dhcprelay: code shrink, and explain its workings a bit more
function old new delta sendto_ip4 - 55 +55 dhcprelay_main 1059 942 -117 ------------------------------------------------------------------------------ (add/remove: 1/0 grow/shrink: 0/1 up/down: 55/-117) Total: -62 bytes Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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Denys Vlasenko
parent
28458c64db
commit
c0f39b0fb2
@ -11,9 +11,12 @@
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*/
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#include "common.h"
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#define SERVER_PORT 67
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#define SELECT_TIMEOUT 5 /* select timeout in sec. */
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#define MAX_LIFETIME 2*60 /* lifetime of an xid entry in sec. */
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#define SERVER_PORT 67
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/* lifetime of an xid entry in sec. */
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#define MAX_LIFETIME 2*60
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/* select timeout in sec. */
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#define SELECT_TIMEOUT (MAX_LIFETIME / 8)
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/* This list holds information about clients. The xid_* functions manipulate this list. */
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struct xid_item {
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@ -67,11 +70,11 @@ static struct xid_item *xid_find(uint32_t xid)
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struct xid_item *item = dhcprelay_xid_list.next;
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while (item != NULL) {
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if (item->xid == xid) {
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return item;
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break;
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}
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item = item->next;
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}
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return NULL;
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return item;
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}
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static void xid_del(uint32_t xid)
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@ -110,62 +113,72 @@ static int get_dhcp_packet_type(struct dhcp_packet *p)
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}
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/**
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* get_client_devices - parses the devices list
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* dev_list - comma separated list of devices
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* make_iface_list - parses client/server interface names
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* returns array
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*/
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static char **get_client_devices(char *dev_list, int *client_number)
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static char **make_iface_list(char **client_and_server_ifaces, int *client_number)
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{
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char *s, **client_dev;
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char *s, **iface_list;
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int i, cn;
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/* copy list */
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dev_list = xstrdup(dev_list);
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/* get number of items, replace ',' with NULs */
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s = dev_list;
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cn = 1;
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/* get number of items */
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cn = 2; /* 1 server iface + at least 1 client one */
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s = client_and_server_ifaces[0]; /* list of client ifaces */
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while (*s) {
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if (*s == ',') {
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*s = '\0';
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if (*s == ',')
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cn++;
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}
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s++;
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}
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*client_number = cn;
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/* create vector of pointers */
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client_dev = xzalloc(cn * sizeof(*client_dev));
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client_dev[0] = dev_list;
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iface_list = xzalloc(cn * sizeof(iface_list[0]));
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iface_list[0] = client_and_server_ifaces[1]; /* server iface */
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i = 1;
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while (i != cn) {
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client_dev[i] = client_dev[i - 1] + strlen(client_dev[i - 1]) + 1;
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i++;
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s = xstrdup(client_and_server_ifaces[0]); /* list of client ifaces */
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goto store_client_iface_name;
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while (i < cn) {
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if (*s++ == ',') {
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s[-1] = '\0';
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store_client_iface_name:
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iface_list[i++] = s;
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}
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}
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return client_dev;
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return iface_list;
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}
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/* Creates listen sockets (in fds) bound to client and server ifaces,
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* and returns numerically max fd.
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*/
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static int init_sockets(char **client_ifaces, int num_clients,
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char *server_iface, int *fds)
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static int init_sockets(char **iface_list, int num_clients, int *fds)
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{
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int i, n;
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/* talk to real server on bootps */
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fds[0] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, server_iface);
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n = fds[0];
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for (i = 1; i < num_clients; i++) {
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/* listen for clients on bootps */
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fds[i] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, client_ifaces[i-1]);
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if (fds[i] > n)
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n = 0;
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for (i = 0; i < num_clients; i++) {
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fds[i] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, iface_list[i]);
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if (n < fds[i])
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n = fds[i];
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}
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return n;
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}
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static int sendto_ip4(int sock, const void *msg, int msg_len, struct sockaddr_in *to)
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{
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int err;
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errno = 0;
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err = sendto(sock, msg, msg_len, 0, (struct sockaddr*) to, sizeof(*to));
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err -= msg_len;
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if (err)
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bb_perror_msg("sendto");
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return err;
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}
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/**
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* pass_to_server() - forwards dhcp packets from client to server
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* p - packet to send
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@ -174,7 +187,7 @@ static int init_sockets(char **client_ifaces, int num_clients,
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static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, int *fds,
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struct sockaddr_in *client_addr, struct sockaddr_in *server_addr)
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{
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int res, type;
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int type;
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/* check packet_type */
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type = get_dhcp_packet_type(p);
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@ -188,13 +201,12 @@ static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, in
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/* create new xid entry */
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xid_add(p->xid, client_addr, client);
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/* forward request to LAN (server) */
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errno = 0;
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res = sendto(fds[0], p, packet_len, 0, (struct sockaddr*)server_addr,
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sizeof(struct sockaddr_in));
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if (res != packet_len) {
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bb_perror_msg("sendto");
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}
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/* forward request to server */
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/* note that we send from fds[0] which is bound to SERVER_PORT (67).
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* IOW: we send _from_ SERVER_PORT! Although this may look strange,
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* RFC 1542 not only allows, but prescribes this for BOOTP relays.
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*/
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sendto_ip4(fds[0], p, packet_len, server_addr);
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}
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/**
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@ -203,7 +215,7 @@ static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, in
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*/
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static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds)
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{
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int res, type;
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int type;
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struct xid_item *item;
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/* check xid */
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@ -218,14 +230,12 @@ static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds)
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return;
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}
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//TODO: also do it if (p->flags & htons(BROADCAST_FLAG)) is set!
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if (item->ip.sin_addr.s_addr == htonl(INADDR_ANY))
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item->ip.sin_addr.s_addr = htonl(INADDR_BROADCAST);
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errno = 0;
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res = sendto(fds[item->client], p, packet_len, 0, (struct sockaddr*) &(item->ip),
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sizeof(item->ip));
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if (res != packet_len) {
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bb_perror_msg("sendto");
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return;
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if (sendto_ip4(fds[item->client], p, packet_len, &item->ip) != 0) {
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return; /* send error occurred */
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}
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/* remove xid entry */
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@ -235,36 +245,30 @@ static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds)
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int dhcprelay_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int dhcprelay_main(int argc, char **argv)
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{
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struct dhcp_packet dhcp_msg;
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struct sockaddr_in server_addr;
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struct sockaddr_in client_addr;
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fd_set rfds;
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char **client_ifaces;
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char **iface_list;
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int *fds;
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int num_sockets, max_socket;
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uint32_t our_nip;
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server_addr.sin_family = AF_INET;
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server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
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server_addr.sin_port = htons(SERVER_PORT);
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/* dhcprelay client_iface1,client_iface2,... server_iface [server_IP] */
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/* dhcprelay CLIENT_IFACE1[,CLIENT_IFACE2...] SERVER_IFACE [SERVER_IP] */
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if (argc == 4) {
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if (!inet_aton(argv[3], &server_addr.sin_addr))
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bb_perror_msg_and_die("bad server IP");
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} else if (argc == 3) {
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server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
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} else {
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} else if (argc != 3) {
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bb_show_usage();
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}
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/* Produce list of client ifaces */
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client_ifaces = get_client_devices(argv[1], &num_sockets);
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iface_list = make_iface_list(argv + 1, &num_sockets);
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num_sockets++; /* for server socket at fds[0] */
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fds = xmalloc(num_sockets * sizeof(fds[0]));
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/* Create sockets and bind one to every iface */
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max_socket = init_sockets(client_ifaces, num_sockets, argv[2], fds);
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max_socket = init_sockets(iface_list, num_sockets, fds);
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/* Get our IP on server_iface */
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if (udhcp_read_interface(argv[2], NULL, &our_nip, NULL))
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@ -272,11 +276,10 @@ int dhcprelay_main(int argc, char **argv)
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/* Main loop */
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while (1) {
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//reinit stuff from time to time? go back to get_client_devices
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//every N minutes?
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// reinit stuff from time to time? go back to make_iface_list
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// every N minutes?
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fd_set rfds;
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struct timeval tv;
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size_t packlen;
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socklen_t addr_size;
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int i;
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FD_ZERO(&rfds);
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@ -285,6 +288,9 @@ int dhcprelay_main(int argc, char **argv)
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tv.tv_sec = SELECT_TIMEOUT;
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tv.tv_usec = 0;
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if (select(max_socket + 1, &rfds, NULL, NULL, &tv) > 0) {
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int packlen;
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struct dhcp_packet dhcp_msg;
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/* server */
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if (FD_ISSET(fds[0], &rfds)) {
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packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]);
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@ -292,24 +298,65 @@ int dhcprelay_main(int argc, char **argv)
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pass_to_client(&dhcp_msg, packlen, fds);
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}
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}
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/* clients */
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for (i = 1; i < num_sockets; i++) {
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struct sockaddr_in client_addr;
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socklen_t addr_size;
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if (!FD_ISSET(fds[i], &rfds))
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continue;
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addr_size = sizeof(struct sockaddr_in);
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addr_size = sizeof(client_addr);
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packlen = recvfrom(fds[i], &dhcp_msg, sizeof(dhcp_msg), 0,
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(struct sockaddr *)(&client_addr), &addr_size);
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if (packlen <= 0)
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continue;
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/* Get our IP on corresponding client_iface */
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//why? what if server can't route such IP?
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if (udhcp_read_interface(client_ifaces[i-1], NULL, &dhcp_msg.gateway_nip, NULL)) {
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/* Fall back to our server_iface's IP */
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//this makes more sense!
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// RFC 1542
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// 4.1 General BOOTP Processing for Relay Agents
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// 4.1.1 BOOTREQUEST Messages
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// If the relay agent does decide to relay the request, it MUST examine
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// the 'giaddr' ("gateway" IP address) field. If this field is zero,
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// the relay agent MUST fill this field with the IP address of the
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// interface on which the request was received. If the interface has
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// more than one IP address logically associated with it, the relay
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// agent SHOULD choose one IP address associated with that interface and
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// use it consistently for all BOOTP messages it relays. If the
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// 'giaddr' field contains some non-zero value, the 'giaddr' field MUST
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// NOT be modified. The relay agent MUST NOT, under any circumstances,
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// fill the 'giaddr' field with a broadcast address as is suggested in
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// [1] (Section 8, sixth paragraph).
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// but why? what if server can't route such IP? Client ifaces may be, say, NATed!
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// 4.1.2 BOOTREPLY Messages
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// BOOTP relay agents relay BOOTREPLY messages only to BOOTP clients.
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// It is the responsibility of BOOTP servers to send BOOTREPLY messages
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// directly to the relay agent identified in the 'giaddr' field.
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// (yeah right, unless it is impossible... see comment above)
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// Therefore, a relay agent may assume that all BOOTREPLY messages it
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// receives are intended for BOOTP clients on its directly-connected
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// networks.
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//
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// When a relay agent receives a BOOTREPLY message, it should examine
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// the BOOTP 'giaddr', 'yiaddr', 'chaddr', 'htype', and 'hlen' fields.
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// These fields should provide adequate information for the relay agent
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// to deliver the BOOTREPLY message to the client.
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//
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// The 'giaddr' field can be used to identify the logical interface from
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// which the reply must be sent (i.e., the host or router interface
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// connected to the same network as the BOOTP client). If the content
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// of the 'giaddr' field does not match one of the relay agent's
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// directly-connected logical interfaces, the BOOTREPLY messsage MUST be
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// silently discarded.
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if (udhcp_read_interface(iface_list[i], NULL, &dhcp_msg.gateway_nip, NULL)) {
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/* Fall back to our IP on server iface */
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// this makes more sense!
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dhcp_msg.gateway_nip = our_nip;
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}
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//maybe set dhcp_msg.flags |= BROADCAST_FLAG too?
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// maybe dhcp_msg.hops++? drop packets with too many hops (RFC 1542 says 4 or 16)?
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pass_to_server(&dhcp_msg, packlen, i, fds, &client_addr, &server_addr);
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}
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}
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