windows: determine RtlVerifyVersionInfo address on global init

Instead of the first internal call to `curlx_verify_windows_version()`.

To avoid the chance of a race, potentially resulting in initializing
this address twice. AFAICT it could not cause an issue before this
patch.

Reported by Codex Security

Follow-up to b17ef873ae #18009

Closes #20853

lib/curlx/version_win32.c

@@ -27,6 +27,7 @@
 
 #include "curlx/version_win32.h"
 
+#ifndef CURL_WINDOWS_UWP
 /* This Unicode version struct works for VerifyVersionInfoW (OSVERSIONINFOEXW)
    and RtlVerifyVersionInfo (RTLOSVERSIONINFOEXW) */
 struct OUR_OSVERSIONINFOEXW {
@@ -43,6 +44,24 @@ struct OUR_OSVERSIONINFOEXW {
   UCHAR  wReserved;
 };
 
+typedef LONG (APIENTRY *RTLVERIFYVERSIONINFO_FN)
+  (struct OUR_OSVERSIONINFOEXW *, ULONG, ULONGLONG);
+static RTLVERIFYVERSIONINFO_FN s_pRtlVerifyVersionInfo;
+
+void curlx_verify_windows_init(void)
+{
+#if defined(__clang__) && __clang_major__ >= 16
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wcast-function-type-strict"
+#endif
+  s_pRtlVerifyVersionInfo = CURLX_FUNCTION_CAST(RTLVERIFYVERSIONINFO_FN,
+    GetProcAddress(GetModuleHandle(TEXT("ntdll")), "RtlVerifyVersionInfo"));
+#if defined(__clang__) && __clang_major__ >= 16
+#pragma clang diagnostic pop
+#endif
+}
+#endif /* !CURL_WINDOWS_UWP */
+
 /*
  * curlx_verify_windows_version()
  *
@@ -115,24 +134,6 @@ bool curlx_verify_windows_version(const unsigned int majorVersion,
   DWORD dwTypeMask = VER_MAJORVERSION | VER_MINORVERSION |
                      VER_SERVICEPACKMAJOR | VER_SERVICEPACKMINOR;
 
-  typedef LONG (APIENTRY *RTLVERIFYVERSIONINFO_FN)
-    (struct OUR_OSVERSIONINFOEXW *, ULONG, ULONGLONG);
-  static RTLVERIFYVERSIONINFO_FN pRtlVerifyVersionInfo;
-  static bool onetime = TRUE; /* safe because first call is during init */
-
-  if(onetime) {
-#if defined(__clang__) && __clang_major__ >= 16
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wcast-function-type-strict"
-#endif
-    pRtlVerifyVersionInfo = CURLX_FUNCTION_CAST(RTLVERIFYVERSIONINFO_FN,
-      GetProcAddress(GetModuleHandle(TEXT("ntdll")), "RtlVerifyVersionInfo"));
-#if defined(__clang__) && __clang_major__ >= 16
-#pragma clang diagnostic pop
-#endif
-    onetime = FALSE;
-  }
-
   switch(condition) {
   case VERSION_LESS_THAN:
     majorCondition = VER_LESS;
@@ -203,8 +204,8 @@ bool curlx_verify_windows_version(const unsigned int majorVersion,
      the real version always, so we use the Rtl variant of the function when
      possible. Note though the function signatures have underlying fundamental
      types that are the same, the return values are different. */
-  if(pRtlVerifyVersionInfo)
+  if(s_pRtlVerifyVersionInfo)
-    matched = !pRtlVerifyVersionInfo(&osver, dwTypeMask, cm);
+    matched = !s_pRtlVerifyVersionInfo(&osver, dwTypeMask, cm);
   else
     matched = !!VerifyVersionInfoW((OSVERSIONINFOEXW *)&osver, dwTypeMask, cm);
 
@@ -222,8 +223,8 @@ bool curlx_verify_windows_version(const unsigned int majorVersion,
 
     cm = VerSetConditionMask(0, VER_BUILDNUMBER, buildCondition);
     dwTypeMask = VER_BUILDNUMBER;
-    if(pRtlVerifyVersionInfo)
+    if(s_pRtlVerifyVersionInfo)
-      matched = !pRtlVerifyVersionInfo(&osver, dwTypeMask, cm);
+      matched = !s_pRtlVerifyVersionInfo(&osver, dwTypeMask, cm);
     else
       matched = !!VerifyVersionInfoW((OSVERSIONINFOEXW *)&osver,
                                      dwTypeMask, cm);

lib/curlx/version_win32.h

@@ -43,6 +43,11 @@ typedef enum {
   PLATFORM_WINNT
 } PlatformIdentifier;
 
+#ifdef CURL_WINDOWS_UWP
+#define curlx_verify_windows_init() Curl_nop_stmt
+#else
+void curlx_verify_windows_init(void);
+#endif
 /* This is used to verify if we are running on a specific Windows version */
 bool curlx_verify_windows_version(const unsigned int majorVersion,
                                   const unsigned int minorVersion,

lib/system_win32.c

@@ -28,6 +28,7 @@
 #include "system_win32.h"
 #include "curl_sspi.h"
 #include "curlx/timeval.h"
+#include "curlx/version_win32.h"  /* for curlx_verify_windows_init() */
 
 /* Curl_win32_init() performs Win32 global initialization */
 CURLcode Curl_win32_init(long flags)
@@ -77,6 +78,7 @@ CURLcode Curl_win32_init(long flags)
   }
 #endif
 
+  curlx_verify_windows_init();
   curlx_now_init();
   return CURLE_OK;
 }

src/tool_doswin.c

@@ -901,6 +901,7 @@ curl_socket_t win32_stdin_read_thread(void)
 
 CURLcode win32_init(void)
 {
+  curlx_verify_windows_init();
   curlx_now_init();
 #ifndef CURL_WINDOWS_UWP
   init_terminal();