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netd: fix several bugs

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1. pads packets to 300 bytes
2. adds broadcast flag
3. adds seconds
4. uses a randomized id
This commit is contained in:
Matheus
2026-02-19 03:01:47 -03:00
parent 05a6738e47
commit ce5c4c4366
1 changed files with 21 additions and 11 deletions
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tools/netd/main.c
+21 -11
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@@ -15,6 +15,7 @@
#include <net/route.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>
#ifndef SIOCADDRT
#define SIOCADDRT 0x890B
@@ -28,7 +29,6 @@
#define DHCPHDR_HTYPE_ETH 1
#define DHCPHDR_HLEN_ETH 6
#define DHCPHDR_COOKIE 0x63825363
#define DHCPHDR_XID 0x12345678
#define DHCP_CLIENT_PORT 68
#define DHCP_SERVER_PORT 67
@@ -78,6 +78,7 @@ static uint8_t discoveropts[] = {
typedef struct {
dhcphdr_t hdr;
uint8_t opts[sizeof(discoveropts)];
uint8_t padding[300 - sizeof(dhcphdr_t) - sizeof(discoveropts)];
} __attribute__((packed)) dhcpdiscover_t;
typedef struct {
@@ -97,6 +98,7 @@ typedef struct {
typedef struct {
dhcphdr_t hdr;
requestopts_t opts;
uint8_t padding[300 - sizeof(dhcphdr_t) - sizeof(requestopts_t)];
} __attribute__((packed)) dhcprequest_t;
typedef struct {
@@ -107,6 +109,8 @@ typedef struct {
static char *name;
static int sockfd;
static uint8_t hwaddr[DHCPHDR_HLEN_ETH];
static uint32_t xid;
static time_t discoverstart;
static void usage() {
fprintf(stderr, "%s: usage: %s device\n", name, name);
@@ -184,7 +188,9 @@ static int discover() {
packet.hdr.op = DHCPHDR_TYPE_CLIENT;
packet.hdr.htype = DHCPHDR_HTYPE_ETH;
packet.hdr.hlen = DHCPHDR_HLEN_ETH;
packet.hdr.xid = htonl(DHCPHDR_XID);
packet.hdr.xid = htonl(xid);
packet.hdr.secs = htons((uint16_t)(time(NULL) - discoverstart));
packet.hdr.flags = htons(0x8000);
memcpy(packet.hdr.clienthw, hwaddr, DHCPHDR_HLEN_ETH);
packet.hdr.cookie = htonl(DHCPHDR_COOKIE);
@@ -302,9 +308,9 @@ static int request(offer_t *offer) {
packet.hdr.op = DHCPHDR_TYPE_CLIENT;
packet.hdr.htype = DHCPHDR_HTYPE_ETH;
packet.hdr.hlen = DHCPHDR_HLEN_ETH;
packet.hdr.xid = htonl(DHCPHDR_XID);
packet.hdr.clientip = htonl(offer->clientip);
packet.hdr.serverip = htonl(offer->serverip);
packet.hdr.xid = htonl(xid);
packet.hdr.secs = htons((uint16_t)(time(NULL) - discoverstart));
packet.hdr.flags = htons(0x8000);
memcpy(packet.hdr.clienthw, hwaddr, DHCPHDR_HLEN_ETH);
packet.hdr.cookie = htonl(DHCPHDR_COOKIE);
@@ -465,6 +471,10 @@ int main(int argc, char *argv[]) {
if (getdevicehwaddr(argv[1]))
return EXIT_FAILURE;
srand(time(NULL));
xid = ((uint32_t)rand() << 16) ^ (uint32_t)rand();
discoverstart = time(NULL);
offer_t offer;
bool gotoffer = false;
@@ -477,13 +487,13 @@ int main(int argc, char *argv[]) {
if (waitforserver(10000))
break;
uint32_t xid;
uint32_t rxid;
if (processoffer(&offer, &xid))
if (processoffer(&offer, &rxid))
return EXIT_FAILURE;
// packet wasn't for this machine
if (xid != DHCPHDR_XID)
if (rxid != xid)
continue;
gotoffer = true;
@@ -499,12 +509,12 @@ int main(int argc, char *argv[]) {
if (waitforserver(10000))
break;
uint32_t xid;
uint32_t rxid;
if (getack(&xid))
if (getack(&rxid))
return EXIT_FAILURE;
if (xid != DHCPHDR_XID)
if (rxid != xid)
continue;
gotack = true;