/* Parse the IPv4 header and the TCP header inside. Return a
* packet_parse_result_t.
* Note that packet_end points to the byte beyond the end of packet.
*/
static int parse_ipv4(struct packet *packet, u8 *header_start, u8 *packet_end,
char **error)
{
struct header *ip_header = NULL;
u8 *p = header_start;
const bool is_outer = (packet->ip_bytes == 0);
bool is_inner = false;
enum packet_parse_result_t result = PACKET_BAD;
struct ipv4 *ipv4 = (struct ipv4 *) (p);
const int ip_header_bytes = ipv4_header_len(ipv4);
assert(ip_header_bytes >= 0);
if (ip_header_bytes < sizeof(*ipv4)) {
asprintf(error, "IP header too short");
goto error_out;
}
if (p + ip_header_bytes > packet_end) {
asprintf(error, "Full IP header overflows packet");
goto error_out;
}
const int ip_total_bytes = ntohs(ipv4->tot_len);
if (p + ip_total_bytes > packet_end) {
asprintf(error, "IP payload overflows packet");
goto error_out;
}
if (ip_header_bytes > ip_total_bytes) {
asprintf(error, "IP header bigger than datagram");
goto error_out;
}
if (ntohs(ipv4->frag_off) & IP_MF) { /* more fragments? */
asprintf(error, "More fragments remaining");
goto error_out;
}
if (ntohs(ipv4->frag_off) & IP_OFFMASK) { /* fragment offset */
asprintf(error, "Non-zero fragment offset");
goto error_out;
}
const u16 checksum = ipv4_checksum(ipv4, ip_header_bytes);
if (checksum != 0) {
asprintf(error, "Bad IP checksum");
goto error_out;
}
ip_header = packet_append_header(packet, HEADER_IPV4, ip_header_bytes);
if (ip_header == NULL) {
asprintf(error, "Too many nested headers at IPv4 header");
goto error_out;
}
ip_header->total_bytes = ip_total_bytes;
/* Move on to the header inside. */
p += ip_header_bytes;
assert(p <= packet_end);
if (DEBUG_LOGGING) {
char src_string[ADDR_STR_LEN];
char dst_string[ADDR_STR_LEN];
struct ip_address src_ip, dst_ip;
ip_from_ipv4(&ipv4->src_ip, &src_ip);
ip_from_ipv4(&ipv4->dst_ip, &dst_ip);
DEBUGP("src IP: %s\n", ip_to_string(&src_ip, src_string));
DEBUGP("dst IP: %s\n", ip_to_string(&dst_ip, dst_string));
}
/* Examine the L4 header. */
const int layer4_bytes = ip_total_bytes - ip_header_bytes;
const int layer4_protocol = ipv4->protocol;
result = parse_layer4(packet, p, layer4_protocol, layer4_bytes,
packet_end, &is_inner, error);
/* If this is the innermost IP header then this is the primary. */
if (is_inner)
packet->ipv4 = ipv4;
/* If this is the outermost IP header then this is the packet length. */
if (is_outer)
packet->ip_bytes = ip_total_bytes;
return result;
error_out:
return PACKET_BAD;
}
/* Parse the IPv4 header and the TCP header inside. Return a
* packet_parse_result_t.
* Note that packet_end points to the byte beyond the end of packet.
*/
static int parse_ipv4(struct packet *packet, u8 *header_start, u8 *packet_end,
char **error)
{
u8 *p = header_start;
packet->ipv4 = (struct ipv4 *) (p);
const int ip_header_bytes = packet_ip_header_len(packet);
assert(ip_header_bytes >= 0);
if (ip_header_bytes < sizeof(*packet->ipv4)) {
asprintf(error, "IP header too short");
goto error_out;
}
if (p + ip_header_bytes > packet_end) {
asprintf(error, "Full IP header overflows packet");
goto error_out;
}
const int ip_total_bytes = ntohs(packet->ipv4->tot_len);
packet->ip_bytes = ip_total_bytes;
if (p + ip_total_bytes > packet_end) {
asprintf(error, "IP payload overflows packet");
goto error_out;
}
if (ip_header_bytes > ip_total_bytes) {
asprintf(error, "IP header bigger than datagram");
goto error_out;
}
if (ntohs(packet->ipv4->frag_off) & IP_MF) { /* more fragments? */
asprintf(error, "More fragments remaining");
goto error_out;
}
if (ntohs(packet->ipv4->frag_off) & IP_OFFMASK) { /* fragment offset */
asprintf(error, "Non-zero fragment offset");
goto error_out;
}
const u16 checksum = ipv4_checksum(packet->ipv4, ip_header_bytes);
if (checksum != 0) {
asprintf(error, "Bad IP checksum");
goto error_out;
}
/* Move on to the header inside. */
p += ip_header_bytes;
assert(p <= packet_end);
if (DEBUG_LOGGING) {
char src_string[ADDR_STR_LEN];
char dst_string[ADDR_STR_LEN];
struct ip_address src_ip, dst_ip;
ip_from_ipv4(&packet->ipv4->src_ip, &src_ip);
ip_from_ipv4(&packet->ipv4->dst_ip, &dst_ip);
DEBUGP("src IP: %s\n", ip_to_string(&src_ip, src_string));
DEBUGP("dst IP: %s\n", ip_to_string(&dst_ip, dst_string));
}
/* Examine the L4 header. */
const int layer4_bytes = ip_total_bytes - ip_header_bytes;
const int layer4_protocol = packet->ipv4->protocol;
return parse_layer4(packet, p, layer4_protocol, layer4_bytes,
packet_end, error);
error_out:
return PACKET_BAD;
}
