Fix windows time (#1136)

* util: Avoid potential uninitialized read in FormatISO8601DateTime(int… …64_t nTime) by checking gmtime_s/gmtime_r return value

* build: Detect gmtime_* definitions via configure

configure.ac

@@ -853,7 +853,23 @@ if test "x$use_thread_local" = xyes || { test "x$use_thread_local" = xauto && te
   LDFLAGS="$TEMP_LDFLAGS"
 fi
 
-# Check for different ways of gathering OS randomness
+dnl check for gmtime_r(), fallback to gmtime_s() if that is unavailable
+dnl fail if neither are available.
+AC_MSG_CHECKING(for gmtime_r)
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <ctime>]],
+  [[ gmtime_r((const time_t *) nullptr, (struct tm *) nullptr); ]])],
+  [ AC_MSG_RESULT(yes); AC_DEFINE(HAVE_GMTIME_R, 1, [Define this symbol if gmtime_r is available]) ],
+  [ AC_MSG_RESULT(no);
+    AC_MSG_CHECKING(for gmtime_s);
+    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <ctime>]],
+       [[ gmtime_s((struct tm *) nullptr, (const time_t *) nullptr); ]])],
+       [ AC_MSG_RESULT(yes)],
+       [ AC_MSG_RESULT(no); AC_MSG_ERROR(Both gmtime_r and gmtime_s are unavailable) ]
+    )
+  ]
+)
+
+dnl Check for different ways of gathering OS randomness
 AC_MSG_CHECKING(for Linux getrandom syscall)
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <unistd.h>
   #include <sys/syscall.h>
@@ -1456,6 +1472,7 @@ AC_SUBST(EVENT_LIBS)
 AC_SUBST(EVENT_PTHREADS_LIBS)
 AC_SUBST(ZMQ_LIBS)
 AC_SUBST(QR_LIBS)
+AC_SUBST(HAVE_GMTIME_R)
 AC_CONFIG_FILES([Makefile src/Makefile doc/man/Makefile share/setup.nsi test/config.ini])
 AC_CONFIG_FILES([contrib/devtools/split-debug.sh],[chmod +x contrib/devtools/split-debug.sh])
 AM_COND_IF([HAVE_DOXYGEN], [AC_CONFIG_FILES([doc/Doxyfile])])

src/util/time.cpp

@@ -93,21 +93,25 @@ void MilliSleep(int64_t n)
 std::string FormatISO8601DateTime(int64_t nTime) {
     struct tm ts;
     time_t time_val = nTime;
-#ifdef _MSC_VER
-    gmtime_s(&ts, &time_val);
+#ifdef HAVE_GMTIME_R
+    if (gmtime_r(&time_val, &ts) == nullptr) {
 #else
-    gmtime_r(&time_val, &ts);
+    if (gmtime_s(&ts, &time_val) != 0) {
 #endif
+        return {};
+    }
     return strprintf("%04i-%02i-%02iT%02i:%02i:%02iZ", ts.tm_year + 1900, ts.tm_mon + 1, ts.tm_mday, ts.tm_hour, ts.tm_min, ts.tm_sec);
 }
 
 std::string FormatISO8601Date(int64_t nTime) {
     struct tm ts;
     time_t time_val = nTime;
-#ifdef _MSC_VER
-    gmtime_s(&ts, &time_val);
+#ifdef HAVE_GMTIME_R
+    if (gmtime_r(&time_val, &ts) == nullptr) {
 #else
-    gmtime_r(&time_val, &ts);
+    if (gmtime_s(&ts, &time_val) != 0) {
 #endif
+        return {};
+    }
     return strprintf("%04i-%02i-%02i", ts.tm_year + 1900, ts.tm_mon + 1, ts.tm_mday);
 }