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

/* SPDX-License-Identifier: LGPL-2.1+ */

#include "fd-util.h"
#include "missing_network.h"
#include "resolved-dns-stub.h"
#include "socket-util.h"

/* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
 * IP and UDP header sizes */
#define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)

static int manager_dns_stub_udp_fd(Manager *m);
static int manager_dns_stub_tcp_fd(Manager *m);

static int dns_stub_make_reply_packet(
                DnsPacket **p,
                size_t max_size,
                DnsQuestion *q,
                DnsAnswer *answer,
                bool *ret_truncated) {

        bool truncated = false;
        DnsResourceRecord *rr;
        unsigned c = 0;
        int r;

        assert(p);

        /* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
         * roundtrips aren't expensive. */

        if (!*p) {
                r = dns_packet_new(p, DNS_PROTOCOL_DNS, 0, max_size);
                if (r < 0)
                        return r;

                r = dns_packet_append_question(*p, q);
                if (r < 0)
                        return r;

                DNS_PACKET_HEADER(*p)->qdcount = htobe16(dns_question_size(q));
        }

        DNS_ANSWER_FOREACH(rr, answer) {

                r = dns_question_matches_rr(q, rr, NULL);
                if (r < 0)
                        return r;
                if (r > 0)
                        goto add;

                r = dns_question_matches_cname_or_dname(q, rr, NULL);
                if (r < 0)
                        return r;
                if (r > 0)
                        goto add;

                continue;
        add:
                r = dns_packet_append_rr(*p, rr, 0, NULL, NULL);
                if (r == -EMSGSIZE) {
                        truncated = true;
                        break;
                }
                if (r < 0)
                        return r;

                c++;
        }

        if (ret_truncated)
                *ret_truncated = truncated;
        else if (truncated)
                return -EMSGSIZE;

        DNS_PACKET_HEADER(*p)->ancount = htobe16(be16toh(DNS_PACKET_HEADER(*p)->ancount) + c);

        return 0;
}

static int dns_stub_finish_reply_packet(
                DnsPacket *p,
                uint16_t id,
                int rcode,
                bool tc,        /* set the Truncated bit? */
                bool add_opt,   /* add an OPT RR to this packet? */
                bool edns0_do,  /* set the EDNS0 DNSSEC OK bit? */
                bool ad) {      /* set the DNSSEC authenticated data bit? */

        int r;

        assert(p);

        if (!add_opt) {
                /* If the client can't to EDNS0, don't do DO either */
                edns0_do = false;

                /* If the client didn't do EDNS, clamp the rcode to 4 bit */
                if (rcode > 0xF)
                        rcode = DNS_RCODE_SERVFAIL;
        }

        /* Don't set the AD bit unless DO is on, too */
        if (!edns0_do)
                ad = false;

        DNS_PACKET_HEADER(p)->id = id;

        DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
                                                              1  /* qr */,
                                                              0  /* opcode */,
                                                              0  /* aa */,
                                                              tc /* tc */,
                                                              1  /* rd */,
                                                              1  /* ra */,
                                                              ad /* ad */,
                                                              0  /* cd */,
                                                              rcode));

        if (add_opt) {
                r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL);
                if (r < 0)
                        return r;
        }

        return 0;
}

static int dns_stub_send(Manager *m, DnsStream *s, DnsPacket *p, DnsPacket *reply) {
        int r;

        assert(m);
        assert(p);
        assert(reply);

        if (s)
                r = dns_stream_write_packet(s, reply);
        else {
                int fd;

                fd = manager_dns_stub_udp_fd(m);
                if (fd < 0)
                        return log_debug_errno(fd, "Failed to get reply socket: %m");

                /* Note that it is essential here that we explicitly choose the source IP address for this packet. This
                 * is because otherwise the kernel will choose it automatically based on the routing table and will
                 * thus pick 127.0.0.1 rather than 127.0.0.53. */

                r = manager_send(m, fd, LOOPBACK_IFINDEX, p->family, &p->sender, p->sender_port, &p->destination, reply);
        }
        if (r < 0)
                return log_debug_errno(r, "Failed to send reply packet: %m");

        return 0;
}

static int dns_stub_send_failure(Manager *m, DnsStream *s, DnsPacket *p, int rcode, bool authenticated) {
        _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
        int r;

        assert(m);
        assert(p);

        r = dns_stub_make_reply_packet(&reply, DNS_PACKET_PAYLOAD_SIZE_MAX(p), p->question, NULL, NULL);
        if (r < 0)
                return log_debug_errno(r, "Failed to make failure packet: %m");

        r = dns_stub_finish_reply_packet(reply, DNS_PACKET_ID(p), rcode, false, !!p->opt, DNS_PACKET_DO(p), authenticated);
        if (r < 0)
                return log_debug_errno(r, "Failed to build failure packet: %m");

        return dns_stub_send(m, s, p, reply);
}

static void dns_stub_query_complete(DnsQuery *q) {
        int r;

        assert(q);
        assert(q->request_dns_packet);

        switch (q->state) {

        case DNS_TRANSACTION_SUCCESS: {
                bool truncated;

                r = dns_stub_make_reply_packet(&q->reply_dns_packet, DNS_PACKET_PAYLOAD_SIZE_MAX(q->request_dns_packet), q->question_idna, q->answer, &truncated);
                if (r < 0) {
                        log_debug_errno(r, "Failed to build reply packet: %m");
                        break;
                }

                r = dns_query_process_cname(q);
                if (r == -ELOOP) {
                        (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
                        break;
                }
                if (r < 0) {
                        log_debug_errno(r, "Failed to process CNAME: %m");
                        break;
                }
                if (r == DNS_QUERY_RESTARTED)
                        return;

                r = dns_stub_finish_reply_packet(
                                q->reply_dns_packet,
                                DNS_PACKET_ID(q->request_dns_packet),
                                q->answer_rcode,
                                truncated,
                                !!q->request_dns_packet->opt,
                                DNS_PACKET_DO(q->request_dns_packet),
                                dns_query_fully_authenticated(q));
                if (r < 0) {
                        log_debug_errno(r, "Failed to finish reply packet: %m");
                        break;
                }

                (void) dns_stub_send(q->manager, q->request_dns_stream, q->request_dns_packet, q->reply_dns_packet);
                break;
        }

        case DNS_TRANSACTION_RCODE_FAILURE:
                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode, dns_query_fully_authenticated(q));
                break;

        case DNS_TRANSACTION_NOT_FOUND:
                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN, dns_query_fully_authenticated(q));
                break;

        case DNS_TRANSACTION_TIMEOUT:
        case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
                /* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
                break;

        case DNS_TRANSACTION_NO_SERVERS:
        case DNS_TRANSACTION_INVALID_REPLY:
        case DNS_TRANSACTION_ERRNO:
        case DNS_TRANSACTION_ABORTED:
        case DNS_TRANSACTION_DNSSEC_FAILED:
        case DNS_TRANSACTION_NO_TRUST_ANCHOR:
        case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
        case DNS_TRANSACTION_NETWORK_DOWN:
                (void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
                break;

        case DNS_TRANSACTION_NULL:
        case DNS_TRANSACTION_PENDING:
        case DNS_TRANSACTION_VALIDATING:
        default:
                assert_not_reached("Impossible state");
        }

        dns_query_free(q);
}

static int dns_stub_stream_complete(DnsStream *s, int error) {
        assert(s);

        log_debug_errno(error, "DNS TCP connection terminated, destroying queries: %m");

        for (;;) {
                DnsQuery *q;

                q = set_first(s->queries);
                if (!q)
                        break;

                dns_query_free(q);
        }

        /* This drops the implicit ref we keep around since it was allocated, as incoming stub connections
         * should be kept as long as the client wants to. */
        dns_stream_unref(s);
        return 0;
}

static void dns_stub_process_query(Manager *m, DnsStream *s, DnsPacket *p) {
        DnsQuery *q = NULL;
        int r;

        assert(m);
        assert(p);
        assert(p->protocol == DNS_PROTOCOL_DNS);

        if (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
            in_addr_is_localhost(p->family, &p->destination) <= 0) {
                log_error("Got packet on unexpected IP range, refusing.");
                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
                goto fail;
        }

        r = dns_packet_extract(p);
        if (r < 0) {
                log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
                dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR, false);
                goto fail;
        }

        if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
                log_debug("Got EDNS OPT field with unsupported version number.");
                dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS, false);
                goto fail;
        }

        if (dns_type_is_obsolete(p->question->keys[0]->type)) {
                log_debug("Got message with obsolete key type, refusing.");
                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
                goto fail;
        }

        if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
                log_debug("Got request for zone transfer, refusing.");
                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
                goto fail;
        }

        if (!DNS_PACKET_RD(p))  {
                /* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
                log_debug("Got request with recursion disabled, refusing.");
                dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED, false);
                goto fail;
        }

        if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
                log_debug("Got request with DNSSEC CD bit set, refusing.");
                dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
                goto fail;
        }

        r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_SEARCH);
        if (r < 0) {
                log_error_errno(r, "Failed to generate query object: %m");
                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
                goto fail;
        }

        /* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
        q->clamp_ttl = true;

        q->request_dns_packet = dns_packet_ref(p);
        q->request_dns_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
        q->complete = dns_stub_query_complete;

        if (s) {
                /* Remember which queries belong to this stream, so that we can cancel them when the stream
                 * is disconnected early */

                r = set_ensure_allocated(&s->queries, &trivial_hash_ops);
                if (r < 0) {
                        log_oom();
                        goto fail;
                }

                if (set_put(s->queries, q) < 0) {
                        log_oom();
                        goto fail;
                }
        }

        r = dns_query_go(q);
        if (r < 0) {
                log_error_errno(r, "Failed to start query: %m");
                dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
                goto fail;
        }

        log_debug("Processing query...");
        return;

fail:
        dns_query_free(q);
}

static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
        Manager *m = userdata;
        int r;

        r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
        if (r <= 0)
                return r;

        if (dns_packet_validate_query(p) > 0) {
                log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));

                dns_stub_process_query(m, NULL, p);
        } else
                log_debug("Invalid DNS stub UDP packet, ignoring.");

        return 0;
}

static int manager_dns_stub_udp_fd(Manager *m) {
        union sockaddr_union sa = {
                .in.sin_family = AF_INET,
                .in.sin_port = htobe16(53),
                .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
        };
        _cleanup_close_ int fd = -1;
        int r;

        if (m->dns_stub_udp_fd >= 0)
                return m->dns_stub_udp_fd;

        fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
        if (fd < 0)
                return -errno;

        r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
        if (r < 0)
                return r;

        r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true);
        if (r < 0)
                return r;

        r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true);
        if (r < 0)
                return r;

        /* Make sure no traffic from outside the local host can leak to onto this socket */
        if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
                return -errno;

        if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
                return -errno;

        r = sd_event_add_io(m->event, &m->dns_stub_udp_event_source, fd, EPOLLIN, on_dns_stub_packet, m);
        if (r < 0)
                return r;

        (void) sd_event_source_set_description(m->dns_stub_udp_event_source, "dns-stub-udp");

        return m->dns_stub_udp_fd = TAKE_FD(fd);
}

static int on_dns_stub_stream_packet(DnsStream *s) {
        _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;

        assert(s);

        p = dns_stream_take_read_packet(s);
        assert(p);

        if (dns_packet_validate_query(p) > 0) {
                log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p));

                dns_stub_process_query(s->manager, s, p);
        } else
                log_debug("Invalid DNS stub TCP packet, ignoring.");

        return 0;
}

static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
        DnsStream *stream;
        Manager *m = userdata;
        int cfd, r;

        cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
        if (cfd < 0) {
                if (IN_SET(errno, EAGAIN, EINTR))
                        return 0;

                return -errno;
        }

        r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL);
        if (r < 0) {
                safe_close(cfd);
                return r;
        }

        stream->on_packet = on_dns_stub_stream_packet;
        stream->complete = dns_stub_stream_complete;

        /* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */

        return 0;
}

static int manager_dns_stub_tcp_fd(Manager *m) {
        union sockaddr_union sa = {
                .in.sin_family = AF_INET,
                .in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
                .in.sin_port = htobe16(53),
        };
        _cleanup_close_ int fd = -1;
        int r;

        if (m->dns_stub_tcp_fd >= 0)
                return m->dns_stub_tcp_fd;

        fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
        if (fd < 0)
                return -errno;

        r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, true);
        if (r < 0)
                return r;

        r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
        if (r < 0)
                return r;

        r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true);
        if (r < 0)
                return r;

        r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true);
        if (r < 0)
                return r;

        /* Make sure no traffic from outside the local host can leak to onto this socket */
        if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
                return -errno;

        if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
                return -errno;

        if (listen(fd, SOMAXCONN) < 0)
                return -errno;

        r = sd_event_add_io(m->event, &m->dns_stub_tcp_event_source, fd, EPOLLIN, on_dns_stub_stream, m);
        if (r < 0)
                return r;

        (void) sd_event_source_set_description(m->dns_stub_tcp_event_source, "dns-stub-tcp");

        return m->dns_stub_tcp_fd = TAKE_FD(fd);
}

int manager_dns_stub_start(Manager *m) {
        const char *t = "UDP";
        int r = 0;

        assert(m);

        if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
                log_debug("Not creating stub listener.");
        else
                log_debug("Creating stub listener using %s.",
                          m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
                          m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
                          "UDP/TCP");

        if (IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_UDP))
                r = manager_dns_stub_udp_fd(m);

        if (r >= 0 &&
            IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_TCP)) {
                t = "TCP";
                r = manager_dns_stub_tcp_fd(m);
        }

        if (IN_SET(r, -EADDRINUSE, -EPERM)) {
                if (r == -EADDRINUSE)
                        log_warning_errno(r,
                                          "Another process is already listening on %s socket 127.0.0.53:53.\n"
                                          "Turning off local DNS stub support.", t);
                else
                        log_warning_errno(r,
                                          "Failed to listen on %s socket 127.0.0.53:53: %m.\n"
                                          "Turning off local DNS stub support.", t);
                manager_dns_stub_stop(m);
        } else if (r < 0)
                return log_error_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m", t);

        return 0;
}

void manager_dns_stub_stop(Manager *m) {
        assert(m);

        m->dns_stub_udp_event_source = sd_event_source_unref(m->dns_stub_udp_event_source);
        m->dns_stub_tcp_event_source = sd_event_source_unref(m->dns_stub_tcp_event_source);

        m->dns_stub_udp_fd = safe_close(m->dns_stub_udp_fd);
        m->dns_stub_tcp_fd = safe_close(m->dns_stub_tcp_fd);
}
Commit	Line	Data
53e1b683	1	/* SPDX-License-Identifier: LGPL-2.1+ */
b30bf55d LP	2
b30bf55d LP	3	#include "fd-util.h"
ef118d00	4	#include "missing_network.h"
b30bf55d LP	5	#include "resolved-dns-stub.h"
	6	#include "socket-util.h"
	7
	8	/* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
	9	* IP and UDP header sizes */
	10	#define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
	11
424e490b ZJS	12	static int manager_dns_stub_udp_fd(Manager *m);
	13	static int manager_dns_stub_tcp_fd(Manager *m);
	14
b30bf55d	15	static int dns_stub_make_reply_packet(
e8d23f92	16	DnsPacket **p,
51027656	17	size_t max_size,
b30bf55d	18	DnsQuestion *q,
51027656 LP	19	DnsAnswer *answer,
51027656 LP	20	bool *ret_truncated) {
b30bf55d	21
51027656	22	bool truncated = false;
b30bf55d LP	23	DnsResourceRecord *rr;
	24	unsigned c = 0;
	25	int r;
	26
e8d23f92 LP	27	assert(p);
e8d23f92 LP	28
b30bf55d LP	29	/* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
	30	* roundtrips aren't expensive. */
	31
e8d23f92	32	if (!*p) {
51027656	33	r = dns_packet_new(p, DNS_PROTOCOL_DNS, 0, max_size);
e8d23f92 LP	34	if (r < 0)
e8d23f92 LP	35	return r;
b30bf55d	36
e8d23f92 LP	37	r = dns_packet_append_question(*p, q);
	38	if (r < 0)
	39	return r;
b30bf55d	40
e8d23f92 LP	41	DNS_PACKET_HEADER(*p)->qdcount = htobe16(dns_question_size(q));
e8d23f92 LP	42	}
b30bf55d LP	43
b30bf55d LP	44	DNS_ANSWER_FOREACH(rr, answer) {
e8d23f92	45
b30bf55d LP	46	r = dns_question_matches_rr(q, rr, NULL);
	47	if (r < 0)
	48	return r;
	49	if (r > 0)
	50	goto add;
	51
	52	r = dns_question_matches_cname_or_dname(q, rr, NULL);
	53	if (r < 0)
	54	return r;
	55	if (r > 0)
	56	goto add;
	57
	58	continue;
	59	add:
01c901e2	60	r = dns_packet_append_rr(*p, rr, 0, NULL, NULL);
51027656 LP	61	if (r == -EMSGSIZE) {
	62	truncated = true;
	63	break;
	64	}
b30bf55d LP	65	if (r < 0)
	66	return r;
	67
	68	c++;
	69	}
e8d23f92	70
51027656 LP	71	if (ret_truncated)
	72	*ret_truncated = truncated;
	73	else if (truncated)
	74	return -EMSGSIZE;
	75
e8d23f92 LP	76	DNS_PACKET_HEADER(p)->ancount = htobe16(be16toh(DNS_PACKET_HEADER(p)->ancount) + c);
	77
	78	return 0;
	79	}
	80
	81	static int dns_stub_finish_reply_packet(
	82	DnsPacket *p,
	83	uint16_t id,
	84	int rcode,
51027656	85	bool tc, /* set the Truncated bit? */
e8d23f92 LP	86	bool add_opt, /* add an OPT RR to this packet? */
	87	bool edns0_do, /* set the EDNS0 DNSSEC OK bit? */
	88	bool ad) { /* set the DNSSEC authenticated data bit? */
	89
	90	int r;
	91
	92	assert(p);
	93
941dd294 LP	94	if (!add_opt) {
	95	/* If the client can't to EDNS0, don't do DO either */
	96	edns0_do = false;
	97
	98	/* If the client didn't do EDNS, clamp the rcode to 4 bit */
	99	if (rcode > 0xF)
	100	rcode = DNS_RCODE_SERVFAIL;
	101	}
	102
	103	/* Don't set the AD bit unless DO is on, too */
	104	if (!edns0_do)
	105	ad = false;
e8d23f92 LP	106
	107	DNS_PACKET_HEADER(p)->id = id;
	108
	109	DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
51027656 LP	110	1 /* qr */,
	111	0 /* opcode */,
	112	0 /* aa */,
	113	tc /* tc */,
	114	1 /* rd */,
	115	1 /* ra */,
e8d23f92	116	ad /* ad */,
51027656	117	0 /* cd */,
e8d23f92	118	rcode));
b30bf55d LP	119
	120	if (add_opt) {
	121	r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL);
	122	if (r < 0)
	123	return r;
	124	}
	125
b30bf55d LP	126	return 0;
	127	}
	128
b30bf55d LP	129	static int dns_stub_send(Manager m, DnsStream s, DnsPacket p, DnsPacket reply) {
	130	int r;
	131
	132	assert(m);
	133	assert(p);
	134	assert(reply);
	135
	136	if (s)
	137	r = dns_stream_write_packet(s, reply);
	138	else {
	139	int fd;
	140
b30bf55d LP	141	fd = manager_dns_stub_udp_fd(m);
	142	if (fd < 0)
	143	return log_debug_errno(fd, "Failed to get reply socket: %m");
	144
	145	/* Note that it is essential here that we explicitly choose the source IP address for this packet. This
	146	* is because otherwise the kernel will choose it automatically based on the routing table and will
	147	* thus pick 127.0.0.1 rather than 127.0.0.53. */
	148
	149	r = manager_send(m, fd, LOOPBACK_IFINDEX, p->family, &p->sender, p->sender_port, &p->destination, reply);
	150	}
	151	if (r < 0)
	152	return log_debug_errno(r, "Failed to send reply packet: %m");
	153
	154	return 0;
	155	}
	156
2b2d98c1	157	static int dns_stub_send_failure(Manager m, DnsStream s, DnsPacket *p, int rcode, bool authenticated) {
b30bf55d LP	158	_cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
	159	int r;
	160
	161	assert(m);
	162	assert(p);
	163
51027656	164	r = dns_stub_make_reply_packet(&reply, DNS_PACKET_PAYLOAD_SIZE_MAX(p), p->question, NULL, NULL);
e8d23f92 LP	165	if (r < 0)
	166	return log_debug_errno(r, "Failed to make failure packet: %m");
	167
51027656	168	r = dns_stub_finish_reply_packet(reply, DNS_PACKET_ID(p), rcode, false, !!p->opt, DNS_PACKET_DO(p), authenticated);
b30bf55d LP	169	if (r < 0)
	170	return log_debug_errno(r, "Failed to build failure packet: %m");
	171
	172	return dns_stub_send(m, s, p, reply);
	173	}
	174
	175	static void dns_stub_query_complete(DnsQuery *q) {
	176	int r;
	177
	178	assert(q);
	179	assert(q->request_dns_packet);
	180
	181	switch (q->state) {
	182
51027656 LP	183	case DNS_TRANSACTION_SUCCESS: {
51027656 LP	184	bool truncated;
e8d23f92	185
51027656	186	r = dns_stub_make_reply_packet(&q->reply_dns_packet, DNS_PACKET_PAYLOAD_SIZE_MAX(q->request_dns_packet), q->question_idna, q->answer, &truncated);
e8d23f92 LP	187	if (r < 0) {
	188	log_debug_errno(r, "Failed to build reply packet: %m");
	189	break;
	190	}
b30bf55d	191
e8d23f92 LP	192	r = dns_query_process_cname(q);
e8d23f92 LP	193	if (r == -ELOOP) {
2b2d98c1	194	(void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
e8d23f92 LP	195	break;
	196	}
	197	if (r < 0) {
	198	log_debug_errno(r, "Failed to process CNAME: %m");
	199	break;
	200	}
	201	if (r == DNS_QUERY_RESTARTED)
	202	return;
	203
	204	r = dns_stub_finish_reply_packet(
	205	q->reply_dns_packet,
b30bf55d LP	206	DNS_PACKET_ID(q->request_dns_packet),
b30bf55d LP	207	q->answer_rcode,
51027656	208	truncated,
b30bf55d LP	209	!!q->request_dns_packet->opt,
b30bf55d LP	210	DNS_PACKET_DO(q->request_dns_packet),
941dd294	211	dns_query_fully_authenticated(q));
b30bf55d	212	if (r < 0) {
e8d23f92	213	log_debug_errno(r, "Failed to finish reply packet: %m");
b30bf55d LP	214	break;
	215	}
	216
e8d23f92	217	(void) dns_stub_send(q->manager, q->request_dns_stream, q->request_dns_packet, q->reply_dns_packet);
b30bf55d	218	break;
51027656	219	}
b30bf55d LP	220
b30bf55d LP	221	case DNS_TRANSACTION_RCODE_FAILURE:
2b2d98c1	222	(void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode, dns_query_fully_authenticated(q));
b30bf55d LP	223	break;
	224
	225	case DNS_TRANSACTION_NOT_FOUND:
2b2d98c1	226	(void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN, dns_query_fully_authenticated(q));
b30bf55d LP	227	break;
	228
	229	case DNS_TRANSACTION_TIMEOUT:
	230	case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
	231	/* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
	232	break;
	233
	234	case DNS_TRANSACTION_NO_SERVERS:
	235	case DNS_TRANSACTION_INVALID_REPLY:
	236	case DNS_TRANSACTION_ERRNO:
	237	case DNS_TRANSACTION_ABORTED:
	238	case DNS_TRANSACTION_DNSSEC_FAILED:
	239	case DNS_TRANSACTION_NO_TRUST_ANCHOR:
	240	case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
	241	case DNS_TRANSACTION_NETWORK_DOWN:
2b2d98c1	242	(void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
b30bf55d LP	243	break;
	244
	245	case DNS_TRANSACTION_NULL:
	246	case DNS_TRANSACTION_PENDING:
	247	case DNS_TRANSACTION_VALIDATING:
	248	default:
	249	assert_not_reached("Impossible state");
	250	}
	251
b30bf55d LP	252	dns_query_free(q);
	253	}
	254
	255	static int dns_stub_stream_complete(DnsStream *s, int error) {
	256	assert(s);
	257
b412af57 LP	258	log_debug_errno(error, "DNS TCP connection terminated, destroying queries: %m");
	259
	260	for (;;) {
	261	DnsQuery *q;
	262
	263	q = set_first(s->queries);
	264	if (!q)
	265	break;
b30bf55d	266
b412af57 LP	267	dns_query_free(q);
b412af57 LP	268	}
b30bf55d	269
b412af57 LP	270	/* This drops the implicit ref we keep around since it was allocated, as incoming stub connections
	271	* should be kept as long as the client wants to. */
	272	dns_stream_unref(s);
b30bf55d LP	273	return 0;
	274	}
	275
	276	static void dns_stub_process_query(Manager m, DnsStream s, DnsPacket *p) {
	277	DnsQuery *q = NULL;
	278	int r;
	279
	280	assert(m);
	281	assert(p);
	282	assert(p->protocol == DNS_PROTOCOL_DNS);
	283
b30bf55d LP	284	if (in_addr_is_localhost(p->family, &p->sender) <= 0 \|\|
	285	in_addr_is_localhost(p->family, &p->destination) <= 0) {
	286	log_error("Got packet on unexpected IP range, refusing.");
2b2d98c1	287	dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
b30bf55d LP	288	goto fail;
	289	}
	290
	291	r = dns_packet_extract(p);
	292	if (r < 0) {
	293	log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
2b2d98c1	294	dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR, false);
b30bf55d LP	295	goto fail;
	296	}
	297
	298	if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
	299	log_debug("Got EDNS OPT field with unsupported version number.");
2b2d98c1	300	dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS, false);
b30bf55d LP	301	goto fail;
	302	}
	303
	304	if (dns_type_is_obsolete(p->question->keys[0]->type)) {
	305	log_debug("Got message with obsolete key type, refusing.");
2b2d98c1	306	dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
b30bf55d LP	307	goto fail;
	308	}
	309
	310	if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
	311	log_debug("Got request for zone transfer, refusing.");
2b2d98c1	312	dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
b30bf55d LP	313	goto fail;
	314	}
	315
	316	if (!DNS_PACKET_RD(p)) {
	317	/* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
	318	log_debug("Got request with recursion disabled, refusing.");
2b2d98c1	319	dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED, false);
b30bf55d LP	320	goto fail;
	321	}
	322
	323	if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
	324	log_debug("Got request with DNSSEC CD bit set, refusing.");
2b2d98c1	325	dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
b30bf55d LP	326	goto fail;
	327	}
	328
e8d23f92	329	r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL\|SD_RESOLVED_NO_SEARCH);
b30bf55d LP	330	if (r < 0) {
b30bf55d LP	331	log_error_errno(r, "Failed to generate query object: %m");
2b2d98c1	332	dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
b30bf55d LP	333	goto fail;
	334	}
	335
	336	/* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
	337	q->clamp_ttl = true;
	338
	339	q->request_dns_packet = dns_packet_ref(p);
	340	q->request_dns_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
	341	q->complete = dns_stub_query_complete;
	342
	343	if (s) {
b412af57 LP	344	/* Remember which queries belong to this stream, so that we can cancel them when the stream
	345	* is disconnected early */
	346
	347	r = set_ensure_allocated(&s->queries, &trivial_hash_ops);
	348	if (r < 0) {
	349	log_oom();
	350	goto fail;
	351	}
	352
	353	if (set_put(s->queries, q) < 0) {
	354	log_oom();
	355	goto fail;
	356	}
b30bf55d LP	357	}
	358
	359	r = dns_query_go(q);
	360	if (r < 0) {
	361	log_error_errno(r, "Failed to start query: %m");
2b2d98c1	362	dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
b30bf55d LP	363	goto fail;
	364	}
	365
52e63427	366	log_debug("Processing query...");
b30bf55d LP	367	return;
	368
	369	fail:
b30bf55d LP	370	dns_query_free(q);
	371	}
	372
	373	static int on_dns_stub_packet(sd_event_source s, int fd, uint32_t revents, void userdata) {
	374	_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
	375	Manager *m = userdata;
	376	int r;
	377
	378	r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
	379	if (r <= 0)
	380	return r;
	381
	382	if (dns_packet_validate_query(p) > 0) {
	383	log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
	384
	385	dns_stub_process_query(m, NULL, p);
	386	} else
	387	log_debug("Invalid DNS stub UDP packet, ignoring.");
	388
	389	return 0;
	390	}
	391
424e490b	392	static int manager_dns_stub_udp_fd(Manager *m) {
b30bf55d LP	393	union sockaddr_union sa = {
	394	.in.sin_family = AF_INET,
	395	.in.sin_port = htobe16(53),
	396	.in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
	397	};
424e490b	398	_cleanup_close_ int fd = -1;
b30bf55d LP	399	int r;
	400
	401	if (m->dns_stub_udp_fd >= 0)
	402	return m->dns_stub_udp_fd;
	403
424e490b ZJS	404	fd = socket(AF_INET, SOCK_DGRAM\|SOCK_CLOEXEC\|SOCK_NONBLOCK, 0);
424e490b ZJS	405	if (fd < 0)
b30bf55d LP	406	return -errno;
b30bf55d LP	407
2ff48e98 LP	408	r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
	409	if (r < 0)
	410	return r;
b30bf55d	411
2ff48e98 LP	412	r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true);
	413	if (r < 0)
	414	return r;
b30bf55d	415
2ff48e98 LP	416	r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true);
	417	if (r < 0)
	418	return r;
b30bf55d LP	419
b30bf55d LP	420	/* Make sure no traffic from outside the local host can leak to onto this socket */
424e490b ZJS	421	if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
424e490b ZJS	422	return -errno;
b30bf55d	423
424e490b ZJS	424	if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
424e490b ZJS	425	return -errno;
b30bf55d	426
424e490b	427	r = sd_event_add_io(m->event, &m->dns_stub_udp_event_source, fd, EPOLLIN, on_dns_stub_packet, m);
b30bf55d	428	if (r < 0)
424e490b	429	return r;
b30bf55d LP	430
	431	(void) sd_event_source_set_description(m->dns_stub_udp_event_source, "dns-stub-udp");
	432
c10d6bdb	433	return m->dns_stub_udp_fd = TAKE_FD(fd);
b30bf55d LP	434	}
	435
	436	static int on_dns_stub_stream_packet(DnsStream *s) {
aa337a5e LP	437	_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
aa337a5e LP	438
b30bf55d	439	assert(s);
b30bf55d	440
aa337a5e LP	441	p = dns_stream_take_read_packet(s);
	442	assert(p);
	443
	444	if (dns_packet_validate_query(p) > 0) {
	445	log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p));
b30bf55d	446
aa337a5e	447	dns_stub_process_query(s->manager, s, p);
b30bf55d LP	448	} else
	449	log_debug("Invalid DNS stub TCP packet, ignoring.");
	450
b30bf55d LP	451	return 0;
	452	}
	453
	454	static int on_dns_stub_stream(sd_event_source s, int fd, uint32_t revents, void userdata) {
	455	DnsStream *stream;
	456	Manager *m = userdata;
	457	int cfd, r;
	458
	459	cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK\|SOCK_CLOEXEC);
	460	if (cfd < 0) {
3742095b	461	if (IN_SET(errno, EAGAIN, EINTR))
b30bf55d LP	462	return 0;
	463
	464	return -errno;
	465	}
	466
652ba568	467	r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL);
b30bf55d LP	468	if (r < 0) {
	469	safe_close(cfd);
	470	return r;
	471	}
	472
	473	stream->on_packet = on_dns_stub_stream_packet;
b412af57	474	stream->complete = dns_stub_stream_complete;
b30bf55d	475
b412af57	476	/* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */
b30bf55d LP	477
	478	return 0;
	479	}
	480
424e490b	481	static int manager_dns_stub_tcp_fd(Manager *m) {
b30bf55d LP	482	union sockaddr_union sa = {
	483	.in.sin_family = AF_INET,
	484	.in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
	485	.in.sin_port = htobe16(53),
	486	};
424e490b	487	_cleanup_close_ int fd = -1;
b30bf55d LP	488	int r;
	489
	490	if (m->dns_stub_tcp_fd >= 0)
	491	return m->dns_stub_tcp_fd;
	492
424e490b ZJS	493	fd = socket(AF_INET, SOCK_STREAM\|SOCK_CLOEXEC\|SOCK_NONBLOCK, 0);
424e490b ZJS	494	if (fd < 0)
b30bf55d LP	495	return -errno;
b30bf55d LP	496
2ff48e98 LP	497	r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, true);
	498	if (r < 0)
	499	return r;
b30bf55d	500
2ff48e98 LP	501	r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
	502	if (r < 0)
	503	return r;
b30bf55d	504
2ff48e98 LP	505	r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true);
	506	if (r < 0)
	507	return r;
b30bf55d	508
2ff48e98 LP	509	r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true);
	510	if (r < 0)
	511	return r;
b30bf55d LP	512
b30bf55d LP	513	/* Make sure no traffic from outside the local host can leak to onto this socket */
424e490b ZJS	514	if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
424e490b ZJS	515	return -errno;
b30bf55d	516
424e490b ZJS	517	if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
424e490b ZJS	518	return -errno;
b30bf55d	519
424e490b ZJS	520	if (listen(fd, SOMAXCONN) < 0)
424e490b ZJS	521	return -errno;
b30bf55d	522
424e490b	523	r = sd_event_add_io(m->event, &m->dns_stub_tcp_event_source, fd, EPOLLIN, on_dns_stub_stream, m);
b30bf55d	524	if (r < 0)
424e490b	525	return r;
b30bf55d LP	526
	527	(void) sd_event_source_set_description(m->dns_stub_tcp_event_source, "dns-stub-tcp");
	528
c10d6bdb	529	return m->dns_stub_tcp_fd = TAKE_FD(fd);
b30bf55d LP	530	}
	531
	532	int manager_dns_stub_start(Manager *m) {
424e490b	533	const char *t = "UDP";
01b0669e	534	int r = 0;
b30bf55d LP	535
	536	assert(m);
	537
d5da7707 ZJS	538	if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
	539	log_debug("Not creating stub listener.");
	540	else
	541	log_debug("Creating stub listener using %s.",
	542	m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
	543	m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
	544	"UDP/TCP");
	545
424e490b	546	if (IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_UDP))
1ae43295	547	r = manager_dns_stub_udp_fd(m);
b30bf55d	548
424e490b ZJS	549	if (r >= 0 &&
	550	IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_TCP)) {
	551	t = "TCP";
1ae43295	552	r = manager_dns_stub_tcp_fd(m);
1ae43295	553	}
b30bf55d	554
0f4db364 ZJS	555	if (IN_SET(r, -EADDRINUSE, -EPERM)) {
	556	if (r == -EADDRINUSE)
	557	log_warning_errno(r,
	558	"Another process is already listening on %s socket 127.0.0.53:53.\n"
	559	"Turning off local DNS stub support.", t);
	560	else
	561	log_warning_errno(r,
	562	"Failed to listen on %s socket 127.0.0.53:53: %m.\n"
	563	"Turning off local DNS stub support.", t);
424e490b ZJS	564	manager_dns_stub_stop(m);
	565	} else if (r < 0)
	566	return log_error_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m", t);
b30bf55d LP	567
	568	return 0;
	569	}
	570
	571	void manager_dns_stub_stop(Manager *m) {
	572	assert(m);
	573
	574	m->dns_stub_udp_event_source = sd_event_source_unref(m->dns_stub_udp_event_source);
	575	m->dns_stub_tcp_event_source = sd_event_source_unref(m->dns_stub_tcp_event_source);
	576
	577	m->dns_stub_udp_fd = safe_close(m->dns_stub_udp_fd);
	578	m->dns_stub_tcp_fd = safe_close(m->dns_stub_tcp_fd);
	579	}