Just use raw sockets for listening to DHCP requests. A UDP SO_BROADCAST

socket was previously used only for receiving RENEWING packets, and it
added needless complexity and was somewhat fragile.

src/arp.c

@@ -447,7 +447,7 @@ void arp_success(struct client_state_t *cs)
         cs->routerAddr = get_option_router(&garp.dhcp_packet);
         arp_get_gw_hwaddr(cs);
     }
-    set_listen_none(cs);
+    stop_dhcp_listen(cs);
     write_leasefile(temp_addr);
     arp_announcement(cs);
     if (client_config.quit_after_lease)

src/dhcp.c

@@ -48,12 +48,6 @@
 #include "options.h"
 #include "sockd.h"
 
-typedef enum {
-    LM_NONE = 0,
-    LM_COOKED,
-    LM_RAW
-} listen_mode_t;
-
 static int get_udp_unicast_socket(struct client_state_t *cs)
 {
     char buf[32];
@@ -67,11 +61,6 @@ static int get_raw_broadcast_socket(void)
     return request_sockd_fd("s", 1, NULL);
 }
 
-static int get_udp_listen_socket(void)
-{
-    return request_sockd_fd("U", 1, NULL);
-}
-
 static int get_raw_listen_socket(struct client_state_t *cs)
 {
     char resp;
@@ -85,8 +74,8 @@ static int get_raw_listen_socket(struct client_state_t *cs)
     return fd;
 }
 
-// Broadcast a DHCP message using a UDP socket.
+// Unicast a DHCP message using a UDP socket.
-static ssize_t send_dhcp_cooked(struct client_state_t *cs,
+static ssize_t send_dhcp_unicast(struct client_state_t *cs,
                                  struct dhcpmsg *payload)
 {
     ssize_t ret = -1;
@@ -127,23 +116,6 @@ static ssize_t send_dhcp_cooked(struct client_state_t *cs,
     return ret;
 }
 
-// Read a packet from a cooked socket.  Returns -1 on fatal error, -2 on
-// transient error.
-static ssize_t get_cooked_packet(struct client_state_t *cs,
-                                 struct dhcpmsg *packet)
-{
-    memset(packet, 0, sizeof *packet);
-    ssize_t bytes = safe_read(cs->listenFd, (char *)packet, sizeof *packet);
-    if (bytes < 0) {
-        if (errno == EAGAIN || errno == EWOULDBLOCK)
-            return -2;
-        log_warning("%s: (%s) read error %s", client_config.interface,
-                    __func__, strerror(errno));
-        return -1;
-    }
-    return bytes;
-}
-
 // When summing ones-complement 16-bit values using a 32-bit unsigned
 // representation, fold the carry bits that have spilled into the upper
 // 16-bits of the 32-bit unsigned value back into the 16-bit ones-complement
@@ -352,39 +324,24 @@ static ssize_t send_dhcp_raw(struct dhcpmsg *payload)
     return ret;
 }
 
-// Switch listen socket between raw (if-bound), kernel (ip-bound), and none
+void start_dhcp_listen(struct client_state_t *cs)
-static void change_listen_mode(struct client_state_t *cs, int new_mode)
 {
-    cs->listenMode = new_mode;
+    if (cs->listenFd >= 0)
-    if (cs->listenFd >= 0) {
+        return;
-        epoll_del(cs->epollFd, cs->listenFd);
+    cs->listenFd = get_raw_listen_socket(cs);
-        close(cs->listenFd);
-        cs->listenFd = -1;
-    }
-    switch (cs->listenMode) {
-    default: return;
-    case LM_RAW: cs->listenFd = get_raw_listen_socket(cs); break;
-    case LM_COOKED: cs->listenFd = get_udp_listen_socket(); break;
-    }
     if (cs->listenFd < 0)
         suicide("%s: FATAL: Couldn't listen on socket: %s",
                 client_config.interface, strerror(errno));
     epoll_add(cs->epollFd, cs->listenFd);
 }
 
-void set_listen_raw(struct client_state_t *cs)
+void stop_dhcp_listen(struct client_state_t *cs)
 {
-    change_listen_mode(cs, LM_RAW);
+    if (cs->listenFd < 0)
-}
+        return;
-
+    epoll_del(cs->epollFd, cs->listenFd);
-void set_listen_cooked(struct client_state_t *cs)
+    close(cs->listenFd);
-{
+    cs->listenFd = -1;
-    change_listen_mode(cs, LM_COOKED);
-}
-
-void set_listen_none(struct client_state_t *cs)
-{
-    change_listen_mode(cs, LM_NONE);
 }
 
 static int validate_dhcp_packet(struct client_state_t *cs, size_t len,
@@ -436,19 +393,17 @@ static int validate_dhcp_packet(struct client_state_t *cs, size_t len,
 
 void handle_packet(struct client_state_t *cs)
 {
+    if (cs->listenFd < 0)
+        return;
     struct dhcpmsg packet;
-    ssize_t r;
+    ssize_t r = get_raw_packet(cs, &packet);
-    switch (cs->listenMode) {
-    case LM_RAW: r = get_raw_packet(cs, &packet); break;
-    case LM_COOKED: r = get_cooked_packet(cs, &packet); break;
-    default: return;
-    }
     if (r < 0) {
         // Not a transient issue handled by packet collection functions.
         if (r != -2) {
             log_error("%s: Error reading from listening socket: %s.  Reopening.",
                       client_config.interface, strerror(errno));
-            change_listen_mode(cs, cs->listenMode);
+            stop_dhcp_listen(cs);
+            start_dhcp_listen(cs);
         }
         return;
     }
@@ -515,7 +470,7 @@ ssize_t send_renew(struct client_state_t *cs)
     add_option_vendor(&packet);
     add_option_hostname(&packet);
     log_line("%s: Sending a renew request...", client_config.interface);
-    return send_dhcp_cooked(cs, &packet);
+    return send_dhcp_unicast(cs, &packet);
 }
 
 ssize_t send_rebind(struct client_state_t *cs)
@@ -548,6 +503,6 @@ ssize_t send_release(struct client_state_t *cs)
     add_option_reqip(&packet, cs->clientAddr);
     add_option_serverid(&packet, cs->serverAddr);
     log_line("%s: Sending a release message...", client_config.interface);
-    return send_dhcp_cooked(cs, &packet);
+    return send_dhcp_unicast(cs, &packet);
 }
 

src/dhcp.h

@@ -81,9 +81,8 @@ struct udp_dhcp_packet {
     struct dhcpmsg data;
 };
 
-void set_listen_raw(struct client_state_t *cs);
+void start_dhcp_listen(struct client_state_t *cs);
-void set_listen_cooked(struct client_state_t *cs);
+void stop_dhcp_listen(struct client_state_t *cs);
-void set_listen_none(struct client_state_t *cs);
 void handle_packet(struct client_state_t *cs);
 ssize_t send_discover(struct client_state_t *cs);
 ssize_t send_selecting(struct client_state_t *cs);

src/ndhc.c

@@ -295,7 +295,7 @@ static void do_ndhc_work(void)
     epoll_add(cs.epollFd, ifchSock[0]);
     epoll_add(cs.epollFd, ifchStream[0]);
     epoll_add(cs.epollFd, sockdStream[0]);
-    set_listen_raw(&cs);
+    start_dhcp_listen(&cs);
     nowts = curms();
     goto jumpstart;
 

src/ndhc.h

@@ -40,7 +40,6 @@ struct client_state_t {
     int ifsPrevState;
     int ifchWorking; // ifch is performing interface changes.
     int ifDeconfig; // Set if the interface has already been deconfigured.
-    int listenMode;
     int epollFd, signalFd, listenFd, arpFd, nlFd;
     int nlPortId;
     uint32_t clientAddr, serverAddr, routerAddr;

src/sockd.c

@@ -245,30 +245,6 @@ out:
     return -1;
 }
 
-// Returns fd of new listen socket bound to 0.0.0.0:@68 on interface @inf
-// on success, or -1 on failure.
-static int create_udp_listen_socket(void)
-{
-    int fd = create_udp_socket(INADDR_ANY, DHCP_CLIENT_PORT,
-                               client_config.interface);
-    if (fd < 0)
-        return -1;
-    int opt = 1;
-    if (setsockopt(fd, SOL_SOCKET, SO_BROADCAST, &opt, sizeof opt) < 0) {
-        log_error("%s: (%s) Set broadcast failed: %s",
-                  client_config.interface, __func__, strerror(errno));
-        close(fd);
-        return -1;
-    }
-    return fd;
-}
-
-static int create_udp_send_socket(uint32_t client_addr)
-{
-    return create_udp_socket(client_addr, DHCP_CLIENT_PORT,
-                             client_config.interface);
-}
-
 static int create_raw_listen_socket(bool *using_bpf)
 {
     static const struct sock_filter sf_dhcp[] = {
@@ -478,7 +454,6 @@ static size_t execute_sockd(char *buf, size_t buflen)
         xfer_fd(fd, using_bpf ? 'L' : 'l');
         return 1;
     }
-    case 'U': xfer_fd(create_udp_listen_socket(), 'U'); return 1;
     case 'a': {
         bool using_bpf;
         int fd = create_arp_basic_socket(&using_bpf);
@@ -505,7 +480,8 @@ static size_t execute_sockd(char *buf, size_t buflen)
             suicide("%s: (%s) 'u' does not have necessary arguments: %zu",
                       client_config.interface, __func__, buflen);
         memcpy(&client_addr, buf + 1, sizeof client_addr);
-        xfer_fd(create_udp_send_socket(client_addr), 'u');
+        xfer_fd(create_udp_socket(client_addr, DHCP_CLIENT_PORT,
+                                  client_config.interface), 'u');
         return 5;
     }
     default: suicide("%s: (%s) received invalid commands: '%c'",

src/state.c

@@ -106,7 +106,7 @@ void reinit_selecting(struct client_state_t *cs, int timeout)
     reinit_shared_deconfig(cs);
     cs->dhcpState = DS_SELECTING;
     dhcp_wake_ts = curms() + timeout;
-    set_listen_raw(cs);
+    start_dhcp_listen(cs);
 }
 
 static void set_released(struct client_state_t *cs)
@@ -114,7 +114,7 @@ static void set_released(struct client_state_t *cs)
     reinit_shared_deconfig(cs);
     cs->dhcpState = DS_RELEASED;
     dhcp_wake_ts = -1;
-    set_listen_none(cs);
+    stop_dhcp_listen(cs);
 }
 
 // Triggered after a DHCP lease request packet has been sent and no reply has
@@ -143,7 +143,7 @@ static void bound_timeout(struct client_state_t *cs, long long nowts)
         return;
     }
     cs->dhcpState = DS_RENEWING;
-    set_listen_cooked(cs);
+    start_dhcp_listen(cs);
     renewing_timeout(cs, nowts);
 }
 
@@ -267,7 +267,7 @@ static void an_packet(struct client_state_t *cs, struct dhcpmsg *packet,
                      client_config.interface, cs->lease);
             cs->dhcpState = DS_BOUND;
             arp_set_defense_mode(cs);
-            set_listen_none(cs);
+            stop_dhcp_listen(cs);
         }
 
     } else if (msgtype == DHCPNAK) {
@@ -358,7 +358,7 @@ static void frenew(struct client_state_t *cs)
     if (cs->dhcpState == DS_BOUND) {
         log_line("%s: Forcing a DHCP renew...", client_config.interface);
         cs->dhcpState = DS_RENEWING;
-        set_listen_cooked(cs);
+        start_dhcp_listen(cs);
         if (send_renew(cs) < 0)
             log_warning("%s: Failed to send a renew request packet.",
                         client_config.interface);