netenv: add redirectBroadcast configuration option to control UDP broadcast redirection

common/platform/config.c

@@ -182,6 +182,11 @@ void netenv_config_load(struct netenv_config *cfg, const wchar_t *filename)
     memset(cfg, 0, sizeof(*cfg));
 
     cfg->enable = GetPrivateProfileIntW(L"netenv", L"enable", 0, filename);
+    cfg->redirect_broadcast = GetPrivateProfileIntW(
+            L"netenv",
+            L"redirectBroadcast",
+            1,
+            filename);
 
     cfg->addr_suffix = GetPrivateProfileIntW(
             L"netenv",

common/platform/netenv.c

@@ -165,6 +165,7 @@ static uint32_t netenv_ip_bcast;
 static uint32_t netenv_ip_iface;
 static uint32_t netenv_ip_router;
 static uint8_t netenv_mac_addr[6];
+static bool netenv_redirect_broadcast;
 static uint32_t netenv_last_logged_broadcast_src;
 static uint32_t netenv_last_logged_broadcast_dest;
 static bool netenv_broadcast_logged;
@@ -191,6 +192,7 @@ HRESULT netenv_hook_init(
     netenv_ip_iface = kc_cfg->subnet | cfg->addr_suffix;
     netenv_ip_router = kc_cfg->subnet | cfg->router_suffix;
     memcpy(netenv_mac_addr, cfg->mac_addr, sizeof(netenv_mac_addr));
+    netenv_redirect_broadcast = cfg->redirect_broadcast;
 
     netenv_hook_apply_hooks(NULL);
 
@@ -570,6 +572,10 @@ static int WINAPI hook_sendto(
 
     const struct sockaddr_in* original_to = (struct sockaddr_in*)to;
 
+    if (!netenv_redirect_broadcast) {
+        return next_sendto(s, buf, len, flags, to, tolen);
+    }
+
     uint32_t bc_addr = _byteswap_ulong(netenv_ip_prefix | 0xFF);
 
     if (original_to->sin_addr.S_un.S_addr == bc_addr) {

common/platform/netenv.h

@@ -9,6 +9,7 @@
 
 struct netenv_config {
     bool enable;
+    bool redirect_broadcast;
     uint8_t addr_suffix;
     uint8_t router_suffix;
     uint8_t mac_addr[6];

doc/config/common.md

@@ -589,6 +589,14 @@ Default: `01:02:03:04:05:06`
 The MAC address of the virtualized Ethernet adapter. The exact value shouldn't
 ever matter.
 
+### `redirectBroadcast`
+
+Default: `1`
+
+Redirect UDP packets sent to the virtual keychip subnet's broadcast address to
+the address configured by `broadcast`. Disable this if you want to preserve the
+original subnet-local broadcast destination.
+
 ### `broadcast`
 
 Default: `255.255.255.255`