4 files changed, 23 insertions, 4 deletions

diff --git a/networking/udhcp/common.h b/networking/udhcp/common.h
index 3cbd2d3c8..cc0abd269 100644
--- a/networking/udhcp/common.h
+++ b/networking/udhcp/common.h
@@ -343,7 +343,8 @@ int udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
 
 int udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
                 uint32_t source_nip, int source_port,
-                uint32_t dest_nip, int dest_port) FAST_FUNC;
+                uint32_t dest_nip, int dest_port,
+                const char *ifname) FAST_FUNC;
 
 void udhcp_sp_setup(void) FAST_FUNC;
 void udhcp_sp_fd_set(struct pollfd *pfds, int extra_fd) FAST_FUNC;
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 66aa38c20..98720b45b 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -702,7 +702,8 @@ static int bcast_or_ucast(struct dhcp_packet *packet, uint32_t ciaddr, uint32_t
         if (server)
                 return udhcp_send_kernel_packet(packet,
                         ciaddr, CLIENT_PORT,
-                        server, SERVER_PORT);
+                        server, SERVER_PORT,
+                        client_data.interface);
         return raw_bcast_from_client_data_ifindex(packet, ciaddr);
 }
 
diff --git a/networking/udhcp/dhcpd.c b/networking/udhcp/dhcpd.c
index de16cf955..9e950ca1f 100644
--- a/networking/udhcp/dhcpd.c
+++ b/networking/udhcp/dhcpd.c
@@ -612,7 +612,8 @@ static void send_packet_to_relay(struct dhcp_packet *dhcp_pkt)
 
         udhcp_send_kernel_packet(dhcp_pkt,
                         server_data.server_nip, SERVER_PORT,
-                        dhcp_pkt->gateway_nip, SERVER_PORT);
+                        dhcp_pkt->gateway_nip, SERVER_PORT,
+                        server_data.interface);
 }
 
 static void send_packet(struct dhcp_packet *dhcp_pkt, int force_broadcast)
diff --git a/networking/udhcp/packet.c b/networking/udhcp/packet.c
index 51374646d..4d8e005d4 100644
--- a/networking/udhcp/packet.c
+++ b/networking/udhcp/packet.c
@@ -189,7 +189,8 @@ int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
 /* Let the kernel do all the work for packet generation */
 int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
                 uint32_t source_nip, int source_port,
-                uint32_t dest_nip, int dest_port)
+                uint32_t dest_nip, int dest_port,
+                const char *ifname)
 {
         struct sockaddr_in sa;
         unsigned padding;
@@ -204,6 +205,21 @@ int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
         }
         setsockopt_reuseaddr(fd);
 
+        /* If interface carrier goes down, unless we
+         * bind socket to a particular netdev, the packet
+         * can go out through another interface, eg. via
+         * default route despite being bound to a specific
+         * source IP. As such, bind to device hard and fail
+         * otherwise. Sending renewal packets on foreign
+         * interfaces makes no sense.
+         */
+        if (ifname) {
+                if (setsockopt_bindtodevice(fd, ifname) < 0) {
+                        msg = "bindtodevice";
+                        goto ret_close;
+                }
+        }
+
         memset(&sa, 0, sizeof(sa));
         sa.sin_family = AF_INET;
         sa.sin_port = htons(source_port);