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

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function                                             old     new   delta
packed_usage                                       33891   33920     +29
dhcprelay_main                                       943     926     -17
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 29/-17)             Total: 12 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2021-09-02 16:23:24 +02:00
parent 62d0c8e028
commit 3f2d969db9
2 changed files with 46 additions and 22 deletions
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7
networking/udhcp/dhcpd.c
View File

@ -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) {

61
networking/udhcp/dhcprelay.c
View File

@ -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 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;
}
/* check packet type */
type = get_dhcp_packet_type(p);
if (type != DHCPOFFER && type != DHCPACK && type != DHCPNAK) {
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