fix(daemon-conf): reject empty hosts/auth allow-lists (C4)

A present hosts allow/hosts deny/auth users key with an empty or
separator-only value produced a zero-length list, silently meaning no
ACL / no auth and contradicting the strict-parse contract.

store_host_list and the auth users parser now track how many entries a
present key actually added and fail the load with a clear error when it
is zero, so a restrictive directive can never silently become open.
Unit tests cover empty, whitespace-only and comma-only values.

src/shared/daemon_conf.c

@@ -133,6 +133,7 @@ static bool store_host_list(char*** list, int* count, const char* value, const c
     return false;
   }
   char* save = NULL;
+  int added = 0;
   for (char* token = strtok_r(copy, ", \t", &save); token; token = strtok_r(NULL, ", \t", &save)) {
     if (!host_pattern_valid(token)) {
       if (module_name)
@@ -163,8 +164,20 @@ static bool store_host_list(char*** list, int* count, const char* value, const c
       return false;
     }
     (*list)[(*count)++] = dup;
+    added++;
   }
   free(copy);
+  /* A present key with an empty (or separator-only) value would otherwise
+   * install a zero-length list, i.e. no ACL at all: a strict-parse config must
+   * never silently turn a restrictive directive into "allow everyone". */
+  if (added == 0) {
+    if (module_name)
+      set_error(err, err_size, "module '%s': '%s' must list at least one host pattern", module_name,
+                key);
+    else
+      set_error(err, err_size, "'%s' must list at least one host pattern", key);
+    return false;
+  }
   return true;
 }
 
@@ -403,6 +416,7 @@ static bool apply_module_key(DaemonModule* module, char* key, char* value, char*
       return false;
     }
     char* save = NULL;
+    int added = 0;
     for (char* token = strtok_r(list, ",", &save); token; token = strtok_r(NULL, ",", &save)) {
       const char* user = trim_ws(token);
       if (*user == '\0')
@@ -430,8 +444,16 @@ static bool apply_module_key(DaemonModule* module, char* key, char* value, char*
         return false;
       }
       module->auth_users[module->auth_user_count++] = dup;
+      added++;
     }
     free(list);
+    /* An empty/separator-only value must not silently disable authentication:
+     * the key's presence is an explicit request for an allow-list. */
+    if (added == 0) {
+      set_error(err, err_size, "module '%s': 'auth users' must list at least one user",
+                module->name);
+      return false;
+    }
     return true;
   }
   if (key_equals(key, "max connections"))

tests/test_daemon_conf.c

@@ -391,6 +391,22 @@ static void test_daemon_conf_auth_users_validated() {
   EXPECT_EQ_STR(ok_conf->modules[0].auth_users[0], "alice");
   EXPECT_EQ_STR(ok_conf->modules[0].auth_users[1], "bob");
   daemon_conf_free(ok_conf);
+
+  /* C4: an empty or separator-only `auth users` value is a parse error.  It
+   * would otherwise leave the module with a zero-length allow-list, silently
+   * disabling the authentication the operator asked for. */
+  const char* empty_auth[] = {
+      "[m]\npath = /x\nauth users = \n",
+      "[m]\npath = /x\nauth users = , ,\n",
+      "[m]\npath = /x\nauth users = \t\n",
+  };
+  for (size_t i = 0; i < sizeof(empty_auth) / sizeof(empty_auth[0]); i++) {
+    EXPECT_EQ_INT(write_conf(empty_auth[i], &path), 0);
+    const DaemonConf* rejected = daemon_conf_load(path, err, sizeof(err));
+    free(path);
+    EXPECT_NULL(rejected);
+    EXPECT_TRUE(strstr(err, "'auth users' must list at least one user") != NULL);
+  }
 }
 
 /* Wave 3 daemon hardening: configurable global/per-module connection caps,
@@ -475,13 +491,33 @@ static void test_daemon_conf_limits_and_hosts_parse() {
   EXPECT_EQ_INT(conf->modules[0].max_connections, 0);
   daemon_conf_free(conf);
 
-  /* An empty hosts list is not an error (no patterns are added). */
-  EXPECT_EQ_INT(write_conf("hosts allow = \n[m]\npath = /x\n", &path), 0);
-  conf = daemon_conf_load(path, err, sizeof(err));
+  /* C4: a present hosts key with an empty/separator-only value must not silently
+   * install a zero-length (allow-everyone) list. */
+  const char* empty_hosts[] = {
+      "hosts allow = \n[m]\npath = /x\n",
+      "hosts deny = \n[m]\npath = /x\n",
+      "hosts allow = , ,\n[m]\npath = /x\n",
+      "hosts deny = \t\n[m]\npath = /x\n",
+  };
+  for (size_t i = 0; i < sizeof(empty_hosts) / sizeof(empty_hosts[0]); i++) {
+    EXPECT_EQ_INT(write_conf(empty_hosts[i], &path), 0);
+    const DaemonConf* rejected = daemon_conf_load(path, err, sizeof(err));
     free(path);
-  EXPECT_NOT_NULL(conf);
-  EXPECT_EQ_INT(conf->global.hosts_allow_count, 0);
-  daemon_conf_free(conf);
+    EXPECT_NULL(rejected);
+    EXPECT_TRUE(strstr(err, "must list at least one host pattern") != NULL);
+  }
+
+  const char* empty_module_hosts[] = {
+      "[m]\npath = /x\nhosts allow = \n",
+      "[m]\npath = /x\nhosts deny = ,\n",
+  };
+  for (size_t i = 0; i < sizeof(empty_module_hosts) / sizeof(empty_module_hosts[0]); i++) {
+    EXPECT_EQ_INT(write_conf(empty_module_hosts[i], &path), 0);
+    const DaemonConf* rejected = daemon_conf_load(path, err, sizeof(err));
+    free(path);
+    EXPECT_NULL(rejected);
+    EXPECT_TRUE(strstr(err, "must list at least one host pattern") != NULL);
+  }
 }
 
 static void test_daemon_hosts_allowed() {