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>
diff --git a/networking/udhcp/dhcprelay.c b/networking/udhcp/dhcprelay.c
index a2c7f35..759a4ba 100644
--- a/networking/udhcp/dhcprelay.c
+++ b/networking/udhcp/dhcprelay.c
@@ -11,9 +11,12 @@
*/
#include "common.h"
-#define SERVER_PORT 67
-#define SELECT_TIMEOUT 5 /* select timeout in sec. */
-#define MAX_LIFETIME 2*60 /* lifetime of an xid entry in sec. */
+#define SERVER_PORT 67
+
+/* lifetime of an xid entry in sec. */
+#define MAX_LIFETIME 2*60
+/* select timeout in sec. */
+#define SELECT_TIMEOUT (MAX_LIFETIME / 8)
/* This list holds information about clients. The xid_* functions manipulate this list. */
struct xid_item {
@@ -67,11 +70,11 @@
struct xid_item *item = dhcprelay_xid_list.next;
while (item != NULL) {
if (item->xid == xid) {
- return item;
+ break;
}
item = item->next;
}
- return NULL;
+ return item;
}
static void xid_del(uint32_t xid)
@@ -110,62 +113,72 @@
}
/**
- * get_client_devices - parses the devices list
- * dev_list - comma separated list of devices
+ * make_iface_list - parses client/server interface names
* returns array
*/
-static char **get_client_devices(char *dev_list, int *client_number)
+static char **make_iface_list(char **client_and_server_ifaces, int *client_number)
{
- char *s, **client_dev;
+ char *s, **iface_list;
int i, cn;
- /* copy list */
- dev_list = xstrdup(dev_list);
-
- /* get number of items, replace ',' with NULs */
- s = dev_list;
- cn = 1;
+ /* get number of items */
+ cn = 2; /* 1 server iface + at least 1 client one */
+ s = client_and_server_ifaces[0]; /* list of client ifaces */
while (*s) {
- if (*s == ',') {
- *s = '\0';
+ if (*s == ',')
cn++;
- }
s++;
}
*client_number = cn;
/* create vector of pointers */
- client_dev = xzalloc(cn * sizeof(*client_dev));
- client_dev[0] = dev_list;
+ iface_list = xzalloc(cn * sizeof(iface_list[0]));
+
+ iface_list[0] = client_and_server_ifaces[1]; /* server iface */
+
i = 1;
- while (i != cn) {
- client_dev[i] = client_dev[i - 1] + strlen(client_dev[i - 1]) + 1;
- i++;
+ s = xstrdup(client_and_server_ifaces[0]); /* list of client ifaces */
+ goto store_client_iface_name;
+
+ while (i < cn) {
+ if (*s++ == ',') {
+ s[-1] = '\0';
+ store_client_iface_name:
+ iface_list[i++] = s;
+ }
}
- return client_dev;
+
+ return iface_list;
}
/* Creates listen sockets (in fds) bound to client and server ifaces,
* and returns numerically max fd.
*/
-static int init_sockets(char **client_ifaces, int num_clients,
- char *server_iface, int *fds)
+static int init_sockets(char **iface_list, int num_clients, int *fds)
{
int i, n;
- /* talk to real server on bootps */
- fds[0] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, server_iface);
- n = fds[0];
-
- for (i = 1; i < num_clients; i++) {
- /* listen for clients on bootps */
- fds[i] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, client_ifaces[i-1]);
- if (fds[i] > n)
+ n = 0;
+ for (i = 0; i < num_clients; i++) {
+ fds[i] = udhcp_listen_socket(/*INADDR_ANY,*/ SERVER_PORT, iface_list[i]);
+ if (n < fds[i])
n = fds[i];
}
return n;
}
+static int sendto_ip4(int sock, const void *msg, int msg_len, struct sockaddr_in *to)
+{
+ int err;
+
+ errno = 0;
+ err = sendto(sock, msg, msg_len, 0, (struct sockaddr*) to, sizeof(*to));
+ err -= msg_len;
+ if (err)
+ bb_perror_msg("sendto");
+ return err;
+}
+
/**
* pass_to_server() - forwards dhcp packets from client to server
* p - packet to send
@@ -174,7 +187,7 @@
static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, int *fds,
struct sockaddr_in *client_addr, struct sockaddr_in *server_addr)
{
- int res, type;
+ int type;
/* check packet_type */
type = get_dhcp_packet_type(p);
@@ -188,13 +201,12 @@
/* create new xid entry */
xid_add(p->xid, client_addr, client);
- /* forward request to LAN (server) */
- errno = 0;
- res = sendto(fds[0], p, packet_len, 0, (struct sockaddr*)server_addr,
- sizeof(struct sockaddr_in));
- if (res != packet_len) {
- bb_perror_msg("sendto");
- }
+ /* forward request to server */
+ /* note that we send from fds[0] which is bound to SERVER_PORT (67).
+ * IOW: we send _from_ SERVER_PORT! Although this may look strange,
+ * RFC 1542 not only allows, but prescribes this for BOOTP relays.
+ */
+ sendto_ip4(fds[0], p, packet_len, server_addr);
}
/**
@@ -203,7 +215,7 @@
*/
static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds)
{
- int res, type;
+ int type;
struct xid_item *item;
/* check xid */
@@ -218,14 +230,12 @@
return;
}
+//TODO: also do it if (p->flags & htons(BROADCAST_FLAG)) is set!
if (item->ip.sin_addr.s_addr == htonl(INADDR_ANY))
item->ip.sin_addr.s_addr = htonl(INADDR_BROADCAST);
- errno = 0;
- res = sendto(fds[item->client], p, packet_len, 0, (struct sockaddr*) &(item->ip),
- sizeof(item->ip));
- if (res != packet_len) {
- bb_perror_msg("sendto");
- return;
+
+ if (sendto_ip4(fds[item->client], p, packet_len, &item->ip) != 0) {
+ return; /* send error occurred */
}
/* remove xid entry */
@@ -235,36 +245,30 @@
int dhcprelay_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int dhcprelay_main(int argc, char **argv)
{
- struct dhcp_packet dhcp_msg;
struct sockaddr_in server_addr;
- struct sockaddr_in client_addr;
- fd_set rfds;
- char **client_ifaces;
+ char **iface_list;
int *fds;
int num_sockets, max_socket;
uint32_t our_nip;
server_addr.sin_family = AF_INET;
+ server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
server_addr.sin_port = htons(SERVER_PORT);
- /* dhcprelay client_iface1,client_iface2,... server_iface [server_IP] */
+ /* dhcprelay CLIENT_IFACE1[,CLIENT_IFACE2...] SERVER_IFACE [SERVER_IP] */
if (argc == 4) {
if (!inet_aton(argv[3], &server_addr.sin_addr))
bb_perror_msg_and_die("bad server IP");
- } else if (argc == 3) {
- server_addr.sin_addr.s_addr = htonl(INADDR_BROADCAST);
- } else {
+ } else if (argc != 3) {
bb_show_usage();
}
- /* Produce list of client ifaces */
- client_ifaces = get_client_devices(argv[1], &num_sockets);
+ iface_list = make_iface_list(argv + 1, &num_sockets);
- num_sockets++; /* for server socket at fds[0] */
fds = xmalloc(num_sockets * sizeof(fds[0]));
/* Create sockets and bind one to every iface */
- max_socket = init_sockets(client_ifaces, num_sockets, argv[2], fds);
+ max_socket = init_sockets(iface_list, num_sockets, fds);
/* Get our IP on server_iface */
if (udhcp_read_interface(argv[2], NULL, &our_nip, NULL))
@@ -272,11 +276,10 @@
/* Main loop */
while (1) {
-//reinit stuff from time to time? go back to get_client_devices
-//every N minutes?
+// reinit stuff from time to time? go back to make_iface_list
+// every N minutes?
+ fd_set rfds;
struct timeval tv;
- size_t packlen;
- socklen_t addr_size;
int i;
FD_ZERO(&rfds);
@@ -285,6 +288,9 @@
tv.tv_sec = SELECT_TIMEOUT;
tv.tv_usec = 0;
if (select(max_socket + 1, &rfds, NULL, NULL, &tv) > 0) {
+ int packlen;
+ struct dhcp_packet dhcp_msg;
+
/* server */
if (FD_ISSET(fds[0], &rfds)) {
packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]);
@@ -292,24 +298,65 @@
pass_to_client(&dhcp_msg, packlen, fds);
}
}
+
/* clients */
for (i = 1; i < num_sockets; i++) {
+ struct sockaddr_in client_addr;
+ socklen_t addr_size;
+
if (!FD_ISSET(fds[i], &rfds))
continue;
- addr_size = sizeof(struct sockaddr_in);
+
+ addr_size = sizeof(client_addr);
packlen = recvfrom(fds[i], &dhcp_msg, sizeof(dhcp_msg), 0,
(struct sockaddr *)(&client_addr), &addr_size);
if (packlen <= 0)
continue;
/* Get our IP on corresponding client_iface */
-//why? what if server can't route such IP?
- if (udhcp_read_interface(client_ifaces[i-1], NULL, &dhcp_msg.gateway_nip, NULL)) {
- /* Fall back to our server_iface's IP */
-//this makes more sense!
+// RFC 1542
+// 4.1 General BOOTP Processing for Relay Agents
+// 4.1.1 BOOTREQUEST Messages
+// If the relay agent does decide to relay the request, it MUST examine
+// the 'giaddr' ("gateway" IP address) field. If this field is zero,
+// the relay agent MUST fill this field with the IP address of the
+// interface on which the request was received. If the interface has
+// more than one IP address logically associated with it, the relay
+// agent SHOULD choose one IP address associated with that interface and
+// use it consistently for all BOOTP messages it relays. If the
+// 'giaddr' field contains some non-zero value, the 'giaddr' field MUST
+// NOT be modified. The relay agent MUST NOT, under any circumstances,
+// fill the 'giaddr' field with a broadcast address as is suggested in
+// [1] (Section 8, sixth paragraph).
+
+// but why? what if server can't route such IP? Client ifaces may be, say, NATed!
+
+// 4.1.2 BOOTREPLY Messages
+// BOOTP relay agents relay BOOTREPLY messages only to BOOTP clients.
+// It is the responsibility of BOOTP servers to send BOOTREPLY messages
+// directly to the relay agent identified in the 'giaddr' field.
+// (yeah right, unless it is impossible... see comment above)
+// Therefore, a relay agent may assume that all BOOTREPLY messages it
+// receives are intended for BOOTP clients on its directly-connected
+// networks.
+//
+// When a relay agent receives a BOOTREPLY message, it should examine
+// the BOOTP 'giaddr', 'yiaddr', 'chaddr', 'htype', and 'hlen' fields.
+// These fields should provide adequate information for the relay agent
+// to deliver the BOOTREPLY message to the client.
+//
+// The 'giaddr' field can be used to identify the logical interface from
+// which the reply must be sent (i.e., the host or router interface
+// connected to the same network as the BOOTP client). If the content
+// of the 'giaddr' field does not match one of the relay agent's
+// directly-connected logical interfaces, the BOOTREPLY messsage MUST be
+// silently discarded.
+ if (udhcp_read_interface(iface_list[i], NULL, &dhcp_msg.gateway_nip, NULL)) {
+ /* Fall back to our IP on server iface */
+// this makes more sense!
dhcp_msg.gateway_nip = our_nip;
}
-//maybe set dhcp_msg.flags |= BROADCAST_FLAG too?
+// maybe dhcp_msg.hops++? drop packets with too many hops (RFC 1542 says 4 or 16)?
pass_to_server(&dhcp_msg, packlen, i, fds, &client_addr, &server_addr);
}
}