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Just use raw sockets for listening to DHCP requests. A UDP SO_BROADCAST

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socket was previously used only for receiving RENEWING packets, and it
added needless complexity and was somewhat fragile.
This commit is contained in:
Nicholas J. Kain
2014-04-16 01:00:36 -04:00
parent ca85a6ba9f
commit 07cbd88049
7 changed files with 31 additions and 102 deletions
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85
src/dhcp.c
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@ -48,12 +48,6 @@
#include "options.h"
#include "sockd.h"
typedef enum {
LM_NONE = 0,
LM_COOKED,
LM_RAW
} listen_mode_t;
static int get_udp_unicast_socket(struct client_state_t *cs)
{
char buf[32];
@ -67,11 +61,6 @@ static int get_raw_broadcast_socket(void)
return request_sockd_fd("s", 1, NULL);
}
static int get_udp_listen_socket(void)
{
return request_sockd_fd("U", 1, NULL);
}
static int get_raw_listen_socket(struct client_state_t *cs)
{
char resp;
@ -85,9 +74,9 @@ static int get_raw_listen_socket(struct client_state_t *cs)
return fd;
}
// Broadcast a DHCP message using a UDP socket.
static ssize_t send_dhcp_cooked(struct client_state_t *cs,
struct dhcpmsg *payload)
// Unicast a DHCP message using a UDP socket.
static ssize_t send_dhcp_unicast(struct client_state_t *cs,
struct dhcpmsg *payload)
{
ssize_t ret = -1;
int fd = get_udp_unicast_socket(cs);
@ -127,23 +116,6 @@ static ssize_t send_dhcp_cooked(struct client_state_t *cs,
return ret;
}
// Read a packet from a cooked socket. Returns -1 on fatal error, -2 on
// transient error.
static ssize_t get_cooked_packet(struct client_state_t *cs,
struct dhcpmsg *packet)
{
memset(packet, 0, sizeof *packet);
ssize_t bytes = safe_read(cs->listenFd, (char *)packet, sizeof *packet);
if (bytes < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK)
return -2;
log_warning("%s: (%s) read error %s", client_config.interface,
__func__, strerror(errno));
return -1;
}
return bytes;
}
// When summing ones-complement 16-bit values using a 32-bit unsigned
// representation, fold the carry bits that have spilled into the upper
// 16-bits of the 32-bit unsigned value back into the 16-bit ones-complement
@ -352,39 +324,24 @@ static ssize_t send_dhcp_raw(struct dhcpmsg *payload)
return ret;
}
// Switch listen socket between raw (if-bound), kernel (ip-bound), and none
static void change_listen_mode(struct client_state_t *cs, int new_mode)
void start_dhcp_listen(struct client_state_t *cs)
{
cs->listenMode = new_mode;
if (cs->listenFd >= 0) {
epoll_del(cs->epollFd, cs->listenFd);
close(cs->listenFd);
cs->listenFd = -1;
}
switch (cs->listenMode) {
default: return;
case LM_RAW: cs->listenFd = get_raw_listen_socket(cs); break;
case LM_COOKED: cs->listenFd = get_udp_listen_socket(); break;
}
if (cs->listenFd >= 0)
return;
cs->listenFd = get_raw_listen_socket(cs);
if (cs->listenFd < 0)
suicide("%s: FATAL: Couldn't listen on socket: %s",
client_config.interface, strerror(errno));
epoll_add(cs->epollFd, cs->listenFd);
}
void set_listen_raw(struct client_state_t *cs)
void stop_dhcp_listen(struct client_state_t *cs)
{
change_listen_mode(cs, LM_RAW);
}
void set_listen_cooked(struct client_state_t *cs)
{
change_listen_mode(cs, LM_COOKED);
}
void set_listen_none(struct client_state_t *cs)
{
change_listen_mode(cs, LM_NONE);
if (cs->listenFd < 0)
return;
epoll_del(cs->epollFd, cs->listenFd);
close(cs->listenFd);
cs->listenFd = -1;
}
static int validate_dhcp_packet(struct client_state_t *cs, size_t len,
@ -436,19 +393,17 @@ static int validate_dhcp_packet(struct client_state_t *cs, size_t len,
void handle_packet(struct client_state_t *cs)
{
if (cs->listenFd < 0)
return;
struct dhcpmsg packet;
ssize_t r;
switch (cs->listenMode) {
case LM_RAW: r = get_raw_packet(cs, &packet); break;
case LM_COOKED: r = get_cooked_packet(cs, &packet); break;
default: return;
}
ssize_t r = get_raw_packet(cs, &packet);
if (r < 0) {
// Not a transient issue handled by packet collection functions.
if (r != -2) {
log_error("%s: Error reading from listening socket: %s. Reopening.",
client_config.interface, strerror(errno));
change_listen_mode(cs, cs->listenMode);
stop_dhcp_listen(cs);
start_dhcp_listen(cs);
}
return;
}
@ -515,7 +470,7 @@ ssize_t send_renew(struct client_state_t *cs)
add_option_vendor(&packet);
add_option_hostname(&packet);
log_line("%s: Sending a renew request...", client_config.interface);
return send_dhcp_cooked(cs, &packet);
return send_dhcp_unicast(cs, &packet);
}
ssize_t send_rebind(struct client_state_t *cs)
@ -548,6 +503,6 @@ ssize_t send_release(struct client_state_t *cs)
add_option_reqip(&packet, cs->clientAddr);
add_option_serverid(&packet, cs->serverAddr);
log_line("%s: Sending a release message...", client_config.interface);
return send_dhcp_cooked(cs, &packet);
return send_dhcp_unicast(cs, &packet);
}