Check string size before Win32 MultiByte <-> WideChar conversions (flutter#99729)

This patch adds an additional check to ensure the target length of a string is within the supported maximum string length prior to calling WideCharToMultiByte/MultiByteToWideChar in the Windows runner template.

This is to prevent resize() from failing if called with a count > std::string::max_size().

According to Win32 API docs (WideCharToMultiByte, MultiByteToWideChar) it's the caller responsibility to make sure the buffers are correctly allocated.

Authored by: Tomasz Gucio <[email protected]>

Author: cbracken

dev/integration_tests/flutter_gallery/windows/runner/utils.cpp

@@ -48,10 +48,10 @@ std::string Utf8FromUtf16(const wchar_t* utf16_string) {
   int target_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,
       -1, nullptr, 0, nullptr, nullptr);
-  if (target_length == 0) {
-    return std::string();
-  }
   std::string utf8_string;
+  if (target_length == 0 || target_length > utf8_string.max_size()) {
+    return utf8_string;
+  }
   utf8_string.resize(target_length);
   int converted_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,

dev/manual_tests/windows/runner/utils.cpp

@@ -48,10 +48,10 @@ std::string Utf8FromUtf16(const wchar_t* utf16_string) {
   int target_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,
       -1, nullptr, 0, nullptr, nullptr);
-  if (target_length == 0) {
-    return std::string();
-  }
   std::string utf8_string;
+  if (target_length == 0 || target_length > utf8_string.max_size()) {
+    return utf8_string;
+  }
   utf8_string.resize(target_length);
   int converted_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,

examples/api/windows/runner/utils.cpp

@@ -48,10 +48,10 @@ std::string Utf8FromUtf16(const wchar_t* utf16_string) {
   int target_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,
       -1, nullptr, 0, nullptr, nullptr);
-  if (target_length == 0) {
-    return std::string();
-  }
   std::string utf8_string;
+  if (target_length == 0 || target_length > utf8_string.max_size()) {
+    return utf8_string;
+  }
   utf8_string.resize(target_length);
   int converted_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,

packages/flutter_tools/templates/app_shared/windows.tmpl/runner/utils.cpp

@@ -48,10 +48,10 @@ std::string Utf8FromUtf16(const wchar_t* utf16_string) {
   int target_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,
       -1, nullptr, 0, nullptr, nullptr);
-  if (target_length == 0) {
-    return std::string();
-  }
   std::string utf8_string;
+  if (target_length == 0 || target_length > utf8_string.max_size()) {
+    return utf8_string;
+  }
   utf8_string.resize(target_length);
   int converted_length = ::WideCharToMultiByte(
       CP_UTF8, WC_ERR_INVALID_CHARS, utf16_string,