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3f2d969db

Denys Vlasenko
Denys Vlasenko
2021-09-02
SUCCESS Duration: 152s

Subject

udhcp: clarify aspects of relay operation, add TODOs and FIXMEs, tweak --help

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Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

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Commit Diff GitHub →

networking/udhcp/dhcpd.c +7 -0networking/udhcp/dhcprelay.c +39 -22
networking/udhcp/dhcpd.c+7 -0
@@ -614,6 +614,10 @@ 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,
+ /* Yes, relay agents receive (and send) all their packets on SERVER_PORT,
+ * even those which are clients' requests and would normally
+ * (i.e. without relay) use CLIENT_PORT. See RFC 1542.
+ */
server_data.interface);
}
@@ -1025,6 +1029,9 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
* socket read inside this call is restarted on caught signals.
*/
bytes = udhcp_recv_kernel_packet(&packet, server_socket);
+//NB: we do not check source port here. Should we?
+//It should be CLIENT_PORT for clients,
+//or SERVER_PORT for relay agents (in which case giaddr must be != 0.0.0.0)
if (bytes < 0) {
/* bytes can also be -2 ("bad packet data") */
if (bytes == -1 && errno != EINTR) {
networking/udhcp/dhcprelay.c+39 -22
@@ -17,7 +17,8 @@
//usage:#define dhcprelay_trivial_usage
//usage: "CLIENT_IFACE[,CLIENT_IFACE2]... SERVER_IFACE [SERVER_IP]"
//usage:#define dhcprelay_full_usage "\n\n"
-//usage: "Relay DHCP requests between clients and server"
+//usage: "Relay DHCP requests between clients and server.\n"
+//usage: "Without SERVER_IP, requests are broadcast on SERVER_IFACE."
#include "common.h"
@@ -31,7 +32,7 @@
/* This list holds information about clients. The xid_* functions manipulate this list. */
struct xid_item {
unsigned timestamp;
- int client;
+ unsigned iface_no;
uint32_t xid;
struct sockaddr_in ip;
struct xid_item *next;
@@ -40,7 +41,7 @@ struct xid_item {
#define dhcprelay_xid_list (*(struct xid_item*)bb_common_bufsiz1)
#define INIT_G() do { setup_common_bufsiz(); } while (0)
-static struct xid_item *xid_add(uint32_t xid, struct sockaddr_in *ip, int client)
+static struct xid_item *xid_add(uint32_t xid, struct sockaddr_in *ip, unsigned iface_no)
{
struct xid_item *item;
@@ -50,7 +51,7 @@ static struct xid_item *xid_add(uint32_t xid, struct sockaddr_in *ip, int client
/* add xid entry */
item->ip = *ip;
item->xid = xid;
- item->client = client;
+ item->iface_no = iface_no;
item->timestamp = monotonic_sec();
item->next = dhcprelay_xid_list.next;
dhcprelay_xid_list.next = item;
@@ -127,7 +128,7 @@ static int get_dhcp_packet_type(struct dhcp_packet *p)
* make_iface_list - parses client/server interface names
* returns array
*/
-static char **make_iface_list(char **client_and_server_ifaces, int *client_number)
+static char **make_iface_list(char **client_and_server_ifaces, unsigned *client_number)
{
char *s, **iface_list;
int i, cn;
@@ -165,9 +166,9 @@ static char **make_iface_list(char **client_and_server_ifaces, int *client_numbe
/* Creates listen sockets (in fds) bound to client and server ifaces,
* and returns numerically max fd.
*/
-static int init_sockets(char **iface_list, int num_clients, int *fds)
+static unsigned init_sockets(char **iface_list, unsigned num_clients, int *fds)
{
- int i, n;
+ unsigned i, n;
n = 0;
for (i = 0; i < num_clients; i++) {
@@ -195,13 +196,14 @@ static int sendto_ip4(int sock, const void *msg, int msg_len, struct sockaddr_in
* p - packet to send
* client - number of the client
*/
-static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, int *fds,
+static void pass_to_server(struct dhcp_packet *p, int packet_len, unsigned from_iface_no, int *fds,
struct sockaddr_in *client_addr, struct sockaddr_in *server_addr)
{
int type;
/* check packet_type */
type = get_dhcp_packet_type(p);
+//FIXME: the above does not consider packet_len!
if (type != DHCPDISCOVER && type != DHCPREQUEST
&& type != DHCPDECLINE && type != DHCPRELEASE
&& type != DHCPINFORM
@@ -210,7 +212,10 @@ static void pass_to_server(struct dhcp_packet *p, int packet_len, int client, in
}
/* create new xid entry */
- xid_add(p->xid, client_addr, client);
+ xid_add(p->xid, client_addr, from_iface_no);
+//TODO: since we key request/reply pairs on xid values, shouldn't we drop new requests
+//with xid accidentally matching a xid of one of requests we currently hold
+//waiting for their replies?
/* forward request to server */
/* note that we send from fds[0] which is bound to SERVER_PORT (67).
@@ -229,25 +234,30 @@ static void pass_to_client(struct dhcp_packet *p, int packet_len, int *fds)
int type;
struct xid_item *item;
- /* check xid */
- item = xid_find(p->xid);
- if (!item) {
- return;
- }
-
/* check packet type */
type = get_dhcp_packet_type(p);
+//FIXME: the above does not consider packet_len!
if (type != DHCPOFFER && type != DHCPACK && type != DHCPNAK) {
return;
}
+ /* check xid */
+ item = xid_find(p->xid);
+ if (!item) {
+ return;
+ }
+//NB: RFC 1542 section 4.1 seems to envision the logic that
+//relay agents use giaddr (dhcp_msg.gateway_nip in our code)
+//to find out on which interface to reply.
+//(server is meant to copy giaddr from our request packet to its reply).
+//Above, we don't use that logic, instead we use xid as a key.
+
//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);
- if (sendto_ip4(fds[item->client], p, packet_len, &item->ip) != 0) {
- return; /* send error occurred */
- }
+ sendto_ip4(fds[item->iface_no], p, packet_len, &item->ip);
+ /* ^^^ if send error occurred, we can't do much, hence no check */
/* remove xid entry */
xid_del(p->xid);
@@ -259,7 +269,7 @@ int dhcprelay_main(int argc UNUSED_PARAM, char **argv)
struct sockaddr_in server_addr;
char **iface_list;
int *fds;
- int num_sockets, max_socket;
+ unsigned num_sockets, max_socket;
uint32_t our_nip;
INIT_G();
@@ -293,7 +303,7 @@ int dhcprelay_main(int argc UNUSED_PARAM, char **argv)
// every N minutes?
fd_set rfds;
struct timeval tv;
- int i;
+ unsigned i;
FD_ZERO(&rfds);
for (i = 0; i < num_sockets; i++)
@@ -304,15 +314,17 @@ int dhcprelay_main(int argc UNUSED_PARAM, char **argv)
int packlen;
struct dhcp_packet dhcp_msg;
- /* server */
+ /* from server */
if (FD_ISSET(fds[0], &rfds)) {
packlen = udhcp_recv_kernel_packet(&dhcp_msg, fds[0]);
+//NB: we do not check source port here. Should we?
+//It should be SERVER_PORT.
if (packlen > 0) {
pass_to_client(&dhcp_msg, packlen, fds);
}
}
- /* clients */
+ /* from clients */
for (i = 1; i < num_sockets; i++) {
struct sockaddr_in client_addr;
socklen_t addr_size;
@@ -325,6 +337,11 @@ int dhcprelay_main(int argc UNUSED_PARAM, char **argv)
(struct sockaddr *)(&client_addr), &addr_size);
if (packlen <= 0)
continue;
+//NB: we do not check source port here. Should we?
+//It should be CLIENT_PORT for clients.
+//It can be SERVER_PORT for relay agents (in which case giaddr must be != 0.0.0.0),
+//but is it even supported to chain relay agents like this?
+//(we still copy client_addr.port and use it to reply to the port we got request from)
/* Get our IP on corresponding client_iface */
// RFC 1542