diff options
Diffstat (limited to 'src/resolve/resolved-dns-stub.c')
| -rw-r--r-- | src/resolve/resolved-dns-stub.c | 1427 |
1 files changed, 1427 insertions, 0 deletions
diff --git a/src/resolve/resolved-dns-stub.c b/src/resolve/resolved-dns-stub.c new file mode 100644 index 0000000..c59e3b7 --- /dev/null +++ b/src/resolve/resolved-dns-stub.c @@ -0,0 +1,1427 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <net/if_arp.h> +#include <netinet/tcp.h> + +#include "capability-util.h" +#include "errno-util.h" +#include "fd-util.h" +#include "missing_network.h" +#include "missing_socket.h" +#include "resolved-dns-stub.h" +#include "socket-netlink.h" +#include "socket-util.h" +#include "stdio-util.h" +#include "string-table.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) + +/* On the extra stubs, use a more conservative choice */ +#define ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX DNS_PACKET_UNICAST_SIZE_LARGE_MAX + +static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type); +static int manager_dns_stub_fd(Manager *m, int family, const union in_addr_union *listen_address, int type); + +static void dns_stub_listener_extra_hash_func(const DnsStubListenerExtra *a, struct siphash *state) { + assert(a); + + siphash24_compress(&a->mode, sizeof(a->mode), state); + siphash24_compress(&a->family, sizeof(a->family), state); + siphash24_compress(&a->address, FAMILY_ADDRESS_SIZE(a->family), state); + siphash24_compress(&a->port, sizeof(a->port), state); +} + +static int dns_stub_listener_extra_compare_func(const DnsStubListenerExtra *a, const DnsStubListenerExtra *b) { + int r; + + assert(a); + assert(b); + + r = CMP(a->mode, b->mode); + if (r != 0) + return r; + + r = CMP(a->family, b->family); + if (r != 0) + return r; + + r = memcmp(&a->address, &b->address, FAMILY_ADDRESS_SIZE(a->family)); + if (r != 0) + return r; + + return CMP(a->port, b->port); +} + +DEFINE_HASH_OPS_WITH_KEY_DESTRUCTOR( + dns_stub_listener_extra_hash_ops, + DnsStubListenerExtra, + dns_stub_listener_extra_hash_func, + dns_stub_listener_extra_compare_func, + dns_stub_listener_extra_free); + +int dns_stub_listener_extra_new( + Manager *m, + DnsStubListenerExtra **ret) { + + DnsStubListenerExtra *l; + + l = new(DnsStubListenerExtra, 1); + if (!l) + return -ENOMEM; + + *l = (DnsStubListenerExtra) { + .manager = m, + }; + + *ret = TAKE_PTR(l); + return 0; +} + +DnsStubListenerExtra *dns_stub_listener_extra_free(DnsStubListenerExtra *p) { + if (!p) + return NULL; + + p->udp_event_source = sd_event_source_disable_unref(p->udp_event_source); + p->tcp_event_source = sd_event_source_disable_unref(p->tcp_event_source); + + hashmap_free(p->queries_by_packet); + + return mfree(p); +} + +static void stub_packet_hash_func(const DnsPacket *p, struct siphash *state) { + assert(p); + + siphash24_compress(&p->protocol, sizeof(p->protocol), state); + siphash24_compress(&p->family, sizeof(p->family), state); + siphash24_compress(&p->sender, sizeof(p->sender), state); + siphash24_compress(&p->ipproto, sizeof(p->ipproto), state); + siphash24_compress(&p->sender_port, sizeof(p->sender_port), state); + siphash24_compress(DNS_PACKET_HEADER(p), sizeof(DnsPacketHeader), state); + + /* We don't bother hashing the full packet here, just the header */ +} + +static int stub_packet_compare_func(const DnsPacket *x, const DnsPacket *y) { + int r; + + r = CMP(x->protocol, y->protocol); + if (r != 0) + return r; + + r = CMP(x->family, y->family); + if (r != 0) + return r; + + r = memcmp(&x->sender, &y->sender, sizeof(x->sender)); + if (r != 0) + return r; + + r = CMP(x->ipproto, y->ipproto); + if (r != 0) + return r; + + r = CMP(x->sender_port, y->sender_port); + if (r != 0) + return r; + + return memcmp(DNS_PACKET_HEADER(x), DNS_PACKET_HEADER(y), sizeof(DnsPacketHeader)); +} + +DEFINE_HASH_OPS(stub_packet_hash_ops, DnsPacket, stub_packet_hash_func, stub_packet_compare_func); + +static int reply_add_with_rrsig( + DnsAnswer **reply, + DnsResourceRecord *rr, + int ifindex, + DnsAnswerFlags flags, + DnsResourceRecord *rrsig, + bool with_rrsig) { + int r; + + assert(reply); + assert(rr); + + r = dns_answer_add_extend(reply, rr, ifindex, flags, rrsig); + if (r < 0) + return r; + + if (with_rrsig && rrsig) { + r = dns_answer_add_extend(reply, rrsig, ifindex, flags, NULL); + if (r < 0) + return r; + } + + return 0; +} + +static int dns_stub_collect_answer_by_question( + DnsAnswer **reply, + DnsAnswer *answer, + DnsQuestion *question, + bool with_rrsig) { /* Add RRSIG RR matching each RR */ + + DnsAnswerItem *item; + int r; + + assert(reply); + + /* Copies all RRs from 'answer' into 'reply', if they match 'question'. */ + + DNS_ANSWER_FOREACH_ITEM(item, answer) { + + /* We have a question, let's see if this RR matches it */ + r = dns_question_matches_rr(question, item->rr, NULL); + if (r < 0) + return r; + if (!r) { + /* Maybe there's a CNAME/DNAME in here? If so, that's an answer too */ + r = dns_question_matches_cname_or_dname(question, item->rr, NULL); + if (r < 0) + return r; + if (!r) + continue; + } + + /* Mask the section info, we want the primary answers to always go without section + * info, so that it is added to the answer section when we synthesize a reply. */ + + r = reply_add_with_rrsig( + reply, + item->rr, + item->ifindex, + item->flags & ~DNS_ANSWER_MASK_SECTIONS, + item->rrsig, + with_rrsig); + if (r < 0) + return r; + } + + return 0; +} + +static int dns_stub_collect_answer_by_section( + DnsAnswer **reply, + DnsAnswer *answer, + DnsAnswerFlags section, + DnsAnswer *exclude1, + DnsAnswer *exclude2, + bool with_dnssec) { /* Include DNSSEC RRs. RRSIG, NSEC, … */ + + DnsAnswerItem *item; + int r; + + assert(reply); + + /* Copies all RRs from 'answer' into 'reply', if they originate from the specified section. Also, + * avoid any RRs listed in 'exclude'. */ + + DNS_ANSWER_FOREACH_ITEM(item, answer) { + + if (dns_answer_contains(exclude1, item->rr) || + dns_answer_contains(exclude2, item->rr)) + continue; + + if (!with_dnssec && + dns_type_is_dnssec(item->rr->key->type)) + continue; + + if (((item->flags ^ section) & DNS_ANSWER_MASK_SECTIONS) != 0) + continue; + + r = reply_add_with_rrsig( + reply, + item->rr, + item->ifindex, + item->flags, + item->rrsig, + with_dnssec); + if (r < 0) + return r; + } + + return 0; +} + +static int dns_stub_assign_sections( + DnsQuery *q, + DnsQuestion *question, + bool edns0_do) { + + int r; + + assert(q); + assert(question); + + /* Let's assign the 'answer' RRs we collected to their respective sections in the reply datagram. We + * try to reproduce a section assignment similar to what the upstream DNS server responded to us. We + * use the DNS_ANSWER_SECTION_xyz flags to match things up, which is where the original upstream's + * packet section assignment is stored in the DnsAnswer object. Not all RRs in the 'answer' objects + * come with section information though (for example, because they were synthesized locally, and not + * from a DNS packet). To deal with that we extend the assignment logic a bit: anything from the + * 'answer' object that directly matches the original question is always put in the ANSWER section, + * regardless if it carries section info, or what that section info says. Then, anything from the + * 'answer' objects that is from the ANSWER or AUTHORITY sections, and wasn't already added to the + * ANSWER section is placed in the AUTHORITY section. Everything else from either object is added to + * the ADDITIONAL section. */ + + /* Include all RRs that directly answer the question in the answer section */ + r = dns_stub_collect_answer_by_question( + &q->reply_answer, + q->answer, + question, + edns0_do); + if (r < 0) + return r; + + /* Include all RRs that originate from the authority sections, and aren't already listed in the + * answer section, in the authority section */ + r = dns_stub_collect_answer_by_section( + &q->reply_authoritative, + q->answer, + DNS_ANSWER_SECTION_AUTHORITY, + q->reply_answer, NULL, + edns0_do); + if (r < 0) + return r; + + /* Include all RRs that originate from the answer or additional sections in the additional section + * (except if already listed in the other two sections). Also add all RRs with no section marking. */ + r = dns_stub_collect_answer_by_section( + &q->reply_additional, + q->answer, + DNS_ANSWER_SECTION_ANSWER, + q->reply_answer, q->reply_authoritative, + edns0_do); + if (r < 0) + return r; + r = dns_stub_collect_answer_by_section( + &q->reply_additional, + q->answer, + DNS_ANSWER_SECTION_ADDITIONAL, + q->reply_answer, q->reply_authoritative, + edns0_do); + if (r < 0) + return r; + r = dns_stub_collect_answer_by_section( + &q->reply_additional, + q->answer, + 0, + q->reply_answer, q->reply_authoritative, + edns0_do); + if (r < 0) + return r; + + return 0; +} + +static int dns_stub_make_reply_packet( + DnsPacket **ret, + size_t max_size, + DnsQuestion *q, + bool *ret_truncated) { + + _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL; + bool tc = false; + int r; + + assert(ret); + + 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 == -EMSGSIZE) + tc = true; + else if (r < 0) + return r; + + if (ret_truncated) + *ret_truncated = tc; + else if (tc) + return -EMSGSIZE; + + DNS_PACKET_HEADER(p)->qdcount = htobe16(dns_question_size(q)); + + *ret = TAKE_PTR(p); + return 0; +} + +static int dns_stub_add_reply_packet_body( + DnsPacket *p, + DnsAnswer *answer, + DnsAnswer *authoritative, + DnsAnswer *additional, + bool edns0_do, /* Client expects DNSSEC RRs? */ + bool *truncated) { + + unsigned n_answer = 0, n_authoritative = 0, n_additional = 0; + bool tc = false; + int r; + + assert(p); + + /* Add the three sections to the packet. If the answer section doesn't fit we'll signal that as + * truncation. If the authoritative section doesn't fit and we are in DNSSEC mode, also signal + * truncation. In all other cases where things don't fit don't signal truncation, as for those cases + * the dropped RRs should not be essential. */ + + r = dns_packet_append_answer(p, answer, &n_answer); + if (r == -EMSGSIZE) + tc = true; + else if (r < 0) + return r; + else { + r = dns_packet_append_answer(p, authoritative, &n_authoritative); + if (r == -EMSGSIZE) { + if (edns0_do) + tc = true; + } else if (r < 0) + return r; + else { + r = dns_packet_append_answer(p, additional, &n_additional); + if (r < 0 && r != -EMSGSIZE) + return r; + } + } + + if (tc) { + if (!truncated) + return -EMSGSIZE; + + *truncated = true; + } + + DNS_PACKET_HEADER(p)->ancount = htobe16(n_answer); + DNS_PACKET_HEADER(p)->nscount = htobe16(n_authoritative); + DNS_PACKET_HEADER(p)->arcount = htobe16(n_additional); + return 0; +} + +static const char *nsid_string(void) { + static char buffer[SD_ID128_STRING_MAX + STRLEN(".resolved.systemd.io")] = ""; + sd_id128_t id; + int r; + + /* Let's generate a string that we can use as RFC5001 NSID identifier. The string shall identify us + * as systemd-resolved, and return a different string for each resolved instance without leaking host + * identity. Hence let's use a fixed suffix that identifies resolved, and a prefix generated from the + * machine ID but from which the machine ID cannot be determined. + * + * Clients can use this to determine whether an answer is originating locally or is proxied from + * upstream. */ + + if (!isempty(buffer)) + return buffer; + + r = sd_id128_get_machine_app_specific( + SD_ID128_MAKE(ed,d3,12,5d,16,b9,41,f9,a1,49,5f,ab,15,62,ab,27), + &id); + if (r < 0) { + log_debug_errno(r, "Failed to determine machine ID, ignoring: %m"); + return NULL; + } + + xsprintf(buffer, SD_ID128_FORMAT_STR ".resolved.systemd.io", SD_ID128_FORMAT_VAL(id)); + return buffer; +} + +static int dns_stub_finish_reply_packet( + DnsPacket *p, + uint16_t id, + int rcode, + bool tc, /* set the Truncated bit? */ + bool aa, /* set the Authoritative Answer bit? */ + bool rd, /* set the Recursion Desired 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? */ + bool cd, /* set the DNSSEC checking disabled bit? */ + uint16_t max_udp_size, /* The maximum UDP datagram size to advertise to clients */ + bool nsid) { /* whether to add NSID */ + + int r; + + assert(p); + + if (add_opt) { + r = dns_packet_append_opt(p, max_udp_size, edns0_do, /* include_rfc6975 = */ false, nsid ? nsid_string() : NULL, rcode, NULL); + if (r == -EMSGSIZE) /* Hit the size limit? then indicate truncation */ + tc = true; + else if (r < 0) + return r; + } else { + /* If the client can't to EDNS0, don't do DO either */ + edns0_do = false; + + /* If we don't do EDNS, clamp the rcode to 4 bit */ + if (rcode > 0xF) + rcode = DNS_RCODE_SERVFAIL; + } + + /* Don't set the CD bit unless DO is on, too */ + if (!edns0_do) + cd = false; + + /* Note that we allow the AD bit to be set even if client didn't signal DO, as per RFC 6840, section + * 5.7 */ + + DNS_PACKET_HEADER(p)->id = id; + + DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS( + 1 /* qr */, + 0 /* opcode */, + aa /* aa */, + tc /* tc */, + rd /* rd */, + 1 /* ra */, + ad /* ad */, + cd /* cd */, + rcode)); + + return 0; +} + +static bool address_is_proxy(int family, const union in_addr_union *a) { + assert(a); + + /* Returns true if the specified address is the DNS "proxy" stub, i.e. where we unconditionally enable bypass mode */ + + if (family != AF_INET) + return false; + + return be32toh(a->in.s_addr) == INADDR_DNS_PROXY_STUB; +} + +static int find_socket_fd( + Manager *m, + DnsStubListenerExtra *l, + int family, + const union in_addr_union *listen_address, + int type) { + + assert(m); + + /* Finds the right socket to use for sending. If we know the extra listener, otherwise go via the + * address to send from */ + if (l) + return manager_dns_stub_fd_extra(m, l, type); + + return manager_dns_stub_fd(m, family, listen_address, type); +} + +static int dns_stub_send( + Manager *m, + DnsStubListenerExtra *l, + 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, ifindex; + + fd = find_socket_fd(m, l, p->family, &p->destination, SOCK_DGRAM); + if (fd < 0) + return fd; + + if (address_is_proxy(p->family, &p->destination)) + /* Force loopback iface if this is the loopback proxy stub + * and ifindex was normalized to 0 by manager_recv(). */ + ifindex = p->ifindex ?: LOOPBACK_IFINDEX; + else + /* Force loopback iface if this is the main listener stub. */ + ifindex = l ? p->ifindex : LOOPBACK_IFINDEX; + + /* 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 127.0.0.53/54. */ + r = manager_send(m, + fd, + 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_reply_with_edns0_do(DnsQuery *q) { + assert(q); + + /* Reply with DNSSEC DO set? Only if client supports it; and we did any DNSSEC verification + * ourselves, or consider the data fully authenticated because we generated it locally, or the client + * set cd */ + + return DNS_PACKET_DO(q->request_packet) && + (q->answer_dnssec_result >= 0 || /* we did proper DNSSEC validation … */ + dns_query_fully_authenticated(q) || /* … or we considered it authentic otherwise … */ + DNS_PACKET_CD(q->request_packet)); /* … or client set CD */ +} + +static void dns_stub_suppress_duplicate_section_rrs(DnsQuery *q) { + /* If we follow a CNAME/DNAME chain we might end up populating our sections with redundant RRs + * because we built up the sections from multiple reply packets (one from each CNAME/DNAME chain + * element). E.g. it could be that an RR that was included in the first reply's additional section + * ends up being relevant as main answer in a subsequent reply in the chain. Let's clean this up, and + * remove everything in the "higher priority" sections from the "lower priority" sections. + * + * Note that this removal matches by RR keys instead of the full RRs. This is because RRsets should + * always end up in one section fully or not at all, but never be split among sections. + * + * Specifically: we remove ANSWER section RRs from the AUTHORITATIVE and ADDITIONAL sections, as well + * as AUTHORITATIVE section RRs from the ADDITIONAL section. */ + + dns_answer_remove_by_answer_keys(&q->reply_authoritative, q->reply_answer); + dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_answer); + dns_answer_remove_by_answer_keys(&q->reply_additional, q->reply_authoritative); +} + +static int dns_stub_send_reply( + DnsQuery *q, + int rcode) { + + _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL; + bool truncated, edns0_do; + int r; + + assert(q); + + edns0_do = dns_stub_reply_with_edns0_do(q); /* let's check if we shall reply with EDNS0 DO? */ + + r = dns_stub_make_reply_packet( + &reply, + DNS_PACKET_PAYLOAD_SIZE_MAX(q->request_packet), + q->request_packet->question, + &truncated); + if (r < 0) + return log_debug_errno(r, "Failed to build reply packet: %m"); + + dns_stub_suppress_duplicate_section_rrs(q); + + r = dns_stub_add_reply_packet_body( + reply, + q->reply_answer, + q->reply_authoritative, + q->reply_additional, + edns0_do, + &truncated); + if (r < 0) + return log_debug_errno(r, "Failed to append reply packet body: %m"); + + r = dns_stub_finish_reply_packet( + reply, + DNS_PACKET_ID(q->request_packet), + rcode, + truncated, + dns_query_fully_authoritative(q), + DNS_PACKET_RD(q->request_packet), + !!q->request_packet->opt, + edns0_do, + (DNS_PACKET_AD(q->request_packet) || DNS_PACKET_DO(q->request_packet)) && dns_query_fully_authenticated(q), + DNS_PACKET_CD(q->request_packet), + q->stub_listener_extra ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX, + dns_packet_has_nsid_request(q->request_packet) > 0 && !q->stub_listener_extra); + if (r < 0) + return log_debug_errno(r, "Failed to build failure packet: %m"); + + return dns_stub_send(q->manager, q->stub_listener_extra, q->request_stream, q->request_packet, reply); +} + +static int dns_stub_send_failure( + Manager *m, + DnsStubListenerExtra *l, + DnsStream *s, + DnsPacket *p, + int rcode, + bool authenticated) { + + _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL; + bool truncated; + int r; + + assert(m); + assert(p); + + r = dns_stub_make_reply_packet( + &reply, + DNS_PACKET_PAYLOAD_SIZE_MAX(p), + p->question, + &truncated); + 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, + truncated, + false, + DNS_PACKET_RD(p), + !!p->opt, + DNS_PACKET_DO(p), + (DNS_PACKET_AD(p) || DNS_PACKET_DO(p)) && authenticated, + DNS_PACKET_CD(p), + l ? ADVERTISE_EXTRA_DATAGRAM_SIZE_MAX : ADVERTISE_DATAGRAM_SIZE_MAX, + dns_packet_has_nsid_request(p) > 0 && !l); + if (r < 0) + return log_debug_errno(r, "Failed to build failure packet: %m"); + + return dns_stub_send(m, l, s, p, reply); +} + +static int dns_stub_patch_bypass_reply_packet( + DnsPacket **ret, /* Where to place the patched packet */ + DnsPacket *original, /* The packet to patch */ + DnsPacket *request) { /* The packet the patched packet shall look like a reply to */ + _cleanup_(dns_packet_unrefp) DnsPacket *c = NULL; + int r; + + assert(ret); + assert(original); + assert(request); + + r = dns_packet_dup(&c, original); + if (r < 0) + return r; + + /* Extract the packet, so that we know where the OPT field is */ + r = dns_packet_extract(c); + if (r < 0) + return r; + + /* Copy over the original client request ID, so that we can make the upstream query look like our own reply. */ + DNS_PACKET_HEADER(c)->id = DNS_PACKET_HEADER(request)->id; + + /* Patch in our own maximum datagram size, if EDNS0 was on */ + r = dns_packet_patch_max_udp_size(c, ADVERTISE_DATAGRAM_SIZE_MAX); + if (r < 0) + return r; + + /* Lower all TTLs by the time passed since we received the datagram. */ + if (timestamp_is_set(original->timestamp)) { + r = dns_packet_patch_ttls(c, original->timestamp); + if (r < 0) + return r; + } + + /* Our upstream connection might have supported larger DNS requests than our downstream one, hence + * set the TC bit if our reply is larger than what the client supports, and truncate. */ + if (c->size > DNS_PACKET_PAYLOAD_SIZE_MAX(request)) { + log_debug("Artificially truncating stub response, as advertised size of client is smaller than upstream one."); + dns_packet_truncate(c, DNS_PACKET_PAYLOAD_SIZE_MAX(request)); + DNS_PACKET_HEADER(c)->flags = htobe16(be16toh(DNS_PACKET_HEADER(c)->flags) | DNS_PACKET_FLAG_TC); + } + + *ret = TAKE_PTR(c); + return 0; +} + +static void dns_stub_query_complete(DnsQuery *query) { + _cleanup_(dns_query_freep) DnsQuery *q = query; + int r; + + assert(q); + assert(q->request_packet); + + if (q->question_bypass) { + /* This is a bypass reply. If so, let's propagate the upstream packet, if we have it and it + * is regular DNS. (We can't do this if the upstream packet is LLMNR or mDNS, since the + * packets are not 100% compatible.) */ + + if (q->answer_full_packet && + q->answer_full_packet->protocol == DNS_PROTOCOL_DNS) { + _cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL; + + r = dns_stub_patch_bypass_reply_packet(&reply, q->answer_full_packet, q->request_packet); + if (r < 0) + log_debug_errno(r, "Failed to patch bypass reply packet: %m"); + else + (void) dns_stub_send(q->manager, q->stub_listener_extra, q->request_stream, q->request_packet, reply); + + return; + } + } + + /* Take all data from the current reply, and merge it into the three reply sections we are building + * up. We do this before processing CNAME redirects, so that we gradually build up our sections, and + * and keep adding all RRs in the CNAME chain. */ + r = dns_stub_assign_sections( + q, + dns_query_question_for_protocol(q, DNS_PROTOCOL_DNS), + dns_stub_reply_with_edns0_do(q)); + if (r < 0) + return (void) log_debug_errno(r, "Failed to assign sections: %m"); + + switch (q->state) { + + case DNS_TRANSACTION_SUCCESS: { + bool first = true; + + for (;;) { + int cname_result; + + cname_result = dns_query_process_cname_one(q); + if (cname_result == -ELOOP) { /* CNAME loop, let's send what we already have */ + log_debug("Detected CNAME loop, returning what we already have."); + (void) dns_stub_send_reply(q, q->answer_rcode); + break; + } + if (cname_result < 0) { + log_debug_errno(cname_result, "Failed to process CNAME: %m"); + break; + } + + if (cname_result == DNS_QUERY_NOMATCH) { + /* This answer doesn't contain any RR that would answer our question + * positively, i.e. neither directly nor via CNAME. */ + + if (first) /* We never followed a CNAME and the answer doesn't match our + * question at all? Then this is final, the empty answer is the + * answer. */ + break; + + /* Otherwise, we already followed a CNAME once within this packet, and the + * packet doesn't answer our question. In that case let's restart the query, + * now with the redirected question. We'll */ + r = dns_query_go(q); + if (r < 0) + return (void) log_debug_errno(r, "Failed to restart query: %m"); + + TAKE_PTR(q); + return; + } + + r = dns_stub_assign_sections( + q, + dns_query_question_for_protocol(q, DNS_PROTOCOL_DNS), + dns_stub_reply_with_edns0_do(q)); + if (r < 0) + return (void) log_debug_errno(r, "Failed to assign sections: %m"); + + if (cname_result == DNS_QUERY_MATCH) /* A match? Then we are done, let's return what we got */ + break; + + /* We followed a CNAME. and collected the RRs that answer the redirected question + * successfully. Let's not try to do this again. */ + assert(cname_result == DNS_QUERY_CNAME); + first = false; + } + + _fallthrough_; + } + + case DNS_TRANSACTION_RCODE_FAILURE: + (void) dns_stub_send_reply(q, q->answer_rcode); + break; + + case DNS_TRANSACTION_NOT_FOUND: + (void) dns_stub_send_reply(q, DNS_RCODE_NXDOMAIN); + 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: + case DNS_TRANSACTION_NO_SOURCE: + case DNS_TRANSACTION_STUB_LOOP: + (void) dns_stub_send_reply(q, DNS_RCODE_SERVFAIL); + break; + + case DNS_TRANSACTION_NULL: + case DNS_TRANSACTION_PENDING: + case DNS_TRANSACTION_VALIDATING: + default: + assert_not_reached(); + } +} + +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, DnsStubListenerExtra *l, DnsStream *s, DnsPacket *p) { + uint64_t protocol_flags = SD_RESOLVED_PROTOCOLS_ALL; + _cleanup_(dns_query_freep) DnsQuery *q = NULL; + Hashmap **queries_by_packet; + DnsQuery *existing; + bool bypass = false; + int r; + + assert(m); + assert(p); + assert(p->protocol == DNS_PROTOCOL_DNS); + + if (!l && /* l == NULL if this is the main stub */ + !address_is_proxy(p->family, &p->destination) && /* don't restrict needlessly for 127.0.0.54 */ + (in_addr_is_localhost(p->family, &p->sender) <= 0 || + in_addr_is_localhost(p->family, &p->destination) <= 0)) { + log_warning("Got packet on unexpected (i.e. non-localhost) IP range, ignoring."); + return; + } + + if (manager_packet_from_our_transaction(m, p)) { + log_debug("Got our own packet looped back, ignoring."); + return; + } + + queries_by_packet = l ? &l->queries_by_packet : &m->stub_queries_by_packet; + existing = hashmap_get(*queries_by_packet, p); + if (existing && dns_packet_equal(existing->request_packet, p)) { + log_debug("Got repeat packet from client, ignoring."); + return; + } + + 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, l, s, p, DNS_RCODE_FORMERR, false); + return; + } + + if (!DNS_PACKET_VERSION_SUPPORTED(p)) { + log_debug("Got EDNS OPT field with unsupported version number."); + dns_stub_send_failure(m, l, s, p, DNS_RCODE_BADVERS, false); + return; + } + + if (dns_type_is_obsolete(dns_question_first_key(p->question)->type)) { + log_debug("Got message with obsolete key type, refusing."); + dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false); + return; + } + + if (dns_type_is_zone_transer(dns_question_first_key(p->question)->type)) { + log_debug("Got request for zone transfer, refusing."); + dns_stub_send_failure(m, l, s, p, DNS_RCODE_REFUSED, false); + return; + } + + 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, l, s, p, DNS_RCODE_REFUSED, false); + return; + } + + r = hashmap_ensure_allocated(queries_by_packet, &stub_packet_hash_ops); + if (r < 0) { + log_oom(); + return; + } + + if (address_is_proxy(p->family, &p->destination)) { + _cleanup_free_ char *dipa = NULL; + + r = in_addr_to_string(p->family, &p->destination, &dipa); + if (r < 0) + return (void) log_error_errno(r, "Failed to format destination address: %m"); + + log_debug("Got request to DNS proxy address 127.0.0.54, enabling bypass logic."); + bypass = true; + protocol_flags = SD_RESOLVED_DNS|SD_RESOLVED_NO_ZONE; /* Turn off mDNS/LLMNR for proxy stub. */ + } else if ((DNS_PACKET_DO(p) && DNS_PACKET_CD(p))) { + log_debug("Got request with DNSSEC checking disabled, enabling bypass logic."); + bypass = true; + } + + if (bypass) + r = dns_query_new(m, &q, NULL, NULL, p, 0, + protocol_flags| + SD_RESOLVED_NO_CNAME| + SD_RESOLVED_NO_SEARCH| + SD_RESOLVED_NO_VALIDATE| + SD_RESOLVED_REQUIRE_PRIMARY| + SD_RESOLVED_CLAMP_TTL); + else + r = dns_query_new(m, &q, p->question, p->question, NULL, 0, + protocol_flags| + SD_RESOLVED_NO_SEARCH| + (DNS_PACKET_DO(p) ? SD_RESOLVED_REQUIRE_PRIMARY : 0)| + SD_RESOLVED_CLAMP_TTL); + if (r < 0) { + log_error_errno(r, "Failed to generate query object: %m"); + dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false); + return; + } + + q->request_packet = dns_packet_ref(p); + q->request_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */ + q->stub_listener_extra = l; + 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_put(&s->queries, NULL, q); + if (r < 0) { + log_oom(); + return; + } + assert(r > 0); + } + + /* Add the query to the hash table we use to determine repeat packets now. We don't care about + * failures here, since in the worst case we'll not recognize duplicate incoming requests, which + * isn't particularly bad. */ + (void) hashmap_put(*queries_by_packet, q->request_packet, q); + + r = dns_query_go(q); + if (r < 0) { + log_error_errno(r, "Failed to start query: %m"); + dns_stub_send_failure(m, l, s, p, DNS_RCODE_SERVFAIL, false); + return; + } + + log_debug("Processing query..."); + TAKE_PTR(q); +} + +static int on_dns_stub_packet_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) { + _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL; + 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, l, NULL, p); + } else + log_debug("Invalid DNS stub UDP packet, ignoring."); + + return 0; +} + +static int on_dns_stub_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) { + return on_dns_stub_packet_internal(s, fd, revents, userdata, NULL); +} + +static int on_dns_stub_packet_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) { + DnsStubListenerExtra *l = ASSERT_PTR(userdata); + + return on_dns_stub_packet_internal(s, fd, revents, l->manager, l); +} + +static int on_dns_stub_stream_packet(DnsStream *s, DnsPacket *p) { + assert(s); + assert(s->manager); + 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->stub_listener_extra, s, p); + } else + log_debug("Invalid DNS stub TCP packet, ignoring."); + + return 0; +} + +static int on_dns_stub_stream_internal(sd_event_source *s, int fd, uint32_t revents, Manager *m, DnsStubListenerExtra *l) { + DnsStream *stream; + int cfd, r; + + cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC); + if (cfd < 0) { + if (ERRNO_IS_ACCEPT_AGAIN(errno)) + return 0; + + return -errno; + } + + r = dns_stream_new(m, &stream, DNS_STREAM_STUB, DNS_PROTOCOL_DNS, cfd, NULL, + on_dns_stub_stream_packet, dns_stub_stream_complete, DNS_STREAM_STUB_TIMEOUT_USEC); + if (r < 0) { + safe_close(cfd); + return r; + } + + stream->stub_listener_extra = l; + + /* We let the reference to the stream dangle here, it will be dropped later by the complete callback. */ + + return 0; +} + +static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) { + return on_dns_stub_stream_internal(s, fd, revents, userdata, NULL); +} + +static int on_dns_stub_stream_extra(sd_event_source *s, int fd, uint32_t revents, void *userdata) { + DnsStubListenerExtra *l = ASSERT_PTR(userdata); + + return on_dns_stub_stream_internal(s, fd, revents, l->manager, l); +} + +static int set_dns_stub_common_socket_options(int fd, int family) { + int r; + + assert(fd >= 0); + assert(IN_SET(family, AF_INET, AF_INET6)); + + r = setsockopt_int(fd, SOL_SOCKET, SO_REUSEADDR, true); + if (r < 0) + return r; + + r = socket_set_recvpktinfo(fd, family, true); + if (r < 0) + return r; + + r = socket_set_recvttl(fd, family, true); + if (r < 0) + return r; + + return 0; +} + +static int set_dns_stub_common_tcp_socket_options(int fd) { + int r; + + assert(fd >= 0); + + r = setsockopt_int(fd, IPPROTO_TCP, TCP_FASTOPEN, 5); /* Everybody appears to pick qlen=5, let's do the same here. */ + if (r < 0) + log_debug_errno(r, "Failed to enable TCP_FASTOPEN on TCP listening socket, ignoring: %m"); + + r = setsockopt_int(fd, IPPROTO_TCP, TCP_NODELAY, true); + if (r < 0) + log_debug_errno(r, "Failed to enable TCP_NODELAY mode, ignoring: %m"); + + return 0; +} + +static int manager_dns_stub_fd( + Manager *m, + int family, + const union in_addr_union *listen_addr, + int type) { + + sd_event_source **event_source; + _cleanup_close_ int fd = -EBADF; + union sockaddr_union sa; + int r; + + assert(m); + assert(listen_addr); + + if (type == SOCK_DGRAM) + event_source = address_is_proxy(family, listen_addr) ? &m->dns_proxy_stub_udp_event_source : &m->dns_stub_udp_event_source; + else if (type == SOCK_STREAM) + event_source = address_is_proxy(family, listen_addr) ? &m->dns_proxy_stub_tcp_event_source : &m->dns_stub_tcp_event_source; + else + return -EPROTONOSUPPORT; + + if (*event_source) + return sd_event_source_get_io_fd(*event_source); + + fd = socket(family, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0); + if (fd < 0) + return -errno; + + r = set_dns_stub_common_socket_options(fd, family); + if (r < 0) + return r; + + if (type == SOCK_STREAM) { + r = set_dns_stub_common_tcp_socket_options(fd); + if (r < 0) + return r; + } + + /* Set slightly different socket options for the non-proxy and the proxy binding. The former we want + * to be accessible only from the local host, for the latter it's OK if people use NAT redirects or + * so to redirect external traffic to it. */ + + if (!address_is_proxy(family, listen_addr)) { + /* Make sure no traffic from outside the local host can leak to onto this socket */ + r = socket_bind_to_ifindex(fd, LOOPBACK_IFINDEX); + if (r < 0) + return r; + + r = socket_set_ttl(fd, family, 1); + if (r < 0) + return r; + } else if (type == SOCK_DGRAM) { + /* Turn off Path MTU Discovery for UDP, for security reasons. See socket_disable_pmtud() for + * a longer discussion. (We only do this for sockets that are potentially externally + * accessible, i.e. the proxy stub one. For the non-proxy one we instead set the TTL to 1, + * see above, so that packets don't get routed at all.) */ + r = socket_disable_pmtud(fd, family); + if (r < 0) + log_debug_errno(r, "Failed to disable UDP PMTUD, ignoring: %m"); + + r = socket_set_recvfragsize(fd, family, true); + if (r < 0) + log_debug_errno(r, "Failed to enable fragment size reception, ignoring: %m"); + } + + r = sockaddr_set_in_addr(&sa, family, listen_addr, 53); + if (r < 0) + return r; + + if (bind(fd, &sa.sa, sizeof(sa.in)) < 0) + return -errno; + + if (type == SOCK_STREAM && + listen(fd, SOMAXCONN_DELUXE) < 0) + return -errno; + + r = sd_event_add_io(m->event, event_source, fd, EPOLLIN, + type == SOCK_DGRAM ? on_dns_stub_packet : on_dns_stub_stream, + m); + if (r < 0) + return r; + + r = sd_event_source_set_io_fd_own(*event_source, true); + if (r < 0) + return r; + + (void) sd_event_source_set_description(*event_source, + type == SOCK_DGRAM ? "dns-stub-udp" : "dns-stub-tcp"); + + return TAKE_FD(fd); +} + +static int manager_dns_stub_fd_extra(Manager *m, DnsStubListenerExtra *l, int type) { + _cleanup_free_ char *pretty = NULL; + _cleanup_close_ int fd = -EBADF; + union sockaddr_union sa; + int r; + + assert(m); + assert(l); + assert(IN_SET(type, SOCK_DGRAM, SOCK_STREAM)); + + sd_event_source **event_source = type == SOCK_DGRAM ? &l->udp_event_source : &l->tcp_event_source; + if (*event_source) + return sd_event_source_get_io_fd(*event_source); + + if (!have_effective_cap(CAP_NET_BIND_SERVICE) && dns_stub_listener_extra_port(l) < 1024) { + log_warning("Missing CAP_NET_BIND_SERVICE capability, not creating extra stub listener on port %hu.", + dns_stub_listener_extra_port(l)); + return 0; + } + + if (l->family == AF_INET) + sa = (union sockaddr_union) { + .in.sin_family = l->family, + .in.sin_port = htobe16(dns_stub_listener_extra_port(l)), + .in.sin_addr = l->address.in, + }; + else + sa = (union sockaddr_union) { + .in6.sin6_family = l->family, + .in6.sin6_port = htobe16(dns_stub_listener_extra_port(l)), + .in6.sin6_addr = l->address.in6, + }; + + fd = socket(l->family, type | SOCK_CLOEXEC | SOCK_NONBLOCK, 0); + if (fd < 0) { + r = -errno; + goto fail; + } + + r = set_dns_stub_common_socket_options(fd, l->family); + if (r < 0) + goto fail; + + if (type == SOCK_STREAM) { + r = set_dns_stub_common_tcp_socket_options(fd); + if (r < 0) + goto fail; + } + + /* Do not set IP_TTL for extra DNS stub listeners, as the address may not be local and in that case + * people may want ttl > 1. */ + + r = socket_set_freebind(fd, l->family, true); + if (r < 0) + goto fail; + + if (type == SOCK_DGRAM) { + r = socket_disable_pmtud(fd, l->family); + if (r < 0) + log_debug_errno(r, "Failed to disable UDP PMTUD, ignoring: %m"); + + r = socket_set_recvfragsize(fd, l->family, true); + if (r < 0) + log_debug_errno(r, "Failed to enable fragment size reception, ignoring: %m"); + } + + r = RET_NERRNO(bind(fd, &sa.sa, SOCKADDR_LEN(sa))); + if (r < 0) + goto fail; + + if (type == SOCK_STREAM && + listen(fd, SOMAXCONN_DELUXE) < 0) { + r = -errno; + goto fail; + } + + r = sd_event_add_io(m->event, event_source, fd, EPOLLIN, + type == SOCK_DGRAM ? on_dns_stub_packet_extra : on_dns_stub_stream_extra, + l); + if (r < 0) + goto fail; + + r = sd_event_source_set_io_fd_own(*event_source, true); + if (r < 0) + goto fail; + + (void) sd_event_source_set_description(*event_source, + type == SOCK_DGRAM ? "dns-stub-udp-extra" : "dns-stub-tcp-extra"); + + if (DEBUG_LOGGING) { + (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty); + log_debug("Listening on %s socket %s.", + type == SOCK_DGRAM ? "UDP" : "TCP", + strnull(pretty)); + } + + return TAKE_FD(fd); + +fail: + assert(r < 0); + (void) in_addr_port_to_string(l->family, &l->address, l->port, &pretty); + return log_warning_errno(r, + r == -EADDRINUSE ? "Another process is already listening on %s socket %s: %m" : + "Failed to listen on %s socket %s: %m", + type == SOCK_DGRAM ? "UDP" : "TCP", + strnull(pretty)); +} + +int manager_dns_stub_start(Manager *m) { + int r; + + assert(m); + + if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_NO) + log_debug("Not creating stub listener."); + else if (!have_effective_cap(CAP_NET_BIND_SERVICE)) + log_warning("Missing CAP_NET_BIND_SERVICE capability, not creating stub listener on port 53."); + else { + static const struct { + uint32_t addr; + int socket_type; + } stub_sockets[] = { + { INADDR_DNS_STUB, SOCK_DGRAM }, + { INADDR_DNS_STUB, SOCK_STREAM }, + { INADDR_DNS_PROXY_STUB, SOCK_DGRAM }, + { INADDR_DNS_PROXY_STUB, SOCK_STREAM }, + }; + + 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"); + + for (size_t i = 0; i < ELEMENTSOF(stub_sockets); i++) { + union in_addr_union a = { + .in.s_addr = htobe32(stub_sockets[i].addr), + }; + + if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_UDP && stub_sockets[i].socket_type == SOCK_STREAM) + continue; + if (m->dns_stub_listener_mode == DNS_STUB_LISTENER_TCP && stub_sockets[i].socket_type == SOCK_DGRAM) + continue; + + r = manager_dns_stub_fd(m, AF_INET, &a, stub_sockets[i].socket_type); + if (r < 0) { + _cleanup_free_ char *busy_socket = NULL; + + if (asprintf(&busy_socket, + "%s socket " IPV4_ADDRESS_FMT_STR ":53", + stub_sockets[i].socket_type == SOCK_DGRAM ? "UDP" : "TCP", + IPV4_ADDRESS_FMT_VAL(a.in)) < 0) + return log_oom(); + + if (IN_SET(r, -EADDRINUSE, -EPERM)) { + log_warning_errno(r, + r == -EADDRINUSE ? "Another process is already listening on %s.\n" + "Turning off local DNS stub support." : + "Failed to listen on %s: %m.\n" + "Turning off local DNS stub support.", + busy_socket); + manager_dns_stub_stop(m); + break; + } + + return log_error_errno(r, "Failed to listen on %s: %m", busy_socket); + } + } + } + + if (!ordered_set_isempty(m->dns_extra_stub_listeners)) { + DnsStubListenerExtra *l; + + log_debug("Creating extra stub listeners."); + + ORDERED_SET_FOREACH(l, m->dns_extra_stub_listeners) { + if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_UDP)) + (void) manager_dns_stub_fd_extra(m, l, SOCK_DGRAM); + if (FLAGS_SET(l->mode, DNS_STUB_LISTENER_TCP)) + (void) manager_dns_stub_fd_extra(m, l, SOCK_STREAM); + } + } + + return 0; +} + +void manager_dns_stub_stop(Manager *m) { + assert(m); + + m->dns_stub_udp_event_source = sd_event_source_disable_unref(m->dns_stub_udp_event_source); + m->dns_stub_tcp_event_source = sd_event_source_disable_unref(m->dns_stub_tcp_event_source); + m->dns_proxy_stub_udp_event_source = sd_event_source_disable_unref(m->dns_proxy_stub_udp_event_source); + m->dns_proxy_stub_tcp_event_source = sd_event_source_disable_unref(m->dns_proxy_stub_tcp_event_source); +} + +static const char* const dns_stub_listener_mode_table[_DNS_STUB_LISTENER_MODE_MAX] = { + [DNS_STUB_LISTENER_NO] = "no", + [DNS_STUB_LISTENER_UDP] = "udp", + [DNS_STUB_LISTENER_TCP] = "tcp", + [DNS_STUB_LISTENER_YES] = "yes", +}; +DEFINE_STRING_TABLE_LOOKUP_WITH_BOOLEAN(dns_stub_listener_mode, DnsStubListenerMode, DNS_STUB_LISTENER_YES); |