[thirdparty/systemd.git] / src / resolve / resolved-dns-synthesize.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include "alloc-util.h"
#include "hostname-util.h"
#include "local-addresses.h"
#include "missing_network.h"
#include "resolved-dns-synthesize.h"

int dns_synthesize_ifindex(int ifindex) {

        /* When the caller asked for resolving on a specific
         * interface, we synthesize the answer for that
         * interface. However, if nothing specific was claimed and we
         * only return localhost RRs, we synthesize the answer for
         * localhost. */

        if (ifindex > 0)
                return ifindex;

        return LOOPBACK_IFINDEX;
}

int dns_synthesize_family(uint64_t flags) {

        /* Picks an address family depending on set flags. This is
         * purely for synthesized answers, where the family we return
         * for the reply should match what was requested in the
         * question, even though we are synthesizing the answer
         * here. */

        if (!(flags & SD_RESOLVED_DNS)) {
                if (flags & (SD_RESOLVED_LLMNR_IPV4|SD_RESOLVED_MDNS_IPV4))
                        return AF_INET;
                if (flags & (SD_RESOLVED_LLMNR_IPV6|SD_RESOLVED_MDNS_IPV6))
                        return AF_INET6;
        }

        return AF_UNSPEC;
}

DnsProtocol dns_synthesize_protocol(uint64_t flags) {

        /* Similar as dns_synthesize_family() but does this for the
         * protocol. If resolving via DNS was requested, we claim it
         * was DNS. Similar, if nothing specific was
         * requested. However, if only resolving via LLMNR was
         * requested we return that. */

        if (flags & SD_RESOLVED_DNS)
                return DNS_PROTOCOL_DNS;
        if (flags & SD_RESOLVED_LLMNR)
                return DNS_PROTOCOL_LLMNR;
        if (flags & SD_RESOLVED_MDNS)
                return DNS_PROTOCOL_MDNS;

        return DNS_PROTOCOL_DNS;
}

static int synthesize_localhost_rr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
        int r;

        assert(m);
        assert(key);
        assert(answer);

        r = dns_answer_reserve(answer, 2);
        if (r < 0)
                return r;

        if (IN_SET(key->type, DNS_TYPE_A, DNS_TYPE_ANY)) {
                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;

                rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_A, dns_resource_key_name(key));
                if (!rr)
                        return -ENOMEM;

                rr->a.in_addr.s_addr = htobe32(INADDR_LOOPBACK);

                r = dns_answer_add(*answer, rr, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED, NULL);
                if (r < 0)
                        return r;
        }

        if (IN_SET(key->type, DNS_TYPE_AAAA, DNS_TYPE_ANY) && socket_ipv6_is_enabled()) {
                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;

                rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_AAAA, dns_resource_key_name(key));
                if (!rr)
                        return -ENOMEM;

                rr->aaaa.in6_addr = in6addr_loopback;

                r = dns_answer_add(*answer, rr, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED, NULL);
                if (r < 0)
                        return r;
        }

        return 0;
}

static int answer_add_ptr(DnsAnswer **answer, const char *from, const char *to, int ifindex, DnsAnswerFlags flags) {
        _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;

        rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_PTR, from);
        if (!rr)
                return -ENOMEM;

        rr->ptr.name = strdup(to);
        if (!rr->ptr.name)
                return -ENOMEM;

        return dns_answer_add(*answer, rr, ifindex, flags, NULL);
}

static int synthesize_localhost_ptr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
        int r;

        assert(m);
        assert(key);
        assert(answer);

        if (IN_SET(key->type, DNS_TYPE_PTR, DNS_TYPE_ANY)) {
                r = dns_answer_reserve(answer, 1);
                if (r < 0)
                        return r;

                r = answer_add_ptr(answer, dns_resource_key_name(key), "localhost", dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
                if (r < 0)
                        return r;
        }

        return 0;
}

static int answer_add_addresses_rr(
                DnsAnswer **answer,
                const char *name,
                struct local_address *addresses,
                unsigned n_addresses) {

        unsigned j;
        int r;

        assert(answer);
        assert(name);

        r = dns_answer_reserve(answer, n_addresses);
        if (r < 0)
                return r;

        for (j = 0; j < n_addresses; j++) {
                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;

                r = dns_resource_record_new_address(&rr, addresses[j].family, &addresses[j].address, name);
                if (r < 0)
                        return r;

                r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED, NULL);
                if (r < 0)
                        return r;
        }

        return 0;
}

static int answer_add_addresses_ptr(
                DnsAnswer **answer,
                const char *name,
                struct local_address *addresses,
                unsigned n_addresses,
                int af, const union in_addr_union *match) {

        bool added = false;
        unsigned j;
        int r;

        assert(answer);
        assert(name);

        for (j = 0; j < n_addresses; j++) {
                _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;

                if (af != AF_UNSPEC) {

                        if (addresses[j].family != af)
                                continue;

                        if (match && !in_addr_equal(af, match, &addresses[j].address))
                                continue;
                }

                r = dns_answer_reserve(answer, 1);
                if (r < 0)
                        return r;

                r = dns_resource_record_new_reverse(&rr, addresses[j].family, &addresses[j].address, name);
                if (r < 0)
                        return r;

                r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED, NULL);
                if (r < 0)
                        return r;

                added = true;
        }

        return added;
}

static int synthesize_system_hostname_rr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
        _cleanup_free_ struct local_address *addresses = NULL;
        int n = 0, af;

        assert(m);
        assert(key);
        assert(answer);

        af = dns_type_to_af(key->type);
        if (af >= 0) {
                n = local_addresses(m->rtnl, ifindex, af, &addresses);
                if (n < 0)
                        return n;

                if (n == 0) {
                        struct local_address buffer[2];

                        /* If we have no local addresses then use ::1
                         * and 127.0.0.2 as local ones. */

                        if (IN_SET(af, AF_INET, AF_UNSPEC))
                                buffer[n++] = (struct local_address) {
                                        .family = AF_INET,
                                        .ifindex = dns_synthesize_ifindex(ifindex),
                                        .address.in.s_addr = htobe32(0x7F000002),
                                };

                        if (IN_SET(af, AF_INET6, AF_UNSPEC) && socket_ipv6_is_enabled())
                                buffer[n++] = (struct local_address) {
                                        .family = AF_INET6,
                                        .ifindex = dns_synthesize_ifindex(ifindex),
                                        .address.in6 = in6addr_loopback,
                                };

                        return answer_add_addresses_rr(answer,
                                                       dns_resource_key_name(key),
                                                       buffer, n);
                }
        }

        return answer_add_addresses_rr(answer, dns_resource_key_name(key), addresses, n);
}

static int synthesize_system_hostname_ptr(Manager *m, int af, const union in_addr_union *address, int ifindex, DnsAnswer **answer) {
        _cleanup_free_ struct local_address *addresses = NULL;
        bool added = false;
        int n, r;

        assert(m);
        assert(address);
        assert(answer);

        if (af == AF_INET && address->in.s_addr == htobe32(0x7F000002)) {

                /* Always map the IPv4 address 127.0.0.2 to the local hostname, in addition to "localhost": */

                r = dns_answer_reserve(answer, 4);
                if (r < 0)
                        return r;

                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->full_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
                if (r < 0)
                        return r;

                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->llmnr_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
                if (r < 0)
                        return r;

                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->mdns_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
                if (r < 0)
                        return r;

                r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", "localhost", dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
                if (r < 0)
                        return r;

                return 1;
        }

        n = local_addresses(m->rtnl, ifindex, af, &addresses);
        if (n <= 0)
                return n;

        r = answer_add_addresses_ptr(answer, m->full_hostname, addresses, n, af, address);
        if (r < 0)
                return r;
        if (r > 0)
                added = true;

        r = answer_add_addresses_ptr(answer, m->llmnr_hostname, addresses, n, af, address);
        if (r < 0)
                return r;
        if (r > 0)
                added = true;

        r = answer_add_addresses_ptr(answer, m->mdns_hostname, addresses, n, af, address);
        if (r < 0)
                return r;
        if (r > 0)
                added = true;

        return added;
}

static int synthesize_gateway_rr(Manager *m, const DnsResourceKey *key, int ifindex, DnsAnswer **answer) {
        _cleanup_free_ struct local_address *addresses = NULL;
        int n = 0, af, r;

        assert(m);
        assert(key);
        assert(answer);

        af = dns_type_to_af(key->type);
        if (af >= 0) {
                n = local_gateways(m->rtnl, ifindex, af, &addresses);
                if (n < 0) /* < 0 means: error */
                        return n;

                if (n == 0) { /* == 0 means we have no gateway */
                        /* See if there's a gateway on the other protocol */
                        if (af == AF_INET)
                                n = local_gateways(m->rtnl, ifindex, AF_INET6, NULL);
                        else {
                                assert(af == AF_INET6);
                                n = local_gateways(m->rtnl, ifindex, AF_INET, NULL);
                        }
                        if (n <= 0) /* error (if < 0) or really no gateway at all (if == 0) */
                                return n;

                        /* We have a gateway on the other protocol. Let's return > 0 without adding any RR to
                         * the answer, i.e. synthesize NODATA (and not NXDOMAIN!) */
                        return 1;
                }
        }

        r = answer_add_addresses_rr(answer, dns_resource_key_name(key), addresses, n);
        if (r < 0)
                return r;

        return 1; /* > 0 means: we have some gateway */
}

static int synthesize_gateway_ptr(Manager *m, int af, const union in_addr_union *address, int ifindex, DnsAnswer **answer) {
        _cleanup_free_ struct local_address *addresses = NULL;
        int n;

        assert(m);
        assert(address);
        assert(answer);

        n = local_gateways(m->rtnl, ifindex, af, &addresses);
        if (n <= 0)
                return n;

        return answer_add_addresses_ptr(answer, "_gateway", addresses, n, af, address);
}

int dns_synthesize_answer(
                Manager *m,
                DnsQuestion *q,
                int ifindex,
                DnsAnswer **ret) {

        _cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
        DnsResourceKey *key;
        bool found = false, nxdomain = false;
        int r;

        assert(m);
        assert(q);

        DNS_QUESTION_FOREACH(key, q) {
                union in_addr_union address;
                const char *name;
                int af;

                if (!IN_SET(key->class, DNS_CLASS_IN, DNS_CLASS_ANY))
                        continue;

                name = dns_resource_key_name(key);

                if (is_localhost(name)) {

                        r = synthesize_localhost_rr(m, key, ifindex, &answer);
                        if (r < 0)
                                return log_error_errno(r, "Failed to synthesize localhost RRs: %m");

                } else if (manager_is_own_hostname(m, name)) {

                        r = synthesize_system_hostname_rr(m, key, ifindex, &answer);
                        if (r < 0)
                                return log_error_errno(r, "Failed to synthesize system hostname RRs: %m");

                } else if (is_gateway_hostname(name)) {

                        r = synthesize_gateway_rr(m, key, ifindex, &answer);
                        if (r < 0)
                                return log_error_errno(r, "Failed to synthesize gateway RRs: %m");
                        if (r == 0) { /* if we have no gateway return NXDOMAIN */
                                nxdomain = true;
                                continue;
                        }

                } else if ((dns_name_endswith(name, "127.in-addr.arpa") > 0 && dns_name_equal(name, "2.0.0.127.in-addr.arpa") == 0) ||
                           dns_name_equal(name, "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa") > 0) {

                        r = synthesize_localhost_ptr(m, key, ifindex, &answer);
                        if (r < 0)
                                return log_error_errno(r, "Failed to synthesize localhost PTR RRs: %m");

                } else if (dns_name_address(name, &af, &address) > 0) {
                        int v, w;

                        v = synthesize_system_hostname_ptr(m, af, &address, ifindex, &answer);
                        if (v < 0)
                                return log_error_errno(v, "Failed to synthesize system hostname PTR RR: %m");

                        w = synthesize_gateway_ptr(m, af, &address, ifindex, &answer);
                        if (w < 0)
                                return log_error_errno(w, "Failed to synthesize gateway hostname PTR RR: %m");

                        if (v == 0 && w == 0) /* This IP address is neither a local one nor a gateway */
                                continue;

                } else
                        continue;

                found = true;
        }

        if (found) {

                if (ret)
                        *ret = TAKE_PTR(answer);

                return 1;
        } else if (nxdomain)
                return -ENXIO;

        return 0;
}
Commit	Line	Data
db9ecf05	1	/* SPDX-License-Identifier: LGPL-2.1-or-later */
839a4a20 LP	2
	3	#include "alloc-util.h"
	4	#include "hostname-util.h"
	5	#include "local-addresses.h"
ef118d00	6	#include "missing_network.h"
839a4a20 LP	7	#include "resolved-dns-synthesize.h"
839a4a20 LP	8
dd0bc0f1	9	int dns_synthesize_ifindex(int ifindex) {
839a4a20 LP	10
	11	/* When the caller asked for resolving on a specific
	12	* interface, we synthesize the answer for that
	13	* interface. However, if nothing specific was claimed and we
	14	* only return localhost RRs, we synthesize the answer for
	15	* localhost. */
	16
	17	if (ifindex > 0)
	18	return ifindex;
	19
	20	return LOOPBACK_IFINDEX;
	21	}
	22
dd0bc0f1	23	int dns_synthesize_family(uint64_t flags) {
839a4a20 LP	24
	25	/* Picks an address family depending on set flags. This is
	26	* purely for synthesized answers, where the family we return
	27	* for the reply should match what was requested in the
	28	* question, even though we are synthesizing the answer
	29	* here. */
	30
	31	if (!(flags & SD_RESOLVED_DNS)) {
	32	if (flags & (SD_RESOLVED_LLMNR_IPV4\|SD_RESOLVED_MDNS_IPV4))
	33	return AF_INET;
	34	if (flags & (SD_RESOLVED_LLMNR_IPV6\|SD_RESOLVED_MDNS_IPV6))
	35	return AF_INET6;
	36	}
	37
	38	return AF_UNSPEC;
	39	}
	40
dd0bc0f1	41	DnsProtocol dns_synthesize_protocol(uint64_t flags) {
839a4a20	42
dd0bc0f1	43	/* Similar as dns_synthesize_family() but does this for the
839a4a20 LP	44	* protocol. If resolving via DNS was requested, we claim it
	45	* was DNS. Similar, if nothing specific was
	46	* requested. However, if only resolving via LLMNR was
	47	* requested we return that. */
	48
	49	if (flags & SD_RESOLVED_DNS)
	50	return DNS_PROTOCOL_DNS;
	51	if (flags & SD_RESOLVED_LLMNR)
	52	return DNS_PROTOCOL_LLMNR;
	53	if (flags & SD_RESOLVED_MDNS)
	54	return DNS_PROTOCOL_MDNS;
	55
	56	return DNS_PROTOCOL_DNS;
	57	}
	58
	59	static int synthesize_localhost_rr(Manager m, const DnsResourceKey key, int ifindex, DnsAnswer **answer) {
	60	int r;
	61
	62	assert(m);
	63	assert(key);
	64	assert(answer);
	65
	66	r = dns_answer_reserve(answer, 2);
	67	if (r < 0)
	68	return r;
	69
	70	if (IN_SET(key->type, DNS_TYPE_A, DNS_TYPE_ANY)) {
	71	_cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
	72
1c02e7ba	73	rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_A, dns_resource_key_name(key));
839a4a20 LP	74	if (!rr)
	75	return -ENOMEM;
	76
	77	rr->a.in_addr.s_addr = htobe32(INADDR_LOOPBACK);
	78
04617bf8	79	r = dns_answer_add(*answer, rr, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED, NULL);
839a4a20 LP	80	if (r < 0)
	81	return r;
	82	}
	83
747b596f	84	if (IN_SET(key->type, DNS_TYPE_AAAA, DNS_TYPE_ANY) && socket_ipv6_is_enabled()) {
839a4a20 LP	85	_cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
839a4a20 LP	86
1c02e7ba	87	rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_AAAA, dns_resource_key_name(key));
839a4a20 LP	88	if (!rr)
	89	return -ENOMEM;
	90
	91	rr->aaaa.in6_addr = in6addr_loopback;
	92
04617bf8	93	r = dns_answer_add(*answer, rr, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED, NULL);
839a4a20 LP	94	if (r < 0)
	95	return r;
	96	}
	97
	98	return 0;
	99	}
	100
	101	static int answer_add_ptr(DnsAnswer *answer, const char from, const char *to, int ifindex, DnsAnswerFlags flags) {
	102	_cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
	103
	104	rr = dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_PTR, from);
	105	if (!rr)
	106	return -ENOMEM;
	107
	108	rr->ptr.name = strdup(to);
	109	if (!rr->ptr.name)
	110	return -ENOMEM;
	111
04617bf8	112	return dns_answer_add(*answer, rr, ifindex, flags, NULL);
839a4a20 LP	113	}
	114
	115	static int synthesize_localhost_ptr(Manager m, const DnsResourceKey key, int ifindex, DnsAnswer **answer) {
	116	int r;
	117
	118	assert(m);
	119	assert(key);
	120	assert(answer);
	121
	122	if (IN_SET(key->type, DNS_TYPE_PTR, DNS_TYPE_ANY)) {
	123	r = dns_answer_reserve(answer, 1);
	124	if (r < 0)
	125	return r;
	126
1c02e7ba	127	r = answer_add_ptr(answer, dns_resource_key_name(key), "localhost", dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
839a4a20 LP	128	if (r < 0)
	129	return r;
	130	}
	131
	132	return 0;
	133	}
	134
	135	static int answer_add_addresses_rr(
	136	DnsAnswer **answer,
	137	const char *name,
	138	struct local_address *addresses,
	139	unsigned n_addresses) {
	140
	141	unsigned j;
	142	int r;
	143
	144	assert(answer);
	145	assert(name);
	146
	147	r = dns_answer_reserve(answer, n_addresses);
	148	if (r < 0)
	149	return r;
	150
	151	for (j = 0; j < n_addresses; j++) {
	152	_cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
	153
	154	r = dns_resource_record_new_address(&rr, addresses[j].family, &addresses[j].address, name);
	155	if (r < 0)
	156	return r;
	157
04617bf8	158	r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED, NULL);
839a4a20 LP	159	if (r < 0)
	160	return r;
	161	}
	162
	163	return 0;
	164	}
	165
	166	static int answer_add_addresses_ptr(
	167	DnsAnswer **answer,
	168	const char *name,
	169	struct local_address *addresses,
	170	unsigned n_addresses,
	171	int af, const union in_addr_union *match) {
	172
2855b6c3	173	bool added = false;
839a4a20 LP	174	unsigned j;
	175	int r;
	176
	177	assert(answer);
	178	assert(name);
	179
	180	for (j = 0; j < n_addresses; j++) {
	181	_cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
	182
	183	if (af != AF_UNSPEC) {
	184
	185	if (addresses[j].family != af)
	186	continue;
	187
	188	if (match && !in_addr_equal(af, match, &addresses[j].address))
	189	continue;
	190	}
	191
	192	r = dns_answer_reserve(answer, 1);
	193	if (r < 0)
	194	return r;
	195
	196	r = dns_resource_record_new_reverse(&rr, addresses[j].family, &addresses[j].address, name);
	197	if (r < 0)
	198	return r;
	199
04617bf8	200	r = dns_answer_add(*answer, rr, addresses[j].ifindex, DNS_ANSWER_AUTHENTICATED, NULL);
839a4a20 LP	201	if (r < 0)
839a4a20 LP	202	return r;
2855b6c3 LP	203
2855b6c3 LP	204	added = true;
839a4a20 LP	205	}
839a4a20 LP	206
2855b6c3	207	return added;
839a4a20 LP	208	}
	209
	210	static int synthesize_system_hostname_rr(Manager m, const DnsResourceKey key, int ifindex, DnsAnswer **answer) {
	211	_cleanup_free_ struct local_address *addresses = NULL;
	212	int n = 0, af;
	213
	214	assert(m);
	215	assert(key);
	216	assert(answer);
	217
	218	af = dns_type_to_af(key->type);
	219	if (af >= 0) {
	220	n = local_addresses(m->rtnl, ifindex, af, &addresses);
	221	if (n < 0)
	222	return n;
	223
	224	if (n == 0) {
	225	struct local_address buffer[2];
	226
	227	/* If we have no local addresses then use ::1
	228	* and 127.0.0.2 as local ones. */
	229
3742095b	230	if (IN_SET(af, AF_INET, AF_UNSPEC))
839a4a20 LP	231	buffer[n++] = (struct local_address) {
839a4a20 LP	232	.family = AF_INET,
dd0bc0f1	233	.ifindex = dns_synthesize_ifindex(ifindex),
839a4a20 LP	234	.address.in.s_addr = htobe32(0x7F000002),
	235	};
	236
747b596f	237	if (IN_SET(af, AF_INET6, AF_UNSPEC) && socket_ipv6_is_enabled())
839a4a20 LP	238	buffer[n++] = (struct local_address) {
839a4a20 LP	239	.family = AF_INET6,
dd0bc0f1	240	.ifindex = dns_synthesize_ifindex(ifindex),
839a4a20 LP	241	.address.in6 = in6addr_loopback,
	242	};
	243
3742095b AR	244	return answer_add_addresses_rr(answer,
	245	dns_resource_key_name(key),
	246	buffer, n);
839a4a20 LP	247	}
	248	}
	249
1c02e7ba	250	return answer_add_addresses_rr(answer, dns_resource_key_name(key), addresses, n);
839a4a20 LP	251	}
	252
	253	static int synthesize_system_hostname_ptr(Manager m, int af, const union in_addr_union address, int ifindex, DnsAnswer **answer) {
	254	_cleanup_free_ struct local_address *addresses = NULL;
2855b6c3	255	bool added = false;
839a4a20 LP	256	int n, r;
	257
	258	assert(m);
	259	assert(address);
	260	assert(answer);
	261
	262	if (af == AF_INET && address->in.s_addr == htobe32(0x7F000002)) {
	263
a4f3375d	264	/* Always map the IPv4 address 127.0.0.2 to the local hostname, in addition to "localhost": */
839a4a20	265
a4f3375d LP	266	r = dns_answer_reserve(answer, 4);
	267	if (r < 0)
	268	return r;
	269
	270	r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->full_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
839a4a20 LP	271	if (r < 0)
	272	return r;
	273
dd0bc0f1	274	r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->llmnr_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
839a4a20 LP	275	if (r < 0)
	276	return r;
	277
dd0bc0f1	278	r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", m->mdns_hostname, dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
839a4a20 LP	279	if (r < 0)
	280	return r;
	281
dd0bc0f1	282	r = answer_add_ptr(answer, "2.0.0.127.in-addr.arpa", "localhost", dns_synthesize_ifindex(ifindex), DNS_ANSWER_AUTHENTICATED);
839a4a20 LP	283	if (r < 0)
	284	return r;
	285
2855b6c3	286	return 1;
839a4a20 LP	287	}
	288
	289	n = local_addresses(m->rtnl, ifindex, af, &addresses);
2855b6c3	290	if (n <= 0)
839a4a20 LP	291	return n;
839a4a20 LP	292
a4f3375d LP	293	r = answer_add_addresses_ptr(answer, m->full_hostname, addresses, n, af, address);
	294	if (r < 0)
	295	return r;
	296	if (r > 0)
	297	added = true;
	298
839a4a20 LP	299	r = answer_add_addresses_ptr(answer, m->llmnr_hostname, addresses, n, af, address);
	300	if (r < 0)
	301	return r;
2855b6c3 LP	302	if (r > 0)
	303	added = true;
	304
	305	r = answer_add_addresses_ptr(answer, m->mdns_hostname, addresses, n, af, address);
	306	if (r < 0)
	307	return r;
	308	if (r > 0)
	309	added = true;
839a4a20	310
2855b6c3	311	return added;
839a4a20 LP	312	}
	313
	314	static int synthesize_gateway_rr(Manager m, const DnsResourceKey key, int ifindex, DnsAnswer **answer) {
	315	_cleanup_free_ struct local_address *addresses = NULL;
acf06088	316	int n = 0, af, r;
839a4a20 LP	317
	318	assert(m);
	319	assert(key);
	320	assert(answer);
	321
	322	af = dns_type_to_af(key->type);
	323	if (af >= 0) {
	324	n = local_gateways(m->rtnl, ifindex, af, &addresses);
877884fc LP	325	if (n < 0) /* < 0 means: error */
	326	return n;
	327
	328	if (n == 0) { /* == 0 means we have no gateway */
	329	/* See if there's a gateway on the other protocol */
	330	if (af == AF_INET)
	331	n = local_gateways(m->rtnl, ifindex, AF_INET6, NULL);
	332	else {
	333	assert(af == AF_INET6);
	334	n = local_gateways(m->rtnl, ifindex, AF_INET, NULL);
	335	}
	336	if (n <= 0) /* error (if < 0) or really no gateway at all (if == 0) */
	337	return n;
	338
	339	/* We have a gateway on the other protocol. Let's return > 0 without adding any RR to
	340	* the answer, i.e. synthesize NODATA (and not NXDOMAIN!) */
	341	return 1;
	342	}
839a4a20 LP	343	}
839a4a20 LP	344
acf06088 LP	345	r = answer_add_addresses_rr(answer, dns_resource_key_name(key), addresses, n);
	346	if (r < 0)
	347	return r;
	348
	349	return 1; /* > 0 means: we have some gateway */
839a4a20 LP	350	}
	351
	352	static int synthesize_gateway_ptr(Manager m, int af, const union in_addr_union address, int ifindex, DnsAnswer **answer) {
	353	_cleanup_free_ struct local_address *addresses = NULL;
	354	int n;
	355
	356	assert(m);
	357	assert(address);
	358	assert(answer);
	359
	360	n = local_gateways(m->rtnl, ifindex, af, &addresses);
2855b6c3	361	if (n <= 0)
839a4a20 LP	362	return n;
839a4a20 LP	363
5248e7e1	364	return answer_add_addresses_ptr(answer, "_gateway", addresses, n, af, address);
839a4a20 LP	365	}
	366
	367	int dns_synthesize_answer(
	368	Manager *m,
	369	DnsQuestion *q,
	370	int ifindex,
dd0bc0f1	371	DnsAnswer **ret) {
839a4a20 LP	372
	373	_cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL;
	374	DnsResourceKey *key;
acf06088	375	bool found = false, nxdomain = false;
839a4a20 LP	376	int r;
	377
	378	assert(m);
	379	assert(q);
	380
	381	DNS_QUESTION_FOREACH(key, q) {
	382	union in_addr_union address;
	383	const char *name;
	384	int af;
	385
4c701096	386	if (!IN_SET(key->class, DNS_CLASS_IN, DNS_CLASS_ANY))
839a4a20 LP	387	continue;
839a4a20 LP	388
1c02e7ba	389	name = dns_resource_key_name(key);
839a4a20 LP	390
	391	if (is_localhost(name)) {
	392
	393	r = synthesize_localhost_rr(m, key, ifindex, &answer);
	394	if (r < 0)
	395	return log_error_errno(r, "Failed to synthesize localhost RRs: %m");
	396
	397	} else if (manager_is_own_hostname(m, name)) {
	398
	399	r = synthesize_system_hostname_rr(m, key, ifindex, &answer);
	400	if (r < 0)
	401	return log_error_errno(r, "Failed to synthesize system hostname RRs: %m");
	402
	403	} else if (is_gateway_hostname(name)) {
	404
	405	r = synthesize_gateway_rr(m, key, ifindex, &answer);
	406	if (r < 0)
	407	return log_error_errno(r, "Failed to synthesize gateway RRs: %m");
acf06088 LP	408	if (r == 0) { /* if we have no gateway return NXDOMAIN */
	409	nxdomain = true;
	410	continue;
	411	}
839a4a20 LP	412
	413	} else if ((dns_name_endswith(name, "127.in-addr.arpa") > 0 && dns_name_equal(name, "2.0.0.127.in-addr.arpa") == 0) \|\|
	414	dns_name_equal(name, "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa") > 0) {
	415
	416	r = synthesize_localhost_ptr(m, key, ifindex, &answer);
	417	if (r < 0)
	418	return log_error_errno(r, "Failed to synthesize localhost PTR RRs: %m");
	419
	420	} else if (dns_name_address(name, &af, &address) > 0) {
2855b6c3	421	int v, w;
839a4a20	422
2855b6c3 LP	423	v = synthesize_system_hostname_ptr(m, af, &address, ifindex, &answer);
2855b6c3 LP	424	if (v < 0)
4a0e9289	425	return log_error_errno(v, "Failed to synthesize system hostname PTR RR: %m");
839a4a20	426
2855b6c3 LP	427	w = synthesize_gateway_ptr(m, af, &address, ifindex, &answer);
2855b6c3 LP	428	if (w < 0)
4a0e9289	429	return log_error_errno(w, "Failed to synthesize gateway hostname PTR RR: %m");
2855b6c3 LP	430
	431	if (v == 0 && w == 0) /* This IP address is neither a local one nor a gateway */
	432	continue;
	433
528e685e LP	434	} else
	435	continue;
	436
	437	found = true;
839a4a20 LP	438	}
839a4a20 LP	439
acf06088	440	if (found) {
839a4a20	441
1cc6c93a YW	442	if (ret)
1cc6c93a YW	443	*ret = TAKE_PTR(answer);
acf06088 LP	444
	445	return 1;
	446	} else if (nxdomain)
	447	return -ENXIO;
839a4a20	448
acf06088	449	return 0;
839a4a20	450	}