Sharedmemory between different sessions - c

Question

I have two applications:
first one: running with SYSTEM Privileges started by a service and the
second one: running still as SYSTEM but with lower privileges (SE_GROUP_INTEGRITY = "S-1-16-4096")
I want both applications to communicate over sharedmemory. Both need to read and write.
In my first application i create the filemapping with specific SECURITY_ATTRIBUTES i learned from this post: How to share memory between services and user processes?
SECURITY_ATTRIBUTES attributes;
ZeroMemory(&attributes, sizeof(attributes));
attributes.nLength = sizeof(attributes);
ConvertStringSecurityDescriptorToSecurityDescriptor(
L"D:P(A;OICI;GA;;;SY)(A;OICI;GA;;;BA)(A;OICI;GWR;;;IU)",
SDDL_REVISION_1,
&attributes.lpSecurityDescriptor,
NULL);
HANDLE test = CreateFileMapping(INVALID_HANDLE_VALUE, NULL, PAGE_READWRITE, 0, 1024, "Global\\Test");
Everything works as expected, but if i then try to open the file mapping in my second application, it crashes with an access violation at OpenFileMapping.
HANDLE test = OpenFileMapping(FILE_ALL_ACCESS, FALSE, 1024, "Global\\Test");

Answer 1

if you want allow access to object for Low Integrity code you need add Low mandatory level (SDDL_ML_LOW) Integrity label (SDDL_MANDATORY_LABEL) to security descriptor. for example
"D:PNO_ACCESS_CONTROLS:(ML;;NW;;;LW)"
so in general code is next:
ULONG CreateSectionWithLowAccess(PHANDLE SectionHandle, ULONG dwMaximumSize, PCWSTR lpName)
{
SECURITY_ATTRIBUTES sa = { sizeof(sa) };
if (ConvertStringSecurityDescriptorToSecurityDescriptorW(L"D:PNO_ACCESS_CONTROLS:(ML;;NW;;;LW)",
SDDL_REVISION_1, &sa.lpSecurityDescriptor, NULL))
{
*SectionHandle = CreateFileMappingW(INVALID_HANDLE_VALUE, &sa, PAGE_READWRITE, 0, dwMaximumSize, lpName);
LocalFree(sa.lpSecurityDescriptor);
return *SectionHandle ? NOERROR : GetLastError();
}
return GetLastError();
}