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fix IP checksum bug, ensure identical IDs for packets

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This commit is contained in:
mykola2312 2024-12-20 03:35:34 +02:00
parent a75a35810a
commit a7bfa0de48
1 changed files with 54 additions and 36 deletions
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90
main.c
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@ -49,20 +49,28 @@ struct linkinterface {
int if_idx;
};
typedef void* frame_t;
typedef struct {
uint16_t id;
void* data;
size_t datalen;
} frame_t;
frame_t frame_new(size_t datalen) {
frame_t frame = malloc(datalen);
memset(frame, '\0', datalen);
frame_t* frame_new(size_t datalen) {
frame_t* frame = (frame_t*)malloc(sizeof(frame_t));
frame->id = (uint16_t)rand();
frame->data = malloc(datalen);
frame->datalen = datalen;
memset(frame->data, '\0', frame->datalen);
return frame;
}
frame_t frame_full() {
frame_t* frame_full() {
return frame_new(MTU);
}
void frame_free(frame_t frame) {
void frame_free(frame_t* frame) {
free(frame->data);
free(frame);
}
@ -117,15 +125,16 @@ void link_free(struct linkinterface* link) {
}
ssize_t link_send(struct linkinterface* link, const uint8_t* dstAddr,
uint16_t type, frame_t frame, size_t len)
uint16_t type, frame_t* frame)
{
// ETHER FRAME MUST NOT BE LESS THAN 64 (60)
size_t frame_len = MAX(60, len + sizeof(struct ether_header));
size_t oldlen = frame->datalen;
frame->datalen = MAX(60, frame->datalen + sizeof(struct ether_header));
// add space for ether header and shift user data
frame = realloc(frame, frame_len);
memmove((uint8_t*)frame + sizeof(struct ether_header), frame, len);
frame->data = realloc(frame->data, frame->datalen);
memmove((uint8_t*)frame->data + sizeof(struct ether_header), frame->data, oldlen);
struct ether_header* ether = (struct ether_header*)frame;
struct ether_header* ether = (struct ether_header*)frame->data;
memcpy(ether->ether_shost, link->host, ETH_ALEN);
memcpy(ether->ether_dhost, dstAddr, ETH_ALEN);
ether->ether_type = htons(type);
@ -136,22 +145,21 @@ ssize_t link_send(struct linkinterface* link, const uint8_t* dstAddr,
ll_addr.sll_halen = ETH_ALEN;
memcpy(ll_addr.sll_addr, dstAddr, ETH_ALEN);
size_t sent = sendto(link->fd, frame, frame_len, 0,
size_t sent = sendto(link->fd, frame->data, frame->datalen, 0,
(const struct sockaddr*)&ll_addr, sizeof(ll_addr));
free(frame);
return sent;
}
size_t link_recv(struct linkinterface* link, const uint8_t* srcAddr,
uint16_t type, frame_t frame, size_t len)
uint16_t type, frame_t* frame)
{
uint16_t want_type = htons(type);
do {
ssize_t rd = recv(link->fd, frame, len, 0);
ssize_t rd = recv(link->fd, frame->data, frame->datalen, 0);
if (rd < 0) return -1;
struct ether_header* ether = (struct ether_header*)frame;
struct ether_header* ether = (struct ether_header*)frame->data;
// check received packet's source MAC
// if its someone else than source - skip
if (memcmp(ether->ether_shost, srcAddr, ETH_ALEN)) {
@ -165,11 +173,11 @@ size_t link_recv(struct linkinterface* link, const uint8_t* srcAddr,
}
// shift back ether header and realloc
size_t datalen = rd - sizeof(struct ether_header);
memmove(frame, (const uint8_t*)frame + sizeof(struct ether_header), datalen);
frame = realloc(frame, datalen);
memmove(frame->data, (const uint8_t*)frame->data + sizeof(struct ether_header), frame->datalen);
frame->datalen = rd - sizeof(struct ether_header);
frame = realloc(frame->data, frame->datalen);
return datalen;
return frame->datalen;
} while (1);
// TODO: timeout
@ -186,19 +194,20 @@ uint16_t checksum(const uint8_t* data, size_t len) {
}
ssize_t ip_send(struct linkinterface* link, const uint8_t* dstAddr,
const uint8_t* dstIp, uint8_t proto, frame_t frame, size_t len)
const uint8_t* dstIp, uint8_t proto, frame_t* frame)
{
// shift data to add space for IP header
size_t iplen = sizeof(struct ip) + len;
frame = realloc(frame, iplen);
memmove((uint8_t*)frame + sizeof(struct ip), frame, len);
size_t oldlen = frame->datalen;
frame->datalen = sizeof(struct ip) + frame->datalen;
frame->data = realloc(frame->data, frame->datalen);
memmove((uint8_t*)frame->data + sizeof(struct ip), frame->data, oldlen);
// create IP packet
struct ip* ip = (struct ip*)frame;
struct ip* ip = (struct ip*)frame->data;
ip->ip_v = 4;
ip->ip_hl = sizeof(struct ip) / 4;
ip->ip_tos = 0;
ip->ip_len = htons(iplen);
ip->ip_id = (uint16_t)rand();
ip->ip_len = htons(frame->datalen);
ip->ip_id = htons(frame->id);
ip->ip_off = 0;
ip->ip_ttl = 64;
ip->ip_p = proto;
@ -206,9 +215,9 @@ ssize_t ip_send(struct linkinterface* link, const uint8_t* dstAddr,
memcpy(&ip->ip_src, link->host_ip, 4);
memcpy(&ip->ip_dst, dstIp, 4);
// calculate header checksum
ip->ip_sum = htons(checksum((const uint8_t*)frame, sizeof(struct ip)));
ip->ip_sum = checksum((const uint8_t*)frame->data, sizeof(struct ip));
return link_send(link, dstAddr, ETHERTYPE_IP, frame, iplen);
return link_send(link, dstAddr, ETHERTYPE_IP, frame);
}
int main(int argc, char** argv) {
@ -228,26 +237,35 @@ int main(int argc, char** argv) {
// ICMP request
size_t hdrlen = sizeof(struct icmphdr);
size_t payloadlen = 32;
size_t payloadlen = 20;
struct icmphdr* icmp = frame_new(hdrlen + payloadlen);
frame_t* frame = frame_new(hdrlen + payloadlen);
struct icmphdr* icmp = (struct icmphdr*)frame->data;
icmp->type = ICMP_ECHO;
icmp->code = 0;
icmp->checksum = 0;
icmp->un.echo.id = (uint16_t)rand();
icmp->un.echo.sequence = 1;
icmp->un.echo.id = htons(frame->id);
icmp->un.echo.sequence = 0;
// set payload
memset(icmp + 1, 69, payloadlen);
//struct timespec ts;
//clock_gettime(CLOCK_REALTIME, &ts);
uint8_t* payload = (uint8_t*)icmp + hdrlen;
for (uint8_t i = 0; i < payloadlen; i++) {
payload[i] = i;
}
//memcpy(payload, &ts, sizeof(struct timespec));
// calculate checksum
icmp->checksum = checksum((const uint8_t*)icmp, hdrlen + payloadlen);
// IPv4 local broadcast
uint8_t ip_broadcast[4] = {255, 255, 255, 255};
ssize_t sent = ip_send(link, target, ip_broadcast,
IPPROTO_ICMP, icmp, hdrlen + payloadlen);
ssize_t sent = ip_send(link, target, ip_broadcast, IPPROTO_ICMP, frame);
printf("sent %ld\n", sent);
frame_free(frame);
link_free(link);
return 0;
}