sd-dhcp-server: bind to a given interface

We will (at least at first), restrict our focus to running the server
on at most one interface.

3 files changed, 25 insertions, 2 deletions

diff --git a/src/libsystemd-network/dhcp-server-internal.h b/src/libsystemd-network/dhcp-server-internal.h
index 8191ef7fd7..6484dd37ec 100644
--- a/src/libsystemd-network/dhcp-server-internal.h
+++ b/src/libsystemd-network/dhcp-server-internal.h
@@ -34,6 +34,8 @@ struct sd_dhcp_server {
         int event_priority;
         sd_event_source *receive_message;
         int fd;
+
+        int index;
 };
 
 DEFINE_TRIVIAL_CLEANUP_FUNC(sd_dhcp_server*, sd_dhcp_server_unref);
diff --git a/src/libsystemd-network/sd-dhcp-server.c b/src/libsystemd-network/sd-dhcp-server.c
index a9768f8fa2..e4396a0c96 100644
--- a/src/libsystemd-network/sd-dhcp-server.c
+++ b/src/libsystemd-network/sd-dhcp-server.c
@@ -46,10 +46,11 @@ sd_dhcp_server *sd_dhcp_server_unref(sd_dhcp_server *server) {
         return NULL;
 }
 
-int sd_dhcp_server_new(sd_dhcp_server **ret) {
+int sd_dhcp_server_new(sd_dhcp_server **ret, int ifindex) {
         _cleanup_dhcp_server_unref_ sd_dhcp_server *server = NULL;
 
         assert_return(ret, -EINVAL);
+        assert_return(ifindex > 0, -EINVAL);
 
         server = new0(sd_dhcp_server, 1);
         if (!server)
@@ -57,6 +58,7 @@ int sd_dhcp_server_new(sd_dhcp_server **ret) {
 
         server->n_ref = REFCNT_INIT;
         server->fd = -1;
+        server->index = ifindex;
 
         *ret = server;
         server = NULL;
@@ -113,12 +115,16 @@ int sd_dhcp_server_stop(sd_dhcp_server *server) {
 static int server_receive_message(sd_event_source *s, int fd,
                                   uint32_t revents, void *userdata) {
         _cleanup_free_ uint8_t *message = NULL;
+        uint8_t cmsgbuf[CMSG_LEN(sizeof(struct in_pktinfo))];
         sd_dhcp_server *server = userdata;
         struct iovec iov = {};
         struct msghdr msg = {
                 .msg_iov = &iov,
                 .msg_iovlen = 1,
+                .msg_control = cmsgbuf,
+                .msg_controllen = sizeof(cmsgbuf),
         };
+        struct cmsghdr *cmsg;
         int buflen = 0, len, r;
 
         assert(server);
@@ -140,6 +146,20 @@ static int server_receive_message(sd_event_source *s, int fd,
         if (len < buflen)
                 return 0;
 
+        for (cmsg = CMSG_FIRSTHDR(&msg); cmsg; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+                if (cmsg->cmsg_level == IPPROTO_IP &&
+                    cmsg->cmsg_type == IP_PKTINFO &&
+                    cmsg->cmsg_len == CMSG_LEN(sizeof(struct in_pktinfo))) {
+                        struct in_pktinfo *info = (struct in_pktinfo*)CMSG_DATA(cmsg);
+
+                        /* TODO figure out if this can be done as a filter on the socket, like for IPv6 */
+                        if (server->index != info->ipi_ifindex)
+                                return 0;
+
+                        break;
+                }
+        }
+
         log_dhcp_server(server, "received message");
 
         return 1;
diff --git a/src/libsystemd-network/test-dhcp-server.c b/src/libsystemd-network/test-dhcp-server.c
index 80d2184b70..2feb124036 100644
--- a/src/libsystemd-network/test-dhcp-server.c
+++ b/src/libsystemd-network/test-dhcp-server.c
@@ -32,7 +32,8 @@
 static void test_basic(sd_event *event) {
         _cleanup_dhcp_server_unref_ sd_dhcp_server *server = NULL;
 
-        assert_se(sd_dhcp_server_new(&server) >= 0);
+        /* attach to loopback interface */
+        assert_se(sd_dhcp_server_new(&server, 1) >= 0);
         assert_se(server);
 
         assert_se(sd_dhcp_server_attach_event(server, event, 0) >= 0);