api: tighten maximum registry key path length

Maximum registry key path length is not 260 (MAX_PATH), but 255 (256
incl. zero terminator).

Signed-off-by: Simon Rozman <simon@rozman.si>

3 files changed, 19 insertions, 15 deletions

diff --git a/api/api.h b/api/api.h
index 3998123..e409b8b 100644
--- a/api/api.h
+++ b/api/api.h
@@ -38,16 +38,20 @@ NciInit();
 void
 NciCleanup();
 
+#define MAX_REG_PATH \
+    256 /* Maximum registry path length \
+           https://support.microsoft.com/en-us/help/256986/windows-registry-information-for-advanced-users */
+
 WINTUN_STATUS
 RegistryOpenKeyWait(
     _In_ HKEY Key,
-    _In_z_count_c_(MAX_PATH) const WCHAR *Path,
+    _In_z_count_c_(MAX_REG_PATH) const WCHAR *Path,
     _In_ DWORD Access,
     _In_ DWORD Timeout,
     _Out_ HKEY *KeyOut);
 
 WINTUN_STATUS
-RegistryWaitForKey(_In_ HKEY Key, _In_z_count_c_(MAX_PATH) const WCHAR *Path, _In_ DWORD Timeout);
+RegistryWaitForKey(_In_ HKEY Key, _In_z_count_c_(MAX_REG_PATH) const WCHAR *Path, _In_ DWORD Timeout);
 
 WINTUN_STATUS
 RegistryGetString(_Inout_ WCHAR **Buf, _In_ DWORD Len, _In_ DWORD ValueType);
diff --git a/api/devmgmt.c b/api/devmgmt.c
index 83a14be..4604bf5 100644
--- a/api/devmgmt.c
+++ b/api/devmgmt.c
@@ -510,11 +510,11 @@ cleanupKey:
  * Returns the device-level registry key path.
  */
 static void
-GetDeviceRegPath(_In_ const WINTUN_ADAPTER *Adapter, _Out_cap_c_(MAX_PATH + MAX_INSTANCE_ID) WCHAR *Path)
+GetDeviceRegPath(_In_ const WINTUN_ADAPTER *Adapter, _Out_cap_c_(MAX_REG_PATH) WCHAR *Path)
 {
     _snwprintf_s(
         Path,
-        MAX_PATH + MAX_INSTANCE_ID,
+        MAX_REG_PATH,
         _TRUNCATE,
         L"SYSTEM\\CurrentControlSet\\Enum\\%.*s",
         MAX_INSTANCE_ID,
@@ -525,12 +525,12 @@ GetDeviceRegPath(_In_ const WINTUN_ADAPTER *Adapter, _Out_cap_c_(MAX_PATH + MAX_
  * Returns the adapter-specific TCP/IP network registry key path.
  */
 static void
-GetTcpipAdapterRegPath(_In_ const WINTUN_ADAPTER *Adapter, _Out_cap_c_(MAX_PATH) WCHAR *Path)
+GetTcpipAdapterRegPath(_In_ const WINTUN_ADAPTER *Adapter, _Out_cap_c_(MAX_REG_PATH) WCHAR *Path)
 {
     WCHAR Guid[MAX_GUID_STRING_LEN];
     _snwprintf_s(
         Path,
-        MAX_PATH,
+        MAX_REG_PATH,
         _TRUNCATE,
         L"SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters\\Adapters\\%.*s",
         StringFromGUID2(&Adapter->CfgInstanceID, Guid, _countof(Guid)),
@@ -541,11 +541,11 @@ GetTcpipAdapterRegPath(_In_ const WINTUN_ADAPTER *Adapter, _Out_cap_c_(MAX_PATH)
  * Returns the interface-specific TCP/IP network registry key path.
  */
 static WINTUN_STATUS
-GetTcpipInterfaceRegPath(_In_ const WINTUN_ADAPTER *Adapter, _Out_cap_c_(MAX_PATH) WCHAR *Path)
+GetTcpipInterfaceRegPath(_In_ const WINTUN_ADAPTER *Adapter, _Out_cap_c_(MAX_REG_PATH) WCHAR *Path)
 {
     DWORD Result;
     HKEY TcpipAdapterRegKey;
-    WCHAR TcpipAdapterRegPath[MAX_PATH];
+    WCHAR TcpipAdapterRegPath[MAX_REG_PATH];
     GetTcpipAdapterRegPath(Adapter, TcpipAdapterRegPath);
     Result = RegOpenKeyExW(HKEY_LOCAL_MACHINE, TcpipAdapterRegPath, 0, KEY_QUERY_VALUE, &TcpipAdapterRegKey);
     if (Result != ERROR_SUCCESS)
@@ -559,7 +559,7 @@ GetTcpipInterfaceRegPath(_In_ const WINTUN_ADAPTER *Adapter, _Out_cap_c_(MAX_PAT
         Result = ERROR_NETWORK_NOT_AVAILABLE;
         goto cleanupPaths;
     }
-    _snwprintf_s(Path, MAX_PATH, _TRUNCATE, L"SYSTEM\\CurrentControlSet\\Services\\%s", Paths);
+    _snwprintf_s(Path, MAX_REG_PATH, _TRUNCATE, L"SYSTEM\\CurrentControlSet\\Services\\%s", Paths);
 cleanupPaths:
     HeapFree(GetProcessHeap(), 0, Paths);
 cleanupTcpipAdapterRegKey:
@@ -743,7 +743,7 @@ WintunSetAdapterName(_In_ const WINTUN_ADAPTER *Adapter, _In_z_count_c_(MAX_ADAP
 
     /* TODO: This should use NetSetup2 so that it doesn't get unset. */
     HKEY DeviceRegKey;
-    WCHAR DeviceRegPath[MAX_PATH + MAX_INSTANCE_ID];
+    WCHAR DeviceRegPath[MAX_REG_PATH];
     GetDeviceRegPath(Adapter, DeviceRegPath);
     Result = RegOpenKeyExW(HKEY_LOCAL_MACHINE, DeviceRegPath, 0, KEY_SET_VALUE, &DeviceRegKey);
     if (Result != ERROR_SUCCESS)
@@ -1056,7 +1056,7 @@ WintunCreateAdapter(
         goto cleanupNetDevRegKey;
 
     HKEY TcpipAdapterRegKey;
-    WCHAR TcpipAdapterRegPath[MAX_PATH];
+    WCHAR TcpipAdapterRegPath[MAX_REG_PATH];
     GetTcpipAdapterRegPath(*Adapter, TcpipAdapterRegPath);
     Result = RegistryOpenKeyWait(
         HKEY_LOCAL_MACHINE,
@@ -1072,7 +1072,7 @@ WintunCreateAdapter(
     HeapFree(Heap, 0, DummyStr);
 
     HKEY TcpipInterfaceRegKey;
-    WCHAR TcpipInterfaceRegPath[MAX_PATH];
+    WCHAR TcpipInterfaceRegPath[MAX_REG_PATH];
     Result = GetTcpipInterfaceRegPath(*Adapter, TcpipInterfaceRegPath);
     if (Result != ERROR_SUCCESS)
         goto cleanupTcpipAdapterRegKey;
diff --git a/api/registry.c b/api/registry.c
index 157527c..7a68e58 100644
--- a/api/registry.c
+++ b/api/registry.c
@@ -66,18 +66,18 @@ OpenKeyWait(_In_ HKEY Key, _Inout_z_ WCHAR *Path, _In_ DWORD Access, _In_ ULONGL
 WINTUN_STATUS
 RegistryOpenKeyWait(
     _In_ HKEY Key,
-    _In_z_count_c_(MAX_PATH) const WCHAR *Path,
+    _In_z_count_c_(MAX_REG_PATH) const WCHAR *Path,
     _In_ DWORD Access,
     _In_ DWORD Timeout,
     _Out_ HKEY *KeyOut)
 {
-    WCHAR Buf[MAX_PATH];
+    WCHAR Buf[MAX_REG_PATH];
     wcscpy_s(Buf, _countof(Buf), Path);
     return OpenKeyWait(Key, Buf, Access, GetTickCount64() + Timeout, KeyOut);
 }
 
 WINTUN_STATUS
-RegistryWaitForKey(_In_ HKEY Key, _In_z_count_c_(MAX_PATH) const WCHAR *Path, _In_ DWORD Timeout)
+RegistryWaitForKey(_In_ HKEY Key, _In_z_count_c_(MAX_REG_PATH) const WCHAR *Path, _In_ DWORD Timeout)
 {
     HKEY k;
     DWORD Result = RegistryOpenKeyWait(Key, Path, KEY_NOTIFY, Timeout, &k);