From 0a8bf9d1ff0f67bf3906b4cb5ef98a166a1a0bdb Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Fri, 30 Oct 2020 14:34:40 +0100
Subject: [PATCH] api: only force close handles if requested

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 api/adapter.c  | 13 +++++++------
 api/adapter.h  |  2 +-
 api/rundll32.c |  5 +++--
 api/wintun.h   | 12 ++++++++----
 4 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/api/adapter.c b/api/adapter.c
index 741cec9..30c3afe 100644
--- a/api/adapter.c
+++ b/api/adapter.c
@@ -1657,16 +1657,17 @@ cleanupToken:
 #ifdef MAYBE_WOW64
 
 static WINTUN_STATUS
-DeleteAdapterNatively(_In_ const WINTUN_ADAPTER *Adapter, _Inout_ BOOL *RebootRequired)
+DeleteAdapterNatively(_In_ const WINTUN_ADAPTER *Adapter, _In_ BOOL ForceCloseSessions, _Inout_ BOOL *RebootRequired)
 {
     LOG(WINTUN_LOG_INFO, L"Spawning native process");
     WCHAR GuidStr[MAX_GUID_STRING_LEN];
-    WCHAR Arguments[14 + MAX_GUID_STRING_LEN + 1];
+    WCHAR Arguments[16 + MAX_GUID_STRING_LEN + 1];
     if (_snwprintf_s(
             Arguments,
             _countof(Arguments),
             _TRUNCATE,
-            L"DeleteAdapter %.*s",
+            L"DeleteAdapter %d %.*s",
+            ForceCloseSessions ? 1 : 0,
             StringFromGUID2(&Adapter->CfgInstanceID, GuidStr, _countof(GuidStr)),
             GuidStr) == -1)
         return LOG(WINTUN_LOG_ERR, L"Command line too long"), ERROR_INVALID_PARAMETER;
@@ -1693,7 +1694,7 @@ cleanupArgv:
 #endif
 
 WINTUN_STATUS WINAPI
-WintunDeleteAdapter(_In_ const WINTUN_ADAPTER *Adapter, _Inout_ BOOL *RebootRequired)
+WintunDeleteAdapter(_In_ const WINTUN_ADAPTER *Adapter, _In_ BOOL ForceCloseSessions, _Inout_ BOOL *RebootRequired)
 {
     if (!ElevateToSystem())
         return LOG(WINTUN_LOG_ERR, L"Failed to impersonate SYSTEM user"), ERROR_ACCESS_DENIED;
@@ -1702,7 +1703,7 @@ WintunDeleteAdapter(_In_ const WINTUN_ADAPTER *Adapter, _Inout_ BOOL *RebootRequ
 #ifdef MAYBE_WOW64
     if (NativeMachine != IMAGE_FILE_PROCESS)
     {
-        Result = DeleteAdapterNatively(Adapter, RebootRequired);
+        Result = DeleteAdapterNatively(Adapter, ForceCloseSessions, RebootRequired);
         RevertToSelf();
         return Result;
     }
@@ -1722,7 +1723,7 @@ WintunDeleteAdapter(_In_ const WINTUN_ADAPTER *Adapter, _Inout_ BOOL *RebootRequ
         goto cleanupToken;
     }
 
-    if (ForceCloseWintunAdapterHandle(DevInfo, &DevInfoData) != ERROR_SUCCESS)
+    if (ForceCloseSessions && ForceCloseWintunAdapterHandle(DevInfo, &DevInfoData) != ERROR_SUCCESS)
         LOG(WINTUN_LOG_WARN, L"Failed to force close adapter handles");
 
     SetQuietInstall(DevInfo, &DevInfoData);
diff --git a/api/adapter.h b/api/adapter.h
index c0e4c53..d57ca35 100644
--- a/api/adapter.h
+++ b/api/adapter.h
@@ -115,4 +115,4 @@ WintunCreateAdapter(
  * @copydoc WINTUN_DELETE_ADAPTER_FUNC
  */
 WINTUN_STATUS WINAPI
-WintunDeleteAdapter(_In_ const WINTUN_ADAPTER *Adapter, _Inout_ BOOL *RebootRequired);
+WintunDeleteAdapter(_In_ const WINTUN_ADAPTER *Adapter, _In_ BOOL ForceCloseSessions, _Inout_ BOOL *RebootRequired);
diff --git a/api/rundll32.c b/api/rundll32.c
index ac678a5..164b305 100644
--- a/api/rundll32.c
+++ b/api/rundll32.c
@@ -121,10 +121,11 @@ VOID __stdcall DeleteAdapter(HWND hwnd, HINSTANCE hinst, LPSTR lpszCmdLine, int
         goto cleanup;
 
     WINTUN_ADAPTER Adapter = { 0 };
-    if (FAILED(CLSIDFromString(Argv[2], &Adapter.CfgInstanceID)))
+    BOOL ForceCloseSessions = wcstoul(Argv[2], NULL, 10);
+    if (FAILED(CLSIDFromString(Argv[3], &Adapter.CfgInstanceID)))
         goto cleanup;
     BOOL RebootRequired = FALSE;
-    WriteFormatted(STD_OUTPUT_HANDLE, L"%1!X! %2!X!", WintunDeleteAdapter(&Adapter, &RebootRequired), RebootRequired);
+    WriteFormatted(STD_OUTPUT_HANDLE, L"%1!X! %2!X!", WintunDeleteAdapter(&Adapter, ForceCloseSessions, &RebootRequired), RebootRequired);
 
 cleanup:
     Done();
diff --git a/api/wintun.h b/api/wintun.h
index ff79d8a..8137155 100644
--- a/api/wintun.h
+++ b/api/wintun.h
@@ -52,15 +52,19 @@ typedef WINTUN_STATUS(WINAPI *WINTUN_CREATE_ADAPTER_FUNC)(
 /**
  * Deletes a Wintun adapter.
  *
- * @param Adapter       Adapter handle obtained with WintunGetAdapter or WintunCreateAdapter.
+ * @param Adapter            Adapter handle obtained with WintunGetAdapter or WintunCreateAdapter.
  *
- * @param RebootRequired  Pointer to a boolean flag to be set to TRUE in case SetupAPI suggests a reboot. Must be
- *                      initialised to FALSE manually before this function is called.
+ * @param ForceCloseSessions Force close adapter handles that may be in use by other processes. Only set this to TRUE
+ *                           with extreme care, as this is resource intensive and may put processes into an undefined
+ *                           or unpredictable state. Most users should set this to FALSE.
+ *
+ * @param RebootRequired     Pointer to a boolean flag to be set to TRUE in case SetupAPI suggests a reboot. Must be
+ *                           initialised to FALSE manually before this function is called.
  *
  * @return ERROR_SUCCESS on success or the adapter was not found; Win32 error code otherwise.
  */
 typedef WINTUN_STATUS(
-    WINAPI *WINTUN_DELETE_ADAPTER_FUNC)(_In_ WINTUN_ADAPTER_HANDLE Adapter, _Inout_ BOOL *RebootRequired);
+    WINAPI *WINTUN_DELETE_ADAPTER_FUNC)(_In_ WINTUN_ADAPTER_HANDLE Adapter, _In_ BOOL ForceCloseSessions, _Inout_ BOOL *RebootRequired);
 
 /**
  * Called by WintunEnumAdapters for each adapter in the pool.