
     end
   end
 end