Don't follow junctions when recursing directories.

When deleting directories recursively, an elevated custom action
following junctions in a user-writable location could recurse into
any directory, including some that you might not want to be deleted.
Therefore, avoid recursing into directories that are actually
junctions (aka "reparse points").

This applies to:

- The RemoveFoldersEx custom action (which doesn't actually do deletions
but would instruct elevated MSI to delete on your behalf).
- DTF's custom action runner.

src/DTF/Tools/SfxCA/SfxUtil.cpp

@@ -93,7 +93,9 @@ bool DeleteDirectory(const wchar_t* szDir)
                 StringCchCopy(szPath + cchDir + 1, cchPathBuf - (cchDir + 1), fd.cFileName);
                 if ((fd.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) != 0)
                 {
-                        if (wcscmp(fd.cFileName, L".") != 0 && wcscmp(fd.cFileName, L"..") != 0)
+                        if (wcscmp(fd.cFileName, L".") != 0
+                            && wcscmp(fd.cFileName, L"..") != 0
+                            && ((fd.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) == 0))
                         {
                                 DeleteDirectory(szPath);
                         }

src/ext/ca/wixca/dll/RemoveFoldersEx.cpp

@@ -24,6 +24,14 @@ static HRESULT RecursePath(
     WIN32_FIND_DATAW wfd;
     LPWSTR sczNext = NULL;
 
+    // Do NOT follow junctions.
+    DWORD dwAttributes = ::GetFileAttributesW(wzPath);
+    if (dwAttributes & FILE_ATTRIBUTE_REPARSE_POINT)
+    {
+        WcaLog(LOGMSG_STANDARD, "Path is a junction; skipping: %ls", wzPath);
+        ExitFunction();
+    }
+
     // First recurse down to all the child directories.
     hr = StrAllocFormatted(&sczSearch, L"%s*", wzPath);
     ExitOnFailure1(hr, "Failed to allocate file search string in path: %S", wzPath);
@@ -159,10 +167,10 @@ extern "C" UINT WINAPI WixRemoveFoldersEx(
 
         hr = PathExpand(&sczExpandedPath, sczPath, PATH_EXPAND_ENVIRONMENT);
         ExitOnFailure2(hr, "Failed to expand path: %S for row: %S", sczPath, sczId);
-        
+
         hr = PathBackslashTerminate(&sczExpandedPath);
         ExitOnFailure1(hr, "Failed to backslash-terminate path: %S", sczExpandedPath);
-    
+
         WcaLog(LOGMSG_STANDARD, "Recursing path: %S for row: %S.", sczExpandedPath, sczId);
         hr = RecursePath(sczExpandedPath, sczId, sczComponent, sczProperty, iMode, &dwCounter, &hTable, &hColumns);
         ExitOnFailure2(hr, "Failed while navigating path: %S for row: %S", sczPath, sczId);