Check Runner Zip Hash on Upgrade (actions#967)

* Check Hash if it exists on runner update

src/Runner.Listener/SelfUpdater.cs

@@ -8,7 +8,9 @@
 using System.Net.Http;
 using System.Threading;
 using System.Threading.Tasks;
+using System.Security.Cryptography;
 using GitHub.Services.WebApi;
+using GitHub.Services.Common;
 using GitHub.Runner.Common;
 using GitHub.Runner.Sdk;
 
@@ -256,6 +258,24 @@ private async Task DownloadLatestRunner(CancellationToken token)
                 }
 
                 // If we got this far, we know that we've successfully downloaded the runner package
+                // Validate Hash Matches if it is provided
+                using (FileStream stream = File.OpenRead(archiveFile))
+                {
+                    if (!String.IsNullOrEmpty(_targetPackage.HashValue))
+                    {
+                        using (SHA256 sha256 = SHA256.Create())
+                        {
+                            byte[] srcHashBytes = await sha256.ComputeHashAsync(stream);
+                            var hash = PrimitiveExtensions.ConvertToHexString(srcHashBytes);
+                            if (hash != _targetPackage.HashValue)
+                            {
+                                // Hash did not match, we can't recover from this, just throw
+                                throw new Exception($"Computed runner hash {hash} did not match expected Runner Hash {_targetPackage.HashValue} for {_targetPackage.Filename}");
+                            }
+                            Trace.Info($"Validated Runner Hash matches {_targetPackage.Filename} : {_targetPackage.HashValue}");
+                        }
+                    }
+                }
                 if (archiveFile.EndsWith(".zip", StringComparison.OrdinalIgnoreCase))
                 {
                     ZipFile.ExtractToDirectory(archiveFile, latestRunnerDirectory);

src/Sdk/Common/Common/Utility/HashAlgorithmExtensions.cs

@@ -0,0 +1,27 @@
+using System.IO;
+using System.Security.Cryptography;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace GitHub.Services.Common
+{
+    public static class HashAlgorithmExtensions
+    {
+        public static async Task<byte[]> ComputeHashAsync(this HashAlgorithm hashAlg, Stream inputStream)
+        {
+            byte[] buffer = new byte[4096];
+
+            while (true)
+            {
+                int read = await inputStream.ReadAsync(buffer, 0, buffer.Length);
+                if (read == 0)
+                    break;
+
+                hashAlg.TransformBlock(buffer, 0, read, null, 0);
+            }
+
+            hashAlg.TransformFinalBlock(buffer, 0, 0);
+            return hashAlg.Hash;
+        }
+    }
+}

src/Sdk/Common/Common/Utility/PrimitiveExtensions.cs

@@ -85,5 +85,19 @@ public static String ConvertToHex(String base64String)
             var bytes = FromBase64StringNoPadding(base64String);
             return BitConverter.ToString(bytes).Replace("-", String.Empty);
         }
+
+        /// <summary>
+        /// Converts byte array into a hex string
+        /// </summary>
+        public static String ConvertToHexString(byte[] bytes)
+        {
+            // Convert byte array to string
+            var sBuilder = new StringBuilder();
+            for (int i = 0; i < bytes.Length; i++)
+            {
+                sBuilder.Append(bytes[i].ToString("x2"));
+            }
+            return sBuilder.ToString();
+        }
     }
 }