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osmo-ggsn/lib/icmpv6.c

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/* Minimal ICMPv6 code for generating router advertisements as required by
* relevant 3GPP specs for a GGSN with IPv6 PDP contexts */
/* (C) 2017 by Harald Welte <laforge@gnumonks.org>
*
* The contents of this file may be used under the terms of the GNU
* General Public License Version 2, provided that the above copyright
* notice and this permission notice is included in all copies or
* substantial portions of the software.
*/
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <netinet/in.h>
#if defined(__FreeBSD__)
#include <sys/types.h> /* FreeBSD 10.x needs this before ip6.h */
#include <sys/endian.h>
#endif
#include <netinet/ip6.h>
#include <osmocom/core/msgb.h>
#include <osmocom/core/utils.h>
#include "checksum.h"
#include "../gtp/gtp.h"
#include "../gtp/pdp.h"
#include "ippool.h"
#include "syserr.h"
#include "icmpv6.h"
#include "config.h"
/* 29.061 11.2.1.3.4 IPv6 Router Configuration Variables in GGSN */
#define GGSN_MaxRtrAdvInterval 21600 /* 6 hours */
#define GGSN_MinRtrAdvInterval 16200 /* 4.5 hours */
#define GGSN_AdvValidLifetime 0xffffffff /* infinite */
#define GGSN_AdvPreferredLifetime 0xffffffff /* infinite */
/* RFC3307 link-local scope multicast address */
const struct in6_addr all_router_mcast_addr = {
.s6_addr = { 0xff,0x02,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,2 }
};
/* Prepends the ipv6 header and returns checksum content */
uint16_t icmpv6_prepend_ip6hdr(struct msgb *msg, const struct in6_addr *saddr,
const struct in6_addr *daddr)
{
uint32_t len;
uint16_t skb_csum;
struct ip6_hdr *i6h;
/* checksum */
skb_csum = csum_partial(msgb_data(msg), msgb_length(msg), 0);
len = msgb_length(msg);
skb_csum = csum_ipv6_magic(saddr, daddr, len, IPPROTO_ICMPV6, skb_csum);
/* Push IPv6 header in front of ICMPv6 packet */
i6h = (struct ip6_hdr *) msgb_push(msg, sizeof(*i6h));
/* 4 bits version, 8 bits TC, 20 bits flow-ID */
i6h->ip6_ctlun.ip6_un1.ip6_un1_flow = htonl(0x60000000);
i6h->ip6_ctlun.ip6_un1.ip6_un1_plen = htons(len);
i6h->ip6_ctlun.ip6_un1.ip6_un1_nxt = IPPROTO_ICMPV6;
i6h->ip6_ctlun.ip6_un1.ip6_un1_hlim = 255;
i6h->ip6_src = *saddr;
i6h->ip6_dst = *daddr;
return skb_csum;
}
/*! construct a RFC4861 compliant ICMPv6 router soliciation
* \param[in] saddr Source IPv6 address for router advertisement
* \param[in] daddr Destination IPv6 address for router advertisement IPv6 header
* \param[in] prefix The single prefix to be advertised (/64 implied!)
* \returns callee-allocated message buffer containing router advertisement */
struct msgb *icmpv6_construct_rs(const struct in6_addr *saddr)
{
struct msgb *msg = msgb_alloc_headroom(512,128, "IPv6 RS");
struct icmpv6_rsol_hdr *rs;
OSMO_ASSERT(msg);
rs = (struct icmpv6_rsol_hdr *) msgb_put(msg, sizeof(*rs));
rs->hdr.type = 133; /* see RFC4861 4.1 */
rs->hdr.code = 0; /* see RFC4861 4.1 */
rs->hdr.csum = 0; /* updated below */
rs->reserved = 0; /* see RFC4861 4.1 */
rs->hdr.csum = icmpv6_prepend_ip6hdr(msg, saddr, &all_router_mcast_addr);
return msg;
}
/*! construct a 3GPP 29.061 compliant router advertisement for a given prefix
* \param[in] saddr Source IPv6 address for router advertisement
* \param[in] daddr Destination IPv6 address for router advertisement IPv6 header
* \param[in] prefix The single prefix to be advertised (/64 implied!)
* \returns callee-allocated message buffer containing router advertisement */
static struct msgb *icmpv6_construct_ra(const struct in6_addr *saddr,
const struct in6_addr *daddr,
const struct in6_addr *prefix)
{
struct msgb *msg = msgb_alloc_headroom(512,128, "IPv6 RA");
struct icmpv6_radv_hdr *ra;
struct icmpv6_opt_prefix *ra_opt_pref;
OSMO_ASSERT(msg);
ra = (struct icmpv6_radv_hdr *) msgb_put(msg, sizeof(*ra));
ra->hdr.type = 134; /* see RFC4861 4.2 */
ra->hdr.code = 0; /* see RFC4861 4.2 */
ra->hdr.csum = 0; /* updated below */
ra->cur_ho_limit = 64; /* seems reasonable? */
/* the GGSN shall leave the M-flag cleared in the Router
* Advertisement messages */
ra->m = 0;
/* The GGSN may set the O-flag if there are additional
* configuration parameters that need to be fetched by the MS */
ra->o = 0; /* no DHCPv6 */
ra->res = 0;
/* RFC4861 Default: 3 * MaxRtrAdvInterval */
ra->router_lifetime = htons(3*GGSN_MaxRtrAdvInterval);
ra->reachable_time = 0; /* Unspecified */
/* RFC4861 Section 4.6.2 */
ra_opt_pref = (struct icmpv6_opt_prefix *) msgb_put(msg, sizeof(*ra_opt_pref));
ra_opt_pref->hdr.type = 3; /* RFC4861 4.6.2 */
ra_opt_pref->hdr.len = 4; /* RFC4861 4.6.2 */
ra_opt_pref->prefix_len = 64; /* only prefix length as per 3GPP */
/* The Prefix is contained in the Prefix Information Option of
* the Router Advertisements and shall have the A-flag set
* and the L-flag cleared */
ra_opt_pref->a = 1;
ra_opt_pref->l = 0;
ra_opt_pref->res = 0;
/* The lifetime of the prefix shall be set to infinity */
ra_opt_pref->valid_lifetime = htonl(GGSN_AdvValidLifetime);
ra_opt_pref->preferred_lifetime = htonl(GGSN_AdvPreferredLifetime);
ra_opt_pref->res2 = 0;
memcpy(ra_opt_pref->prefix, prefix, sizeof(ra_opt_pref->prefix));
/* checksum */
ra->hdr.csum = icmpv6_prepend_ip6hdr(msg, saddr, daddr);
return msg;
}
/* Validate an ICMPv6 router solicitation according to RFC4861 6.1.1 */
static bool icmpv6_validate_router_solicit(const uint8_t *pack, unsigned len)
{
const struct ip6_hdr *ip6h = (struct ip6_hdr *)pack;
//const struct icmpv6_hdr *ic6h = (struct icmpv6_hdr *) (pack + sizeof(*ip6h));
/* Hop limit field must have 255 */
if (ip6h->ip6_ctlun.ip6_un1.ip6_un1_hlim != 255)
return false;
/* FIXME: ICMP checksum is valid */
/* ICMP length (derived from IP length) is 8 or more octets */
if (ip6h->ip6_ctlun.ip6_un1.ip6_un1_plen < 8)
return false;
/* FIXME: All included options have a length > 0 */
/* FIXME: If IP source is unspecified, no source link-layer addr option */
return true;
}
/* Validate an ICMPv6 router advertisement according to RFC4861 6.1.2.
Returns pointer packet header on success, NULL otherwise. */
struct icmpv6_radv_hdr *icmpv6_validate_router_adv(const uint8_t *pack, unsigned len)
{
const struct ip6_hdr *ip6h = (struct ip6_hdr *)pack;
const struct icmpv6_hdr *ic6h = (struct icmpv6_hdr *) (pack + sizeof(*ip6h));
/* ICMP length (derived from IP length) is 16 or more octets */
if (len < sizeof(*ip6h) + 16)
return NULL;
if (ic6h->type != 134) /* router advertismenet type */
return NULL;
/*Routers must use their link-local address */
if (!IN6_IS_ADDR_LINKLOCAL(&ip6h->ip6_src))
return NULL;
/* Hop limit field must have 255 */
if (ip6h->ip6_ctlun.ip6_un1.ip6_un1_hlim != 255)
return NULL;
/* ICMP Code is 0 */
if (ic6h->code != 0)
return NULL;
/* ICMP length (derived from IP length) is 16 or more octets */
if (ip6h->ip6_ctlun.ip6_un1.ip6_un1_plen < 16)
return NULL;
/* FIXME: All included options have a length > 0 */
/* FIXME: If IP source is unspecified, no source link-layer addr option */
return (struct icmpv6_radv_hdr *)ic6h;
}
/* handle incoming packets to the all-routers multicast address */
int handle_router_mcast(struct gsn_t *gsn, struct pdp_t *pdp,
const struct in6_addr *pdp_prefix,
const struct in6_addr *own_ll_addr,
const uint8_t *pack, unsigned len)
{
const struct ip6_hdr *ip6h = (struct ip6_hdr *)pack;
const struct icmpv6_hdr *ic6h = (struct icmpv6_hdr *) (pack + sizeof(*ip6h));
struct msgb *msg;
if (len < sizeof(*ip6h)) {
LOGP(DICMP6, LOGL_NOTICE, "Packet too short: %u bytes\n", len);
return -1;
}
/* we only treat ICMPv6 here */
if (ip6h->ip6_ctlun.ip6_un1.ip6_un1_nxt != IPPROTO_ICMPV6) {
LOGP(DICMP6, LOGL_DEBUG, "Ignoring non-ICMP to all-routers mcast\n");
return 0;
}
if (len < sizeof(*ip6h) + sizeof(*ic6h)) {
LOGP(DICMP6, LOGL_NOTICE, "Short ICMPv6 packet: %s\n", osmo_hexdump(pack, len));
return -1;
}
switch (ic6h->type) {
case 133: /* router solicitation */
if (ic6h->code != 0) {
LOGP(DICMP6, LOGL_NOTICE, "ICMPv6 type 133 but code %d\n", ic6h->code);
return -1;
}
if (!icmpv6_validate_router_solicit(pack, len)) {
LOGP(DICMP6, LOGL_NOTICE, "Invalid Router Solicitation: %s\n",
osmo_hexdump(pack, len));
return -1;
}
/* Send router advertisement from GGSN link-local
* address to MS link-local address, including prefix
* allocated to this PDP context */
msg = icmpv6_construct_ra(own_ll_addr, &ip6h->ip6_src, pdp_prefix);
/* Send the constructed RA to the MS */
gtp_data_req(gsn, pdp, msgb_data(msg), msgb_length(msg));
msgb_free(msg);
break;
default:
LOGP(DICMP6, LOGL_DEBUG, "Unknown ICMPv6 type %u\n", ic6h->type);
break;
}
return 0;
}
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