[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 void dns_stub_detach_stream(DnsStream *s) {
        assert(s);

        s->complete = NULL;
        s->on_packet = NULL;
        s->query = NULL;
}

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");
        }

        /* If there's a packet to write set, let's leave the stream around */
        if (q->request_dns_stream && DNS_STREAM_QUEUED(q->request_dns_stream)) {

                /* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
                 * default completion action of the stream will drop the reference. */

                dns_stub_detach_stream(q->request_dns_stream);
                q->request_dns_stream = NULL;
        }

        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 query: %m");

        assert(s->query);
        dns_query_free(s->query);

        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);

        /* Takes ownership of the *s stream object */

        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) {
                s->on_packet = NULL;
                s->complete = dns_stub_stream_complete;
                s->query = q;
        }

        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:
        if (s && DNS_STREAM_QUEUED(s))
                dns_stub_detach_stream(s);

        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.");

        /* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
         * or that didn't happen in which case we want to free the stream */
        dns_stream_unref(s);

        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;

        /* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
         * of the stream, or by our packet callback, or when the manager is shut down. */

        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
	129	static void dns_stub_detach_stream(DnsStream *s) {
	130	assert(s);
	131
	132	s->complete = NULL;
	133	s->on_packet = NULL;
	134	s->query = NULL;
	135	}
	136
	137	static int dns_stub_send(Manager m, DnsStream s, DnsPacket p, DnsPacket reply) {
	138	int r;
	139
	140	assert(m);
	141	assert(p);
	142	assert(reply);
	143
	144	if (s)
	145	r = dns_stream_write_packet(s, reply);
	146	else {
	147	int fd;
	148
b30bf55d LP	149	fd = manager_dns_stub_udp_fd(m);
	150	if (fd < 0)
	151	return log_debug_errno(fd, "Failed to get reply socket: %m");
	152
	153	/* Note that it is essential here that we explicitly choose the source IP address for this packet. This
	154	* is because otherwise the kernel will choose it automatically based on the routing table and will
	155	* thus pick 127.0.0.1 rather than 127.0.0.53. */
	156
	157	r = manager_send(m, fd, LOOPBACK_IFINDEX, p->family, &p->sender, p->sender_port, &p->destination, reply);
	158	}
	159	if (r < 0)
	160	return log_debug_errno(r, "Failed to send reply packet: %m");
	161
	162	return 0;
	163	}
	164
2b2d98c1	165	static int dns_stub_send_failure(Manager m, DnsStream s, DnsPacket *p, int rcode, bool authenticated) {
b30bf55d LP	166	_cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
	167	int r;
	168
	169	assert(m);
	170	assert(p);
	171
51027656	172	r = dns_stub_make_reply_packet(&reply, DNS_PACKET_PAYLOAD_SIZE_MAX(p), p->question, NULL, NULL);
e8d23f92 LP	173	if (r < 0)
	174	return log_debug_errno(r, "Failed to make failure packet: %m");
	175
51027656	176	r = dns_stub_finish_reply_packet(reply, DNS_PACKET_ID(p), rcode, false, !!p->opt, DNS_PACKET_DO(p), authenticated);
b30bf55d LP	177	if (r < 0)
	178	return log_debug_errno(r, "Failed to build failure packet: %m");
	179
	180	return dns_stub_send(m, s, p, reply);
	181	}
	182
	183	static void dns_stub_query_complete(DnsQuery *q) {
	184	int r;
	185
	186	assert(q);
	187	assert(q->request_dns_packet);
	188
	189	switch (q->state) {
	190
51027656 LP	191	case DNS_TRANSACTION_SUCCESS: {
51027656 LP	192	bool truncated;
e8d23f92	193
51027656	194	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	195	if (r < 0) {
	196	log_debug_errno(r, "Failed to build reply packet: %m");
	197	break;
	198	}
b30bf55d	199
e8d23f92 LP	200	r = dns_query_process_cname(q);
e8d23f92 LP	201	if (r == -ELOOP) {
2b2d98c1	202	(void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
e8d23f92 LP	203	break;
	204	}
	205	if (r < 0) {
	206	log_debug_errno(r, "Failed to process CNAME: %m");
	207	break;
	208	}
	209	if (r == DNS_QUERY_RESTARTED)
	210	return;
	211
	212	r = dns_stub_finish_reply_packet(
	213	q->reply_dns_packet,
b30bf55d LP	214	DNS_PACKET_ID(q->request_dns_packet),
b30bf55d LP	215	q->answer_rcode,
51027656	216	truncated,
b30bf55d LP	217	!!q->request_dns_packet->opt,
b30bf55d LP	218	DNS_PACKET_DO(q->request_dns_packet),
941dd294	219	dns_query_fully_authenticated(q));
b30bf55d	220	if (r < 0) {
e8d23f92	221	log_debug_errno(r, "Failed to finish reply packet: %m");
b30bf55d LP	222	break;
	223	}
	224
e8d23f92	225	(void) dns_stub_send(q->manager, q->request_dns_stream, q->request_dns_packet, q->reply_dns_packet);
b30bf55d	226	break;
51027656	227	}
b30bf55d LP	228
b30bf55d LP	229	case DNS_TRANSACTION_RCODE_FAILURE:
2b2d98c1	230	(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	231	break;
	232
	233	case DNS_TRANSACTION_NOT_FOUND:
2b2d98c1	234	(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	235	break;
	236
	237	case DNS_TRANSACTION_TIMEOUT:
	238	case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
	239	/* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
	240	break;
	241
	242	case DNS_TRANSACTION_NO_SERVERS:
	243	case DNS_TRANSACTION_INVALID_REPLY:
	244	case DNS_TRANSACTION_ERRNO:
	245	case DNS_TRANSACTION_ABORTED:
	246	case DNS_TRANSACTION_DNSSEC_FAILED:
	247	case DNS_TRANSACTION_NO_TRUST_ANCHOR:
	248	case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
	249	case DNS_TRANSACTION_NETWORK_DOWN:
2b2d98c1	250	(void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL, false);
b30bf55d LP	251	break;
	252
	253	case DNS_TRANSACTION_NULL:
	254	case DNS_TRANSACTION_PENDING:
	255	case DNS_TRANSACTION_VALIDATING:
	256	default:
	257	assert_not_reached("Impossible state");
	258	}
	259
	260	/* If there's a packet to write set, let's leave the stream around */
	261	if (q->request_dns_stream && DNS_STREAM_QUEUED(q->request_dns_stream)) {
	262
	263	/* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
	264	* default completion action of the stream will drop the reference. */
	265
	266	dns_stub_detach_stream(q->request_dns_stream);
	267	q->request_dns_stream = NULL;
	268	}
	269
	270	dns_query_free(q);
	271	}
	272
	273	static int dns_stub_stream_complete(DnsStream *s, int error) {
	274	assert(s);
	275
	276	log_debug_errno(error, "DNS TCP connection terminated, destroying query: %m");
	277
	278	assert(s->query);
	279	dns_query_free(s->query);
	280
	281	return 0;
	282	}
	283
	284	static void dns_stub_process_query(Manager m, DnsStream s, DnsPacket *p) {
	285	DnsQuery *q = NULL;
	286	int r;
	287
	288	assert(m);
	289	assert(p);
	290	assert(p->protocol == DNS_PROTOCOL_DNS);
	291
	292	/* Takes ownership of the s stream object /
	293
	294	if (in_addr_is_localhost(p->family, &p->sender) <= 0 \|\|
	295	in_addr_is_localhost(p->family, &p->destination) <= 0) {
	296	log_error("Got packet on unexpected IP range, refusing.");
2b2d98c1	297	dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
b30bf55d LP	298	goto fail;
	299	}
	300
	301	r = dns_packet_extract(p);
	302	if (r < 0) {
	303	log_debug_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
2b2d98c1	304	dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR, false);
b30bf55d LP	305	goto fail;
	306	}
	307
	308	if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
	309	log_debug("Got EDNS OPT field with unsupported version number.");
2b2d98c1	310	dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS, false);
b30bf55d LP	311	goto fail;
	312	}
	313
	314	if (dns_type_is_obsolete(p->question->keys[0]->type)) {
	315	log_debug("Got message with obsolete key type, refusing.");
2b2d98c1	316	dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
b30bf55d LP	317	goto fail;
	318	}
	319
	320	if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
	321	log_debug("Got request for zone transfer, refusing.");
2b2d98c1	322	dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
b30bf55d LP	323	goto fail;
	324	}
	325
	326	if (!DNS_PACKET_RD(p)) {
	327	/* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
	328	log_debug("Got request with recursion disabled, refusing.");
2b2d98c1	329	dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED, false);
b30bf55d LP	330	goto fail;
	331	}
	332
	333	if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
	334	log_debug("Got request with DNSSEC CD bit set, refusing.");
2b2d98c1	335	dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP, false);
b30bf55d LP	336	goto fail;
	337	}
	338
e8d23f92	339	r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL\|SD_RESOLVED_NO_SEARCH);
b30bf55d LP	340	if (r < 0) {
b30bf55d LP	341	log_error_errno(r, "Failed to generate query object: %m");
2b2d98c1	342	dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL, false);
b30bf55d LP	343	goto fail;
	344	}
	345
	346	/* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
	347	q->clamp_ttl = true;
	348
	349	q->request_dns_packet = dns_packet_ref(p);
	350	q->request_dns_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
	351	q->complete = dns_stub_query_complete;
	352
	353	if (s) {
	354	s->on_packet = NULL;
	355	s->complete = dns_stub_stream_complete;
	356	s->query = q;
	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:
	370	if (s && DNS_STREAM_QUEUED(s))
	371	dns_stub_detach_stream(s);
	372
	373	dns_query_free(q);
	374	}
	375
	376	static int on_dns_stub_packet(sd_event_source s, int fd, uint32_t revents, void userdata) {
	377	_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
	378	Manager *m = userdata;
	379	int r;
	380
	381	r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
	382	if (r <= 0)
	383	return r;
	384
	385	if (dns_packet_validate_query(p) > 0) {
	386	log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
	387
	388	dns_stub_process_query(m, NULL, p);
	389	} else
	390	log_debug("Invalid DNS stub UDP packet, ignoring.");
	391
	392	return 0;
	393	}
	394
424e490b	395	static int manager_dns_stub_udp_fd(Manager *m) {
b30bf55d LP	396	union sockaddr_union sa = {
	397	.in.sin_family = AF_INET,
	398	.in.sin_port = htobe16(53),
	399	.in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
	400	};
424e490b	401	_cleanup_close_ int fd = -1;
b30bf55d LP	402	int r;
	403
	404	if (m->dns_stub_udp_fd >= 0)
	405	return m->dns_stub_udp_fd;
	406
424e490b ZJS	407	fd = socket(AF_INET, SOCK_DGRAM\|SOCK_CLOEXEC\|SOCK_NONBLOCK, 0);
424e490b ZJS	408	if (fd < 0)
b30bf55d LP	409	return -errno;
b30bf55d LP	410
2ff48e98 LP	411	r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
	412	if (r < 0)
	413	return r;
b30bf55d	414
2ff48e98 LP	415	r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true);
	416	if (r < 0)
	417	return r;
b30bf55d	418
2ff48e98 LP	419	r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true);
	420	if (r < 0)
	421	return r;
b30bf55d LP	422
b30bf55d LP	423	/* Make sure no traffic from outside the local host can leak to onto this socket */
424e490b ZJS	424	if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
424e490b ZJS	425	return -errno;
b30bf55d	426
424e490b ZJS	427	if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
424e490b ZJS	428	return -errno;
b30bf55d	429
424e490b	430	r = sd_event_add_io(m->event, &m->dns_stub_udp_event_source, fd, EPOLLIN, on_dns_stub_packet, m);
b30bf55d	431	if (r < 0)
424e490b	432	return r;
b30bf55d LP	433
	434	(void) sd_event_source_set_description(m->dns_stub_udp_event_source, "dns-stub-udp");
	435
c10d6bdb	436	return m->dns_stub_udp_fd = TAKE_FD(fd);
b30bf55d LP	437	}
	438
	439	static int on_dns_stub_stream_packet(DnsStream *s) {
aa337a5e LP	440	_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
aa337a5e LP	441
b30bf55d	442	assert(s);
b30bf55d	443
aa337a5e LP	444	p = dns_stream_take_read_packet(s);
	445	assert(p);
	446
	447	if (dns_packet_validate_query(p) > 0) {
	448	log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(p));
b30bf55d	449
aa337a5e	450	dns_stub_process_query(s->manager, s, p);
b30bf55d LP	451	} else
	452	log_debug("Invalid DNS stub TCP packet, ignoring.");
	453
	454	/* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
	455	* or that didn't happen in which case we want to free the stream */
	456	dns_stream_unref(s);
	457
	458	return 0;
	459	}
	460
	461	static int on_dns_stub_stream(sd_event_source s, int fd, uint32_t revents, void userdata) {
	462	DnsStream *stream;
	463	Manager *m = userdata;
	464	int cfd, r;
	465
	466	cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK\|SOCK_CLOEXEC);
	467	if (cfd < 0) {
3742095b	468	if (IN_SET(errno, EAGAIN, EINTR))
b30bf55d LP	469	return 0;
	470
	471	return -errno;
	472	}
	473
652ba568	474	r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL);
b30bf55d LP	475	if (r < 0) {
	476	safe_close(cfd);
	477	return r;
	478	}
	479
	480	stream->on_packet = on_dns_stub_stream_packet;
	481
	482	/* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
	483	* of the stream, or by our packet callback, or when the manager is shut down. */
	484
	485	return 0;
	486	}
	487
424e490b	488	static int manager_dns_stub_tcp_fd(Manager *m) {
b30bf55d LP	489	union sockaddr_union sa = {
	490	.in.sin_family = AF_INET,
	491	.in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
	492	.in.sin_port = htobe16(53),
	493	};
424e490b	494	_cleanup_close_ int fd = -1;
b30bf55d LP	495	int r;
	496
	497	if (m->dns_stub_tcp_fd >= 0)
	498	return m->dns_stub_tcp_fd;
	499
424e490b ZJS	500	fd = socket(AF_INET, SOCK_STREAM\|SOCK_CLOEXEC\|SOCK_NONBLOCK, 0);
424e490b ZJS	501	if (fd < 0)
b30bf55d LP	502	return -errno;
b30bf55d LP	503
2ff48e98 LP	504	r = setsockopt_int(fd, IPPROTO_IP, IP_TTL, true);
	505	if (r < 0)
	506	return r;
b30bf55d	507
2ff48e98 LP	508	r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true);
	509	if (r < 0)
	510	return r;
b30bf55d	511
2ff48e98 LP	512	r = setsockopt_int(fd, IPPROTO_IP, IP_PKTINFO, true);
	513	if (r < 0)
	514	return r;
b30bf55d	515
2ff48e98 LP	516	r = setsockopt_int(fd, IPPROTO_IP, IP_RECVTTL, true);
	517	if (r < 0)
	518	return r;
b30bf55d LP	519
b30bf55d LP	520	/* Make sure no traffic from outside the local host can leak to onto this socket */
424e490b ZJS	521	if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
424e490b ZJS	522	return -errno;
b30bf55d	523
424e490b ZJS	524	if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
424e490b ZJS	525	return -errno;
b30bf55d	526
424e490b ZJS	527	if (listen(fd, SOMAXCONN) < 0)
424e490b ZJS	528	return -errno;
b30bf55d	529
424e490b	530	r = sd_event_add_io(m->event, &m->dns_stub_tcp_event_source, fd, EPOLLIN, on_dns_stub_stream, m);
b30bf55d	531	if (r < 0)
424e490b	532	return r;
b30bf55d LP	533
	534	(void) sd_event_source_set_description(m->dns_stub_tcp_event_source, "dns-stub-tcp");
	535
c10d6bdb	536	return m->dns_stub_tcp_fd = TAKE_FD(fd);
b30bf55d LP	537	}
	538
	539	int manager_dns_stub_start(Manager *m) {
424e490b	540	const char *t = "UDP";
01b0669e	541	int r = 0;
b30bf55d LP	542
	543	assert(m);
	544
d5da7707 ZJS	545	if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO)
	546	log_debug("Not creating stub listener.");
	547	else
	548	log_debug("Creating stub listener using %s.",
	549	m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP ? "UDP" :
	550	m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP ? "TCP" :
	551	"UDP/TCP");
	552
424e490b	553	if (IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_UDP))
1ae43295	554	r = manager_dns_stub_udp_fd(m);
b30bf55d	555
424e490b ZJS	556	if (r >= 0 &&
	557	IN_SET(m->dns_stub_listener_mode, DNS_STUB_LISTENER_YES, DNS_STUB_LISTENER_TCP)) {
	558	t = "TCP";
1ae43295	559	r = manager_dns_stub_tcp_fd(m);
1ae43295	560	}
b30bf55d	561
0f4db364 ZJS	562	if (IN_SET(r, -EADDRINUSE, -EPERM)) {
	563	if (r == -EADDRINUSE)
	564	log_warning_errno(r,
	565	"Another process is already listening on %s socket 127.0.0.53:53.\n"
	566	"Turning off local DNS stub support.", t);
	567	else
	568	log_warning_errno(r,
	569	"Failed to listen on %s socket 127.0.0.53:53: %m.\n"
	570	"Turning off local DNS stub support.", t);
424e490b ZJS	571	manager_dns_stub_stop(m);
	572	} else if (r < 0)
	573	return log_error_errno(r, "Failed to listen on %s socket 127.0.0.53:53: %m", t);
b30bf55d LP	574
	575	return 0;
	576	}
	577
	578	void manager_dns_stub_stop(Manager *m) {
	579	assert(m);
	580
	581	m->dns_stub_udp_event_source = sd_event_source_unref(m->dns_stub_udp_event_source);
	582	m->dns_stub_tcp_event_source = sd_event_source_unref(m->dns_stub_tcp_event_source);
	583
	584	m->dns_stub_udp_fd = safe_close(m->dns_stub_udp_fd);
	585	m->dns_stub_tcp_fd = safe_close(m->dns_stub_tcp_fd);
	586	}