From 901478a2d04fcae70cf1f99f19b7508256633fa0 Mon Sep 17 00:00:00 2001
From: Mitya Selivanov <automainint@guattari.tech>
Date: Sat, 17 Dec 2022 23:16:55 +0100
Subject: Secure random fallback: thread safety

---
 source/kit/secure_random.c                 | 36 +++++++++++++++++++++++++-----
 source/kit/secure_random.h                 |  5 +++++
 source/kit/time.h                          |  8 +++----
 source/test/unittests/secure_random.test.c |  4 ++++
 4 files changed, 44 insertions(+), 9 deletions(-)

diff --git a/source/kit/secure_random.c b/source/kit/secure_random.c
index 8852524..8f48c9d 100644
--- a/source/kit/secure_random.c
+++ b/source/kit/secure_random.c
@@ -1,6 +1,7 @@
 #include "secure_random.h"
 
 #include "mersenne_twister_64.h"
+#include "mutex.h"
 #include "time.h"
 #include <stdio.h>
 
@@ -26,8 +27,16 @@ static uint64_t get_available_memory() {
 #endif
 }
 
+#ifndef KIT_DISABLE_SYSTEM_THREADS
+static mtx_t kit_secure_random_fallback_mutex;
+#endif
+
 static void secure_random_fallback(ptrdiff_t const size,
                                    void *const     data) {
+#ifndef KIT_DISABLE_SYSTEM_THREADS
+  mtx_lock(&kit_secure_random_fallback_mutex);
+#endif
+
   /*  Try to get some unpredictable system properties and use them to
    *  seed the pseudo random number generator.
    */
@@ -42,11 +51,11 @@ static void secure_random_fallback(ptrdiff_t const size,
   kit_mt64_state_t state;
 
   if (time_sec == 0 && time_nsec == 0) {
-    uint64_t seed[4] = { n++, get_available_memory(),
+    uint64_t seed[4] = { n, get_available_memory(),
                          (uint64_t) t.tv_sec, (uint64_t) t.tv_nsec };
     kit_mt64_init_array(&state, sizeof seed / sizeof *seed, seed);
   } else {
-    uint64_t seed[6] = { n++,
+    uint64_t seed[6] = { n,
                          get_available_memory(),
                          (uint64_t) t.tv_sec,
                          (uint64_t) t.tv_nsec,
@@ -55,17 +64,34 @@ static void secure_random_fallback(ptrdiff_t const size,
     kit_mt64_init_array(&state, sizeof seed / sizeof *seed, seed);
   }
 
-  time_sec  = (uint64_t) t.tv_sec;
-  time_nsec = (uint64_t) t.tv_nsec;
-
   /*  Bootstrap the generator.
    */
   for (ptrdiff_t i = 0; i < KIT_MT64_N; i++)
     kit_mt64_generate(&state);
 
+  n         = kit_mt64_generate(&state);
+  time_sec  = (uint64_t) t.tv_sec;
+  time_nsec = (uint64_t) t.tv_nsec;
+
   for (ptrdiff_t i = 0; i < size; i++)
     ((uint8_t *) data)[i] = (uint8_t) (kit_mt64_generate(&state) >>
                                        56);
+
+#ifndef KIT_DISABLE_SYSTEM_THREADS
+  mtx_unlock(&kit_secure_random_fallback_mutex);
+#endif
+}
+
+void kit_secure_random_init() {
+#ifndef KIT_DISABLE_SYSTEM_THREADS
+  mtx_init(&kit_secure_random_fallback_mutex, mtx_plain);
+#endif
+}
+
+void kit_secure_random_cleanup() {
+#ifndef KIT_DISABLE_SYSTEM_THREADS
+  mtx_destroy(&kit_secure_random_fallback_mutex);
+#endif
 }
 
 void kit_secure_random(ptrdiff_t const size, void *const data) {
diff --git a/source/kit/secure_random.h b/source/kit/secure_random.h
index 758478d..5b461f9 100644
--- a/source/kit/secure_random.h
+++ b/source/kit/secure_random.h
@@ -9,9 +9,14 @@
 extern "C" {
 #endif
 
+void kit_secure_random_init();
+void kit_secure_random_cleanup();
+
 void kit_secure_random(ptrdiff_t size, void *data);
 
 #ifndef KIT_DISABLE_SHORT_NAMES
+#  define secure_random_init kit_secure_random_init
+#  define secure_random_cleanup kit_secure_random_cleanup
 #  define secure_random kit_secure_random
 #endif
 
diff --git a/source/kit/time.h b/source/kit/time.h
index dbf8883..0d995f4 100644
--- a/source/kit/time.h
+++ b/source/kit/time.h
@@ -38,21 +38,21 @@ struct timespec {
 /*-------------------------- functions --------------------------*/
 
 #if !defined(KIT_HAVE_TIMESPEC_GET)
-#  define KIT_HAVE_TIMESPEC_GET_NEED_DECL_
+#  define KIT_TIMESPEC_GET_NEED_DECL_
 #elif defined(__APPLE__) && defined(__cplusplus) && \
     (__cplusplus < 201703L)
 /* On macOS, the guard for declaration of timespec_get is by
  * (defined(__cplusplus) && __cplusplus >= 201703L),
  * fix the declaration for C++14 and lower here
  */
-#  define KIT_HAVE_TIMESPEC_GET_NEED_DECL_
+#  define KIT_TIMESPEC_GET_NEED_DECL_
 #endif
 
-#ifdef KIT_HAVE_TIMESPEC_GET_NEED_DECL_
+#ifdef KIT_TIMESPEC_GET_NEED_DECL_
 /*-------------------- 7.25.7 Time functions --------------------*/
 // 7.25.6.1
 int timespec_get(struct timespec *ts, int base);
-#  undef KIT_HAVE_TIMESPEC_GET_NEED_DECL_
+#  undef KIT_TIMESPEC_GET_NEED_DECL_
 #endif
 
 #ifdef __cplusplus
diff --git a/source/test/unittests/secure_random.test.c b/source/test/unittests/secure_random.test.c
index ec0a7b2..eadae65 100644
--- a/source/test/unittests/secure_random.test.c
+++ b/source/test/unittests/secure_random.test.c
@@ -8,9 +8,13 @@ TEST("secure random") {
   int v[20];
   memset(v, 0, sizeof v);
 
+  secure_random_init();
+
   secure_random(40, v);
   secure_random(40, v + 10);
 
+  secure_random_cleanup();
+
   int repeats = 0;
 
   for (int i = 1; i < sizeof v / sizeof *v; i++)
-- 
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