Enumerating Windows processes without using CreateToolhelp32Snapshot

I know how to use CreateToolhelp32Snapshot or EnumProcesses to enumerate processes but I was trying to experiment with different ways of doing it (I'm still learning and am trying to experiment with different ways of doing things and different ways of approaching problems).

I thought perhaps using for (DWORD i = 0; i < 1000; i++) {OpenProcess(PROCESS_VM_READ, FALSE, i)} to iterate over the processes and if OpenProcess succeeds I know I have a valid PID. I picked 1000 just for testing purposes to limit the results. Code as follows:

VOID getProcessList() {

    LPSTR procName[MAX_PATH];
    HANDLE pHandle = NULL;

    //try and open a handle to the process ID. Returns NULL if not a valid process ID
    for (DWORD i = 0; i < 1000; i++) {
        pHandle = OpenProcess(PROCESS_VM_READ | PROCESS_QUERY_INFORMATION, FALSE, i);
        
        //if process ID does not exist try the next one
        if (pHandle == NULL) {
            continue;
        }

        //get module name
        GetModuleBaseName(pHandle, NULL, procName, MAX_PATH);

        //if process exists print it's details
        wprintf(L"%s                %d\n", procName, i);

        CloseHandle(pHandle);
    }

    printf("All processes enumerated");

}


int main() {

    printf("Process Name        Process ID\n\n");
    getProcessList();
}

It works, but when compared to task manager it does not return all of the processes that are listed on task manager - only the ones that I have started (as opposed to CreateToolhelp32Snapshot which returns everything). I assume it has something to do with permissions and the PROCESS_VM_READ permission, but I was looking through the other available permissions and couldn't find anything else to use.

It is possible to do with NtQuerySystemInformation using the SYSTEM_PROCESS_ID_INFORMATION class. The output formatting would need some work but this gets you what you want:

#include <stdio.h>
#include <windows.h>
#include <winternl.h>

#define STATUS_SUCCESS   ((NTSTATUS)0x00000000L)

typedef struct _SYSTEM_PROCESS_ID_INFORMATION {
    PVOID ProcessID;                    //PID
    UNICODE_STRING ImageName;           //Process name
} SYSTEM_PROCESS_ID_INFORMATION;

typedef NTSTATUS(NTAPI* pNtQuerySystemInformation)(
    SYSTEM_INFORMATION_CLASS SystemInformationClass,        //internal reference to systeminfoclass SYSTEM_PROCESS_ID_INFORMATION
    PVOID                    SystemInformation,             //the systeminformation we want
    ULONG                    SystemInformationLength,       //buffer to hold the information
    PULONG                   ReturnLength                   
    );



void getProcess(int pid) {

    pNtQuerySystemInformation NtQuerySystemInformation;   //handle to NtQuerySystemInformation
    SYSTEM_PROCESS_ID_INFORMATION pidInfo;                //SYSTEM_PROCESS_ID_INFORMATION stucture to be used
    WCHAR processName[256];                               //buffer to hold process name (pidInfo.ImageName.Buffer) - must be WCHAR to match PWSTR UNICODE_STRING structure
    ULONG returnLength = 0;                               //from above - not sure what it is ?????
    NTSTATUS status;                                      //to test success
    HANDLE hNtDLL;                                        //handle for loading NTDLL.DLL
    SYSTEM_INFORMATION_CLASS sysProcIdInfo = 0x58;        //SYSTEM_INFORMATION_CLASS for SYSTEM_PROCESS_ID_INFORMATION

    //load ntdll.dll
    hNtDLL = GetModuleHandleA("ntdll.dll");
    if (hNtDLL == NULL) {
        printf("[!] Failed to load ntdll.dll with error %d\n", GetLastError());
        return -1;
    }

    //get a handle to NtQuerySystemInformation
    NtQuerySystemInformation = (pNtQuerySystemInformation)GetProcAddress(hNtDLL, "NtQuerySystemInformation");
    if (NtQuerySystemInformation == NULL) {
        printf("[!] Failed to get address of NtQuerySystemInformation with error %d\n", GetLastError());
        return -1;
    }

    //initialize the SYSTEM_PROCESS_ID_INFORMATION structure
    pidInfo.ProcessID = (PVOID)pid;
    pidInfo.ImageName.Buffer = processName;
    pidInfo.ImageName.Length = 0;
    pidInfo.ImageName.MaximumLength = sizeof(processName);

    //Query the PID for information
    status = NtQuerySystemInformation(sysProcIdInfo, &pidInfo, sizeof(pidInfo), &returnLength);
    if (status == STATUS_SUCCESS) {
        wprintf(L"[+] The process ID %d is %s\n", pid, processName);
    }

}

int main() {
    
    for (int i = 0; i < 1000; i++) {
        getProcess(i);
    }

    return 0;
}