- 1 year ago
Change permissions on shared memory after creation on Windows
Once shared memory is created on Windows, changing the permissions on it can be a bit challenging. By default, the permissions on shared memory are determined at the time of creation and cannot be modified directly. However, you can work around this limitation by using the following steps:
Open the shared memory object: Use the
OpenFileMapping
function to open the shared memory object. This function returns a handle to the shared memory object that can be used for further operations.Duplicate the handle: Use the
DuplicateHandle
function to duplicate the handle obtained fromOpenFileMapping
. This will create a new handle that you can modify the permissions on.Adjust the permissions: Call the
SetSecurityInfo
function to modify the security descriptor on the shared memory object. This allows you to change the permissions associated with the object. Ensure that you have appropriate permissions to modify the security descriptor.Close the handles: Close the original handle obtained from
OpenFileMapping
and the duplicated handle created withDuplicateHandle
to release the resources.
Here's an example in C++ that demonstrates these steps:
cpp#include <Windows.h>
int main() {
// Open the shared memory object
HANDLE hSharedMemory = OpenFileMapping(FILE_MAP_ALL_ACCESS, FALSE, L"MySharedMemory");
if (hSharedMemory == NULL) {
// Handle error
return 1;
}
// Duplicate the handle
HANDLE hDuplicated;
if (!DuplicateHandle(GetCurrentProcess(), hSharedMemory, GetCurrentProcess(), &hDuplicated, 0, FALSE, DUPLICATE_SAME_ACCESS)) {
// Handle error
CloseHandle(hSharedMemory);
return 1;
}
// Adjust the permissions
if (SetSecurityInfo(hDuplicated, SE_KERNEL_OBJECT, DACL_SECURITY_INFORMATION, NULL, NULL, NULL, NULL) != ERROR_SUCCESS) {
// Handle error
CloseHandle(hDuplicated);
CloseHandle(hSharedMemory);
return 1;
}
// Close the handles
CloseHandle(hDuplicated);
CloseHandle(hSharedMemory);
return 0;
}
In this example, the OpenFileMapping
function is used to open the shared memory object with the desired access rights. The DuplicateHandle
function creates a new handle that can be modified. The SetSecurityInfo
function is then used to adjust the permissions on the shared memory object. Finally, the handles are closed to release the resources.
Please note that modifying the permissions on shared memory objects can have security implications, so exercise caution and ensure that you have appropriate privileges and understanding of the implications before making any changes.