Fix sudo usage in exports write within linux host cap

Only move new exports file to destination without sudo when the
file has write access and the directory has write access. Always
use sudo when changing file ownership.

plugins/hosts/linux/cap/nfs.rb

@@ -173,16 +173,14 @@ module VagrantPlugins
         def self.nfs_write_exports(new_exports_content)
           if(nfs_exports_content != new_exports_content.strip)
             begin
+              exports_path = Pathname.new(NFS_EXPORTS_PATH)
+
               # Write contents out to temporary file
               new_exports_file = Tempfile.create('vagrant')
               new_exports_file.puts(new_exports_content)
               new_exports_file.close
               new_exports_path = new_exports_file.path
 
-              # Only use "sudo" if we can't write to /etc/exports directly
-              sudo_command = ""
-              sudo_command = "sudo " if !File.writable?(NFS_EXPORTS_PATH)
-
               # Ensure new file mode and uid/gid match existing file to replace
               existing_stat = File.stat(NFS_EXPORTS_PATH)
               new_stat = File.stat(new_exports_path)
@@ -190,7 +188,7 @@ module VagrantPlugins
                 File.chmod(existing_stat.mode, new_exports_path)
               end
               if existing_stat.uid != new_stat.uid || existing_stat.gid != new_stat.gid
-                chown_cmd = "#{sudo_command}chown #{existing_stat.uid}:#{existing_stat.gid} #{new_exports_path}"
+                chown_cmd = "sudo chown #{existing_stat.uid}:#{existing_stat.gid} #{new_exports_path}"
                 result = Vagrant::Util::Subprocess.execute(*Shellwords.split(chown_cmd))
                 if result.exit_code != 0
                   raise Vagrant::Errors::NFSExportsFailed,
@@ -200,6 +198,7 @@ module VagrantPlugins
                 end
               end
               # Always force move the file to prevent overwrite prompting
+              sudo_command = "sudo " if !exports_path.writable? || !exports_path.dirname.writable?
               mv_cmd = "#{sudo_command}mv -f #{new_exports_path} #{NFS_EXPORTS_PATH}"
               result = Vagrant::Util::Subprocess.execute(*Shellwords.split(mv_cmd))
               if result.exit_code != 0

test/unit/plugins/hosts/linux/cap/nfs_test.rb

@@ -269,14 +269,72 @@ EOH
       expect{ described_class.nfs_write_exports("new content") }.to raise_error(Vagrant::Errors::NFSExportsFailed)
     end
 
-    it "should retain existing file owner and group IDs" do
-      pending("investigate using a simulated FS to test")
-      test_with_simulated_fs
-    end
+    context "exports file modification" do
+      let(:tmp_stat) { double("tmp_stat", uid: 100, gid: 100, mode: tmp_mode) }
+      let(:tmp_mode) { 0 }
+      let(:exports_stat) { double("stat", uid: exports_uid, gid: exports_gid, mode: exports_mode) }
+      let(:exports_uid) { -1 }
+      let(:exports_gid) { -1 }
+      let(:exports_mode) { 0 }
+      let(:new_exports_file) { double("new_exports_file", path: "/dev/null/exports") }
 
-    it "should raise custom exception when chown fails" do
-      pending("investigate using a simulated FS to test")
-      test_with_simulated_fs
+      before do
+        allow(File).to receive(:stat).with(new_exports_file.path).and_return(tmp_stat)
+        allow(File).to receive(:stat).with(tmp_exports_path.to_s).and_return(exports_stat)
+        allow(new_exports_file).to receive(:puts)
+        allow(new_exports_file).to receive(:close)
+        allow(Vagrant::Util::Subprocess).to receive(:execute).and_return(Vagrant::Util::Subprocess::Result.new(0, "", ""))
+        allow(Tempfile).to receive(:create).with("vagrant").and_return(new_exports_file)
+      end
+
+      it "should retain existing file owner and group IDs" do
+        expect(Vagrant::Util::Subprocess).to receive(:execute) { |*args|
+          expect(args).to include("sudo")
+          expect(args).to include("chown")
+        }.and_return(Vagrant::Util::Subprocess::Result.new(0, "", ""))
+        described_class.nfs_write_exports("new content")
+      end
+
+      it "should raise custom exception when chown fails" do
+        expect(Vagrant::Util::Subprocess).to receive(:execute) { |*args|
+          expect(args).to include("sudo")
+          expect(args).to include("chown")
+        }.and_return(Vagrant::Util::Subprocess::Result.new(1, "", ""))
+        expect { described_class.nfs_write_exports("new content") }.to raise_error(Vagrant::Errors::NFSExportsFailed)
+      end
+
+      context "when user has write access to exports file" do
+        let(:file_writable?) { true }
+        let(:dir_writable?) { false }
+        let(:exports_pathname) { double("exports_pathname", writable?: file_writable?, dirname: exports_dir_pathname) }
+        let(:exports_dir_pathname) { double("exports_dir_pathname", writable?: dir_writable?) }
+
+        before do
+          allow(File).to receive(:stat).and_return(exports_stat)
+          allow(File).to receive(:exist?).and_return(false)
+          allow(Pathname).to receive(:new).with(tmp_exports_path.to_s).and_return(exports_pathname)
+        end
+
+        it "should use sudo when moving new file" do
+          expect(Vagrant::Util::Subprocess).to receive(:execute) { |*args|
+            expect(args).to include("sudo")
+            expect(args).to include("mv")
+          }.and_return(Vagrant::Util::Subprocess::Result.new(0, "", ""))
+          described_class.nfs_write_exports("new content")
+        end
+
+        context "and write access to exports parent directory" do
+          let(:dir_writable?) { true }
+
+          it "should not use sudo when moving new file" do
+            expect(Vagrant::Util::Subprocess).to receive(:execute) { |*args|
+              expect(args).not_to include("sudo")
+              expect(args).to include("mv")
+            }.and_return(Vagrant::Util::Subprocess::Result.new(0, "", ""))
+            described_class.nfs_write_exports("new content")
+          end
+        end
+      end
     end
   end
 end