[3.6] bpo-39401: Avoid unsafe DLL load on Windows 7 and earlier (GH-18231) (GH-18233)

Author: zooba

Misc/NEWS.d/next/Security/2020-01-28-20-54-09.bpo-39401.he7h_A.rst

@@ -0,0 +1 @@
+Avoid unsafe load of ``api-ms-win-core-path-l1-1-0.dll`` at startup on Windows 7.

PC/getpathp.c

@@ -224,7 +224,8 @@ static void
 join(wchar_t *buffer, const wchar_t *stuff)
 {
  if (_PathCchCombineEx_Initialized == 0) {
- HMODULE pathapi = LoadLibraryW(L"api-ms-win-core-path-l1-1-0.dll");
+ HMODULE pathapi = LoadLibraryExW(L"api-ms-win-core-path-l1-1-0.dll", NULL,
+ LOAD_LIBRARY_SEARCH_SYSTEM32);
  if (pathapi)
  _PathCchCombineEx = (PPathCchCombineEx)GetProcAddress(pathapi, "PathCchCombineEx");
  else
@@ -249,7 +250,8 @@ static PPathCchCanonicalizeEx _PathCchCanonicalizeEx;
 static void canonicalize(wchar_t *buffer, const wchar_t *path)
 {
  if (_PathCchCanonicalizeEx_Initialized == 0) {
- HMODULE pathapi = LoadLibraryW(L"api-ms-win-core-path-l1-1-0.dll");
+ HMODULE pathapi = LoadLibraryExW(L"api-ms-win-core-path-l1-1-0.dll", NULL,
+ LOAD_LIBRARY_SEARCH_SYSTEM32);
  if (pathapi) {
  _PathCchCanonicalizeEx = (PPathCchCanonicalizeEx)GetProcAddress(pathapi, "PathCchCanonicalizeEx");
  }

Tools/msi/bundle/bootstrap/PythonBootstrapperApplication.cpp

@@ -3042,8 +3042,16 @@ class PythonBootstrapperApplication : public CBalBaseBootstrapperApplication {
  }
  } else {
  if (IsWindows7SP1OrGreater()) {
- BalLog(BOOTSTRAPPER_LOG_LEVEL_STANDARD, "Target OS is Windows 7 SP1 or later");
- return;
+ HMODULE hKernel32 = GetModuleHandleW(L"kernel32");
+ if (hKernel32 && !GetProcAddress(hKernel32, "AddDllDirectory")) {
+ BalLog(BOOTSTRAPPER_LOG_LEVEL_ERROR, "Detected Windows 7 SP1 without KB2533623");
+ BalLog(BOOTSTRAPPER_LOG_LEVEL_ERROR, "KB2533623 update is required to continue.");
+ /* The "MissingSP1" error also specifies updates are required */
+ LocGetString(_wixLoc, L"#(loc.FailureWin7MissingSP1)", &pLocString);
+ } else {
+ BalLog(BOOTSTRAPPER_LOG_LEVEL_STANDARD, "Target OS is Windows 7 SP1 or later");
+ return;
+ }
  } else if (IsWindows7OrGreater()) {
  BalLog(BOOTSTRAPPER_LOG_LEVEL_ERROR, "Detected Windows 7 RTM");
  BalLog(BOOTSTRAPPER_LOG_LEVEL_ERROR, "Service Pack 1 is required to continue installation");