Reasons for SetEntriesInAcl error 87 in MSDN sample

问题

I do not know a lot about security descriptors for windows. To learn I was closely following their example posted here. My code kept having the same error (87- Invalid Parameter) when calling SetEntriesInAcl. I could not figure it out so I copied and pasted the exact code from the sample and ran it. I ended up having the same error; Does anyone with experience in this area have any idea what is going on? Here is the same code from the example:

    #pragma comment(lib, "advapi32.lib")

#include <windows.h>
#include <stdio.h>
#include <aclapi.h>
#include <tchar.h>

void main()
{

    DWORD dwRes, dwDisposition;
    PSID pEveryoneSID = NULL, pAdminSID = NULL;
    PACL pACL = NULL;
    PSECURITY_DESCRIPTOR pSD = NULL;
    EXPLICIT_ACCESS ea[2];
    SID_IDENTIFIER_AUTHORITY SIDAuthWorld =
        SECURITY_WORLD_SID_AUTHORITY;
    SID_IDENTIFIER_AUTHORITY SIDAuthNT = SECURITY_NT_AUTHORITY;
    SECURITY_ATTRIBUTES sa;
    LONG lRes;
    HKEY hkSub = NULL;

    // Create a well-known SID for the Everyone group.
    if (!AllocateAndInitializeSid(&SIDAuthWorld, 1,
        SECURITY_WORLD_RID,
        0, 0, 0, 0, 0, 0, 0,
        &pEveryoneSID))
    {
        _tprintf(_T("AllocateAndInitializeSid Error %u\n"), GetLastError());
        goto Cleanup;
    }

    // Initialize an EXPLICIT_ACCESS structure for an ACE.
    // The ACE will allow Everyone read access to the key.
    ZeroMemory(&ea, 2 * sizeof(EXPLICIT_ACCESS));
    ea[0].grfAccessPermissions = KEY_READ;
    ea[0].grfAccessMode = SET_ACCESS;
    ea[0].grfInheritance = NO_INHERITANCE;
    ea[0].Trustee.TrusteeForm = TRUSTEE_IS_SID;
    ea[0].Trustee.TrusteeType = TRUSTEE_IS_WELL_KNOWN_GROUP;
    ea[0].Trustee.ptstrName = (LPTSTR)pEveryoneSID;

    // Create a SID for the BUILTIN\Administrators group.
    if (!AllocateAndInitializeSid(&SIDAuthNT, 2,
        SECURITY_BUILTIN_DOMAIN_RID,
        DOMAIN_ALIAS_RID_ADMINS,
        0, 0, 0, 0, 0, 0,
        &pAdminSID))
    {
        _tprintf(_T("AllocateAndInitializeSid Error %u\n"), GetLastError());
        goto Cleanup;
    }

    // Initialize an EXPLICIT_ACCESS structure for an ACE.
    // The ACE will allow the Administrators group full access to
    // the key.
    ea[1].grfAccessPermissions = KEY_ALL_ACCESS;
    ea[1].grfAccessMode = SET_ACCESS;
    ea[1].grfInheritance = NO_INHERITANCE;
    ea[1].Trustee.TrusteeForm = TRUSTEE_IS_SID;
    ea[1].Trustee.TrusteeType = TRUSTEE_IS_GROUP;
    ea[1].Trustee.ptstrName = (LPTSTR)pAdminSID;

    // Create a new ACL that contains the new ACEs.
    dwRes = SetEntriesInAcl(2, ea, NULL, &pACL);
    if (ERROR_SUCCESS != dwRes)
    {
        _tprintf(_T("SetEntriesInAcl Error %u\n"), GetLastError());
        goto Cleanup;
    }

    // Initialize a security descriptor.  
    pSD = (PSECURITY_DESCRIPTOR)LocalAlloc(LPTR,
        SECURITY_DESCRIPTOR_MIN_LENGTH);
    if (NULL == pSD)
    {
        _tprintf(_T("LocalAlloc Error %u\n"), GetLastError());
        goto Cleanup;
    }

    if (!InitializeSecurityDescriptor(pSD,
        SECURITY_DESCRIPTOR_REVISION))
    {
        _tprintf(_T("InitializeSecurityDescriptor Error %u\n"),
            GetLastError());
        goto Cleanup;
    }

    // Add the ACL to the security descriptor. 
    if (!SetSecurityDescriptorDacl(pSD,
        TRUE,     // bDaclPresent flag   
        pACL,
        FALSE))   // not a default DACL 
    {
        _tprintf(_T("SetSecurityDescriptorDacl Error %u\n"),
            GetLastError());
        goto Cleanup;
    }

    // Initialize a security attributes structure.
    sa.nLength = sizeof(SECURITY_ATTRIBUTES);
    sa.lpSecurityDescriptor = pSD;
    sa.bInheritHandle = FALSE;

    // Use the security attributes to set the security descriptor 
    // when you create a key.
    lRes = RegCreateKeyEx(HKEY_CURRENT_USER, _T("mykey"), 0, _T(""), 0,
        KEY_READ | KEY_WRITE, &sa, &hkSub, &dwDisposition);
    _tprintf(_T("RegCreateKeyEx result %u\n"), lRes);

Cleanup:

    if (pEveryoneSID)
        FreeSid(pEveryoneSID);
    if (pAdminSID)
        FreeSid(pAdminSID);
    if (pACL)
        LocalFree(pACL);
    if (pSD)
        LocalFree(pSD);
    if (hkSub)
        RegCloseKey(hkSub);

    return;

}

回答1:

The reason the function SetEntriesInAcl kept failing with the error code 87 - Invalid Parameter is because a compiler option (/Zp1) was set. Zp1 sets the default struct member alignment to one byte. When the compiler option was set back to default the function worked normally. Zp1 was changing the size of the EXPLICIT_ACCESS_W structure from 48 to 40, causing the invalid parameter error to occur.

After this experience I would recommend not setting the global structure packing (/Zp) and instead use #pragma pack(n) for the structures you need packed; then reset back to default with #pragma pack() after the definition(s). I am pretty sure the Zp option will affect other structures such as a SECURITY_DESCRIPTOR and some of its members as well. I noticed a similar issue when using security attributes with a memory mapped file, which was resolved when removing Zp#.

来源：https://stackoverflow.com/questions/39960007/reasons-for-setentriesinacl-error-87-in-msdn-sample