api: don't auto-elevate

There's no longer a need to do this for every API call. This only exists
now for the pnp guid reuse workaround hack.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

api/adapter.c

@@ -668,18 +668,13 @@ WintunFreeAdapter(_In_ WINTUN_ADAPTER *Adapter)
 _Return_type_success_(return != NULL) WINTUN_ADAPTER *WINAPI
     WintunOpenAdapter(_In_z_ const WCHAR *Pool, _In_z_ const WCHAR *Name)
 {
-    if (!ElevateToSystem())
-    {
-        LOG(WINTUN_LOG_ERR, L"Failed to impersonate SYSTEM user");
-        return NULL;
-    }
     DWORD LastError;
     WINTUN_ADAPTER *Adapter = NULL;
     HANDLE Mutex = NamespaceTakePoolMutex(Pool);
     if (!Mutex)
     {
         LastError = LOG(WINTUN_LOG_ERR, L"Failed to take %s pool mutex", Pool);
-        goto cleanupToken;
+        goto cleanup;
     }
 
     HDEVINFO DevInfo = SetupDiGetClassDevsExW(&GUID_DEVCLASS_NET, NULL, NULL, DIGCF_PRESENT, NULL, NULL, NULL);
@@ -759,8 +754,7 @@ cleanupDevInfo:
     SetupDiDestroyDeviceInfoList(DevInfo);
 cleanupMutex:
     NamespaceReleaseMutex(Mutex);
-cleanupToken:
+cleanup:
-    RevertToSelf();
     SetLastError(LastError);
     return Adapter;
 }
@@ -1840,11 +1834,6 @@ _Return_type_success_(return != NULL) WINTUN_ADAPTER *WINAPI WintunCreateAdapter
     _In_opt_ const GUID *RequestedGUID,
     _Out_opt_ BOOL *RebootRequired)
 {
-    if (!ElevateToSystem())
-    {
-        LOG(WINTUN_LOG_ERR, L"Failed to impersonate SYSTEM user");
-        return NULL;
-    }
     BOOL DummyRebootRequired;
     if (!RebootRequired)
         RebootRequired = &DummyRebootRequired;
@@ -1855,12 +1844,11 @@ _Return_type_success_(return != NULL) WINTUN_ADAPTER *WINAPI WintunCreateAdapter
     {
         Adapter = CreateAdapterViaRundll32(Pool, Name, RequestedGUID, RebootRequired);
         LastError = Adapter ? ERROR_SUCCESS : GetLastError();
-        goto cleanupToken;
+        goto cleanup;
     }
     Adapter = CreateAdapter(Pool, Name, RequestedGUID, RebootRequired);
     LastError = Adapter ? ERROR_SUCCESS : GetLastError();
-cleanupToken:
+cleanup:
-    RevertToSelf();
     return RET_ERROR(Adapter, LastError);
 }
 
@@ -1869,11 +1857,6 @@ _Return_type_success_(return != FALSE) BOOL WINAPI WintunDeleteAdapter(
     _In_ BOOL ForceCloseSessions,
     _Out_opt_ BOOL *RebootRequired)
 {
-    if (!ElevateToSystem())
-    {
-        LOG(WINTUN_LOG_ERR, L"Failed to impersonate SYSTEM user");
-        return FALSE;
-    }
     BOOL DummyRebootRequired;
     if (!RebootRequired)
         RebootRequired = &DummyRebootRequired;
@@ -1883,14 +1866,14 @@ _Return_type_success_(return != FALSE) BOOL WINAPI WintunDeleteAdapter(
     {
         LastError =
             DeleteAdapterViaRundll32(Adapter, ForceCloseSessions, RebootRequired) ? ERROR_SUCCESS : GetLastError();
-        goto cleanupToken;
+        goto cleanup;
     }
 
     HANDLE Mutex = NamespaceTakePoolMutex(Adapter->Pool);
     if (!Mutex)
     {
         LastError = LOG(WINTUN_LOG_ERR, L"Failed to take %s pool mutex", Adapter->Pool);
-        goto cleanupToken;
+        goto cleanup;
     }
 
     HDEVINFO DevInfo;
@@ -1930,8 +1913,7 @@ cleanupDevInfo:
     SetupDiDestroyDeviceInfoList(DevInfo);
 cleanupMutex:
     NamespaceReleaseMutex(Mutex);
-cleanupToken:
+cleanup:
-    RevertToSelf();
     return RET_ERROR(TRUE, LastError);
 }
 
@@ -1990,12 +1972,6 @@ cleanupMutex:
 _Return_type_success_(return != FALSE) BOOL WINAPI
     WintunDeletePoolDriver(_In_z_ const WCHAR *Pool, _Out_opt_ BOOL *RebootRequired)
 {
-    if (!ElevateToSystem())
-    {
-        LOG(WINTUN_LOG_ERR, L"Failed to impersonate SYSTEM user");
-        return FALSE;
-    }
-
     BOOL DummyRebootRequired;
     if (!RebootRequired)
         RebootRequired = &DummyRebootRequired;
@@ -2005,20 +1981,20 @@ _Return_type_success_(return != FALSE) BOOL WINAPI
     if (MAYBE_WOW64 && NativeMachine != IMAGE_FILE_PROCESS)
     {
         LastError = DeletePoolDriverViaRundll32(Pool, RebootRequired) ? ERROR_SUCCESS : GetLastError();
-        goto cleanupToken;
+        goto cleanup;
     }
 
     if (!DeleteAllOurAdapters(Pool, RebootRequired))
     {
         LastError = GetLastError();
-        goto cleanupToken;
+        goto cleanup;
     }
 
     HANDLE DriverInstallationLock = NamespaceTakeDriverInstallationMutex();
     if (!DriverInstallationLock)
     {
         LastError = LOG(WINTUN_LOG_ERR, L"Failed to take driver installation mutex");
-        goto cleanupToken;
+        goto cleanup;
     }
     HDEVINFO DeviceInfoSet = SetupDiGetClassDevsW(&GUID_DEVCLASS_NET, NULL, NULL, 0);
     if (!DeviceInfoSet)
@@ -2060,25 +2036,19 @@ cleanupDeviceInfoSet:
     SetupDiDestroyDeviceInfoList(DeviceInfoSet);
 cleanupDriverInstallationLock:
     NamespaceReleaseMutex(DriverInstallationLock);
-cleanupToken:
+cleanup:
-    RevertToSelf();
     return RET_ERROR(TRUE, LastError);
 }
 
 _Return_type_success_(return != FALSE) BOOL WINAPI
     WintunEnumAdapters(_In_z_ const WCHAR *Pool, _In_ WINTUN_ENUM_CALLBACK Func, _In_ LPARAM Param)
 {
-    if (!ElevateToSystem())
-    {
-        LOG(WINTUN_LOG_ERR, L"Failed to impersonate SYSTEM user");
-        return FALSE;
-    }
     DWORD LastError = ERROR_SUCCESS;
     HANDLE Mutex = NamespaceTakePoolMutex(Pool);
     if (!Mutex)
     {
         LastError = LOG(WINTUN_LOG_ERR, L"Failed to take %s pool mutex", Pool);
-        goto cleanupToken;
+        goto cleanup;
     }
     HDEVINFO DevInfo = SetupDiGetClassDevsExW(&GUID_DEVCLASS_NET, NULL, NULL, DIGCF_PRESENT, NULL, NULL, NULL);
     if (DevInfo == INVALID_HANDLE_VALUE)
@@ -2112,7 +2082,6 @@ _Return_type_success_(return != FALSE) BOOL WINAPI
     SetupDiDestroyDeviceInfoList(DevInfo);
 cleanupMutex:
     NamespaceReleaseMutex(Mutex);
-cleanupToken:
+cleanup:
-    RevertToSelf();
     return RET_ERROR(TRUE, LastError);
 }

api/elevate.c

@@ -9,19 +9,19 @@
 #include <Windows.h>
 #include <TlHelp32.h>
 
-_Return_type_success_(return != FALSE) BOOL ElevateToSystem(void)
+static _Return_type_success_(return != FALSE) BOOL ElevateToSystem(void)
 {
     HANDLE CurrentProcessToken, ThreadToken, ProcessSnapshot, WinlogonProcess, WinlogonToken, DuplicatedToken;
     PROCESSENTRY32W ProcessEntry = { .dwSize = sizeof(PROCESSENTRY32W) };
     BOOL Ret;
     DWORD LastError = ERROR_SUCCESS;
     TOKEN_PRIVILEGES Privileges = { .PrivilegeCount = 1, .Privileges = { { .Attributes = SE_PRIVILEGE_ENABLED } } };
-    CHAR LocalSystemSid[0x400];
+    CHAR LocalSystemSid[MAX_SID_SIZE];
     DWORD RequiredBytes = sizeof(LocalSystemSid);
     struct
     {
         TOKEN_USER MaybeLocalSystem;
-        CHAR LargeEnoughForLocalSystem[0x400];
+        CHAR LargeEnoughForLocalSystem[MAX_SID_SIZE];
     } TokenUserBuffer;
 
     Ret = CreateWellKnownSid(WinLocalSystemSid, NULL, &LocalSystemSid, &RequiredBytes);
@@ -46,7 +46,7 @@ _Return_type_success_(return != FALSE) BOOL ElevateToSystem(void)
         goto cleanup;
     }
     if (EqualSid(TokenUserBuffer.MaybeLocalSystem.User.Sid, LocalSystemSid))
-        return TRUE;
+        return ImpersonateSelf(SecurityImpersonation);
     Ret = LookupPrivilegeValueW(NULL, SE_DEBUG_NAME, &Privileges.Privileges[0].Luid);
     if (!Ret)
     {
@@ -122,81 +122,6 @@ cleanup:
     return FALSE;
 }
 
-_Return_type_success_(return != NULL) HANDLE GetPrimarySystemTokenFromThread(void)
-{
-    HANDLE CurrentToken, DuplicatedToken;
-    BOOL Ret;
-    DWORD LastError;
-    TOKEN_PRIVILEGES Privileges = { .PrivilegeCount = 1, .Privileges = { { .Attributes = SE_PRIVILEGE_ENABLED } } };
-    CHAR LocalSystemSid[0x400];
-    DWORD RequiredBytes = sizeof(LocalSystemSid);
-    struct
-    {
-        TOKEN_USER MaybeLocalSystem;
-        CHAR LargeEnoughForLocalSystem[0x400];
-    } TokenUserBuffer;
-
-    Ret = CreateWellKnownSid(WinLocalSystemSid, NULL, &LocalSystemSid, &RequiredBytes);
-    if (!Ret)
-    {
-        LastError = LOG_LAST_ERROR(L"Failed to create SID");
-        return NULL;
-    }
-    Ret = OpenThreadToken(
-        GetCurrentThread(), TOKEN_QUERY | TOKEN_ADJUST_PRIVILEGES | TOKEN_DUPLICATE, FALSE, &CurrentToken);
-    if (!Ret && GetLastError() == ERROR_NO_TOKEN)
-        Ret = OpenProcessToken(
-            GetCurrentProcess(), TOKEN_QUERY | TOKEN_ADJUST_PRIVILEGES | TOKEN_DUPLICATE, &CurrentToken);
-    if (!Ret)
-    {
-        LastError = LOG_LAST_ERROR(L"Failed to open token");
-        return NULL;
-    }
-    Ret = GetTokenInformation(CurrentToken, TokenUser, &TokenUserBuffer, sizeof(TokenUserBuffer), &RequiredBytes);
-    if (!Ret)
-    {
-        LastError = LOG_LAST_ERROR(L"Failed to get token information");
-        goto cleanup;
-    }
-    if (!EqualSid(TokenUserBuffer.MaybeLocalSystem.User.Sid, LocalSystemSid))
-    {
-        LOG(WINTUN_LOG_ERR, L"Not SYSTEM");
-        LastError = ERROR_ACCESS_DENIED;
-        goto cleanup;
-    }
-    Ret = LookupPrivilegeValueW(NULL, SE_ASSIGNPRIMARYTOKEN_NAME, &Privileges.Privileges[0].Luid);
-    if (!Ret)
-    {
-        LastError = LOG_LAST_ERROR(L"Failed to lookup privilege value");
-        goto cleanup;
-    }
-    Ret = AdjustTokenPrivileges(CurrentToken, FALSE, &Privileges, 0, NULL, NULL);
-    if (!Ret)
-    {
-        LastError = LOG_LAST_ERROR(L"Failed to adjust token privileges");
-        goto cleanup;
-    }
-    Ret = DuplicateTokenEx(
-        CurrentToken,
-        TOKEN_QUERY | TOKEN_DUPLICATE | TOKEN_ASSIGN_PRIMARY,
-        NULL,
-        SecurityImpersonation,
-        TokenPrimary,
-        &DuplicatedToken);
-    if (!Ret)
-    {
-        LastError = LOG_LAST_ERROR(L"Failed to duplicate token");
-        goto cleanup;
-    }
-    CloseHandle(CurrentToken);
-    return DuplicatedToken;
-
-cleanup:
-    CloseHandle(CurrentToken);
-    SetLastError(LastError);
-    return NULL;
-}
-
 _Return_type_success_(return != FALSE) BOOL ImpersonateService(_In_z_ WCHAR *ServiceName, _In_ HANDLE *OriginalToken)
 {
     HANDLE ThreadToken, ServiceProcess, ServiceToken, DuplicatedToken;
@@ -212,20 +137,14 @@ _Return_type_success_(return != FALSE) BOOL ImpersonateService(_In_z_ WCHAR *Ser
         GetLastError() != ERROR_NO_TOKEN)
         return FALSE;
 
+    if (!ElevateToSystem())
+        goto cleanup;
+
     if (!LookupPrivilegeValueW(NULL, SE_DEBUG_NAME, &Privileges.Privileges[0].Luid))
     {
         LastError = LOG_LAST_ERROR(L"Failed to lookup privilege value");
         goto cleanup;
     }
-    if (!*OriginalToken)
-    {
-        RevertToSelf();
-        if (!ImpersonateSelf(SecurityImpersonation))
-        {
-            LastError = LOG_LAST_ERROR(L"Failed to impersonate self");
-            goto cleanup;
-        }
-    }
     if (!OpenThreadToken(GetCurrentThread(), TOKEN_ADJUST_PRIVILEGES, FALSE, &ThreadToken))
     {
         LastError = LOG_LAST_ERROR(L"Failed to open thread token");

api/elevate.h

@@ -7,10 +7,6 @@
 
 #include <Windows.h>
 
-_Return_type_success_(return != FALSE) BOOL ElevateToSystem(void);
-
-_Return_type_success_(return != NULL) HANDLE GetPrimarySystemTokenFromThread(void);
-
 _Return_type_success_(return != FALSE) BOOL ImpersonateService(_In_z_ WCHAR *ServiceName, _In_ HANDLE *OriginalToken);
 
 _Return_type_success_(return != FALSE) BOOL RestoreToken(_In_ HANDLE OriginalToken);

api/entry.c

@@ -21,6 +21,7 @@
 HINSTANCE ResourceModule;
 HANDLE ModuleHeap;
 SECURITY_ATTRIBUTES SecurityAttributes = { .nLength = sizeof(SECURITY_ATTRIBUTES) };
+BOOL IsLocalSystem;
 
 static FARPROC WINAPI
 DelayedLoadLibraryHook(unsigned dliNotify, PDelayLoadInfo pdli)
@@ -35,6 +36,41 @@ DelayedLoadLibraryHook(unsigned dliNotify, PDelayLoadInfo pdli)
 
 const PfnDliHook __pfnDliNotifyHook2 = DelayedLoadLibraryHook;
 
+static BOOL
+InitializeSecurityObjects(void)
+{
+    BYTE LocalSystemSid[MAX_SID_SIZE];
+    DWORD RequiredBytes = sizeof(LocalSystemSid);
+    HANDLE CurrentProcessToken;
+    struct
+    {
+        TOKEN_USER MaybeLocalSystem;
+        CHAR LargeEnoughForLocalSystem[MAX_SID_SIZE];
+    } TokenUserBuffer;
+    BOOL Ret = FALSE;
+
+    if (!CreateWellKnownSid(WinLocalSystemSid, NULL, LocalSystemSid, &RequiredBytes))
+        return FALSE;
+
+    if (!OpenProcessToken(GetCurrentProcess(), TOKEN_QUERY, &CurrentProcessToken))
+        return FALSE;
+
+    if (!GetTokenInformation(CurrentProcessToken, TokenUser, &TokenUserBuffer, sizeof(TokenUserBuffer), &RequiredBytes))
+        goto cleanupProcessToken;
+
+    IsLocalSystem = EqualSid(TokenUserBuffer.MaybeLocalSystem.User.Sid, LocalSystemSid);
+    Ret = ConvertStringSecurityDescriptorToSecurityDescriptorW(
+        IsLocalSystem ? L"O:SYD:P(A;;GA;;;SY)(A;;GA;;;BA)S:(ML;;NWNRNX;;;HI)"
+                      : L"O:BAD:P(A;;GA;;;SY)(A;;GA;;;BA)S:(ML;;NWNRNX;;;HI)",
+        SDDL_REVISION_1,
+        &SecurityAttributes.lpSecurityDescriptor,
+        NULL);
+
+cleanupProcessToken:
+    CloseHandle(CurrentProcessToken);
+    return Ret;
+}
+
 BOOL APIENTRY
 DllMain(_In_ HINSTANCE hinstDLL, _In_ DWORD fdwReason, _In_ LPVOID lpvReserved)
 {
@@ -47,8 +83,11 @@ DllMain(_In_ HINSTANCE hinstDLL, _In_ DWORD fdwReason, _In_ LPVOID lpvReserved)
         ModuleHeap = HeapCreate(0, 0, 0);
         if (!ModuleHeap)
             return FALSE;
-        ConvertStringSecurityDescriptorToSecurityDescriptorW(
+        if (!InitializeSecurityObjects())
-            L"O:SYD:P(A;;GA;;;SY)", SDDL_REVISION_1, &SecurityAttributes.lpSecurityDescriptor, NULL);
+        {
+            HeapDestroy(ModuleHeap);
+            return FALSE;
+        }
         AdapterInit();
         NamespaceInit();
         break;

api/entry.h

@@ -29,3 +29,4 @@
 extern HINSTANCE ResourceModule;
 extern HANDLE ModuleHeap;
 extern SECURITY_ATTRIBUTES SecurityAttributes;
+extern BOOL IsLocalSystem;

api/namespace.c

@@ -59,8 +59,8 @@ static _Return_type_success_(return != FALSE) BOOL NamespaceRuntimeInit(void)
     }
 
     BYTE Sid[MAX_SID_SIZE];
-    DWORD SidSize = MAX_SID_SIZE;
+    DWORD SidSize = sizeof(Sid);
-    if (!CreateWellKnownSid(WinLocalSystemSid, NULL, Sid, &SidSize))
+    if (!CreateWellKnownSid(IsLocalSystem ? WinLocalSystemSid : WinBuiltinAdministratorsSid, NULL, Sid, &SidSize))
     {
         LastError = LOG_LAST_ERROR(L"Failed to create SID");
         goto cleanupBCryptCloseAlgorithmProvider;

api/rundll32_i.c

@@ -176,23 +176,15 @@ static _Return_type_success_(return != FALSE) BOOL ExecuteRunDll32(
                         .hStdOutput = StreamWStdout,
                         .hStdError = StreamWStderr };
     PROCESS_INFORMATION pi;
-    HANDLE ProcessToken = GetPrimarySystemTokenFromThread();
+    if (!CreateProcessW(RunDll32Path, CommandLine, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi))
-    if (!ProcessToken)
-    {
-        LastError = LOG(WINTUN_LOG_ERR, L"Failed to get primary system token from thread");
-        goto cleanupThreads;
-    }
-    if (!CreateProcessAsUserW(ProcessToken, RunDll32Path, CommandLine, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi))
     {
         LastError = LOG_LAST_ERROR(L"Failed to create process: %s", CommandLine);
-        goto cleanupToken;
+        goto cleanupThreads;
     }
     LastError = ERROR_SUCCESS;
     WaitForSingleObject(pi.hProcess, INFINITE);
     CloseHandle(pi.hProcess);
     CloseHandle(pi.hThread);
-cleanupToken:
-    CloseHandle(ProcessToken);
 cleanupThreads:
     if (ThreadStderr)
     {

api/session.c

@@ -77,7 +77,7 @@ _Return_type_success_(return != NULL) TUN_SESSION *WINAPI
     if (!Session)
     {
         LastError = GetLastError();
-        goto out;
+        goto cleanup;
     }
     const ULONG RingSize = TUN_RING_SIZE(Capacity);
     BYTE *AllocatedRegion = VirtualAlloc(0, (size_t)RingSize * 2, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
@@ -86,18 +86,13 @@ _Return_type_success_(return != NULL) TUN_SESSION *WINAPI
         LastError = LOG_LAST_ERROR(L"Failed to allocate ring memory (requested size: 0x%zx)", (size_t)RingSize * 2);
         goto cleanupRings;
     }
-    if (!ElevateToSystem())
-    {
-        LastError = LOG(WINTUN_LOG_ERR, L"Failed to impersonate SYSTEM user");
-        goto cleanupAllocatedRegion;
-    }
     Session->Descriptor.Send.RingSize = RingSize;
     Session->Descriptor.Send.Ring = (TUN_RING *)AllocatedRegion;
     Session->Descriptor.Send.TailMoved = CreateEventW(&SecurityAttributes, FALSE, FALSE, NULL);
     if (!Session->Descriptor.Send.TailMoved)
     {
         LastError = LOG_LAST_ERROR(L"Failed to create send event");
-        goto cleanupToken;
+        goto cleanupAllocatedRegion;
     }
 
     Session->Descriptor.Receive.RingSize = RingSize;
@@ -129,7 +124,6 @@ _Return_type_success_(return != NULL) TUN_SESSION *WINAPI
         LastError = LOG_LAST_ERROR(L"Failed to register rings");
         goto cleanupHandle;
     }
-    RevertToSelf();
     Session->Capacity = Capacity;
     (void)InitializeCriticalSectionAndSpinCount(&Session->Receive.Lock, LOCK_SPIN_COUNT);
     (void)InitializeCriticalSectionAndSpinCount(&Session->Send.Lock, LOCK_SPIN_COUNT);
@@ -140,13 +134,11 @@ cleanupReceiveTailMoved:
     CloseHandle(Session->Descriptor.Receive.TailMoved);
 cleanupSendTailMoved:
     CloseHandle(Session->Descriptor.Send.TailMoved);
-cleanupToken:
-    RevertToSelf();
 cleanupAllocatedRegion:
     VirtualFree(AllocatedRegion, 0, MEM_RELEASE);
 cleanupRings:
     Free(Session);
-out:
+cleanup:
     SetLastError(LastError);
     return NULL;
 }