wrap rand() in functions explicitly marked as non-secure

src/bootstrap.c

@@ -624,16 +624,18 @@ int load_DHT_nodeslist(void)
 static void DHT_bootstrap(Tox *m)
 {
     pthread_mutex_lock(&thread_data.lock);
-    const size_t num_nodes = Nodes.count;
+    size_t num_nodes = Nodes.count;
     pthread_mutex_unlock(&thread_data.lock);
 
     if (num_nodes == 0) {
         return;
     }
 
+    size_t i;
+
     pthread_mutex_lock(&thread_data.lock);
 
-    for (size_t i = 0; i < NUM_BOOTSTRAP_NODES; ++i) {
+    for (i = 0; i < NUM_BOOTSTRAP_NODES; ++i) {
         struct Node *node = &Nodes.list[rand() % Nodes.count];
         const char *addr = node->have_ip4 ? node->ip4 : node->ip6;
 

src/game_base.c

@@ -967,8 +967,8 @@ void game_random_coords(const GameData *game, Coords *coords)
     const int y_top_bound    = ((max_y - game_max_y) / 2) + 1;
     const int y_bottom_bound = ((max_y + game_max_y) / 2) - 1;
 
-    coords->x = (rand() % (x_right_bound - x_left_bound + 1)) + x_left_bound;
-    coords->y = (rand() % (y_bottom_bound - y_top_bound + 1)) + y_top_bound;
+    coords->x = (int)rand_range_not_secure(x_right_bound - x_left_bound + 1) + x_left_bound;
+    coords->y = (int)rand_range_not_secure(y_bottom_bound - y_top_bound + 1) + y_top_bound;
 }
 
 void game_max_x_y(const GameData *game, int *x, int *y)

src/game_centipede.c

@@ -288,7 +288,7 @@ static size_t cent_enemy_agent_speed(size_t base_speed, size_t level)
         return base_speed;
     }
 
-    int r = rand() % (level / 2);
+    const unsigned int r = rand_range_not_secure(level / 2);
 
     return MIN(base_speed + r, CENT_MAX_ENEMY_AGENT_SPEED);
 }
@@ -520,7 +520,7 @@ static int cent_birth_centipede(const GameData *game, CentState *state, size_t l
 
 static int cent_init_level_centipedes(const GameData *game, CentState *state, size_t level)
 {
-    Direction dir = rand() % 2 == 0 ? WEST : EAST;
+    Direction dir = rand_range_not_secure(2) == 0 ? WEST : EAST;
 
     // First level we spawn one full size centipede
     if (level == 1) {
@@ -1093,11 +1093,11 @@ static void cent_do_reproduce(const GameData *game, CentState *state, Segment *h
         return;
     }
 
-    Direction dir = rand() % 2 == 0 ? WEST : EAST;
+    const Direction dir = rand_range_not_secure(2) == 0 ? WEST : EAST;
 
     Coords new_coords;
     new_coords.x = dir == EAST ? x_left : x_right;
-    new_coords.y = y_bottom - (rand() % CENT_INVISIBLE_H_WALL);
+    new_coords.y = MAX(0, y_bottom - (int)rand_range_not_secure(CENT_INVISIBLE_H_WALL));
 
     if (cent_birth_centipede(game, state, 0, dir, &new_coords) == 0) {
         head->last_time_reproduced = get_unix_time();
@@ -1151,7 +1151,7 @@ static void cent_try_spawn_flea(const GameData *game, EnemyAgent *flea)
 
     flea->was_killed = false;
 
-    if (rand() % 4 == 0) {
+    if (rand_range_not_secure(4) == 0) {
         return;
     }
 
@@ -1169,7 +1169,7 @@ static void cent_try_spawn_flea(const GameData *game, EnemyAgent *flea)
     const int x_right = game_x_right_bound(game);
 
     flea->coords.y = y_top;
-    flea->coords.x = (rand() % (x_right - x_left + 1)) + x_left;
+    flea->coords.x = (int)rand_range_not_secure(x_right - x_left + 1) + x_left;
 }
 
 static void cent_do_flea(GameData *game, CentState *state, TIME_MS cur_time)
@@ -1189,7 +1189,7 @@ static void cent_do_flea(GameData *game, CentState *state, TIME_MS cur_time)
 
     const int y_bottom = game_y_bottom_bound(game);
 
-    if (flea->coords.y < (y_bottom - 5) && rand() % 4 == 0) {
+    if (flea->coords.y < y_bottom - 5 && rand_range_not_secure(4) == 0) {
         cent_mushroom_grow(game, state, &flea->coords, false);
     }
 
@@ -1215,7 +1215,7 @@ static bool cent_scorpion_spawn_check(EnemyAgent *scorpion, size_t level)
 
     scorpion->last_time_despawned = get_unix_time();
 
-    return (rand() % 4) < 3;
+    return rand_range_not_secure(4) < 3;
 }
 
 static void cent_try_spawn_scorpion(const GameData *game, CentState *state, EnemyAgent *scorpion)
@@ -1235,7 +1235,7 @@ static void cent_try_spawn_scorpion(const GameData *game, CentState *state, Enem
     scorpion->attributes = CENT_SCORPION_DEFAULT_ATTR;
     scorpion->display_char = CENT_SCORPTION_CHAR;
     scorpion->health = CENT_SCORPTION_START_HEALTH;
-    scorpion->direction = rand() % 2 == 0 ? WEST : EAST;
+    scorpion->direction = rand_range_not_secure(2) == 0 ? WEST : EAST;
 
     const int y_bottom = game_y_bottom_bound(game);
     const int x_left = game_x_left_bound(game);
@@ -1244,7 +1244,7 @@ static void cent_try_spawn_scorpion(const GameData *game, CentState *state, Enem
     const int y_mid = y_top + ((y_bottom - y_top) / 2);
 
     scorpion->coords.x = scorpion->direction == WEST ? x_right : x_left;
-    scorpion->coords.y = (y_mid - 5) + (rand() % 5);
+    scorpion->coords.y = (y_mid - 5) + (int)rand_range_not_secure(5);
 }
 
 static void cent_do_scorpion(GameData *game, CentState *state, TIME_MS cur_time)
@@ -1286,7 +1286,7 @@ static void cent_try_spawn_spider(const GameData *game, EnemyAgent *spider)
         return;
     }
 
-    if (rand() % 4 == 0) {
+    if (rand_range_not_secure(4) == 0) {
         spider->last_time_despawned = get_unix_time();
         return;
     }
@@ -1297,7 +1297,7 @@ static void cent_try_spawn_spider(const GameData *game, EnemyAgent *spider)
     spider->speed = cent_enemy_agent_speed(CENT_SPIDER_DEFAULT_SPEED, level);
     spider->attributes = CENT_SPIDER_DEFAULT_ATTR;
     spider->display_char = CENT_SPIDER_CHAR;
-    spider->start_direction = rand() % 2 == 0 ? WEST : EAST;
+    spider->start_direction = rand_range_not_secure(2) == 0 ? WEST : EAST;
     spider->direction = spider->start_direction;
     spider->health = CENT_SPIDER_START_HEALTH;
 
@@ -1306,7 +1306,8 @@ static void cent_try_spawn_spider(const GameData *game, EnemyAgent *spider)
     const int x_right = game_x_right_bound(game);
 
     spider->coords.x = spider->direction == WEST ? x_right : x_left;
-    spider->coords.y = (rand() % (y_bottom - (y_bottom - CENT_INVISIBLE_H_WALL))) + (y_bottom - CENT_INVISIBLE_H_WALL);
+    spider->coords.y = (int)rand_range_not_secure(y_bottom - (y_bottom - CENT_INVISIBLE_H_WALL))
+                       + (y_bottom - CENT_INVISIBLE_H_WALL);
 }
 
 static void cent_do_spider(GameData *game, CentState *state, TIME_MS cur_time)
@@ -1329,7 +1330,7 @@ static void cent_do_spider(GameData *game, CentState *state, TIME_MS cur_time)
                spider->coords.y,
     };
 
-    int r = rand();
+    const unsigned int r = rand_not_secure();
 
     if (spider->direction == spider->start_direction) {
         if (r % 4 == 0) {
@@ -1634,7 +1635,7 @@ static void cent_populate_mushrooms(const GameData *game, CentState *state, int
     const int y_floor_bound = game_y_bottom_bound(game);
 
     for (size_t i = 0; i < CENT_MUSHROOMS_LENGTH; ++i) {
-        if (rand() % population_const != 0) {
+        if (rand_range_not_secure(population_const) != 0) {
             continue;
         }
 
@@ -1674,7 +1675,7 @@ static int cent_init_state(GameData *game, CentState *state)
     Centipedes *centipedes = &state->centipedes;
     memset(centipedes->heads, 0, sizeof(centipedes->heads));
 
-    Direction dir = rand() % 2 == 0 ? WEST : EAST;
+    Direction dir = rand_range_not_secure(2) == 0 ? WEST : EAST;
 
     if (cent_birth_centipede(game, state, CENT_MAX_NUM_SEGMENTS, dir, NULL) == -1) {
         free(mushrooms);

src/game_chess.c

@@ -2118,7 +2118,7 @@ int chess_initialize(GameData *game, const uint8_t *init_data, size_t length, bo
         return -3;
     }
 
-    bool self_is_white = rand() % 2 == 0;
+    bool self_is_white = rand_range_not_secure(2) == 0;
 
     if (!self_host) {
         if (length != CHESS_PACKET_SEND_INVITE_LENGTH) {

src/game_util.c

@@ -25,6 +25,7 @@
 #include <stdint.h>
 
 #include "game_util.h"
+#include "misc_tools.h"
 #include "toxic.h"
 #include "windows.h"
 
@@ -80,7 +81,7 @@ Direction game_util_move_towards(const Coords *coords_a, const Coords *coords_b,
 
 Direction game_util_random_direction(void)
 {
-    int r = rand() % 4;
+    const unsigned int r = rand_range_not_secure(4);
 
     switch (r) {
         case 0:
@@ -137,7 +138,7 @@ void game_util_move_coords(Direction direction, Coords *coords)
 
 int game_util_random_colour(void)
 {
-    int r = rand() % 6;
+    const unsigned int r = rand_range_not_secure(6);
 
     switch (r) {
         case 0:

src/global_commands.c

@@ -362,8 +362,8 @@ void cmd_game(WINDOW *window, ToxWindow *self, Tox *m, int argc, char (*argv)[MA
         return;
     }
 
-    uint32_t id = rand();
-    int ret = game_initialize(self, m, type, id, NULL, 0, true);
+    const unsigned int id = rand_not_secure();
+    const int ret = game_initialize(self, m, type, (uint32_t)id, NULL, 0, true);
 
     switch (ret) {
         case 0: {
@@ -798,7 +798,7 @@ void cmd_note(WINDOW *window, ToxWindow *self, Tox *m, int argc, char (*argv)[MA
 
 void cmd_nospam(WINDOW *window, ToxWindow *self, Tox *m, int argc, char (*argv)[MAX_STR_SIZE])
 {
-    long int nospam = rand();
+    long int nospam = (long int)rand_not_secure();  // the nospam isn't cryptographically sensitive
 
     if (argc > 0) {
         nospam = strtol(argv[1], NULL, 16);

src/misc_tools.c

@@ -737,3 +737,17 @@ void **malloc_ptr_array(size_t length, size_t bytes)
 
     return arr;
 }
+
+unsigned int rand_range_not_secure(unsigned int upper_bound)
+{
+    const unsigned int n = (unsigned int)rand();
+
+    return n % MIN(RAND_MAX, upper_bound);
+}
+
+unsigned int rand_not_secure(void)
+{
+    const unsigned int n = (unsigned int)rand();
+
+    return n;
+}

src/misc_tools.h

@@ -235,4 +235,19 @@ void free_ptr_array(void **arr);
  */
 void **malloc_ptr_array(size_t length, size_t bytes);
 
+/*
+ * Returns a non-cryptographically secure random unsigned integer between zero and `upper_bound`
+ * which is limited by RAND_MAX.
+ *
+ * This function should only be used for non-crypto related things.
+ */
+unsigned int rand_range_not_secure(unsigned int upper_bound);
+
+/*
+ * Returns a non-cryptographically secure random unsigned integer between zero and RAND_MAX.
+ *
+ * This function should only be used for non-crypto related things.
+ */
+unsigned int rand_not_secure(void);
+
 #endif /* MISC_TOOLS_H */