dhcp: Add option to bind the receive socket to a different interface

This can be useful if the DHCP server runs on the same server. On Linux,
the response is then sent via `lo`, so packets won't be received if both
sockets are bound to e.g. a bridge interface.

diff --git a/conf/plugins/dhcp.opt b/conf/plugins/dhcp.opt
index 7c6d31c879cba0dfdc54ee69a0898fddc59a6430..ecc6537dcd03ee7bf8680fadb3cfffd320d41e54 100644 (file)
--- a/conf/plugins/dhcp.opt
+++ b/conf/plugins/dhcp.opt
@@ -36,3 +36,13 @@ charon.plugins.dhcp.interface
        Interface name the plugin uses for address allocation. The default is to
        bind to any (0.0.0.0) and let the system decide which way to route the
        packets to the DHCP server.
+
+charon.plugins.dhcp.interface_receive = charon.plugins.dhcp.interface
+       Interface name the plugin uses to bind its receive socket.
+
+       Interface name the plugin uses to bind its receive socket. The default is
+       to use the same interface as the send socket. Set it to the empty string
+       to avoid binding the receive socket to any interface while the send socket
+       is bound to one. If the server runs on the same host and the send socket is
+       bound to an interface, it might be necessary to set this to `lo` or the
+       empty string.

diff --git a/src/libcharon/plugins/dhcp/dhcp_socket.c b/src/libcharon/plugins/dhcp/dhcp_socket.c
index d144e27959415b068b1334d1edc5281141ac5934..ae4952f2426c725c645dd35d4ee77e377f9a8b7a 100644 (file)
--- a/src/libcharon/plugins/dhcp/dhcp_socket.c
+++ b/src/libcharon/plugins/dhcp/dhcp_socket.c
@@ -716,7 +716,7 @@ dhcp_socket_t *dhcp_socket_create()
                },
        };
        socklen_t addr_len;
-       char *iface;
+       char *iface, *iface_receive;
        int on = 1, rcvbuf = 0;
 
 #if !defined(__APPLE__) && !defined(__FreeBSD__)
@@ -809,8 +809,11 @@ dhcp_socket_t *dhcp_socket_create()
        this->dst = host_create_from_string(lib->settings->get_str(lib->settings,
                                                                "%s.plugins.dhcp.server", "255.255.255.255",
                                                                lib->ns), DHCP_SERVER_PORT);
-       iface = lib->settings->get_str(lib->settings, "%s.plugins.dhcp.interface",
-                                                                  NULL, lib->ns);
+       iface = lib->settings->get_str(lib->settings,
+                                                               "%s.plugins.dhcp.interface", NULL, lib->ns);
+       iface_receive = lib->settings->get_str(lib->settings,
+                                                               "%s.plugins.dhcp.interface_receive", NULL,
+                                                               lib->ns) ?: iface;
        if (!this->dst)
        {
                DBG1(DBG_CFG, "configured DHCP server address invalid");
@@ -873,8 +876,8 @@ dhcp_socket_t *dhcp_socket_create()
                return NULL;
        }
 
-       this->pf_handler = pf_handler_create("DHCP", iface, receive_dhcp, this,
-                                                                                &dhcp_filter);
+       this->pf_handler = pf_handler_create("DHCP", iface_receive, receive_dhcp,
+                                                                                this, &dhcp_filter);
        if (!this->pf_handler)
        {
                destroy(this);