Ensure that cache dirs and files have appropriate permissions (#24669)

Fixes https://github.com/flutter/flutter/issues/24413

bin/internal/update_dart_sdk.sh

@@ -27,9 +27,11 @@ if [ ! -f "$ENGINE_STAMP" ] || [ "$ENGINE_VERSION" != `cat "$ENGINE_STAMP"` ]; t
   case "$(uname -s)" in
     Darwin)
       DART_ZIP_NAME="dart-sdk-darwin-x64.zip"
+      IS_USER_EXECUTABLE="-perm +100"
       ;;
     Linux)
       DART_ZIP_NAME="dart-sdk-linux-x64.zip"
+      IS_USER_EXECUTABLE="-perm /u+x"
       ;;
     *)
       echo "Unknown operating system. Cannot install Dart SDK."
@@ -48,7 +50,7 @@ if [ ! -f "$ENGINE_STAMP" ] || [ "$ENGINE_VERSION" != `cat "$ENGINE_STAMP"` ]; t
 
   # install the new sdk
   rm -rf -- "$DART_SDK_PATH"
-  mkdir -p -- "$DART_SDK_PATH"
+  mkdir -m 755 -p -- "$DART_SDK_PATH"
   DART_SDK_ZIP="$FLUTTER_ROOT/bin/cache/$DART_ZIP_NAME"
 
   curl --continue-at - --location --output "$DART_SDK_ZIP" "$DART_SDK_URL" 2>&1 || {
@@ -70,6 +72,8 @@ if [ ! -f "$ENGINE_STAMP" ] || [ "$ENGINE_VERSION" != `cat "$ENGINE_STAMP"` ]; t
     exit 1
   }
   rm -f -- "$DART_SDK_ZIP"
+  find "$DART_SDK_PATH" -type d -exec chmod 755 {} \;
+  find "$DART_SDK_PATH" -type f $IS_USER_EXECUTABLE -exec chmod a+x,a+r {} \;
   echo "$ENGINE_VERSION" > "$ENGINE_STAMP"
 
   # delete any temporary sdk path

packages/flutter_tools/lib/src/base/os.dart

@@ -25,7 +25,15 @@ abstract class OperatingSystemUtils {
   OperatingSystemUtils._private();
 
   /// Make the given file executable. This may be a no-op on some platforms.
-  ProcessResult makeExecutable(File file);
+  void makeExecutable(File file);
+
+  /// Updates the specified file system [entity] to have the file mode
+  /// bits set to the value defined by [mode], which can be specified in octal
+  /// (e.g. `644`) or symbolically (e.g. `u+x`).
+  ///
+  /// On operating systems that do not support file mode bits, this will be a
+  /// no-op.
+  void chmod(FileSystemEntity entity, String mode);
 
   /// Return the path (with symlinks resolved) to the given executable, or null
   /// if `which` was not able to locate the binary.
@@ -78,8 +86,13 @@ class _PosixUtils extends OperatingSystemUtils {
   _PosixUtils() : super._private();
 
   @override
-  ProcessResult makeExecutable(File file) {
-    return processManager.runSync(<String>['chmod', 'a+x', file.path]);
+  void makeExecutable(File file) {
+    chmod(file, 'a+x');
+  }
+
+  @override
+  void chmod(FileSystemEntity entity, String mode) {
+    processManager.runSync(<String>['chmod', mode, entity.path]);
   }
 
   @override
@@ -152,11 +165,11 @@ class _PosixUtils extends OperatingSystemUtils {
 class _WindowsUtils extends OperatingSystemUtils {
   _WindowsUtils() : super._private();
 
-  // This is a no-op.
   @override
-  ProcessResult makeExecutable(File file) {
-    return ProcessResult(0, 0, null, null);
-  }
+  void makeExecutable(File file) {}
+
+  @override
+  void chmod(FileSystemEntity entity, String mode) {}
 
   @override
   List<File> _which(String execName, {bool all = false}) {

packages/flutter_tools/lib/src/cache.dart

@@ -145,8 +145,10 @@ class Cache {
   /// Return a directory in the cache dir. For `pkg`, this will return `bin/cache/pkg`.
   Directory getCacheDir(String name) {
     final Directory dir = fs.directory(fs.path.join(getRoot().path, name));
-    if (!dir.existsSync())
+    if (!dir.existsSync()) {
       dir.createSync(recursive: true);
+      os.chmod(dir, '755');
+    }
     return dir;
   }
 
@@ -194,8 +196,10 @@ class Cache {
     final Directory thirdPartyDir = getArtifactDirectory('third_party');
 
     final Directory serviceDir = fs.directory(fs.path.join(thirdPartyDir.path, serviceName));
-    if (!serviceDir.existsSync())
+    if (!serviceDir.existsSync()) {
       serviceDir.createSync(recursive: true);
+      os.chmod(serviceDir, '755');
+    }
 
     final File cachedFile = fs.file(fs.path.join(serviceDir.path, url.pathSegments.last));
     if (!cachedFile.existsSync()) {
@@ -552,13 +556,16 @@ class FlutterEngine extends CachedArtifact {
     return result;
   }
 
-
   void _makeFilesExecutable(Directory dir) {
-    for (FileSystemEntity entity in dir.listSync()) {
+    os.chmod(dir, 'a+r,a+x');
+    for (FileSystemEntity entity in dir.listSync(recursive: true)) {
       if (entity is File) {
-        final String name = fs.path.basename(entity.path);
-        if (name == 'flutter_tester')
-          os.makeExecutable(entity);
+        final FileStat stat = entity.statSync();
+        final bool isUserExecutable = ((stat.mode >> 6) & 0x1) == 1;
+        if (entity.basename == 'flutter_tester' || isUserExecutable) {
+          // Make the file readable and executable by all users.
+          os.chmod(entity, 'a+r,a+x');
+        }
       }
     }
   }