fix(installer): refuse an untrusted data folder

.github/workflows/ci.yml

@@ -1394,6 +1394,21 @@ jobs:
         run: dotnet test package/AgentWindowsManaged.Tests/DevolutionsAgent.Installer.Tests.csproj
         shell: pwsh
 
+  gateway-installer-tests:
+    name: Gateway installer tests
+    runs-on: windows-2022
+    needs: [preflight]
+
+    steps:
+      - name: Checkout ${{ github.repository }}
+        uses: actions/checkout@v6
+        with:
+          ref: ${{ needs.preflight.outputs.ref }}
+
+      - name: Tests
+        run: dotnet test package/WindowsManaged.UnitTests/DevolutionsGateway.Installer.Tests.csproj
+        shell: pwsh
+
   winapi-sanitizer-tests:
     name: Windows API sanitizer tests
     runs-on: windows-2022
@@ -1655,7 +1670,7 @@ jobs:
   success:
     name: Success
     if: ${{ always() }}
-    needs: [tests, agent-tunnel-e2e, agent-policy-e2e, lints, oracle-markers, oracle-markers-tests, skill-links, check-dependencies, jetsocat-lipo, devolutions-gateway-powershell, gateway-service-account-tests, devolutions-gateway, devolutions-gateway-merge, devolutions-pedm-desktop, devolutions-agent, devolutions-agent-merge, devolutions-pedm-client, dotnet-utils-tests, agent-identity-vectors, agent-installer-event-log-tests, winapi-sanitizer-tests, winapi-miri, pedm-simulator, secure-memory-verifier]
+    needs: [tests, agent-tunnel-e2e, agent-policy-e2e, lints, oracle-markers, oracle-markers-tests, skill-links, check-dependencies, jetsocat-lipo, devolutions-gateway-powershell, gateway-service-account-tests, devolutions-gateway, devolutions-gateway-merge, devolutions-pedm-desktop, devolutions-agent, devolutions-agent-merge, devolutions-pedm-client, dotnet-utils-tests, agent-identity-vectors, agent-installer-event-log-tests, gateway-installer-tests, winapi-sanitizer-tests, winapi-miri, pedm-simulator, secure-memory-verifier]
     runs-on: ubuntu-latest
 
     steps:

package/WindowsManaged.UnitTests/DevolutionsGateway.Installer.Tests.csproj

@@ -0,0 +1,21 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net471</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <IsPackable>false</IsPackable>
+    <AssemblyName>DevolutionsGateway.Installer.Tests</AssemblyName>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\WindowsManaged\DevolutionsGateway.csproj" Targets="CoreBuild;GetTargetPath" />
+  </ItemGroup>
+</Project>

package/WindowsManaged.UnitTests/InstallerSession.cs

@@ -0,0 +1,82 @@
+using System;
+using System.IO;
+using System.Linq;
+
+using DevolutionsGateway.Actions;
+
+using Microsoft.Deployment.WindowsInstaller;
+
+using WixSharp;
+
+using Xunit;
+
+using MsiInstaller = Microsoft.Deployment.WindowsInstaller.Installer;
+
+namespace DevolutionsGateway.Installer.Tests;
+
+/// <summary>
+/// The installer's actions, and Windows Installer sessions to evaluate them in.
+/// </summary>
+internal static class InstallerSession
+{
+    /// <summary>
+    /// The test collection of every test class that opens a session.
+    /// </summary>
+    /// <remarks>
+    /// Windows Installer opens one package at a time in a process, and xUnit runs the tests of one collection one at a
+    /// time.
+    /// </remarks>
+    public const string Collection = "Windows Installer session";
+
+    /// <summary>
+    /// The installer's action that runs the custom action <paramref name="methodName"/>.
+    /// </summary>
+    public static ManagedAction ActionOf(string methodName) =>
+        Assert.Single(GatewayActions.Actions.OfType<ManagedAction>(), a => a.MethodName == methodName);
+
+    /// <summary>
+    /// Evaluates <paramref name="condition"/> with the Windows Installer engine, in a session where
+    /// <paramref name="properties"/> (<c>NAME=value</c>) are set.
+    /// </summary>
+    public static bool EvaluateCondition(string condition, string[] properties) =>
+        WithSession(properties, session => session.EvaluateCondition(condition));
+
+    public static T WithSession<T>(string[] properties, Func<Session, T> action) =>
+        WithSession(AppContext.BaseDirectory, properties, action);
+
+    /// <summary>
+    /// Runs <paramref name="action"/> in a Windows Installer session of an empty package in <paramref name="folder"/>
+    /// where <paramref name="properties"/> (<c>NAME=value</c>) are set.
+    /// </summary>
+    public static T WithSession<T>(string folder, string[] properties, Func<Session, T> action)
+    {
+        string path = Path.Combine(folder, $"session-{Guid.NewGuid():N}.msi");
+
+        try
+        {
+            using (Database database = new(path, DatabaseOpenMode.CreateDirect))
+            {
+                database.Execute("CREATE TABLE `Property` (`Property` CHAR(72) NOT NULL, `Value` CHAR(0) NOT NULL LOCALIZABLE PRIMARY KEY `Property`)");
+                database.Execute($"INSERT INTO `Property` (`Property`, `Value`) VALUES ('ProductCode', '{Guid.NewGuid():B}')");
+                database.SummaryInfo.Template = "x64;1033";
+                database.SummaryInfo.RevisionNumber = Guid.NewGuid().ToString("B");
+                database.SummaryInfo.PageCount = 500;
+                database.Commit();
+            }
+
+            using Session session = MsiInstaller.OpenPackage(path, ignoreMachineState: true);
+
+            foreach (string property in properties)
+            {
+                string[] parts = property.Split(['='], 2);
+                session[parts[0]] = parts[1];
+            }
+
+            return action(session);
+        }
+        finally
+        {
+            System.IO.File.Delete(path);
+        }
+    }
+}

package/WindowsManaged.UnitTests/OutputLogger.cs

@@ -0,0 +1,15 @@
+using DevolutionsGateway.Actions;
+
+using Xunit.Abstractions;
+
+namespace DevolutionsGateway.Installer.Tests;
+
+/// <summary>
+/// Writes the log of the code under test to the test's output.
+/// </summary>
+internal sealed class OutputLogger(ITestOutputHelper output) : ILogger
+{
+    public void Log(string msg) => output.WriteLine(msg);
+
+    public void Log(string format, params object[] args) => output.WriteLine(format, args);
+}