Example: Reading File Permissions

Example: Reading File Permissions Program 15-4 is the function ReadFilePermissions, which is used by Programs 15-1 and 15-2. This program methodically uses the preceding functions to extract the information. Its correct operation depends on the fact that the ACL was created by Program 15-3. The function is in the same source module as Program 15-3, so the definitions are not repeated. Program 15-4. ReadFilePermissions: Reading Security Attributes DWORD ReadFilePermissions (LPCTSTR lpFileName, LPTSTR UsrNm, LPTSTR GrpNm) /* Return the UNIX-style permissions for a file. */ { PSECURITY_DESCRIPTOR pSD = NULL; DWORD LenNeeded, PBits, iAce; BOOL DaclF, AclDefF, OwnerDefF, GroupDefF; BYTE DAcl [ACL_SIZE]; PACL pAcl = (PACL) &DAcl; ACL_SIZE_INFORMATION ASizeInfo; PACCESS_ALLOWED_ACE pAce; BYTE AType; HANDLE ProcHeap = GetProcessHeap (); PSID pOwnerSid, pGroupSid; TCHAR RefDomain [2] [DOM_SIZE]; DWORD RefDomCnt [] = {DOM_SIZE, DOM_SIZE}; DWORD AcctSize [] = {ACCT_NAME_SIZE, ACCT_NAME_SIZE}; SID_NAME_USE sNamUse [] = {SidTypeUser, SidTypeGroup}; /* Get the required size for the security descriptor. */ GetFileSecurity (lpFileName, OWNER_SECURITY_INFORMATION | GROUP_SECURITY_INFORMATION | DACL_SECURITY_INFORMATION, pSD, 0, &LenNeeded); pSD = HeapAlloc (ProcHeap, HEAP_GENERATE_EXCEPTIONS, LenNeeded); GetFileSecurity (lpFileName, OWNER_SECURITY_INFORMATION | GROUP_SECURITY_INFORMATION | DACL_SECURITY_INFORMATION, pSD, LenNeeded, &LenNeeded); GetSecurityDescriptorDacl (pSD, &DaclF, &pAcl, &AclDefF); GetAclInformation (pAcl, &ASizeInfo, sizeof (ACL_SIZE_INFORMATION), AclSizeInformation); PBits = 0; /* Compute the permissions from the ACL. */ for (iAce = 0; iAce < ASizeInfo.AceCount; iAce++) { GetAce (pAcl, iAce, &pAce); AType = pAce->Header.AceType; if (AType == ACCESS_ALLOWED_ACE_TYPE) PBits |= (0x1 << (8-iAce)); } /* Find the name of the owner and owning group. */ GetSecurityDescriptorOwner (pSD, &pOwnerSid, &OwnerDefF); GetSecurityDescriptorGroup (pSD, &pGroupSid, &GroupDefF); LookupAccountSid (NULL, pOwnerSid, UsrNm, &AcctSize [0], RefDomain [0], &RefDomCnt [0], &sNamUse [0]); LookupAccountSid (NULL, pGroupSid, GrpNm, &AcctSize [1], RefDomain [1], &RefDomCnt [1], &sNamUse [1]); return PBits; }