QWebEngine crash when debug build is launched from a mounted drive

When you add a new HDD to Windows, you have two options: assign it a letter (DOS-style) or mount it in an empty NTFS folder (Unix-style). Both are done via Control Panel -> Computer Management -> Disk Management.

When a second method is used to mount a drive in an empty NTFS folder, QWebEngine/chromium is built with OFFICIAL_BUILD macro not defined (debug build), and deployed on such a mounted drive, it crashes on any attempt to use QWebEngine. UPD: This crash is reproducible with the official binary build of Qt 5.15.2, which is the latest build with web engine at the moment.

This happens because:

src\qtwebengine\src\3rdparty\chromium\services\service_manager\sandbox\win\sandbox_win.cc:

// Add the policy for read-only PDB file access for stack traces.
#if !defined(OFFICIAL_BUILD)
base::FilePath exe;
if (!base::PathService::Get(base::FILE_EXE, &exe))
return sandbox::SBOX_ERROR_GENERIC;
base::FilePath pdb_path = exe.DirName().Append(L"*.pdb");
result = policy->AddRule(sandbox::TargetPolicy::SUBSYS_FILES,
sandbox::TargetPolicy::FILES_ALLOW_READONLY,
pdb_path.value().c_str());
if (result != sandbox::SBOX_ALL_OK)
return result;
#endif

From there it goes (via a few intermediate methods) to:

src\qtwebengine\src\3rdparty\chromium\sandbox\win\src\filesystem_policy.cc

FileSystemPolicy::GenerateRules(<path on a mounted drive*.pdb>)

->

FileSystemPolicy::PreProcessName(<path on a mounted drive*.pdb>)

->

src\qtwebengine\src\3rdparty\chromium\sandbox\win\src\win_utils.cc

IsReparsePoint(<path on a mounted drive*.pdb>)

The last function calls ::GetFileAttributes for every component of the path and checks FILE_ATTRIBUTE_REPARSE_POINT attribute. This attribute is set for the directory where a drive is mounted, which is correct. Therefore IsReparsePoint returns ERROR_SUCCESS.

This causes StartSandboxesProcess to fail and the application to crash in the LogMessage destructor:

#if defined(OFFICIAL_BUILD) && defined(NDEBUG)
  IMMEDIATE_CRASH();
#else
  base::debug::BreakDebugger();
#endif