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Send a full DHCP Request in dhcp_bitbanger
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@klange
klange committed May 26, 2021
1 parent 3d9d4da commit 1490175
Showing 1 changed file with 122 additions and 72 deletions.
194 changes: 122 additions & 72 deletions apps/dhcp_bitbanger.c
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Original file line number Diff line number Diff line change
Expand Up @@ -159,6 +159,66 @@ void ip_ntoa(uint32_t src_addr, char * out) {
(src_addr & 0xFF));
}

uint8_t mac_addr[6];

void fill(struct payload *it, size_t payload_size) {

it->eth_header.source[0] = mac_addr[0];
it->eth_header.source[1] = mac_addr[1];
it->eth_header.source[2] = mac_addr[2];
it->eth_header.source[3] = mac_addr[3];
it->eth_header.source[4] = mac_addr[4];
it->eth_header.source[5] = mac_addr[5];

it->eth_header.destination[0] = 0xFF;
it->eth_header.destination[1] = 0xFF;
it->eth_header.destination[2] = 0xFF;
it->eth_header.destination[3] = 0xFF;
it->eth_header.destination[4] = 0xFF;
it->eth_header.destination[5] = 0xFF;

it->eth_header.type = htons(0x0800);

it->ip_header.version_ihl = ((0x4 << 4) | (0x5 << 0));
it->ip_header.dscp_ecn = 0;
it->ip_header.length = htons(sizeof(struct ipv4_packet) + sizeof(struct udp_packet) + sizeof(struct dhcp_packet) + payload_size);
it->ip_header.ident = htons(1);
it->ip_header.flags_fragment = 0;
it->ip_header.ttl = 0x40;
it->ip_header.protocol = IPV4_PROT_UDP;
it->ip_header.checksum = 0;
it->ip_header.source = htonl(0);
it->ip_header.destination = htonl(0xFFFFFFFF);

it->ip_header.checksum = htons(calculate_ipv4_checksum(&it->ip_header));

it->udp_header.source_port = htons(68);
it->udp_header.destination_port = htons(67);
it->udp_header.length = htons(sizeof(struct udp_packet) + sizeof(struct dhcp_packet) + payload_size);
it->udp_header.checksum = 0; /* uh */

it->dhcp_header.op = 1;
it->dhcp_header.htype = 1;
it->dhcp_header.hlen = 6;
it->dhcp_header.hops = 0;
it->dhcp_header.xid = htons(0x1337); /* transaction id... */
it->dhcp_header.secs = 0;
it->dhcp_header.flags = 0;

it->dhcp_header.ciaddr = 0;
it->dhcp_header.yiaddr = 0;
it->dhcp_header.siaddr = 0;
it->dhcp_header.giaddr = 0;
it->dhcp_header.chaddr[0] = mac_addr[0];
it->dhcp_header.chaddr[1] = mac_addr[1];
it->dhcp_header.chaddr[2] = mac_addr[2];
it->dhcp_header.chaddr[3] = mac_addr[3];
it->dhcp_header.chaddr[4] = mac_addr[4];
it->dhcp_header.chaddr[5] = mac_addr[5];

it->dhcp_header.magic = htonl(DHCP_MAGIC);
}

int main(int argc, char * argv[]) {

/* Let's make a socket. */
Expand All @@ -181,7 +241,6 @@ int main(int argc, char * argv[]) {

fprintf(stderr, "Configuring %s\n", if_name);

uint8_t mac_addr[6];
if (ioctl(netdev, 0x12340001, &mac_addr)) {
fprintf(stderr, "could not get mac address\n");
return 1;
Expand All @@ -192,75 +251,19 @@ int main(int argc, char * argv[]) {
mac_addr[3], mac_addr[4], mac_addr[5]);

/* Try to frob the whatsit */
struct payload thething = {0};
size_t payload_size = 8;

thething.eth_header.source[0] = mac_addr[0];
thething.eth_header.source[1] = mac_addr[1];
thething.eth_header.source[2] = mac_addr[2];
thething.eth_header.source[3] = mac_addr[3];
thething.eth_header.source[4] = mac_addr[4];
thething.eth_header.source[5] = mac_addr[5];

thething.eth_header.destination[0] = 0xFF;
thething.eth_header.destination[1] = 0xFF;
thething.eth_header.destination[2] = 0xFF;
thething.eth_header.destination[3] = 0xFF;
thething.eth_header.destination[4] = 0xFF;
thething.eth_header.destination[5] = 0xFF;

thething.eth_header.type = htons(0x0800);

thething.ip_header.version_ihl = ((0x4 << 4) | (0x5 << 0));
thething.ip_header.dscp_ecn = 0;
thething.ip_header.length = htons(sizeof(struct ipv4_packet) + sizeof(struct udp_packet) + sizeof(struct dhcp_packet) + payload_size);
thething.ip_header.ident = htons(1);
thething.ip_header.flags_fragment = 0;
thething.ip_header.ttl = 0x40;
thething.ip_header.protocol = IPV4_PROT_UDP;
thething.ip_header.checksum = 0;
thething.ip_header.source = htonl(0);
thething.ip_header.destination = htonl(0xFFFFFFFF);

thething.ip_header.checksum = htons(calculate_ipv4_checksum(&thething.ip_header));

thething.udp_header.source_port = htons(68);
thething.udp_header.destination_port = htons(67);
thething.udp_header.length = htons(sizeof(struct udp_packet) + sizeof(struct dhcp_packet) + payload_size);
thething.udp_header.checksum = 0; /* uh */

thething.dhcp_header.op = 1;
thething.dhcp_header.htype = 1;
thething.dhcp_header.hlen = 6;
thething.dhcp_header.hops = 0;
thething.dhcp_header.xid = htons(0x1337); /* transaction id... */
thething.dhcp_header.secs = 0;
thething.dhcp_header.flags = 0;

thething.dhcp_header.ciaddr = 0;
thething.dhcp_header.yiaddr = 0;
thething.dhcp_header.siaddr = 0;
thething.dhcp_header.giaddr = 0;
thething.dhcp_header.chaddr[0] = mac_addr[0];
thething.dhcp_header.chaddr[1] = mac_addr[1];
thething.dhcp_header.chaddr[2] = mac_addr[2];
thething.dhcp_header.chaddr[3] = mac_addr[3];
thething.dhcp_header.chaddr[4] = mac_addr[4];
thething.dhcp_header.chaddr[5] = mac_addr[5];

//thething.dhcp_header.sname
thething.dhcp_header.magic = htonl(DHCP_MAGIC);

thething.payload[0] = 53; /* message type */
thething.payload[1] = 1; /* length */
thething.payload[2] = 1; /* discover */
thething.payload[3] = 55;
thething.payload[4] = 2;
thething.payload[5] = 3;
thething.payload[6] = 6;
thething.payload[7] = 255;

write(netdev, &thething, sizeof(struct payload));
{
struct payload thething = {
.payload = {53,1,1,55,2,3,6,255,0}
};

fill(&thething, 8);

write(netdev, &thething, sizeof(struct payload));
}

uint32_t yiaddr;
uint32_t siaddr;

do {
char buf[8092] = {0};
ssize_t rsize = read(netdev, &buf, 8092);
Expand All @@ -277,11 +280,58 @@ int main(int argc, char * argv[]) {
continue;
}

uint32_t yiaddr = ntohl(response->dhcp_header.yiaddr);
yiaddr = response->dhcp_header.yiaddr;
siaddr = response->dhcp_header.siaddr;
char yiaddr_ip[16];
ip_ntoa(yiaddr, yiaddr_ip);
ip_ntoa(ntohl(yiaddr), yiaddr_ip);

printf("Response from DHCP Discover: %s\n", yiaddr_ip);

break;
} while (1);

{
printf("Writing request\n");
struct payload thething = {
.payload = {53,1,3,50,4,
(yiaddr) & 0xFF,
(yiaddr >> 8) & 0xFF,
(yiaddr >> 16) & 0xFF,
(yiaddr >> 24) & 0xFF,
55,2,3,6,255,0}
};

fill(&thething, 14);

thething.dhcp_header.ciaddr = yiaddr;
thething.dhcp_header.siaddr = siaddr;

write(netdev, &thething, sizeof(struct payload));
}

do {
char buf[8092] = {0};
ssize_t rsize = read(netdev, &buf, 8092);

if (rsize <= 0) {
printf("bad size? %zd\n", rsize);
continue;
}

struct payload * response = (void*)buf;

if (ntohs(response->udp_header.destination_port) != 68) {
printf("not what I was expecting\n");
continue;
}

yiaddr = response->dhcp_header.yiaddr;
siaddr = response->dhcp_header.siaddr;
char yiaddr_ip[16];
ip_ntoa(ntohl(yiaddr), yiaddr_ip);

printf("ACK returns: %s\n", yiaddr_ip);

break;
} while (1);

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