b30bf55d5c
In order to improve compatibility with local clients that speak DNS directly (and do not use NSS or our bus API) listen locally on 127.0.0.53:53 and process any queries made that way. Note that resolved does not implement a full DNS server on this port, but simply enough to allow normal, local clients to resolve RRs through resolved. Specifically it does not implement queries without the RD bit set (these are requests where recursive lookups are explicitly disabled), and neither queries with DNSSEC DO set in combination with DNSSEC CD (i.e. DNSSEC lookups with validation turned off). It also refuses zone transfers and obsolete RR types. All lookups done this way will be rejected with a clean error code, so that the client side can repeat the query with a reduced feature set. The code will set the DNSSEC AD flag however, depending on whether the data resolved has been validated (or comes from a local, trusted source). Lookups made via this mechanisms are propagated to LLMNR and mDNS as necessary, but this is only partially useful as DNS packets cannot carry IP scope data (i.e. the ifindex), and hence link-local addresses returned cannot be used properly (and given that LLMNR/mDNS are mostly about link-local communication this is quite a limitation). Also, given that DNS tends to use IDNA for non-ASCII names, while LLMNR/mDNS uses UTF-8 lookups cannot be mapped 1:1. In general this should improve compatibility with clients bypassing NSS but it is highly recommended for clients to instead use NSS or our native bus API. This patch also beefs up the DnsStream logic, as it reuses the code for local TCP listening. DnsStream now provides proper reference counting for its objects. In order to avoid feedback loops resolved will no silently ignore 127.0.0.53 specified as DNS server when reading configuration. resolved listens on 127.0.0.53:53 instead of 127.0.0.1:53 in order to leave the latter free for local, external DNS servers or forwarders. This also changes the "etc.conf" tmpfiles snippet to create a symlink from /etc/resolv.conf to /usr/lib/systemd/resolv.conf by default, thus making this stub the default mode of operation if /etc is not populated.
142 lines
4.5 KiB
C
142 lines
4.5 KiB
C
#pragma once
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/***
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This file is part of systemd.
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Copyright 2014 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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***/
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#include "sd-bus.h"
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#include "set.h"
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typedef struct DnsQueryCandidate DnsQueryCandidate;
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typedef struct DnsQuery DnsQuery;
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#include "resolved-dns-answer.h"
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#include "resolved-dns-question.h"
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#include "resolved-dns-stream.h"
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#include "resolved-dns-search-domain.h"
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struct DnsQueryCandidate {
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DnsQuery *query;
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DnsScope *scope;
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DnsSearchDomain *search_domain;
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int error_code;
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Set *transactions;
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LIST_FIELDS(DnsQueryCandidate, candidates_by_query);
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LIST_FIELDS(DnsQueryCandidate, candidates_by_scope);
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};
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struct DnsQuery {
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Manager *manager;
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/* When resolving a service, we first create a TXT+SRV query,
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* and then for the hostnames we discover auxiliary A+AAAA
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* queries. This pointer always points from the auxiliary
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* queries back to the TXT+SRV query. */
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DnsQuery *auxiliary_for;
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LIST_HEAD(DnsQuery, auxiliary_queries);
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unsigned n_auxiliary_queries;
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int auxiliary_result;
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/* The question, formatted in IDNA for use on classic DNS, and as UTF8 for use in LLMNR or mDNS. Note that even
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* on classic DNS some labels might use UTF8 encoding. Specifically, DNS-SD service names (in contrast to their
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* domain suffixes) use UTF-8 encoding even on DNS. Thus, the difference between these two fields is mostly
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* relevant only for explicit *hostname* lookups as well as the domain suffixes of service lookups. */
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DnsQuestion *question_idna;
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DnsQuestion *question_utf8;
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uint64_t flags;
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int ifindex;
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/* If true, A or AAAA RR lookups will be suppressed on links with no routable address of the matching address
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* family */
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bool suppress_unroutable_family;
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/* If true, the RR TTLs of the answer will be clamped by their current left validity in the cache */
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bool clamp_ttl;
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DnsTransactionState state;
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unsigned n_cname_redirects;
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LIST_HEAD(DnsQueryCandidate, candidates);
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sd_event_source *timeout_event_source;
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/* Discovered data */
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DnsAnswer *answer;
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int answer_rcode;
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DnssecResult answer_dnssec_result;
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bool answer_authenticated;
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DnsProtocol answer_protocol;
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int answer_family;
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DnsSearchDomain *answer_search_domain;
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int answer_errno; /* if state is DNS_TRANSACTION_ERRNO */
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/* Bus client information */
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sd_bus_message *request;
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int request_family;
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bool request_address_valid;
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union in_addr_union request_address;
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unsigned block_all_complete;
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char *request_address_string;
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/* DNS stub information */
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DnsPacket *request_dns_packet;
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DnsStream *request_dns_stream;
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/* Completion callback */
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void (*complete)(DnsQuery* q);
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unsigned block_ready;
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sd_bus_track *bus_track;
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LIST_FIELDS(DnsQuery, queries);
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LIST_FIELDS(DnsQuery, auxiliary_queries);
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};
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enum {
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DNS_QUERY_MATCH,
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DNS_QUERY_NOMATCH,
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DNS_QUERY_RESTARTED,
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};
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DnsQueryCandidate* dns_query_candidate_free(DnsQueryCandidate *c);
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void dns_query_candidate_notify(DnsQueryCandidate *c);
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int dns_query_new(Manager *m, DnsQuery **q, DnsQuestion *question_utf8, DnsQuestion *question_idna, int family, uint64_t flags);
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DnsQuery *dns_query_free(DnsQuery *q);
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int dns_query_make_auxiliary(DnsQuery *q, DnsQuery *auxiliary_for);
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int dns_query_go(DnsQuery *q);
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void dns_query_ready(DnsQuery *q);
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int dns_query_process_cname(DnsQuery *q);
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int dns_query_bus_track(DnsQuery *q, sd_bus_message *m);
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DnsQuestion* dns_query_question_for_protocol(DnsQuery *q, DnsProtocol protocol);
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const char *dns_query_string(DnsQuery *q);
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DEFINE_TRIVIAL_CLEANUP_FUNC(DnsQuery*, dns_query_free);
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