From 90d3b9a3131ac7094e4bfbf0330769c546560651 Mon Sep 17 00:00:00 2001
From: Paul Gofman <pgofman@codeweavers.com>
Date: Thu, 29 Jul 2021 11:08:19 +0300
Subject: [PATCH] kernelbase: Don't allow converting thread to fiber more than
 once.

Signed-off-by: Paul Gofman <pgofman@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>
---
 dlls/kernel32/tests/fiber.c | 14 ++++++++++++++
 dlls/kernelbase/thread.c    |  6 ++++++
 2 files changed, 20 insertions(+)

diff --git a/dlls/kernel32/tests/fiber.c b/dlls/kernel32/tests/fiber.c
index 3c54351fa7b..9ae45c2091b 100644
--- a/dlls/kernel32/tests/fiber.c
+++ b/dlls/kernel32/tests/fiber.c
@@ -128,10 +128,17 @@ static VOID WINAPI FiberMainProc(LPVOID lpFiberParameter)
 
 static void test_ConvertThreadToFiber(void)
 {
+    void *ret;
+
     if (pConvertThreadToFiber)
     {
         fibers[0] = pConvertThreadToFiber(&testparam);
         ok(fibers[0] != NULL, "ConvertThreadToFiber failed with error %u\n", GetLastError());
+
+        SetLastError(0xdeadbeef);
+        ret = pConvertThreadToFiber(&testparam);
+        ok(!ret, "Got non NULL ret.\n");
+        ok(GetLastError() == ERROR_ALREADY_FIBER, "Got unexpected error %u.\n", GetLastError());
     }
     else
     {
@@ -141,10 +148,17 @@ static void test_ConvertThreadToFiber(void)
 
 static void test_ConvertThreadToFiberEx(void)
 {
+    void *ret;
+
     if (pConvertThreadToFiberEx)
     {
         fibers[0] = pConvertThreadToFiberEx(&testparam, 0);
         ok(fibers[0] != NULL, "ConvertThreadToFiberEx failed with error %u\n", GetLastError());
+
+        SetLastError(0xdeadbeef);
+        ret = pConvertThreadToFiberEx(&testparam, 0);
+        ok(!ret, "Got non NULL ret.\n");
+        ok(GetLastError() == ERROR_ALREADY_FIBER, "Got unexpected error %u.\n", GetLastError());
     }
     else
     {
diff --git a/dlls/kernelbase/thread.c b/dlls/kernelbase/thread.c
index 61cb74c6222..9b97c4a8914 100644
--- a/dlls/kernelbase/thread.c
+++ b/dlls/kernelbase/thread.c
@@ -990,6 +990,12 @@ LPVOID WINAPI DECLSPEC_HOTPATCH ConvertThreadToFiberEx( LPVOID param, DWORD flag
 {
     struct fiber_data *fiber;
 
+    if (NtCurrentTeb()->Tib.u.FiberData)
+    {
+        SetLastError( ERROR_ALREADY_FIBER );
+        return NULL;
+    }
+
     if (!(fiber = HeapAlloc( GetProcessHeap(), 0, sizeof(*fiber) )))
     {
         SetLastError( ERROR_NOT_ENOUGH_MEMORY );