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osmo-ggsn
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Implement ICMP response for inactive IP address. 

Send ICMP Host Unreachable packets back on the tun device
in reponse to a packet received for an IP address that is
not active in our pool (No active pdp context)

Only IPv4 implemented.

Change-Id: Ia2c708feab14bb4cada00b0a90e0cb56d680d1aa
This commit is contained in:
Keith Whyte 2020-10-20 08:40:50 +02:00 committed by Keith Whyte
parent 848ec697e2
commit cb18dbfb77
1 changed files with 63 additions and 0 deletions
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63
ggsn/ggsn.c
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@ -40,6 +40,7 @@
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip6.h>
#include <osmocom/core/timer.h>
@ -584,6 +585,64 @@ err_wrong_af:
return 0;
}
static uint16_t inet_checksum(void *data, int len) {
int nleft = len;
int sum = 0;
unsigned short *w = data;
unsigned short checksum = 0;
while (nleft > 1) {
sum += *w++;
nleft -= 2;
}
if (nleft == 1){
*(unsigned char *)(&checksum) = *(unsigned char *)w;
sum += checksum;
}
sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
checksum = ~sum;
return (checksum);
}
/* Generate and send an ICMP HOST UNREACHABLE Packet */
static void ipv4_host_unreach(struct tun_t *tun, void *pack, unsigned len)
{
char send_buf[sizeof(struct ip) + sizeof(struct icmp) + len];
len = len - 20;
struct iphdr *iph = (struct iphdr *)pack;
memset(send_buf, 0, sizeof(send_buf));
struct ip *ip = (struct ip *)send_buf;
struct icmp *icmp = (struct icmp *)(ip + 1);
ip->ip_v = 4;
ip->ip_hl = 5;
ip->ip_tos = 0;
ip->ip_len = htons(sizeof(send_buf));
ip->ip_id = rand();
ip->ip_off = 0;
ip->ip_ttl = 64;
ip->ip_sum = 0;
ip->ip_p = IPPROTO_ICMP;
ip->ip_src.s_addr = iph->daddr;
ip->ip_dst.s_addr = iph->saddr;
ip->ip_sum = inet_checksum(ip, sizeof(send_buf));
icmp->icmp_type = ICMP_DEST_UNREACH;
icmp->icmp_code = ICMP_HOST_UNREACH;
icmp->icmp_id = 0;
icmp->icmp_seq = 0;
icmp->icmp_cksum = 0;
memcpy(send_buf + sizeof(ip) + sizeof(icmp) + 12, pack, len);
icmp->icmp_cksum = inet_checksum(icmp, sizeof(icmp) + 12 + len);
tun_encaps(tun, send_buf, sizeof(send_buf));
}
/* Internet-originated IP packet, needs to be sent via GTP towards MS */
static int cb_tun_ind(struct tun_t *tun, void *pack, unsigned len)
{
@ -660,6 +719,10 @@ static int cb_tun_ind(struct tun_t *tun, void *pack, unsigned len)
iph->version == 4 ?
inet_ntop(AF_INET, &iph->saddr, straddr[1], sizeof(straddr[1])) :
inet_ntop(AF_INET6, &ip6h->ip6_src, straddr[1], sizeof(straddr[1])));
/* TODO: Implement ipv6 */
if (iph->version != 4)
return 0;
ipv4_host_unreach(tun, pack, len);
}
return 0;
}