Use gmtime_r() when available instead of gmtime()

Although gmtime_r() improves thread safety of date/time conversion
because it is reentrant, it is only used by tr31-tool which is single
threaded. This change is purely to make CodeQL happy.

Author: leonlynch

src/CMakeLists.txt

@@ -50,8 +50,8 @@ if(NOT argp_FOUND)
 endif()
 
 # check for features required for date/time conversion:
-# locale.h, time.h, setlocale(), strptime(), timegm(), _mkgmtime(), and
-# localtime_r()
+# locale.h, time.h, setlocale(), strptime(), timegm(), _mkgmtime(),
+# localtime_r(), and gmtime_r()
 include(CheckIncludeFile)
 include(CheckSymbolExists)
 CHECK_INCLUDE_FILE(locale.h HAVE_LOCALE_H)
@@ -94,6 +94,17 @@ if(NOT HAVE_LOCALTIME_R)
 		set(TIME_H_DEFINITIONS ${TIME_H_DEFINITIONS_TRY} CACHE INTERNAL "Definitions required for time.h")
 	endif()
 endif()
+check_symbol_exists(gmtime_r time.h HAVE_GMTIME_R)
+if(NOT HAVE_GMTIME_R)
+	unset(HAVE_GMTIME_R CACHE)
+	list(APPEND CMAKE_REQUIRED_DEFINITIONS -D${TIME_H_DEFINITIONS_TRY})
+	check_symbol_exists(gmtime_r time.h HAVE_GMTIME_R)
+	list(REMOVE_ITEM CMAKE_REQUIRED_DEFINITIONS -D${TIME_H_DEFINITIONS_TRY})
+	if(HAVE_GMTIME_R)
+		# set as cache entry to persist across multiple builds
+		set(TIME_H_DEFINITIONS ${TIME_H_DEFINITIONS_TRY} CACHE INTERNAL "Definitions required for time.h")
+	endif()
+endif()
 # Only setlocale() and either timegm() or _mkgmtime() are required for
 # date/time conversion. If strptime() is absent, sscanf() will be used instead.
 if(HAVE_SETLOCALE AND (HAVE_TIMEGM OR HAVE_MKGMTIME))
@@ -166,6 +177,13 @@ install(
 # TR-31 command line tool
 if(BUILD_TR31_TOOL)
 	add_executable(tr31-tool tr31-tool.c)
+	if(HAVE_GMTIME_R AND TIME_H_DEFINITIONS)
+		set_source_files_properties(tr31-tool.c
+			PROPERTIES
+				COMPILE_DEFINITIONS ${TIME_H_DEFINITIONS}
+		)
+	endif()
+	target_include_directories(tr31-tool PRIVATE ${CMAKE_CURRENT_BINARY_DIR}) # for generated config file
 	target_link_libraries(tr31-tool PRIVATE crypto_mem tr31)
 	if(TARGET libargp::argp)
 		target_link_libraries(tr31-tool PRIVATE libargp::argp)

src/tr31-tool.c

@@ -19,6 +19,7 @@
  */
 
 #include "tr31.h"
+#include "tr31_config.h"
 #include "tr31_strings.h"
 
 #include "crypto_mem.h"
@@ -1361,20 +1362,30 @@ static int populate_opt_blocks(const struct tr31_tool_options_t* options, struct
 
 		if (strcmp(options->export_opt_block_TC_str, "now") == 0) {
 			time_t lt; // Calendar/Unix/POSIX time in local time
-			struct tm* ztm; // Time structure in UTC
+			struct tm ztm; // Time structure in UTC
+			struct tm* tm_ptr; // Result of gmtime functions
 			size_t ret;
 
 			lt = time(NULL);
 			if (lt == (time_t)-1) {
 				fprintf(stderr, "Failed to obtain current date/time: %s\n", strerror(errno));
 				return 1;
 			}
-			ztm = gmtime(&lt);
-			if (ztm == NULL) {
+#ifdef HAVE_GMTIME_R
+			tm_ptr = gmtime_r(&lt, &ztm);
+			if (!tm_ptr) {
 				fprintf(stderr, "Failed to convert current date/time to UTC\n");
 				return 1;
 			}
-			ret = strftime(iso8601_now, sizeof(iso8601_now), "%Y%m%d%H%M%SZ", ztm);
+#else
+			tm_ptr = gmtime(&lt);
+			if (!tm_ptr) {
+				fprintf(stderr, "Failed to convert current date/time to UTC\n");
+				return 1;
+			}
+			ztm = *tm_ptr;
+#endif
+			ret = strftime(iso8601_now, sizeof(iso8601_now), "%Y%m%d%H%M%SZ", &ztm);
 			if (!ret) {
 				fprintf(stderr, "Failed to convert current date/time to ISO 8601\n");
 				return 1;
@@ -1396,20 +1407,30 @@ static int populate_opt_blocks(const struct tr31_tool_options_t* options, struct
 
 		if (strcmp(options->export_opt_block_TS_str, "now") == 0) {
 			time_t lt; // Calendar/Unix/POSIX time in local time
-			struct tm* ztm; // Time structure in UTC
+			struct tm ztm; // Time structure in UTC
+			struct tm* tm_ptr; // Result of gmtime functions
 			size_t ret;
 
 			lt = time(NULL);
 			if (lt == (time_t)-1) {
 				fprintf(stderr, "Failed to obtain current date/time: %s\n", strerror(errno));
 				return 1;
 			}
-			ztm = gmtime(&lt);
-			if (ztm == NULL) {
+#ifdef HAVE_GMTIME_R
+			tm_ptr = gmtime_r(&lt, &ztm);
+			if (!tm_ptr) {
 				fprintf(stderr, "Failed to convert current date/time to UTC\n");
 				return 1;
 			}
-			ret = strftime(iso8601_now, sizeof(iso8601_now), "%Y%m%d%H%M%SZ", ztm);
+#else
+			tm_ptr = gmtime(&lt);
+			if (!tm_ptr) {
+				fprintf(stderr, "Failed to convert current date/time to UTC\n");
+				return 1;
+			}
+			ztm = *tm_ptr;
+#endif
+			ret = strftime(iso8601_now, sizeof(iso8601_now), "%Y%m%d%H%M%SZ", &ztm);
 			if (!ret) {
 				fprintf(stderr, "Failed to convert current date/time to ISO 8601\n");
 				return 1;

src/tr31_config.h.in

@@ -33,6 +33,7 @@
 #cmakedefine HAVE_TIMEGM
 #cmakedefine HAVE_MKGMTIME
 #cmakedefine HAVE_LOCALTIME_R
+#cmakedefine HAVE_GMTIME_R
 #cmakedefine TR31_ENABLE_DATETIME_CONVERSION
 
 #endif