483 lines
18 KiB
C
483 lines
18 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#include <resolv.h>
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#include <netinet/in.h>
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#include <arpa/inet.h>
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#include "alloc-util.h"
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#include "fd-util.h"
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#include "resolved-manager.h"
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#include "resolved-mdns.h"
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#include "sort-util.h"
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#define CLEAR_CACHE_FLUSH(x) (~MDNS_RR_CACHE_FLUSH & (x))
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void manager_mdns_stop(Manager *m) {
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assert(m);
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m->mdns_ipv4_event_source = sd_event_source_unref(m->mdns_ipv4_event_source);
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m->mdns_ipv4_fd = safe_close(m->mdns_ipv4_fd);
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m->mdns_ipv6_event_source = sd_event_source_unref(m->mdns_ipv6_event_source);
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m->mdns_ipv6_fd = safe_close(m->mdns_ipv6_fd);
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}
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int manager_mdns_start(Manager *m) {
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int r;
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assert(m);
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if (m->mdns_support == RESOLVE_SUPPORT_NO)
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return 0;
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r = manager_mdns_ipv4_fd(m);
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if (r == -EADDRINUSE)
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goto eaddrinuse;
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if (r < 0)
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return r;
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if (socket_ipv6_is_supported()) {
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r = manager_mdns_ipv6_fd(m);
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if (r == -EADDRINUSE)
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goto eaddrinuse;
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if (r < 0)
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return r;
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}
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return 0;
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eaddrinuse:
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log_warning("Another mDNS responder prohibits binding the socket to the same port. Turning off mDNS support.");
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m->mdns_support = RESOLVE_SUPPORT_NO;
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manager_mdns_stop(m);
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return 0;
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}
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static int mdns_rr_compare(DnsResourceRecord * const *a, DnsResourceRecord * const *b) {
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DnsResourceRecord *x = *(DnsResourceRecord **) a, *y = *(DnsResourceRecord **) b;
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size_t m;
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int r;
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assert(x);
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assert(y);
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r = CMP(CLEAR_CACHE_FLUSH(x->key->class), CLEAR_CACHE_FLUSH(y->key->class));
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if (r != 0)
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return r;
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r = CMP(x->key->type, y->key->type);
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if (r != 0)
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return r;
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r = dns_resource_record_to_wire_format(x, false);
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if (r < 0) {
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log_warning_errno(r, "Can't wire-format RR: %m");
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return 0;
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}
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r = dns_resource_record_to_wire_format(y, false);
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if (r < 0) {
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log_warning_errno(r, "Can't wire-format RR: %m");
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return 0;
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}
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m = MIN(DNS_RESOURCE_RECORD_RDATA_SIZE(x), DNS_RESOURCE_RECORD_RDATA_SIZE(y));
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r = memcmp(DNS_RESOURCE_RECORD_RDATA(x), DNS_RESOURCE_RECORD_RDATA(y), m);
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if (r != 0)
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return r;
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return CMP(DNS_RESOURCE_RECORD_RDATA_SIZE(x), DNS_RESOURCE_RECORD_RDATA_SIZE(y));
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}
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static int proposed_rrs_cmp(DnsResourceRecord **x, unsigned x_size, DnsResourceRecord **y, unsigned y_size) {
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unsigned m;
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int r;
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m = MIN(x_size, y_size);
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for (unsigned i = 0; i < m; i++) {
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r = mdns_rr_compare(&x[i], &y[i]);
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if (r != 0)
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return r;
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}
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return CMP(x_size, y_size);
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}
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static int mdns_packet_extract_matching_rrs(DnsPacket *p, DnsResourceKey *key, DnsResourceRecord ***ret_rrs) {
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_cleanup_free_ DnsResourceRecord **list = NULL;
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unsigned n = 0, size = 0;
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int r;
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assert(p);
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assert(key);
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assert(ret_rrs);
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assert_return(DNS_PACKET_NSCOUNT(p) > 0, -EINVAL);
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for (size_t i = DNS_PACKET_ANCOUNT(p); i < (DNS_PACKET_ANCOUNT(p) + DNS_PACKET_NSCOUNT(p)); i++) {
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r = dns_resource_key_match_rr(key, p->answer->items[i].rr, NULL);
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if (r < 0)
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return r;
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if (r > 0)
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size++;
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}
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if (size == 0)
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return 0;
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list = new(DnsResourceRecord *, size);
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if (!list)
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return -ENOMEM;
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for (size_t i = DNS_PACKET_ANCOUNT(p); i < (DNS_PACKET_ANCOUNT(p) + DNS_PACKET_NSCOUNT(p)); i++) {
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r = dns_resource_key_match_rr(key, p->answer->items[i].rr, NULL);
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if (r < 0)
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return r;
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if (r > 0)
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list[n++] = p->answer->items[i].rr;
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}
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assert(n == size);
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typesafe_qsort(list, size, mdns_rr_compare);
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*ret_rrs = TAKE_PTR(list);
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return size;
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}
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static int mdns_do_tiebreak(DnsResourceKey *key, DnsAnswer *answer, DnsPacket *p) {
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_cleanup_free_ DnsResourceRecord **our = NULL, **remote = NULL;
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DnsResourceRecord *rr;
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size_t i = 0, size;
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int r;
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size = dns_answer_size(answer);
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our = new(DnsResourceRecord *, size);
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if (!our)
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return -ENOMEM;
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DNS_ANSWER_FOREACH(rr, answer)
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our[i++] = rr;
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typesafe_qsort(our, size, mdns_rr_compare);
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r = mdns_packet_extract_matching_rrs(p, key, &remote);
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if (r < 0)
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return r;
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assert(r > 0);
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if (proposed_rrs_cmp(remote, r, our, size) > 0)
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return 1;
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return 0;
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}
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static int mdns_scope_process_query(DnsScope *s, DnsPacket *p) {
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_cleanup_(dns_answer_unrefp) DnsAnswer *full_answer = NULL;
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_cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
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DnsResourceKey *key = NULL;
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DnsResourceRecord *rr;
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bool tentative = false;
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int r;
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assert(s);
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assert(p);
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r = dns_packet_extract(p);
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if (r < 0)
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return log_debug_errno(r, "Failed to extract resource records from incoming packet: %m");
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assert_return((dns_question_size(p->question) > 0), -EINVAL);
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DNS_QUESTION_FOREACH(key, p->question) {
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_cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL, *soa = NULL;
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r = dns_zone_lookup(&s->zone, key, 0, &answer, &soa, &tentative);
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if (r < 0)
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return log_debug_errno(r, "Failed to look up key: %m");
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if (tentative && DNS_PACKET_NSCOUNT(p) > 0) {
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/*
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* A race condition detected with the probe packet from
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* a remote host.
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* Do simultaneous probe tiebreaking as described in
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* RFC 6762, Section 8.2. In case we lost don't reply
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* the question and withdraw conflicting RRs.
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*/
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r = mdns_do_tiebreak(key, answer, p);
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if (r < 0)
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return log_debug_errno(r, "Failed to do tiebreaking");
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if (r > 0) { /* we lost */
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DNS_ANSWER_FOREACH(rr, answer) {
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DnsZoneItem *i;
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i = dns_zone_get(&s->zone, rr);
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if (i)
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dns_zone_item_conflict(i);
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}
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continue;
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}
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}
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r = dns_answer_extend(&full_answer, answer);
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if (r < 0)
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return log_debug_errno(r, "Failed to extend answer: %m");
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}
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if (dns_answer_isempty(full_answer))
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return 0;
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r = dns_scope_make_reply_packet(s, DNS_PACKET_ID(p), DNS_RCODE_SUCCESS, NULL, full_answer, NULL, false, &reply);
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if (r < 0)
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return log_debug_errno(r, "Failed to build reply packet: %m");
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if (!ratelimit_below(&s->ratelimit))
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return 0;
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r = dns_scope_emit_udp(s, -1, reply);
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if (r < 0)
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return log_debug_errno(r, "Failed to send reply packet: %m");
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return 0;
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}
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static int on_mdns_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
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_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
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Manager *m = userdata;
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DnsScope *scope;
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int r;
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r = manager_recv(m, fd, DNS_PROTOCOL_MDNS, &p);
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if (r <= 0)
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return r;
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if (manager_our_packet(m, p))
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return 0;
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scope = manager_find_scope(m, p);
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if (!scope) {
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log_debug("Got mDNS UDP packet on unknown scope. Ignoring.");
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return 0;
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}
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if (dns_packet_validate_reply(p) > 0) {
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DnsResourceRecord *rr;
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log_debug("Got mDNS reply packet");
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/*
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* mDNS is different from regular DNS and LLMNR with regard to handling responses.
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* While on other protocols, we can ignore every answer that doesn't match a question
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* we broadcast earlier, RFC6762, section 18.1 recommends looking at and caching all
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* incoming information, regardless of the DNS packet ID.
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*
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* Hence, extract the packet here, and try to find a transaction for answer the we got
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* and complete it. Also store the new information in scope's cache.
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*/
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r = dns_packet_extract(p);
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if (r < 0) {
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log_debug("mDNS packet extraction failed.");
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return 0;
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}
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dns_scope_check_conflicts(scope, p);
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DNS_ANSWER_FOREACH(rr, p->answer) {
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const char *name = dns_resource_key_name(rr->key);
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DnsTransaction *t;
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/* If the received reply packet contains ANY record that is not .local or .in-addr.arpa,
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* we assume someone's playing tricks on us and discard the packet completely. */
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if (!(dns_name_endswith(name, "in-addr.arpa") > 0 ||
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dns_name_endswith(name, "local") > 0))
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return 0;
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if (rr->ttl == 0) {
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log_debug("Got a goodbye packet");
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/* See the section 10.1 of RFC6762 */
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rr->ttl = 1;
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}
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t = dns_scope_find_transaction(scope, rr->key, false);
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if (t)
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dns_transaction_process_reply(t, p);
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/* Also look for the various types of ANY transactions */
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t = dns_scope_find_transaction(scope, &DNS_RESOURCE_KEY_CONST(rr->key->class, DNS_TYPE_ANY, dns_resource_key_name(rr->key)), false);
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if (t)
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dns_transaction_process_reply(t, p);
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t = dns_scope_find_transaction(scope, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY, rr->key->type, dns_resource_key_name(rr->key)), false);
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if (t)
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dns_transaction_process_reply(t, p);
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t = dns_scope_find_transaction(scope, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY, DNS_TYPE_ANY, dns_resource_key_name(rr->key)), false);
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if (t)
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dns_transaction_process_reply(t, p);
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}
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dns_cache_put(&scope->cache, scope->manager->enable_cache, NULL, DNS_PACKET_RCODE(p), p->answer, false, (uint32_t) -1, 0, p->family, &p->sender);
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} else if (dns_packet_validate_query(p) > 0) {
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log_debug("Got mDNS query packet for id %u", DNS_PACKET_ID(p));
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r = mdns_scope_process_query(scope, p);
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if (r < 0) {
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log_debug_errno(r, "mDNS query processing failed: %m");
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return 0;
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}
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} else
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log_debug("Invalid mDNS UDP packet.");
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return 0;
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}
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int manager_mdns_ipv4_fd(Manager *m) {
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union sockaddr_union sa = {
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.in.sin_family = AF_INET,
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.in.sin_port = htobe16(MDNS_PORT),
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};
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_cleanup_close_ int s = -1;
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int r;
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assert(m);
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if (m->mdns_ipv4_fd >= 0)
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return m->mdns_ipv4_fd;
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s = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
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if (s < 0)
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return log_error_errno(errno, "mDNS-IPv4: Failed to create socket: %m");
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r = setsockopt_int(s, IPPROTO_IP, IP_TTL, 255);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv4: Failed to set IP_TTL: %m");
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r = setsockopt_int(s, IPPROTO_IP, IP_MULTICAST_TTL, 255);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv4: Failed to set IP_MULTICAST_TTL: %m");
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r = setsockopt_int(s, IPPROTO_IP, IP_MULTICAST_LOOP, true);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv4: Failed to set IP_MULTICAST_LOOP: %m");
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r = setsockopt_int(s, IPPROTO_IP, IP_PKTINFO, true);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv4: Failed to set IP_PKTINFO: %m");
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r = setsockopt_int(s, IPPROTO_IP, IP_RECVTTL, true);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv4: Failed to set IP_RECVTTL: %m");
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/* Disable Don't-Fragment bit in the IP header */
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r = setsockopt_int(s, IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_DONT);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv4: Failed to set IP_MTU_DISCOVER: %m");
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/* See the section 15.1 of RFC6762 */
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/* first try to bind without SO_REUSEADDR to detect another mDNS responder */
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r = bind(s, &sa.sa, sizeof(sa.in));
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if (r < 0) {
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if (errno != EADDRINUSE)
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return log_error_errno(errno, "mDNS-IPv4: Failed to bind socket: %m");
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log_warning("mDNS-IPv4: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
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/* try again with SO_REUSEADDR */
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r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
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r = bind(s, &sa.sa, sizeof(sa.in));
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if (r < 0)
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return log_error_errno(errno, "mDNS-IPv4: Failed to bind socket: %m");
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} else {
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/* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
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r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
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}
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r = sd_event_add_io(m->event, &m->mdns_ipv4_event_source, s, EPOLLIN, on_mdns_packet, m);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv4: Failed to create event source: %m");
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return m->mdns_ipv4_fd = TAKE_FD(s);
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}
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int manager_mdns_ipv6_fd(Manager *m) {
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union sockaddr_union sa = {
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.in6.sin6_family = AF_INET6,
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.in6.sin6_port = htobe16(MDNS_PORT),
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};
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_cleanup_close_ int s = -1;
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int r;
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assert(m);
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if (m->mdns_ipv6_fd >= 0)
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return m->mdns_ipv6_fd;
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s = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
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if (s < 0)
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return log_error_errno(errno, "mDNS-IPv6: Failed to create socket: %m");
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r = setsockopt_int(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS, 255);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_UNICAST_HOPS: %m");
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/* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
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r = setsockopt_int(s, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, 255);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_MULTICAST_HOPS: %m");
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r = setsockopt_int(s, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, true);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_MULTICAST_LOOP: %m");
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r = setsockopt_int(s, IPPROTO_IPV6, IPV6_V6ONLY, true);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_V6ONLY: %m");
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r = setsockopt_int(s, IPPROTO_IPV6, IPV6_RECVPKTINFO, true);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_RECVPKTINFO: %m");
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r = setsockopt_int(s, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, true);
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if (r < 0)
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return log_error_errno(r, "mDNS-IPv6: Failed to set IPV6_RECVHOPLIMIT: %m");
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/* See the section 15.1 of RFC6762 */
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/* first try to bind without SO_REUSEADDR to detect another mDNS responder */
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r = bind(s, &sa.sa, sizeof(sa.in6));
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if (r < 0) {
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if (errno != EADDRINUSE)
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return log_error_errno(errno, "mDNS-IPv6: Failed to bind socket: %m");
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log_warning("mDNS-IPv6: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
|
|
|
|
/* try again with SO_REUSEADDR */
|
|
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
|
|
if (r < 0)
|
|
return log_error_errno(r, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
|
|
|
|
r = bind(s, &sa.sa, sizeof(sa.in6));
|
|
if (r < 0)
|
|
return log_error_errno(errno, "mDNS-IPv6: Failed to bind socket: %m");
|
|
} else {
|
|
/* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
|
|
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
|
|
if (r < 0)
|
|
return log_error_errno(r, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
|
|
}
|
|
|
|
r = sd_event_add_io(m->event, &m->mdns_ipv6_event_source, s, EPOLLIN, on_mdns_packet, m);
|
|
if (r < 0)
|
|
return log_error_errno(r, "mDNS-IPv6: Failed to create event source: %m");
|
|
|
|
return m->mdns_ipv6_fd = TAKE_FD(s);
|
|
}
|