gnrc_ipv6_auto_subnets.c

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/*
 * Copyright (C) 2021 ML!PA Consulting GmbH
 *
 * This file is subject to the terms and conditions of the GNU Lesser
 * General Public License v2.1. See the file LICENSE in the top level
 * directory for more details.
 */
 
#include "compiler_hints.h"
#include "net/gnrc/ipv6.h"
#include "net/gnrc/netif.h"
#include "net/gnrc/netif/hdr.h"
#include "net/gnrc/udp.h"
#include "net/gnrc/ipv6/nib.h"
#include "net/gnrc/ndp.h"
#include "net/gnrc/rpl.h"
#include "random.h"
#include "xtimer.h"
 
#ifndef CONFIG_GNRC_IPV6_AUTO_SUBNETS_PORT
#define CONFIG_GNRC_IPV6_AUTO_SUBNETS_PORT          (16179)
#endif
 
#ifndef CONFIG_GNRC_IPV6_AUTO_SUBNETS_PEERS_MAX
#define CONFIG_GNRC_IPV6_AUTO_SUBNETS_PEERS_MAX     (4)
#endif
 
#ifndef CONFIG_GNRC_IPV6_AUTO_SUBNETS_TX_PER_PERIOD
#define CONFIG_GNRC_IPV6_AUTO_SUBNETS_TX_PER_PERIOD (3)
#endif
 
#ifndef CONFIG_GNRC_IPV6_AUTO_SUBNETS_TIMEOUT_MS
#define CONFIG_GNRC_IPV6_AUTO_SUBNETS_TIMEOUT_MS    (50)
#endif
 
#ifndef CONFIG_GNRC_IPV6_AUTO_SUBNETS_PREFIX_FIX_LEN
#define CONFIG_GNRC_IPV6_AUTO_SUBNETS_PREFIX_FIX_LEN (0)
#endif
 
#ifndef CONFIG_GNRC_IPV6_AUTO_SUBNETS_PREFIX_MIN_LEN
#define CONFIG_GNRC_IPV6_AUTO_SUBNETS_PREFIX_MIN_LEN (0)
#endif
 
#ifndef CONFIG_GNRC_IPV6_AUTO_SUBNETS_NUMOF
#define CONFIG_GNRC_IPV6_AUTO_SUBNETS_NUMOF         (1)
#endif
 
#ifndef CONFIG_GNRC_IPV6_AUTO_SUBNETS_STATIC
#define CONFIG_GNRC_IPV6_AUTO_SUBNETS_STATIC        (0)
#endif
 
/* Code below should not be included by Doxygen */
#ifndef DOXYGEN
 
#define SERVER_THREAD_STACKSIZE                     (THREAD_STACKSIZE_DEFAULT)
#define SERVER_MSG_QUEUE_SIZE                       (CONFIG_GNRC_IPV6_AUTO_SUBNETS_PEERS_MAX)
#define SERVER_MSG_TYPE_TIMEOUT                     (0x8fae)
 
#define ENABLE_DEBUG 0
#include "debug.h"
 
static char addr_str[IPV6_ADDR_MAX_STR_LEN];
 
#if !IS_USED(MODULE_GNRC_IPV6_AUTO_SUBNETS_SIMPLE)
 
typedef struct __attribute__((packed)) {
    uint8_t version;        
    uint8_t num_subnets;    
} _auto_subnets_request_v0_t;
 
/* keep a copy of PIO information in memory */
static gnrc_netif_t *_upstream;
static ndp_opt_pi_t _pio_cache[CONFIG_GNRC_IPV6_AUTO_SUBNETS_NUMOF];
static mutex_t _pio_cache_lock;
 
static char auto_subnets_stack[SERVER_THREAD_STACKSIZE];
static msg_t server_queue[SERVER_MSG_QUEUE_SIZE];
 
/* store neighbor routers l2 address to ignore duplicate packets */
static uint8_t l2addrs[CONFIG_GNRC_IPV6_AUTO_SUBNETS_PEERS_MAX]
                      [CONFIG_GNRC_IPV6_NIB_L2ADDR_MAX_LEN];
 
/* PID of the event thread */
static kernel_pid_t _server_pid;
 
static bool _store_pio(const ndp_opt_pi_t *pio)
{
    mutex_lock(&_pio_cache_lock);
 
    for (unsigned i = 0; i < ARRAY_SIZE(_pio_cache); ++i) {
        if (_pio_cache[i].len == 0) {
            _pio_cache[i] = *pio;
 
            mutex_unlock(&_pio_cache_lock);
            return true;
        }
    }
 
    mutex_unlock(&_pio_cache_lock);
    return false;
}
 
static int _send_udp(gnrc_netif_t *netif, const ipv6_addr_t *addr,
                     uint16_t port, const void *data, size_t len)
{
    gnrc_pktsnip_t *payload, *udp, *ip;
 
    /* allocate payload */
    payload = gnrc_pktbuf_add(NULL, data, len, GNRC_NETTYPE_UNDEF);
    if (payload == NULL) {
        DEBUG("auto_subnets: unable to copy data to packet buffer\n");
        return -ENOBUFS;
    }
 
    /* allocate UDP header, set source port := destination port */
    udp = gnrc_udp_hdr_build(payload, port, port);
    if (udp == NULL) {
        DEBUG("auto_subnets: unable to allocate UDP header\n");
        gnrc_pktbuf_release(payload);
        return -ENOBUFS;
    }
 
    /* allocate IPv6 header */
    ip = gnrc_ipv6_hdr_build(udp, NULL, addr);
    if (ip == NULL) {
        DEBUG("auto_subnets: unable to allocate IPv6 header\n");
        gnrc_pktbuf_release(udp);
        return -ENOBUFS;
    }
 
    /* add netif header, if interface was given */
    if (netif != NULL) {
        gnrc_pktsnip_t *netif_hdr = gnrc_netif_hdr_build(NULL, 0, NULL, 0);
        if (netif_hdr == NULL) {
            DEBUG("auto_subnets: unable to allocate netif header\n");
            gnrc_pktbuf_release(ip);
            return -ENOBUFS;
        }
 
        gnrc_netif_hdr_set_netif(netif_hdr->data, netif);
        ip = gnrc_pkt_prepend(ip, netif_hdr);
    }
 
    /* send packet */
    if (!gnrc_netapi_dispatch_send(GNRC_NETTYPE_UDP,
                                   GNRC_NETREG_DEMUX_CTX_ALL, ip)) {
        DEBUG("auto_subnets: unable to locate UDP thread\n");
        gnrc_pktbuf_release(ip);
        return -ENETUNREACH;
    }
 
    return 0;
}
#endif /* !IS_USED(MODULE_GNRC_IPV6_AUTO_SUBNETS_SIMPLE) */
 
static void _init_sub_prefix(ipv6_addr_t *out,
                             const ipv6_addr_t *prefix, uint8_t bits,
                             uint8_t idx, uint8_t idx_bits)
{
    uint8_t bytes = bits / 8;
    uint8_t rem   = bits % 8;
    int8_t shift  = 8 - rem - idx_bits;
 
    /* first copy old prefix */
    memset(out, 0, sizeof(*out));
    ipv6_addr_init_prefix(out, prefix, bits);
 
    /* if new bits are between bytes, first copy over the most significant bits */
    if (shift < 0) {
        out->u8[bytes] |= idx >> -shift;
        out->u8[++bytes] = 0;
        shift += 8;
    }
 
    /* shift remaining bits at the end of the prefix */
    out->u8[bytes] |= idx << shift;
}
 
/* returns true if a new prefix was added, false if nothing changed */
static bool _remove_old_prefix(gnrc_netif_t *netif,
                               const ipv6_addr_t *pfx, uint8_t pfx_len,
                               gnrc_pktsnip_t **ext_opts)
{
    gnrc_ipv6_nib_pl_t entry;
    gnrc_pktsnip_t *tmp;
    void *state = NULL;
    ipv6_addr_t old_pfx;
    uint8_t old_pfx_len = CONFIG_GNRC_IPV6_AUTO_SUBNETS_PREFIX_FIX_LEN;
 
    /* iterate prefix list to see if the prefix already exists */
    while (gnrc_ipv6_nib_pl_iter(netif->pid, &state, &entry)) {
        uint8_t match_len = ipv6_addr_match_prefix(&entry.pfx, pfx);
 
        /* The prefix did not change - nothing to do here */
        if (match_len >= pfx_len && pfx_len == entry.pfx_len) {
            return false;
        }
 
        /* find prefix that is closest to the new prefix */
        if (match_len > old_pfx_len) {
            old_pfx_len = entry.pfx_len;
            old_pfx = entry.pfx;
        }
    }
 
    /* no prefix found */
    if (old_pfx_len == CONFIG_GNRC_IPV6_AUTO_SUBNETS_PREFIX_FIX_LEN) {
        return true;
    }
 
    DEBUG("auto_subnets: remove old prefix %s/%u\n",
          ipv6_addr_to_str(addr_str, &old_pfx, sizeof(addr_str)), old_pfx_len);
 
    /* invalidate old prefix in RIO */
    tmp = gnrc_ndp_opt_ri_build(&old_pfx, old_pfx_len, 0,
                                NDP_OPT_RI_FLAGS_PRF_ZERO, *ext_opts);
    if (tmp) {
        *ext_opts = tmp;
    }
 
    /* remove the prefix */
    gnrc_ipv6_nib_pl_del(netif->pid, &old_pfx, old_pfx_len);
 
    return true;
}
 
static void _configure_subnets(uint8_t subnets, uint8_t start_idx, gnrc_netif_t *upstream,
                               const ndp_opt_pi_t *pio)
{
    gnrc_netif_t *downstream = NULL;
    gnrc_pktsnip_t *ext_opts = NULL;
    const ipv6_addr_t *prefix = &pio->prefix;
    uint32_t valid_ltime = byteorder_ntohl(pio->valid_ltime);
    uint32_t pref_ltime = byteorder_ntohl(pio->pref_ltime);
    const uint8_t prefix_len = pio->prefix_len;
    uint8_t new_prefix_len, subnet_len;
 
    DEBUG("auto_subnets: create %u subnets, start with %u\n", subnets, start_idx);
 
    /* Calculate remaining prefix length.
     * For n subnets we consume floor(log_2 n) + 1 bits.
     * To calculate floor(log_2 n) quickly, find the position of the
     * most significant set bit by counting leading zeros.
     */
    subnet_len = 32 - __builtin_clz(subnets);
    new_prefix_len = prefix_len + subnet_len;
 
    if (new_prefix_len > 64) {
        DEBUG("auto_subnets: can't split /%u into %u subnets\n", prefix_len, subnets);
        return;
    }
 
    if (new_prefix_len < may_be_zero(CONFIG_GNRC_IPV6_AUTO_SUBNETS_PREFIX_MIN_LEN)) {
        new_prefix_len = CONFIG_GNRC_IPV6_AUTO_SUBNETS_PREFIX_MIN_LEN;
    }
 
    while ((downstream = gnrc_netif_iter(downstream))) {
        gnrc_pktsnip_t *tmp;
        ipv6_addr_t new_prefix;
        int idx;
 
        if (downstream == upstream) {
            continue;
        }
 
        /* create subnet from upstream prefix */
        _init_sub_prefix(&new_prefix, prefix, prefix_len, ++start_idx, subnet_len);
 
        DEBUG("auto_subnets: configure prefix %s/%u on %u\n",
              ipv6_addr_to_str(addr_str, &new_prefix, sizeof(addr_str)),
              new_prefix_len, downstream->pid);
 
        /* first remove old prefix if the prefix changed */
        if (_remove_old_prefix(downstream, &new_prefix, new_prefix_len, &ext_opts)) {
 
            /* configure subnet on downstream interface */
            idx = gnrc_netif_ipv6_add_prefix(downstream, &new_prefix, new_prefix_len,
                                         valid_ltime, pref_ltime);
            if (idx < 0) {
                DEBUG("auto_subnets: adding prefix to %u failed\n", downstream->pid);
                continue;
            }
 
            /* start advertising subnet */
            gnrc_ipv6_nib_change_rtr_adv_iface(downstream, true);
 
            /* configure RPL root if applicable */
            gnrc_rpl_configure_root(downstream, &downstream->ipv6.addrs[idx]);
        }
 
        /* add route information option with new subnet */
        tmp = gnrc_ndp_opt_ri_build(&new_prefix, new_prefix_len, valid_ltime,
                                    NDP_OPT_RI_FLAGS_PRF_ZERO, ext_opts);
        if (tmp == NULL) {
            DEBUG("auto_subnets: No space left in packet buffer. Not adding RIO\n");
        } else {
            ext_opts = tmp;
        }
    }
 
    /* immediately send an RA with RIO */
    if (ext_opts) {
        gnrc_ndp_rtr_adv_send(upstream, NULL, NULL, true, ext_opts);
    } else {
        DEBUG("auto_subnets: Options empty, not sending RA\n");
    }
}
 
void gnrc_ipv6_nib_rtr_adv_pio_cb(gnrc_netif_t *upstream, const ndp_opt_pi_t *pio)
{
    /* create a subnet for each downstream interface */
    unsigned subnets = gnrc_netif_numof() - 1;
 
    if (subnets == 0) {
        return;
    }
 
    if (pio->valid_ltime.u32 == 0) {
        return;
    }
 
    /* only consider prefix meant for autonomous address configuration */
    if (!(pio->flags & NDP_OPT_PI_FLAGS_A)) {
        return;
    }
 
#if IS_USED(MODULE_GNRC_IPV6_AUTO_SUBNETS_SIMPLE)
    /* if we are the only router on this bus, we can directly choose a prefix */
    _configure_subnets(subnets, 0, upstream, pio);
#else
 
    /* store PIO information for later use */
    if (!_store_pio(pio)) {
        DEBUG("auto_subnets: no space left in PIO cache, increase CONFIG_GNRC_IPV6_AUTO_SUBNETS_NUMOF\n");
        return;
    }
    _upstream  = upstream;
 
    /* start advertising by sending timeout message to the server thread */
    msg_t m = {
        .type = SERVER_MSG_TYPE_TIMEOUT
    };
 
    msg_send(&m, _server_pid);
#endif /* !IS_USED(MODULE_GNRC_IPV6_AUTO_SUBNETS_SIMPLE) */
}
 
#if !IS_USED(MODULE_GNRC_IPV6_AUTO_SUBNETS_SIMPLE)
static bool _all_zero(const uint8_t *addr, size_t len)
{
    for (const uint8_t *end = addr + len; addr != end; ++addr) {
        if (*addr) {
            return false;
        }
    }
    return true;
}
 
static int _alloc_l2addr_entry(const void *addr, size_t len)
{
    int empty = -1;
    for (unsigned i = 0; i < CONFIG_GNRC_IPV6_AUTO_SUBNETS_PEERS_MAX; ++i) {
        if (_all_zero(l2addrs[i], len)) {
            empty = i;
            continue;
        }
        if (memcmp(addr, l2addrs[i], len) == 0) {
            return 0;
        }
    }
 
    if (empty < 0) {
        return -1;
    }
 
    memcpy(l2addrs[empty], addr, len);
    return 1;
}
 
static int _get_my_l2addr_rank(gnrc_netif_t *iface, gnrc_pktsnip_t *pkt)
{
    const void *src_addr;
    gnrc_pktsnip_t *netif_hdr;
    gnrc_netif_hdr_t *hdr;
 
    if (iface == NULL) {
        return 0;
    }
 
    netif_hdr = gnrc_pktsnip_search_type(pkt, GNRC_NETTYPE_NETIF);
    if (netif_hdr == NULL) {
        return 0;
    }
 
    /* ignore packet if it was received on the wrong interface */
    hdr = netif_hdr->data;
    if (iface->pid != hdr->if_pid) {
        return 0;
    }
 
    /* ignore packets without source address */
    src_addr = gnrc_netif_hdr_get_src_addr(hdr);
    if (src_addr == NULL) {
        return 0;
    }
 
    /* check if we have seen the host before */
    if (_alloc_l2addr_entry(src_addr, iface->l2addr_len) == 0) {
        return 0;
    }
 
    return memcmp(iface->l2addr, src_addr, iface->l2addr_len);
}
 
static void _receive_announce(gnrc_pktsnip_t *pkt, uint8_t *subnets, uint8_t *idx_start)
{
    _auto_subnets_request_v0_t *request = pkt->data;
 
    /* Check if we already got an announcement from that host, */
    /* in this case, res will be 0. */
    int res = _get_my_l2addr_rank(_upstream, pkt);
    if (res) {
        /* calculate total number of subnets */
        *subnets += request->num_subnets;
 
        DEBUG("auto_subnets: %u new remote subnets, total %u\n",
              request->num_subnets, *subnets);
 
        /* If other host is before us in order of MAC addresses, add
         * their subnets to our offset */
        if (res > 0) {
            *idx_start += request->num_subnets;
        }
    }
 
    gnrc_pktbuf_release(pkt);
}
 
static void _send_announce(uint8_t local_subnets, xtimer_t *timer, msg_t *msg)
{
    uint32_t timeout_us;
    _auto_subnets_request_v0_t request = {
        .num_subnets = local_subnets,
    };
 
    /* broadcast the number of subnets we want to create */
    _send_udp(_upstream, &ipv6_addr_all_routers_link_local,
              CONFIG_GNRC_IPV6_AUTO_SUBNETS_PORT,
              &request, sizeof(request));
 
    /* configure timeout for resend */
    timeout_us = random_uint32_range(
                    CONFIG_GNRC_IPV6_AUTO_SUBNETS_TIMEOUT_MS * US_PER_MS / 2,
                    CONFIG_GNRC_IPV6_AUTO_SUBNETS_TIMEOUT_MS * US_PER_MS);
    xtimer_set_msg(timer, timeout_us, msg, _server_pid);
    DEBUG("auto_subnets: announce sent, next timeout in %" PRIu32 " µs\n", timeout_us);
}
 
static void _process_pio_cache(uint8_t subnets, uint8_t idx_start, gnrc_netif_t *upstream)
{
    mutex_lock(&_pio_cache_lock);
 
    for (unsigned i = 0; i < ARRAY_SIZE(_pio_cache); ++i) {
        if (!_pio_cache[i].len) {
            continue;
        }
 
        /* use PIO for prefix configuration */
        _configure_subnets(subnets, idx_start, upstream, &_pio_cache[i]);
 
        /* invalidate entry */
        _pio_cache[i].len = 0;
    }
 
    mutex_unlock(&_pio_cache_lock);
}
 
static void *_eventloop(void *arg)
{
    (void)arg;
 
    xtimer_t timeout_timer;
    msg_t msg, timeout_msg = { .type = SERVER_MSG_TYPE_TIMEOUT };
    gnrc_netreg_entry_t server = GNRC_NETREG_ENTRY_INIT_PID(0, KERNEL_PID_UNDEF);
    const uint8_t local_subnets = gnrc_netif_numof() - 1;
    uint8_t idx_start = 0;
    uint8_t subnets = local_subnets;
    uint8_t tx_period = CONFIG_GNRC_IPV6_AUTO_SUBNETS_TX_PER_PERIOD;
 
    /* only used with CONFIG_GNRC_IPV6_AUTO_SUBNETS_STATIC set */
    uint8_t idx_old = 0;
    uint8_t subnets_old = 0;
 
    DEBUG("auto_subnets: %u local subnets\n", subnets);
 
    if (subnets == 0) {
        return NULL;
    }
 
    /* setup the message queue */
    msg_init_queue(server_queue, SERVER_MSG_QUEUE_SIZE);
 
    /* register server to receive messages from given port */
    gnrc_netreg_entry_init_pid(&server, CONFIG_GNRC_IPV6_AUTO_SUBNETS_PORT, thread_getpid());
    gnrc_netreg_register(GNRC_NETTYPE_UDP, &server);
 
    while (1) {
        msg_receive(&msg);
 
        switch (msg.type) {
        case GNRC_NETAPI_MSG_TYPE_RCV:
            _receive_announce(msg.content.ptr, &subnets, &idx_start);
            break;
        case SERVER_MSG_TYPE_TIMEOUT:
            if (tx_period--) {
                /* send subnet announcement */
                _send_announce(local_subnets, &timeout_timer, &timeout_msg);
            } else {
 
                /* don't re-enumerate subnets of a downstream router goes down */
                if (CONFIG_GNRC_IPV6_AUTO_SUBNETS_STATIC) {
                    /* If we got less subnets than before, use the old value */
                    if (subnets < subnets_old) {
                        subnets = subnets_old;
                        idx_start = idx_old;
                    }
                    /* Store subnet high water mark for later use */
                    else {
                        subnets_old = subnets;
                        idx_old = idx_start;
                    }
                }
 
                /* config round done, configure subnets */
                _process_pio_cache(subnets, idx_start, _upstream);
 
                /* start a new round of counting */
                tx_period = CONFIG_GNRC_IPV6_AUTO_SUBNETS_TX_PER_PERIOD;
                memset(l2addrs, 0, sizeof(l2addrs));
                idx_start = 0;
                subnets = local_subnets;
            }
            break;
        }
    }
 
    /* never reached */
    return NULL;
}
 
void gnrc_ipv6_auto_subnets_init(void)
{
    /* initiate auto_subnets thread */
    _server_pid = thread_create(auto_subnets_stack, sizeof(auto_subnets_stack),
                                THREAD_PRIORITY_MAIN - 1, THREAD_CREATE_STACKTEST,
                                _eventloop, NULL, "auto_subnets");
}
#endif /* !IS_USED(MODULE_GNRC_IPV6_AUTO_SUBNETS_SIMPLE) */
#endif /* !DOXYGEN */