539 lines
19 KiB
C
539 lines
19 KiB
C
/***
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This file is part of systemd.
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Copyright 2016 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 "fd-util.h"
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#include "resolved-dns-stub.h"
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#include "socket-util.h"
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/* The MTU of the loopback device is 64K on Linux, advertise that as maximum datagram size, but subtract the Ethernet,
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* IP and UDP header sizes */
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#define ADVERTISE_DATAGRAM_SIZE_MAX (65536U-14U-20U-8U)
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static int manager_dns_stub_udp_fd(Manager *m);
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static int manager_dns_stub_tcp_fd(Manager *m);
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static int dns_stub_make_reply_packet(
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uint16_t id,
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int rcode,
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DnsQuestion *q,
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DnsAnswer *answer,
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bool add_opt, /* add an OPT RR to this packet */
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bool edns0_do, /* set the EDNS0 DNSSEC OK bit */
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bool ad, /* set the DNSSEC authenticated data bit */
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DnsPacket **ret) {
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_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
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DnsResourceRecord *rr;
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unsigned c = 0;
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int r;
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/* Note that we don't bother with any additional RRs, as this is stub is for local lookups only, and hence
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* roundtrips aren't expensive. */
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r = dns_packet_new(&p, DNS_PROTOCOL_DNS, 0);
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if (r < 0)
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return r;
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/* If the client didn't do EDNS, clamp the rcode to 4 bit */
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if (!add_opt && rcode > 0xF)
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rcode = DNS_RCODE_SERVFAIL;
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DNS_PACKET_HEADER(p)->id = id;
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DNS_PACKET_HEADER(p)->flags = htobe16(DNS_PACKET_MAKE_FLAGS(
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1 /* qr */,
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0 /* opcode */,
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0 /* aa */,
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0 /* tc */,
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1 /* rd */,
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1 /* ra */,
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ad /* ad */,
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0 /* cd */,
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rcode));
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r = dns_packet_append_question(p, q);
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if (r < 0)
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return r;
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DNS_PACKET_HEADER(p)->qdcount = htobe16(dns_question_size(q));
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DNS_ANSWER_FOREACH(rr, answer) {
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r = dns_question_matches_rr(q, 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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goto add;
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r = dns_question_matches_cname_or_dname(q, 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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goto add;
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continue;
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add:
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r = dns_packet_append_rr(p, rr, 0, NULL, NULL);
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if (r < 0)
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return r;
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c++;
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}
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DNS_PACKET_HEADER(p)->ancount = htobe16(c);
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if (add_opt) {
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r = dns_packet_append_opt(p, ADVERTISE_DATAGRAM_SIZE_MAX, edns0_do, rcode, NULL);
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if (r < 0)
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return r;
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}
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*ret = p;
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p = NULL;
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return 0;
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}
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static void dns_stub_detach_stream(DnsStream *s) {
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assert(s);
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s->complete = NULL;
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s->on_packet = NULL;
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s->query = NULL;
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}
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static int dns_stub_send(Manager *m, DnsStream *s, DnsPacket *p, DnsPacket *reply) {
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int r;
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assert(m);
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assert(p);
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assert(reply);
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if (s)
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r = dns_stream_write_packet(s, reply);
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else {
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int fd;
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/* Truncate the message to the right size */
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if (reply->size > DNS_PACKET_PAYLOAD_SIZE_MAX(p)) {
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dns_packet_truncate(reply, DNS_PACKET_UNICAST_SIZE_MAX);
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DNS_PACKET_HEADER(reply)->flags = htobe16(be16toh(DNS_PACKET_HEADER(reply)->flags) | DNS_PACKET_FLAG_TC);
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}
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fd = manager_dns_stub_udp_fd(m);
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if (fd < 0)
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return log_debug_errno(fd, "Failed to get reply socket: %m");
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/* Note that it is essential here that we explicitly choose the source IP address for this packet. This
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* is because otherwise the kernel will choose it automatically based on the routing table and will
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* thus pick 127.0.0.1 rather than 127.0.0.53. */
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r = manager_send(m, fd, LOOPBACK_IFINDEX, p->family, &p->sender, p->sender_port, &p->destination, reply);
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}
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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 dns_stub_send_failure(Manager *m, DnsStream *s, DnsPacket *p, int rcode) {
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_cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
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int r;
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assert(m);
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assert(p);
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r = dns_stub_make_reply_packet(DNS_PACKET_ID(p), rcode, p->question, NULL, !!p->opt, DNS_PACKET_DO(p), false, &reply);
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if (r < 0)
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return log_debug_errno(r, "Failed to build failure packet: %m");
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return dns_stub_send(m, s, p, reply);
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}
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static void dns_stub_query_complete(DnsQuery *q) {
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int r;
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assert(q);
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assert(q->request_dns_packet);
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switch (q->state) {
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case DNS_TRANSACTION_SUCCESS: {
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_cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
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r = dns_stub_make_reply_packet(
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DNS_PACKET_ID(q->request_dns_packet),
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q->answer_rcode,
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q->question_idna,
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q->answer,
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!!q->request_dns_packet->opt,
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DNS_PACKET_DO(q->request_dns_packet),
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DNS_PACKET_DO(q->request_dns_packet) && q->answer_authenticated,
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&reply);
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if (r < 0) {
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log_debug_errno(r, "Failed to build reply packet: %m");
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break;
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}
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(void) dns_stub_send(q->manager, q->request_dns_stream, q->request_dns_packet, reply);
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break;
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}
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case DNS_TRANSACTION_RCODE_FAILURE:
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(void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, q->answer_rcode);
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break;
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case DNS_TRANSACTION_NOT_FOUND:
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(void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_NXDOMAIN);
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break;
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case DNS_TRANSACTION_TIMEOUT:
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case DNS_TRANSACTION_ATTEMPTS_MAX_REACHED:
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/* Propagate a timeout as a no packet, i.e. that the client also gets a timeout */
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break;
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case DNS_TRANSACTION_NO_SERVERS:
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case DNS_TRANSACTION_INVALID_REPLY:
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case DNS_TRANSACTION_ERRNO:
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case DNS_TRANSACTION_ABORTED:
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case DNS_TRANSACTION_DNSSEC_FAILED:
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case DNS_TRANSACTION_NO_TRUST_ANCHOR:
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case DNS_TRANSACTION_RR_TYPE_UNSUPPORTED:
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case DNS_TRANSACTION_NETWORK_DOWN:
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(void) dns_stub_send_failure(q->manager, q->request_dns_stream, q->request_dns_packet, DNS_RCODE_SERVFAIL);
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break;
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case DNS_TRANSACTION_NULL:
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case DNS_TRANSACTION_PENDING:
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case DNS_TRANSACTION_VALIDATING:
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default:
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assert_not_reached("Impossible state");
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}
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/* If there's a packet to write set, let's leave the stream around */
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if (q->request_dns_stream && DNS_STREAM_QUEUED(q->request_dns_stream)) {
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/* Detach the stream from our query (make it an orphan), but do not drop the reference to it. The
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* default completion action of the stream will drop the reference. */
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dns_stub_detach_stream(q->request_dns_stream);
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q->request_dns_stream = NULL;
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}
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dns_query_free(q);
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}
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static int dns_stub_stream_complete(DnsStream *s, int error) {
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assert(s);
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log_debug_errno(error, "DNS TCP connection terminated, destroying query: %m");
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assert(s->query);
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dns_query_free(s->query);
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return 0;
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}
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static void dns_stub_process_query(Manager *m, DnsStream *s, DnsPacket *p) {
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DnsQuery *q = NULL;
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int r;
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assert(m);
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assert(p);
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assert(p->protocol == DNS_PROTOCOL_DNS);
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/* Takes ownership of the *s stream object */
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if (in_addr_is_localhost(p->family, &p->sender) <= 0 ||
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in_addr_is_localhost(p->family, &p->destination) <= 0) {
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log_error("Got packet on unexpected IP range, refusing.");
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dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL);
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goto fail;
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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_errno(r, "Failed to extract resources from incoming packet, ignoring packet: %m");
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dns_stub_send_failure(m, s, p, DNS_RCODE_FORMERR);
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goto fail;
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}
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if (!DNS_PACKET_VERSION_SUPPORTED(p)) {
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log_debug("Got EDNS OPT field with unsupported version number.");
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dns_stub_send_failure(m, s, p, DNS_RCODE_BADVERS);
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goto fail;
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}
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if (dns_type_is_obsolete(p->question->keys[0]->type)) {
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log_debug("Got message with obsolete key type, refusing.");
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dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP);
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goto fail;
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}
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if (dns_type_is_zone_transer(p->question->keys[0]->type)) {
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log_debug("Got request for zone transfer, refusing.");
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dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP);
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goto fail;
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}
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if (!DNS_PACKET_RD(p)) {
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/* If the "rd" bit is off (i.e. recursion was not requested), then refuse operation */
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log_debug("Got request with recursion disabled, refusing.");
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dns_stub_send_failure(m, s, p, DNS_RCODE_REFUSED);
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goto fail;
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}
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if (DNS_PACKET_DO(p) && DNS_PACKET_CD(p)) {
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log_debug("Got request with DNSSEC CD bit set, refusing.");
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dns_stub_send_failure(m, s, p, DNS_RCODE_NOTIMP);
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goto fail;
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}
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r = dns_query_new(m, &q, p->question, p->question, 0, SD_RESOLVED_PROTOCOLS_ALL|SD_RESOLVED_NO_SEARCH|SD_RESOLVED_NO_CNAME);
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if (r < 0) {
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log_error_errno(r, "Failed to generate query object: %m");
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dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL);
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goto fail;
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}
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/* Request that the TTL is corrected by the cached time for this lookup, so that we return vaguely useful TTLs */
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q->clamp_ttl = true;
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q->request_dns_packet = dns_packet_ref(p);
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q->request_dns_stream = dns_stream_ref(s); /* make sure the stream stays around until we can send a reply through it */
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q->complete = dns_stub_query_complete;
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if (s) {
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s->on_packet = NULL;
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s->complete = dns_stub_stream_complete;
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s->query = q;
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}
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r = dns_query_go(q);
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if (r < 0) {
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log_error_errno(r, "Failed to start query: %m");
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dns_stub_send_failure(m, s, p, DNS_RCODE_SERVFAIL);
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goto fail;
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}
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log_info("Processing query...");
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return;
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fail:
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if (s && DNS_STREAM_QUEUED(s))
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dns_stub_detach_stream(s);
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dns_query_free(q);
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}
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static int on_dns_stub_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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int r;
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r = manager_recv(m, fd, DNS_PROTOCOL_DNS, &p);
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if (r <= 0)
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return r;
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if (dns_packet_validate_query(p) > 0) {
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log_debug("Got DNS stub UDP query packet for id %u", DNS_PACKET_ID(p));
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dns_stub_process_query(m, NULL, p);
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} else
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log_debug("Invalid DNS stub UDP packet, ignoring.");
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return 0;
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}
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static int manager_dns_stub_udp_fd(Manager *m) {
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static const int one = 1;
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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(53),
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.in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
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};
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_cleanup_close_ int fd = -1;
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int r;
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if (m->dns_stub_udp_fd >= 0)
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return m->dns_stub_udp_fd;
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fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
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if (fd < 0)
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return -errno;
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if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one) < 0)
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return -errno;
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if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof one) < 0)
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return -errno;
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if (setsockopt(fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof one) < 0)
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return -errno;
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/* Make sure no traffic from outside the local host can leak to onto this socket */
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if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
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return -errno;
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if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
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return -errno;
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r = sd_event_add_io(m->event, &m->dns_stub_udp_event_source, fd, EPOLLIN, on_dns_stub_packet, m);
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if (r < 0)
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return r;
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(void) sd_event_source_set_description(m->dns_stub_udp_event_source, "dns-stub-udp");
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m->dns_stub_udp_fd = fd;
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fd = -1;
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return m->dns_stub_udp_fd;
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}
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static int on_dns_stub_stream_packet(DnsStream *s) {
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assert(s);
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assert(s->read_packet);
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if (dns_packet_validate_query(s->read_packet) > 0) {
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log_debug("Got DNS stub TCP query packet for id %u", DNS_PACKET_ID(s->read_packet));
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dns_stub_process_query(s->manager, s, s->read_packet);
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} else
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log_debug("Invalid DNS stub TCP packet, ignoring.");
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/* Drop the reference to the stream. Either a query was created and added its own reference to the stream now,
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* or that didn't happen in which case we want to free the stream */
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dns_stream_unref(s);
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return 0;
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}
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static int on_dns_stub_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
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DnsStream *stream;
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Manager *m = userdata;
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int cfd, r;
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cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
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if (cfd < 0) {
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if (errno == EAGAIN || errno == EINTR)
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return 0;
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return -errno;
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}
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r = dns_stream_new(m, &stream, DNS_PROTOCOL_DNS, cfd);
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if (r < 0) {
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safe_close(cfd);
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return r;
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}
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stream->on_packet = on_dns_stub_stream_packet;
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/* We let the reference to the stream dangling here, it will either be dropped by the default "complete" action
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* of the stream, or by our packet callback, or when the manager is shut down. */
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return 0;
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}
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static int manager_dns_stub_tcp_fd(Manager *m) {
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static const int one = 1;
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union sockaddr_union sa = {
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.in.sin_family = AF_INET,
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.in.sin_addr.s_addr = htobe32(INADDR_DNS_STUB),
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.in.sin_port = htobe16(53),
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};
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_cleanup_close_ int fd = -1;
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int r;
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if (m->dns_stub_tcp_fd >= 0)
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return m->dns_stub_tcp_fd;
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fd = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
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if (fd < 0)
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return -errno;
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if (setsockopt(fd, IPPROTO_IP, IP_TTL, &one, sizeof one) < 0)
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return -errno;
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if (setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof one) < 0)
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return -errno;
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if (setsockopt(fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof one) < 0)
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return -errno;
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if (setsockopt(fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof one) < 0)
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return -errno;
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/* Make sure no traffic from outside the local host can leak to onto this socket */
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if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, "lo", 3) < 0)
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return -errno;
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if (bind(fd, &sa.sa, sizeof(sa.in)) < 0)
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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");
|
|
m->dns_stub_tcp_fd = fd;
|
|
fd = -1;
|
|
|
|
return m->dns_stub_tcp_fd;
|
|
}
|
|
|
|
int manager_dns_stub_start(Manager *m) {
|
|
const char *t = "UDP";
|
|
int r = 0;
|
|
|
|
assert(m);
|
|
|
|
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);
|
|
}
|