void ip_checksum(void *buf, size_t len) {
struct ip *ip;
int hl, off, sum;
if (len < sizeof(struct ip))
return;
ip = (struct ip *)buf;
hl = ip->ip_hl << 2;
ip->ip_sum = 0;
sum = ip_cksum_add(ip, hl, 0);
ip->ip_sum = ip_cksum_carry(sum);
off = htons(ip->ip_off);
if ((off & IP_OFFMASK) != 0 || (off & IP_MF) != 0)
return;
len -= hl;
if (ip->ip_p == IPPROTO_UDP) {
struct udphdr *udp = (struct udphdr *)((u_char *)ip + hl);
if (len >= sizeof(struct udphdr)) {
udp->uh_sum = 0;
sum = ip_cksum_add(udp, len, 0) + htons(ip->ip_p + len);
sum = ip_cksum_add(&ip->ip_src, 8, sum);
udp->uh_sum = ip_cksum_carry(sum);
if (!udp->uh_sum)
udp->uh_sum = 0xffff; /* RFC 768 */
}
}
}
int gre_encapsulate(ip_t *honeyd_ip, struct addr *src, struct addr *dst,
struct ip_hdr *iip, u_int iiplen)
{
struct ip_hdr *oip = (struct ip_hdr *) pkt;
struct gre_hdr *gre = (struct gre_hdr *) (oip + 1);
u_char *data = (u_char *) (gre + 1);
u_int iplen, sum;
iplen = sizeof(struct ip_hdr) + sizeof(struct gre_hdr) + iiplen;
if (iplen > sizeof(pkt))
{
syslog(LOG_ERR, "%s: packet too long: %d", __func__, iplen);
return (-1);
}
ip_pack_hdr(pkt, 0, iplen, rand_uint16(honeyd_rand), 0, honeyd_ttl,
IP_PROTO_GRE, src->addr_ip, dst->addr_ip);
memset(gre, 0, sizeof(struct gre_hdr));
gre->gre_flags = htons(GRE_CHECKSUM | GRE_VERSION);
gre->gre_proto = htons(GRE_IP4PROTO);
/* Copy the payload */
memcpy(data, iip, iiplen);
/* Calculate the checksum */
sum = ip_cksum_add(gre, iiplen + sizeof(struct gre_hdr), 0);
gre->gre_sum = ip_cksum_carry(sum);
ip_checksum(oip, iplen);
return (ip_send(honeyd_ip, pkt, iplen) != iplen ? -1 : 0);
}
void
ip6_checksum(void *buf, size_t len)
{
struct ip6_hdr *ip6 = (struct ip6_hdr *)buf;
struct ip6_ext_hdr *ext;
u_char *p, nxt;
int i, sum;
nxt = ip6->ip6_nxt;
for (i = IP6_HDR_LEN; IP6_IS_EXT(nxt); i += (ext->ext_len + 1) << 3) {
if (i >= (int)len) return;
ext = (struct ip6_ext_hdr *)((u_char *)buf + i);
nxt = ext->ext_nxt;
}
p = (u_char *)buf + i;
len -= i;
if (nxt == IP_PROTO_TCP) {
struct tcp_hdr *tcp = (struct tcp_hdr *)p;
if (len >= TCP_HDR_LEN) {
tcp->th_sum = 0;
sum = ip_cksum_add(tcp, len, 0) + htons(nxt + (u_short)len);
sum = ip_cksum_add(&ip6->ip6_src, 32, sum);
tcp->th_sum = ip_cksum_carry(sum);
}
} else if (nxt == IP_PROTO_UDP) {
struct udp_hdr *udp = (struct udp_hdr *)p;
if (len >= UDP_HDR_LEN) {
udp->uh_sum = 0;
sum = ip_cksum_add(udp, len, 0) + htons(nxt + (u_short)len);
sum = ip_cksum_add(&ip6->ip6_src, 32, sum);
if ((udp->uh_sum = ip_cksum_carry(sum)) == 0)
udp->uh_sum = 0xffff;
}
} else if (nxt == IP_PROTO_ICMPV6) {
struct icmp_hdr *icmp = (struct icmp_hdr *)p;
if (len >= ICMP_HDR_LEN) {
icmp->icmp_cksum = 0;
sum = ip_cksum_add(icmp, len, 0) + htons(nxt + (u_short)len);
sum = ip_cksum_add(&ip6->ip6_src, 32, sum);
icmp->icmp_cksum = ip_cksum_carry(sum);
}
} else if (nxt == IP_PROTO_ICMP || nxt == IP_PROTO_IGMP) {
struct icmp_hdr *icmp = (struct icmp_hdr *)p;
if (len >= ICMP_HDR_LEN) {
icmp->icmp_cksum = 0;
sum = ip_cksum_add(icmp, len, 0);
icmp->icmp_cksum = ip_cksum_carry(sum);
}
}
}
// Calculate IP checksum over the buffer :
void ip_checksum(void *buf, size_t len)
{
struct ip_hdr *ip;
int hl, off, sum;
if (len < IP_HDR_LEN)
return;
ip = (struct ip_hdr *)buf;
hl = ip->ip_hl << 2;
ip->ip_sum = 0;
sum = ip_cksum_add(ip, hl, 0);
ip->ip_sum = ip_cksum_carry(sum);
off = htons(ip->ip_off);
if ((off & IP_OFFMASK) != 0 || (off & IP_MF) != 0)
return;
len -= hl;
if (ip->ip_p == IP_PROTO_TCP) {
struct tcp_hdr *tcp = (struct tcp_hdr *)((u_char *)ip + hl);
if (len >= TCP_HDR_LEN) {
tcp->th_sum = 0;
sum = ip_cksum_add(tcp, len, 0) +
htons(ip->ip_p + (unsigned short) len);
sum = ip_cksum_add(&ip->ip_src, 8, sum);
tcp->th_sum = ip_cksum_carry(sum);
}
} else if (ip->ip_p == IP_PROTO_UDP) {
struct udp_hdr *udp = (struct udp_hdr *)((u_char *)ip + hl);
if (len >= UDP_HDR_LEN) {
udp->uh_sum = 0;
sum = ip_cksum_add(udp, len, 0) +
htons(ip->ip_p + (unsigned short) len);
sum = ip_cksum_add(&ip->ip_src, 8, sum);
udp->uh_sum = ip_cksum_carry(sum);
if (!udp->uh_sum)
udp->uh_sum = 0xffff; /* RFC 768 */
}
} else if (ip->ip_p == IP_PROTO_ICMP || ip->ip_p == IP_PROTO_IGMP) {
struct icmp_hdr *icmp = (struct icmp_hdr *)((u_char *)ip + hl);
if (len >= ICMP_HDR_LEN) {
icmp->icmp_cksum = 0;
sum = ip_cksum_add(icmp, len, 0);
icmp->icmp_cksum = ip_cksum_carry(sum);
}
}
}
int gre_decapsulate(struct ip_hdr *oip, u_short oiplen, struct ip_hdr **pip,
u_short *piplen)
{
struct gre_hdr *gre;
struct ip_hdr *ip;
u_char *end = (u_char *) oip + oiplen;
u_char *data;
uint16_t flags, proto, iplen;
gre = (struct gre_hdr *) ((u_char *) oip + (oip->ip_hl << 2));
data = (u_char *) (gre + 1);
if (end <= data)
return (-1);
/* We support only RFC 2784 */
flags = ntohs(gre->gre_flags);
if ((flags & ~GRE_CHECKSUM) != 0)
{
syslog(LOG_DEBUG, "%s: dropping RFC 1701 encapsulation: flags = %x",
__func__, flags);
return (-1);
}
proto = ntohs(gre->gre_proto);
if (proto != GRE_IP4PROTO)
{
syslog(LOG_DEBUG, "%s: dropping encapsulated packet: bad protocol %d",
__func__, proto);
return (-1);
}
if (!(flags & GRE_CHECKSUM))
data = GRE_NOCKSUM_DATA(gre);
/* Check for the proper length of the packet */
ip = (struct ip_hdr *) data;
if (data + sizeof(struct ip_hdr) > end)
return (-1);
iplen = ntohs(ip->ip_len);
if (data + iplen > end)
return (-1);
if (flags & GRE_CHECKSUM)
{
u_int sum = gre->gre_sum, tmp;
gre->gre_sum = 0;
tmp = ip_cksum_add(gre, sizeof(struct gre_hdr) + iplen, 0);
tmp = ip_cksum_carry(tmp);
if (sum != tmp)
{
syslog(LOG_INFO,
"%s: dropping encapsulated packet: bad checksum: %x vs %x",
__func__, ntohs(sum), ntohs(tmp));
return (-1);
}
}
*pip = ip;
*piplen = iplen;
return (0);
}
