dhcpv4: offer a valid configuration with DHCP NAK
[project/odhcpd.git] / src / dhcpv4.c
index 62ddab8..0d75730 100644 (file)
@@ -20,6 +20,7 @@
 #include <stddef.h>
 #include <stdlib.h>
 #include <resolv.h>
+#include <limits.h>
 #include <net/if.h>
 #include <net/if_arp.h>
 #include <netinet/ip.h>
@@ -33,7 +34,7 @@
 
 
 static void handle_dhcpv4(void *addr, void *data, size_t len,
-               struct interface *iface);
+               struct interface *iface, void *dest_addr);
 static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
                enum dhcpv4_msg msg, const uint8_t *mac, struct in_addr reqaddr,
                const char *hostname);
@@ -155,17 +156,22 @@ int setup_dhcpv4_interface(struct interface *iface, bool enable)
                        a->addr = ntohl(lease->ipaddr.s_addr);
                        memcpy(a->hwaddr, lease->mac.ether_addr_octet, sizeof(a->hwaddr));
                        memcpy(a->hostname, lease->hostname, hostlen);
+                       a->valid_until = LONG_MAX;
 
                        // Assign to all interfaces
                        struct dhcpv4_assignment *c;
                        list_for_each_entry(c, &iface->dhcpv4_assignments, head) {
                                if (c->addr > a->addr) {
                                        list_add_tail(&a->head, &c->head);
+                                       break;
                                } else if (c->addr == a->addr) {
                                        // Already an assignment with that number
                                        break;
                                }
                        }
+                       if (&c->head == &iface->dhcpv4_assignments) {
+                               list_add(&a->head, &iface->dhcpv4_assignments);
+                       }
 
                        if (!a->head.next)
                                free(a);
@@ -175,7 +181,7 @@ int setup_dhcpv4_interface(struct interface *iface, bool enable)
                struct dhcpv4_assignment *a, *n;
                list_for_each_entry_safe(a, n, &iface->dhcpv4_assignments, head) {
                        if ((htonl(a->addr) & smask->sin_addr.s_addr) !=
-                                       (saddr->sin_addr.s_addr & smask->sin_addr.s_addr)) {
+                                       (iface->dhcpv4_start.s_addr & smask->sin_addr.s_addr)) {
                                list_del(&a->head);
                                free(a);
                        }
@@ -219,7 +225,7 @@ static void dhcpv4_put(struct dhcpv4_message *msg, uint8_t **cookie,
 
 // Simple DHCPv6-server for information requests
 static void handle_dhcpv4(void *addr, void *data, size_t len,
-               struct interface *iface)
+               struct interface *iface, _unused void *dest_addr)
 {
        if (!iface->dhcpv4)
                return;
@@ -325,6 +331,19 @@ static void handle_dhcpv4(void *addr, void *data, size_t len,
                        return;
        } else if (reqmsg == DHCPV4_MSG_DISCOVER) {
                msg = DHCPV4_MSG_OFFER;
+       } else if (reqmsg == DHCPV4_MSG_REQUEST && reqaddr.s_addr &&
+                       reqaddr.s_addr != htonl(lease->addr)) {
+               msg = DHCPV4_MSG_NAK;
+               /*
+                * DHCP client requested an IP which we can't offer to him. Probably the
+                * client changed the network. The reply type is set to DHCPV4_MSG_NAK,
+                * because the client should not use that IP.
+                *
+                * For modern devices we build an answer that includes a valid IP, like
+                * a DHCPV4_MSG_ACK. The client will use that IP and doesn't need to
+                * perform additional DHCP round trips.
+                *
+                */
        }
 
        if (reqmsg == DHCPV4_MSG_DECLINE || reqmsg == DHCPV4_MSG_RELEASE)
@@ -395,7 +414,7 @@ static void handle_dhcpv4(void *addr, void *data, size_t len,
                dest.sin_addr = req->ciaddr;
                dest.sin_port = htons(DHCPV4_CLIENT_PORT);
        } else if ((ntohs(req->flags) & DHCPV4_FLAG_BROADCAST) ||
-                       req->hlen != reply.hlen) {
+                       req->hlen != reply.hlen || !reply.yiaddr.s_addr) {
                dest.sin_addr.s_addr = INADDR_BROADCAST;
                dest.sin_port = htons(DHCPV4_CLIENT_PORT);
        } else {
@@ -471,16 +490,16 @@ static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
 
        struct dhcpv4_assignment *c, *n, *a = NULL;
        list_for_each_entry_safe(c, n, &iface->dhcpv4_assignments, head) {
-               if (c->addr == raddr && !memcmp(c->hwaddr, mac, 6)) {
+               if (!memcmp(c->hwaddr, mac, 6)) {
                        a = c;
-                       break;
+                       if (c->addr == raddr)
+                               break;
                } else if (c->valid_until < now) {
                        list_del(&c->head);
                        free(c);
                }
        }
 
-       bool update_state = false;
        if (msg == DHCPV4_MSG_DISCOVER || msg == DHCPV4_MSG_REQUEST) {
                bool assigned = !!a;
                size_t hostlen = strlen(hostname) + 1;
@@ -519,24 +538,18 @@ static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
                        a = NULL;
                }
 
-               if (a)
-                       update_state = true;
-
                if (assigned && a)
                        lease = a;
        } else if (msg == DHCPV4_MSG_RELEASE) {
                if (a) {
                        a->valid_until = 0;
-                       update_state = true;
                }
        } else if (msg == DHCPV4_MSG_DECLINE) {
                memset(a->hwaddr, 0, sizeof(a->hwaddr));
                a->valid_until = now + 3600; // Block address for 1h
-               update_state = true;
        }
 
-       if (update_state)
-               dhcpv6_write_statefile();
+       dhcpv6_write_statefile();
 
        return lease;
 }