systemd-stable/src/libsystemd-network/sd-radv.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */
/***
  Copyright © 2017 Intel Corporation. All rights reserved.
***/

#include <netinet/icmp6.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include "sd-radv.h"

#include "alloc-util.h"
#include "dns-domain.h"
#include "ether-addr-util.h"
#include "event-util.h"
#include "fd-util.h"
#include "icmp6-util.h"
#include "in-addr-util.h"
#include "io-util.h"
#include "macro.h"
#include "memory-util.h"
#include "network-common.h"
#include "radv-internal.h"
#include "random-util.h"
#include "socket-util.h"
#include "string-util.h"
#include "strv.h"

_public_ int sd_radv_new(sd_radv **ret) {
        _cleanup_(sd_radv_unrefp) sd_radv *ra = NULL;

        assert_return(ret, -EINVAL);

        ra = new(sd_radv, 1);
        if (!ra)
                return -ENOMEM;

        *ra = (sd_radv) {
                .n_ref = 1,
                .fd = -1,
        };

        *ret = TAKE_PTR(ra);

        return 0;
}

_public_ int sd_radv_attach_event(sd_radv *ra, sd_event *event, int64_t priority) {
        int r;

        assert_return(ra, -EINVAL);
        assert_return(!ra->event, -EBUSY);

        if (event)
                ra->event = sd_event_ref(event);
        else {
                r = sd_event_default(&ra->event);
                if (r < 0)
                        return 0;
        }

        ra->event_priority = priority;

        return 0;
}

_public_ int sd_radv_detach_event(sd_radv *ra) {

        assert_return(ra, -EINVAL);

        ra->event = sd_event_unref(ra->event);
        return 0;
}

_public_ sd_event *sd_radv_get_event(sd_radv *ra) {
        assert_return(ra, NULL);

        return ra->event;
}

_public_ int sd_radv_is_running(sd_radv *ra) {
        assert_return(ra, false);

        return ra->state != SD_RADV_STATE_IDLE;
}

static void radv_reset(sd_radv *ra) {
        assert(ra);

        (void) event_source_disable(ra->timeout_event_source);

        ra->recv_event_source =
                sd_event_source_unref(ra->recv_event_source);

        ra->ra_sent = 0;
}

static sd_radv *radv_free(sd_radv *ra) {
        if (!ra)
                return NULL;

        while (ra->prefixes) {
                sd_radv_prefix *p = ra->prefixes;

                LIST_REMOVE(prefix, ra->prefixes, p);
                sd_radv_prefix_unref(p);
        }

        while (ra->route_prefixes) {
                sd_radv_route_prefix *p = ra->route_prefixes;

                LIST_REMOVE(prefix, ra->route_prefixes, p);
                sd_radv_route_prefix_unref(p);
        }

        free(ra->rdnss);
        free(ra->dnssl);

        ra->timeout_event_source = sd_event_source_unref(ra->timeout_event_source);

        radv_reset(ra);

        sd_radv_detach_event(ra);

        ra->fd = safe_close(ra->fd);
        free(ra->ifname);

        return mfree(ra);
}

DEFINE_PUBLIC_TRIVIAL_REF_UNREF_FUNC(sd_radv, sd_radv, radv_free);

static int radv_send(sd_radv *ra, const struct in6_addr *dst, uint32_t router_lifetime) {
        sd_radv_route_prefix *rt;
        sd_radv_prefix *p;
        struct sockaddr_in6 dst_addr = {
                .sin6_family = AF_INET6,
                .sin6_addr = IN6ADDR_ALL_NODES_MULTICAST_INIT,
        };
        struct nd_router_advert adv = {};
        struct {
                struct nd_opt_hdr opthdr;
                struct ether_addr slladdr;
        } _packed_ opt_mac = {
                .opthdr = {
                        .nd_opt_type = ND_OPT_SOURCE_LINKADDR,
                        .nd_opt_len = (sizeof(struct nd_opt_hdr) +
                                       sizeof(struct ether_addr) - 1) /8 + 1,
                },
        };
        struct nd_opt_mtu opt_mtu =  {
                .nd_opt_mtu_type = ND_OPT_MTU,
                .nd_opt_mtu_len = 1,
        };
        /* Reserve iov space for RA header, linkaddr, MTU, N prefixes, N routes, RDNSS
           and DNSSL */
        struct iovec iov[5 + ra->n_prefixes + ra->n_route_prefixes];
        struct msghdr msg = {
                .msg_name = &dst_addr,
                .msg_namelen = sizeof(dst_addr),
                .msg_iov = iov,
        };
        usec_t time_now;
        int r;

        assert(ra);

        r = sd_event_now(ra->event, clock_boottime_or_monotonic(), &time_now);
        if (r < 0)
                return r;

        if (dst && in6_addr_is_set(dst))
                dst_addr.sin6_addr = *dst;

        adv.nd_ra_type = ND_ROUTER_ADVERT;
        adv.nd_ra_curhoplimit = ra->hop_limit;
        adv.nd_ra_flags_reserved = ra->flags;
        adv.nd_ra_router_lifetime = htobe16(router_lifetime);
        iov[msg.msg_iovlen++] = IOVEC_MAKE(&adv, sizeof(adv));

        /* MAC address is optional, either because the link does not use L2
           addresses or load sharing is desired. See RFC 4861, Section 4.2 */
        if (!ether_addr_is_null(&ra->mac_addr)) {
                opt_mac.slladdr = ra->mac_addr;
                iov[msg.msg_iovlen++] = IOVEC_MAKE(&opt_mac, sizeof(opt_mac));
        }

        if (ra->mtu) {
                opt_mtu.nd_opt_mtu_mtu = htobe32(ra->mtu);
                iov[msg.msg_iovlen++] = IOVEC_MAKE(&opt_mtu, sizeof(opt_mtu));
        }

        LIST_FOREACH(prefix, p, ra->prefixes) {
                if (p->valid_until) {

                        if (time_now > p->valid_until)
                                p->opt.valid_lifetime = 0;
                        else
                                p->opt.valid_lifetime = htobe32((p->valid_until - time_now) / USEC_PER_SEC);

                        if (time_now > p->preferred_until)
                                p->opt.preferred_lifetime = 0;
                        else
                                p->opt.preferred_lifetime = htobe32((p->preferred_until - time_now) / USEC_PER_SEC);
                }
                iov[msg.msg_iovlen++] = IOVEC_MAKE(&p->opt, sizeof(p->opt));
        }

        LIST_FOREACH(prefix, rt, ra->route_prefixes)
                iov[msg.msg_iovlen++] = IOVEC_MAKE(&rt->opt, sizeof(rt->opt));

        if (ra->rdnss)
                iov[msg.msg_iovlen++] = IOVEC_MAKE(ra->rdnss, ra->rdnss->length * 8);

        if (ra->dnssl)
                iov[msg.msg_iovlen++] = IOVEC_MAKE(ra->dnssl, ra->dnssl->length * 8);

        if (sendmsg(ra->fd, &msg, 0) < 0)
                return -errno;

        return 0;
}

static int radv_recv(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
        sd_radv *ra = userdata;
        _cleanup_free_ char *addr = NULL;
        struct in6_addr src;
        triple_timestamp timestamp;
        int r;
        ssize_t buflen;
        _cleanup_free_ char *buf = NULL;

        assert(s);
        assert(ra);
        assert(ra->event);

        buflen = next_datagram_size_fd(fd);
        if (buflen < 0)
                return (int) buflen;

        buf = new0(char, buflen);
        if (!buf)
                return -ENOMEM;

        r = icmp6_receive(fd, buf, buflen, &src, &timestamp);
        if (r < 0) {
                switch (r) {
                case -EADDRNOTAVAIL:
                        (void) in_addr_to_string(AF_INET6, (const union in_addr_union*) &src, &addr);
                        log_radv(ra, "Received RS from non-link-local address %s. Ignoring", addr);
                        break;

                case -EMULTIHOP:
                        log_radv(ra, "Received RS with invalid hop limit. Ignoring.");
                        break;

                case -EPFNOSUPPORT:
                        log_radv(ra, "Received invalid source address from ICMPv6 socket. Ignoring.");
                        break;

                case -EAGAIN: /* ignore spurious wakeups */
                        break;

                default:
                        log_radv_errno(ra, r, "Unexpected error receiving from ICMPv6 socket, Ignoring: %m");
                        break;
                }

                return 0;
        }

        if ((size_t) buflen < sizeof(struct nd_router_solicit)) {
                log_radv(ra, "Too short packet received, ignoring");
                return 0;
        }

        (void) in_addr_to_string(AF_INET6, (const union in_addr_union*) &src, &addr);

        r = radv_send(ra, &src, ra->lifetime);
        if (r < 0)
                log_radv_errno(ra, r, "Unable to send solicited Router Advertisement to %s, ignoring: %m", strnull(addr));
        else
                log_radv(ra, "Sent solicited Router Advertisement to %s", strnull(addr));

        return 0;
}

static usec_t radv_compute_timeout(usec_t min, usec_t max) {
        assert_return(min <= max, SD_RADV_DEFAULT_MIN_TIMEOUT_USEC);

        /* RFC 4861: min must be no less than 3s, max must be no less than 4s */
        min = MAX(min, 3*USEC_PER_SEC);
        max = MAX(max, 4*USEC_PER_SEC);

        return min + (random_u32() % (max - min));
}

static int radv_timeout(sd_event_source *s, uint64_t usec, void *userdata) {
        int r;
        sd_radv *ra = userdata;
        usec_t min_timeout = SD_RADV_DEFAULT_MIN_TIMEOUT_USEC;
        usec_t max_timeout = SD_RADV_DEFAULT_MAX_TIMEOUT_USEC;
        usec_t time_now, timeout;

        assert(s);
        assert(ra);
        assert(ra->event);

        r = sd_event_now(ra->event, clock_boottime_or_monotonic(), &time_now);
        if (r < 0)
                goto fail;

        r = radv_send(ra, NULL, ra->lifetime);
        if (r < 0)
                log_radv_errno(ra, r, "Unable to send Router Advertisement: %m");

        /* RFC 4861, Section 6.2.4, sending initial Router Advertisements */
        if (ra->ra_sent < SD_RADV_MAX_INITIAL_RTR_ADVERTISEMENTS) {
                max_timeout = SD_RADV_MAX_INITIAL_RTR_ADVERT_INTERVAL_USEC;
                min_timeout = SD_RADV_MAX_INITIAL_RTR_ADVERT_INTERVAL_USEC / 3;
        }

        /* RFC 4861, Section 6.2.1, lifetime must be at least MaxRtrAdvInterval,
           so lower the interval here */
        if (ra->lifetime > 0 && (ra->lifetime * USEC_PER_SEC) < max_timeout) {
                max_timeout = ra->lifetime * USEC_PER_SEC;
                min_timeout = max_timeout / 3;
        }

        timeout = radv_compute_timeout(min_timeout, max_timeout);
        log_radv(ra, "Next Router Advertisement in %s", FORMAT_TIMESPAN(timeout, USEC_PER_SEC));

        r = event_reset_time(ra->event, &ra->timeout_event_source,
                             clock_boottime_or_monotonic(),
                             time_now + timeout, MSEC_PER_SEC,
                             radv_timeout, ra,
                             ra->event_priority, "radv-timeout", true);
        if (r < 0)
                goto fail;

        ra->ra_sent++;

        return 0;

fail:
        sd_radv_stop(ra);

        return 0;
}

_public_ int sd_radv_stop(sd_radv *ra) {
        int r;

        if (!ra)
                return 0;

        if (ra->state == SD_RADV_STATE_IDLE)
                return 0;

        log_radv(ra, "Stopping IPv6 Router Advertisement daemon");

        /* RFC 4861, Section 6.2.5, send at least one Router Advertisement
           with zero lifetime  */
        r = radv_send(ra, NULL, 0);
        if (r < 0)
                log_radv_errno(ra, r, "Unable to send last Router Advertisement with router lifetime set to zero: %m");

        radv_reset(ra);
        ra->fd = safe_close(ra->fd);
        ra->state = SD_RADV_STATE_IDLE;

        return 0;
}

_public_ int sd_radv_start(sd_radv *ra) {
        int r;

        assert_return(ra, -EINVAL);
        assert_return(ra->event, -EINVAL);
        assert_return(ra->ifindex > 0, -EINVAL);

        if (ra->state != SD_RADV_STATE_IDLE)
                return 0;

        r = event_reset_time(ra->event, &ra->timeout_event_source,
                             clock_boottime_or_monotonic(),
                             0, 0,
                             radv_timeout, ra,
                             ra->event_priority, "radv-timeout", true);
        if (r < 0)
                goto fail;

        r = icmp6_bind_router_advertisement(ra->ifindex);
        if (r < 0)
                goto fail;

        ra->fd = r;

        r = sd_event_add_io(ra->event, &ra->recv_event_source, ra->fd, EPOLLIN, radv_recv, ra);
        if (r < 0)
                goto fail;

        r = sd_event_source_set_priority(ra->recv_event_source, ra->event_priority);
        if (r < 0)
                goto fail;

        (void) sd_event_source_set_description(ra->recv_event_source, "radv-receive-message");

        ra->state = SD_RADV_STATE_ADVERTISING;

        log_radv(ra, "Started IPv6 Router Advertisement daemon");

        return 0;

 fail:
        radv_reset(ra);

        return r;
}

_public_ int sd_radv_set_ifindex(sd_radv *ra, int ifindex) {
        assert_return(ra, -EINVAL);
        assert_return(ifindex > 0, -EINVAL);

        if (ra->state != SD_RADV_STATE_IDLE)
                return -EBUSY;

        ra->ifindex = ifindex;

        return 0;
}

int sd_radv_set_ifname(sd_radv *ra, const char *ifname) {
        assert_return(ra, -EINVAL);
        assert_return(ifname, -EINVAL);

        if (!ifname_valid_full(ifname, IFNAME_VALID_ALTERNATIVE))
                return -EINVAL;

        return free_and_strdup(&ra->ifname, ifname);
}

const char *sd_radv_get_ifname(sd_radv *ra) {
        if (!ra)
                return NULL;

        return get_ifname(ra->ifindex, &ra->ifname);
}

_public_ int sd_radv_set_mac(sd_radv *ra, const struct ether_addr *mac_addr) {
        assert_return(ra, -EINVAL);

        if (ra->state != SD_RADV_STATE_IDLE)
                return -EBUSY;

        if (mac_addr)
                ra->mac_addr = *mac_addr;
        else
                zero(ra->mac_addr);

        return 0;
}

_public_ int sd_radv_set_mtu(sd_radv *ra, uint32_t mtu) {
        assert_return(ra, -EINVAL);
        assert_return(mtu >= 1280, -EINVAL);

        ra->mtu = mtu;

        return 0;
}

_public_ int sd_radv_set_hop_limit(sd_radv *ra, uint8_t hop_limit) {
        assert_return(ra, -EINVAL);

        if (ra->state != SD_RADV_STATE_IDLE)
                return -EBUSY;

        ra->hop_limit = hop_limit;

        return 0;
}

_public_ int sd_radv_set_router_lifetime(sd_radv *ra, uint16_t router_lifetime) {
        assert_return(ra, -EINVAL);

        if (ra->state != SD_RADV_STATE_IDLE)
                return -EBUSY;

        /* RFC 4191, Section 2.2, "...If the Router Lifetime is zero, the preference value MUST be set
         * to (00) by the sender..." */
        if (router_lifetime == 0 &&
            (ra->flags & (0x3 << 3)) != (SD_NDISC_PREFERENCE_MEDIUM << 3))
                return -ETIME;

        ra->lifetime = router_lifetime;

        return 0;
}

_public_ int sd_radv_set_managed_information(sd_radv *ra, int managed) {
        assert_return(ra, -EINVAL);

        if (ra->state != SD_RADV_STATE_IDLE)
                return -EBUSY;

        SET_FLAG(ra->flags, ND_RA_FLAG_MANAGED, managed);

        return 0;
}

_public_ int sd_radv_set_other_information(sd_radv *ra, int other) {
        assert_return(ra, -EINVAL);

        if (ra->state != SD_RADV_STATE_IDLE)
                return -EBUSY;

        SET_FLAG(ra->flags, ND_RA_FLAG_OTHER, other);

        return 0;
}

_public_ int sd_radv_set_preference(sd_radv *ra, unsigned preference) {
        assert_return(ra, -EINVAL);
        assert_return(IN_SET(preference,
                             SD_NDISC_PREFERENCE_LOW,
                             SD_NDISC_PREFERENCE_MEDIUM,
                             SD_NDISC_PREFERENCE_HIGH), -EINVAL);

        /* RFC 4191, Section 2.2, "...If the Router Lifetime is zero, the preference value MUST be set
         * to (00) by the sender..." */
        if (ra->lifetime == 0 && preference != SD_NDISC_PREFERENCE_MEDIUM)
                return -EINVAL;

        ra->flags = (ra->flags & ~(0x3 << 3)) | (preference << 3);

        return 0;
}

_public_ int sd_radv_add_prefix(sd_radv *ra, sd_radv_prefix *p, int dynamic) {
        sd_radv_prefix *cur;
        int r;
        _cleanup_free_ char *addr_p = NULL;
        usec_t time_now, valid, preferred, valid_until, preferred_until;

        assert_return(ra, -EINVAL);

        if (!p)
                return -EINVAL;

        /* Refuse prefixes that don't have a prefix set */
        if (in6_addr_is_null(&p->opt.in6_addr))
                return -ENOEXEC;

        (void) in_addr_prefix_to_string(AF_INET6,
                                        (const union in_addr_union*) &p->opt.in6_addr,
                                        p->opt.prefixlen, &addr_p);

        LIST_FOREACH(prefix, cur, ra->prefixes) {

                r = in_addr_prefix_intersect(AF_INET6,
                                             (const union in_addr_union*) &cur->opt.in6_addr,
                                             cur->opt.prefixlen,
                                             (const union in_addr_union*) &p->opt.in6_addr,
                                             p->opt.prefixlen);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                if (dynamic && cur->opt.prefixlen == p->opt.prefixlen)
                        goto update;

                _cleanup_free_ char *addr_cur = NULL;
                (void) in_addr_prefix_to_string(AF_INET6,
                                                (const union in_addr_union*) &cur->opt.in6_addr,
                                                cur->opt.prefixlen, &addr_cur);
                return log_radv_errno(ra, SYNTHETIC_ERRNO(EEXIST),
                                      "IPv6 prefix %s already configured, ignoring %s",
                                      strna(addr_cur), strna(addr_p));
        }

        p = sd_radv_prefix_ref(p);

        LIST_APPEND(prefix, ra->prefixes, p);

        ra->n_prefixes++;

        if (!dynamic) {
                log_radv(ra, "Added prefix %s", strna(addr_p));
                return 0;
        }

        cur = p;

        /* If RAs have already been sent, send an RA immediately to announce the newly-added prefix */
        if (ra->ra_sent > 0) {
                r = radv_send(ra, NULL, ra->lifetime);
                if (r < 0)
                        log_radv_errno(ra, r, "Unable to send Router Advertisement for added prefix: %m");
                else
                        log_radv(ra, "Sent Router Advertisement for added prefix");
        }

 update:
        r = sd_event_now(ra->event, clock_boottime_or_monotonic(), &time_now);
        if (r < 0)
                return r;

        valid = be32toh(p->opt.valid_lifetime) * USEC_PER_SEC;
        valid_until = usec_add(valid, time_now);
        if (valid_until == USEC_INFINITY)
                return -EOVERFLOW;

        preferred = be32toh(p->opt.preferred_lifetime) * USEC_PER_SEC;
        preferred_until = usec_add(preferred, time_now);
        if (preferred_until == USEC_INFINITY)
                return -EOVERFLOW;

        cur->valid_until = valid_until;
        cur->preferred_until = preferred_until;

        log_radv(ra, "Updated prefix %s preferred %s valid %s",
                 strna(addr_p),
                 FORMAT_TIMESPAN(preferred, USEC_PER_SEC),
                 FORMAT_TIMESPAN(valid, USEC_PER_SEC));

        return 0;
}

_public_ sd_radv_prefix *sd_radv_remove_prefix(sd_radv *ra,
                                               const struct in6_addr *prefix,
                                               unsigned char prefixlen) {
        sd_radv_prefix *cur, *next;

        assert_return(ra, NULL);
        assert_return(prefix, NULL);

        LIST_FOREACH_SAFE(prefix, cur, next, ra->prefixes) {
                if (prefixlen != cur->opt.prefixlen)
                        continue;

                if (!in6_addr_equal(prefix, &cur->opt.in6_addr))
                        continue;

                LIST_REMOVE(prefix, ra->prefixes, cur);
                ra->n_prefixes--;
                sd_radv_prefix_unref(cur);

                break;
        }

        return cur;
}

_public_ int sd_radv_add_route_prefix(sd_radv *ra, sd_radv_route_prefix *p, int dynamic) {
        usec_t time_now, valid, valid_until;
        _cleanup_free_ char *pretty = NULL;
        sd_radv_route_prefix *cur;
        int r;

        assert_return(ra, -EINVAL);

        if (!p)
                return -EINVAL;

        (void) in_addr_prefix_to_string(AF_INET6,
                                        (const union in_addr_union*) &p->opt.in6_addr,
                                        p->opt.prefixlen, &pretty);

        LIST_FOREACH(prefix, cur, ra->route_prefixes) {

                r = in_addr_prefix_intersect(AF_INET6,
                                             (const union in_addr_union*) &cur->opt.in6_addr,
                                             cur->opt.prefixlen,
                                             (const union in_addr_union*) &p->opt.in6_addr,
                                             p->opt.prefixlen);
                if (r < 0)
                        return r;
                if (r == 0)
                        continue;

                if (dynamic && cur->opt.prefixlen == p->opt.prefixlen)
                        goto update;

                _cleanup_free_ char *addr = NULL;
                (void) in_addr_prefix_to_string(AF_INET6,
                                                (const union in_addr_union*) &cur->opt.in6_addr,
                                                cur->opt.prefixlen, &addr);
                return log_radv_errno(ra, SYNTHETIC_ERRNO(EEXIST),
                                      "IPv6 route prefix %s already configured, ignoring %s",
                                      strna(addr), strna(pretty));
        }

        p = sd_radv_route_prefix_ref(p);

        LIST_APPEND(prefix, ra->route_prefixes, p);
        ra->n_route_prefixes++;

        if (!dynamic) {
                log_radv(ra, "Added prefix %s", strna(pretty));
                return 0;
        }

        /* If RAs have already been sent, send an RA immediately to announce the newly-added route prefix */
        if (ra->ra_sent > 0) {
                r = radv_send(ra, NULL, ra->lifetime);
                if (r < 0)
                        log_radv_errno(ra, r, "Unable to send Router Advertisement for added route prefix: %m");
                else
                        log_radv(ra, "Sent Router Advertisement for added route prefix");
        }

 update:
        r = sd_event_now(ra->event, clock_boottime_or_monotonic(), &time_now);
        if (r < 0)
                return r;

        valid = be32toh(p->opt.lifetime) * USEC_PER_SEC;
        valid_until = usec_add(valid, time_now);
        if (valid_until == USEC_INFINITY)
                return -EOVERFLOW;

        log_radv(ra, "Updated route prefix %s valid %s",
                 strna(pretty),
                 FORMAT_TIMESPAN(valid, USEC_PER_SEC));

        return 0;
}

_public_ int sd_radv_set_rdnss(sd_radv *ra, uint32_t lifetime,
                               const struct in6_addr *dns, size_t n_dns) {
        _cleanup_free_ struct sd_radv_opt_dns *opt_rdnss = NULL;
        size_t len;

        assert_return(ra, -EINVAL);
        assert_return(n_dns < 128, -EINVAL);

        if (!dns || n_dns == 0) {
                ra->rdnss = mfree(ra->rdnss);
                ra->n_rdnss = 0;

                return 0;
        }

        len = sizeof(struct sd_radv_opt_dns) + sizeof(struct in6_addr) * n_dns;

        opt_rdnss = malloc0(len);
        if (!opt_rdnss)
                return -ENOMEM;

        opt_rdnss->type = SD_RADV_OPT_RDNSS;
        opt_rdnss->length = len / 8;
        opt_rdnss->lifetime = htobe32(lifetime);

        memcpy(opt_rdnss + 1, dns, n_dns * sizeof(struct in6_addr));

        free_and_replace(ra->rdnss, opt_rdnss);

        ra->n_rdnss = n_dns;

        return 0;
}

_public_ int sd_radv_set_dnssl(sd_radv *ra, uint32_t lifetime,
                               char **search_list) {
        _cleanup_free_ struct sd_radv_opt_dns *opt_dnssl = NULL;
        size_t len = 0;
        char **s;
        uint8_t *p;

        assert_return(ra, -EINVAL);

        if (strv_isempty(search_list)) {
                ra->dnssl = mfree(ra->dnssl);
                return 0;
        }

        STRV_FOREACH(s, search_list)
                len += strlen(*s) + 2;

        len = (sizeof(struct sd_radv_opt_dns) + len + 7) & ~0x7;

        opt_dnssl = malloc0(len);
        if (!opt_dnssl)
                return -ENOMEM;

        opt_dnssl->type = SD_RADV_OPT_DNSSL;
        opt_dnssl->length = len / 8;
        opt_dnssl->lifetime = htobe32(lifetime);

        p = (uint8_t *)(opt_dnssl + 1);
        len -= sizeof(struct sd_radv_opt_dns);

        STRV_FOREACH(s, search_list) {
                int r;

                r = dns_name_to_wire_format(*s, p, len, false);
                if (r < 0)
                        return r;

                if (len < (size_t)r)
                        return -ENOBUFS;

                p += r;
                len -= r;
        }

        free_and_replace(ra->dnssl, opt_dnssl);

        return 0;
}

_public_ int sd_radv_prefix_new(sd_radv_prefix **ret) {
        sd_radv_prefix *p;

        assert_return(ret, -EINVAL);

        p = new(sd_radv_prefix, 1);
        if (!p)
                return -ENOMEM;

        *p = (sd_radv_prefix) {
                .n_ref = 1,

                .opt.type = ND_OPT_PREFIX_INFORMATION,
                .opt.length = (sizeof(p->opt) - 1)/8 + 1,
                .opt.prefixlen = 64,

                /* RFC 4861, Section 6.2.1 */
                .opt.flags = ND_OPT_PI_FLAG_ONLINK|ND_OPT_PI_FLAG_AUTO,

                .opt.preferred_lifetime = htobe32(604800),
                .opt.valid_lifetime = htobe32(2592000),
        };

        *ret = p;
        return 0;
}

DEFINE_PUBLIC_TRIVIAL_REF_UNREF_FUNC(sd_radv_prefix, sd_radv_prefix, mfree);

_public_ int sd_radv_prefix_set_prefix(sd_radv_prefix *p, const struct in6_addr *in6_addr,
                                       unsigned char prefixlen) {
        assert_return(p, -EINVAL);
        assert_return(in6_addr, -EINVAL);

        if (prefixlen < 3 || prefixlen > 128)
                return -EINVAL;

        if (prefixlen > 64)
                /* unusual but allowed, log it */
                log_radv(NULL, "Unusual prefix length %d greater than 64", prefixlen);

        p->opt.in6_addr = *in6_addr;
        p->opt.prefixlen = prefixlen;

        return 0;
}

_public_ int sd_radv_prefix_get_prefix(sd_radv_prefix *p, struct in6_addr *ret_in6_addr,
                                       unsigned char *ret_prefixlen) {
        assert_return(p, -EINVAL);
        assert_return(ret_in6_addr, -EINVAL);
        assert_return(ret_prefixlen, -EINVAL);

        *ret_in6_addr = p->opt.in6_addr;
        *ret_prefixlen = p->opt.prefixlen;

        return 0;
}

_public_ int sd_radv_prefix_set_onlink(sd_radv_prefix *p, int onlink) {
        assert_return(p, -EINVAL);

        SET_FLAG(p->opt.flags, ND_OPT_PI_FLAG_ONLINK, onlink);

        return 0;
}

_public_ int sd_radv_prefix_set_address_autoconfiguration(sd_radv_prefix *p,
                                                          int address_autoconfiguration) {
        assert_return(p, -EINVAL);

        SET_FLAG(p->opt.flags, ND_OPT_PI_FLAG_AUTO, address_autoconfiguration);

        return 0;
}

_public_ int sd_radv_prefix_set_valid_lifetime(sd_radv_prefix *p,
                                               uint32_t valid_lifetime) {
        assert_return(p, -EINVAL);

        p->opt.valid_lifetime = htobe32(valid_lifetime);

        return 0;
}

_public_ int sd_radv_prefix_set_preferred_lifetime(sd_radv_prefix *p,
                                                   uint32_t preferred_lifetime) {
        assert_return(p, -EINVAL);

        p->opt.preferred_lifetime = htobe32(preferred_lifetime);

        return 0;
}

_public_ int sd_radv_route_prefix_new(sd_radv_route_prefix **ret) {
        sd_radv_route_prefix *p;

        assert_return(ret, -EINVAL);

        p = new(sd_radv_route_prefix, 1);
        if (!p)
                return -ENOMEM;

        *p = (sd_radv_route_prefix) {
                .n_ref = 1,

                .opt.type = SD_RADV_OPT_ROUTE_INFORMATION,
                .opt.length = DIV_ROUND_UP(sizeof(p->opt), 8),
                .opt.prefixlen = 64,

                .opt.lifetime = htobe32(604800),
        };

        *ret = p;
        return 0;
}

DEFINE_PUBLIC_TRIVIAL_REF_UNREF_FUNC(sd_radv_route_prefix, sd_radv_route_prefix, mfree);

_public_ int sd_radv_prefix_set_route_prefix(sd_radv_route_prefix *p, const struct in6_addr *in6_addr,
                                             unsigned char prefixlen) {
        assert_return(p, -EINVAL);
        assert_return(in6_addr, -EINVAL);

        if (prefixlen > 128)
                return -EINVAL;

        if (prefixlen > 64)
                /* unusual but allowed, log it */
                log_radv(NULL, "Unusual prefix length %u greater than 64", prefixlen);

        p->opt.in6_addr = *in6_addr;
        p->opt.prefixlen = prefixlen;

        return 0;
}

_public_ int sd_radv_route_prefix_set_lifetime(sd_radv_route_prefix *p, uint32_t valid_lifetime) {
        assert_return(p, -EINVAL);

        p->opt.lifetime = htobe32(valid_lifetime);

        return 0;
}