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Systemd/src/resolve/resolved-mdns.c
Yu Watanabe 71a047d2f7 resolved: detect and warn other running mDNS stack 
Previously, `SO_REUSEADDR` is set before `bind`-ing socket, Thus,
even if another mDNS stack (e.g. avahi) is running, `bind` always
success and we cannot detect the other stack.
By this commit, we first try to `bind` without `SO_REUSEADDR`,
and if it fails, show warning and retry with `SO_REUSEADDR`.
2017-03-21 13:34:52 +09:00

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/***
This file is part of systemd.
Copyright 2015 Daniel Mack
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <resolv.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include "fd-util.h"
#include "resolved-manager.h"
#include "resolved-mdns.h"
void manager_mdns_stop(Manager *m) {
assert(m);
m->mdns_ipv4_event_source = sd_event_source_unref(m->mdns_ipv4_event_source);
m->mdns_ipv4_fd = safe_close(m->mdns_ipv4_fd);
m->mdns_ipv6_event_source = sd_event_source_unref(m->mdns_ipv6_event_source);
m->mdns_ipv6_fd = safe_close(m->mdns_ipv6_fd);
}
int manager_mdns_start(Manager *m) {
int r;
assert(m);
if (m->mdns_support == RESOLVE_SUPPORT_NO)
return 0;
r = manager_mdns_ipv4_fd(m);
if (r == -EADDRINUSE)
goto eaddrinuse;
if (r < 0)
return r;
if (socket_ipv6_is_supported()) {
r = manager_mdns_ipv6_fd(m);
if (r == -EADDRINUSE)
goto eaddrinuse;
if (r < 0)
return r;
}
return 0;
eaddrinuse:
log_warning("Another mDNS responder prohibits binding the socket to the same port. Turning off mDNS support.");
m->mdns_support = RESOLVE_SUPPORT_NO;
manager_mdns_stop(m);
return 0;
}
static int mdns_scope_process_query(DnsScope *s, DnsPacket *p) {
_cleanup_(dns_answer_unrefp) DnsAnswer *answer = NULL, *soa = NULL;
_cleanup_(dns_packet_unrefp) DnsPacket *reply = NULL;
DnsResourceKey *key = NULL;
bool tentative = false;
int r;
assert(s);
assert(p);
r = dns_packet_extract(p);
if (r < 0)
return log_debug_errno(r, "Failed to extract resource records from incoming packet: %m");
/* TODO: there might be more than one question in mDNS queries. */
assert_return((dns_question_size(p->question) > 0), -EINVAL);
key = p->question->keys[0];
r = dns_zone_lookup(&s->zone, key, 0, &answer, &soa, &tentative);
if (r < 0) {
log_debug_errno(r, "Failed to lookup key: %m");
return r;
}
if (r == 0)
return 0;
r = dns_scope_make_reply_packet(s, DNS_PACKET_ID(p), DNS_RCODE_SUCCESS, NULL, answer, NULL, false, &reply);
if (r < 0) {
log_debug_errno(r, "Failed to build reply packet: %m");
return r;
}
if (!ratelimit_test(&s->ratelimit))
return 0;
r = dns_scope_emit_udp(s, -1, reply);
if (r < 0) {
log_debug_errno(r, "Failed to send reply packet: %m");
return r;
}
return 0;
}
static int on_mdns_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
Manager *m = userdata;
DnsScope *scope;
int r;
r = manager_recv(m, fd, DNS_PROTOCOL_MDNS, &p);
if (r <= 0)
return r;
if (manager_our_packet(m, p))
return 0;
scope = manager_find_scope(m, p);
if (!scope) {
log_warning("Got mDNS UDP packet on unknown scope. Ignoring.");
return 0;
}
if (dns_packet_validate_reply(p) > 0) {
DnsResourceRecord *rr;
log_debug("Got mDNS reply packet");
/*
* mDNS is different from regular DNS and LLMNR with regard to handling responses.
* While on other protocols, we can ignore every answer that doesn't match a question
* we broadcast earlier, RFC6762, section 18.1 recommends looking at and caching all
* incoming information, regardless of the DNS packet ID.
*
* Hence, extract the packet here, and try to find a transaction for answer the we got
* and complete it. Also store the new information in scope's cache.
*/
r = dns_packet_extract(p);
if (r < 0) {
log_debug("mDNS packet extraction failed.");
return 0;
}
dns_scope_check_conflicts(scope, p);
DNS_ANSWER_FOREACH(rr, p->answer) {
const char *name = dns_resource_key_name(rr->key);
DnsTransaction *t;
/* If the received reply packet contains ANY record that is not .local or .in-addr.arpa,
* we assume someone's playing tricks on us and discard the packet completely. */
if (!(dns_name_endswith(name, "in-addr.arpa") > 0 ||
dns_name_endswith(name, "local") > 0))
return 0;
if (rr->ttl == 0) {
log_debug("Got a goodbye packet");
/* See the section 10.1 of RFC6762 */
rr->ttl = 1;
}
t = dns_scope_find_transaction(scope, rr->key, false);
if (t)
dns_transaction_process_reply(t, p);
/* Also look for the various types of ANY transactions */
t = dns_scope_find_transaction(scope, &DNS_RESOURCE_KEY_CONST(rr->key->class, DNS_TYPE_ANY, dns_resource_key_name(rr->key)), false);
if (t)
dns_transaction_process_reply(t, p);
t = dns_scope_find_transaction(scope, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY, rr->key->type, dns_resource_key_name(rr->key)), false);
if (t)
dns_transaction_process_reply(t, p);
t = dns_scope_find_transaction(scope, &DNS_RESOURCE_KEY_CONST(DNS_CLASS_ANY, DNS_TYPE_ANY, dns_resource_key_name(rr->key)), false);
if (t)
dns_transaction_process_reply(t, p);
}
dns_cache_put(&scope->cache, NULL, DNS_PACKET_RCODE(p), p->answer, false, (uint32_t) -1, 0, p->family, &p->sender);
} else if (dns_packet_validate_query(p) > 0) {
log_debug("Got mDNS query packet for id %u", DNS_PACKET_ID(p));
r = mdns_scope_process_query(scope, p);
if (r < 0) {
log_debug_errno(r, "mDNS query processing failed: %m");
return 0;
}
} else
log_debug("Invalid mDNS UDP packet.");
return 0;
}
int manager_mdns_ipv4_fd(Manager *m) {
union sockaddr_union sa = {
.in.sin_family = AF_INET,
.in.sin_port = htobe16(MDNS_PORT),
};
static const int one = 1, pmtu = IP_PMTUDISC_DONT, ttl = 255;
int r;
assert(m);
if (m->mdns_ipv4_fd >= 0)
return m->mdns_ipv4_fd;
m->mdns_ipv4_fd = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
if (m->mdns_ipv4_fd < 0)
return log_error_errno(errno, "mDNS-IPv4: Failed to create socket: %m");
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to set IP_TTL: %m");
goto fail;
}
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to set IP_MULTICAST_TTL: %m");
goto fail;
}
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to set IP_MULTICAST_LOOP: %m");
goto fail;
}
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to set IP_PKTINFO: %m");
goto fail;
}
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to set IP_RECVTTL: %m");
goto fail;
}
/* Disable Don't-Fragment bit in the IP header */
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_MTU_DISCOVER, &pmtu, sizeof(pmtu));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to set IP_MTU_DISCOVER: %m");
goto fail;
}
/* See the section 15.1 of RFC6762 */
/* first try to bind without SO_REUSEADDR to detect another mDNS responder */
r = bind(m->mdns_ipv4_fd, &sa.sa, sizeof(sa.in));
if (r < 0) {
if (errno != EADDRINUSE) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to bind socket: %m");
goto fail;
}
log_warning("mDNS-IPv4: There appears to be another mDNS responder running, or previously systemd-resolved crashed with some outstanding transfers.");
/* try again with SO_REUSEADDR */
r = setsockopt(m->mdns_ipv4_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
goto fail;
}
r = bind(m->mdns_ipv4_fd, &sa.sa, sizeof(sa.in));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to bind socket: %m");
goto fail;
}
} else {
/* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
r = setsockopt(m->mdns_ipv4_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv4: Failed to set SO_REUSEADDR: %m");
goto fail;
}
}
r = sd_event_add_io(m->event, &m->mdns_ipv4_event_source, m->mdns_ipv4_fd, EPOLLIN, on_mdns_packet, m);
if (r < 0)
goto fail;
return m->mdns_ipv4_fd;
fail:
m->mdns_ipv4_fd = safe_close(m->mdns_ipv4_fd);
return r;
}
int manager_mdns_ipv6_fd(Manager *m) {
union sockaddr_union sa = {
.in6.sin6_family = AF_INET6,
.in6.sin6_port = htobe16(MDNS_PORT),
};
static const int one = 1, ttl = 255;
int r;
assert(m);
if (m->mdns_ipv6_fd >= 0)
return m->mdns_ipv6_fd;
m->mdns_ipv6_fd = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
if (m->mdns_ipv6_fd < 0)
return log_error_errno(errno, "mDNS-IPv6: Failed to create socket: %m");
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to set IPV6_UNICAST_HOPS: %m");
goto fail;
}
/* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, &ttl, sizeof(ttl));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to set IPV6_MULTICAST_HOPS: %m");
goto fail;
}
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to set IPV6_MULTICAST_LOOP: %m");
goto fail;
}
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to set IPV6_V6ONLY: %m");
goto fail;
}
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to set IPV6_RECVPKTINFO: %m");
goto fail;
}
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to set IPV6_RECVHOPLIMIT: %m");
goto fail;
}
/* See the section 15.1 of RFC6762 */
/* first try to bind without SO_REUSEADDR to detect another mDNS responder */
r = bind(m->mdns_ipv6_fd, &sa.sa, sizeof(sa.in6));
if (r < 0) {
if (errno != EADDRINUSE) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to bind socket: %m");
goto fail;
}
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(m->mdns_ipv6_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
goto fail;
}
r = bind(m->mdns_ipv6_fd, &sa.sa, sizeof(sa.in6));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to bind socket: %m");
goto fail;
}
} else {
/* enable SO_REUSEADDR for the case that the user really wants multiple mDNS responders */
r = setsockopt(m->mdns_ipv6_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
if (r < 0) {
r = log_error_errno(errno, "mDNS-IPv6: Failed to set SO_REUSEADDR: %m");
goto fail;
}
}
r = sd_event_add_io(m->event, &m->mdns_ipv6_event_source, m->mdns_ipv6_fd, EPOLLIN, on_mdns_packet, m);
if (r < 0)
goto fail;
return m->mdns_ipv6_fd;
fail:
m->mdns_ipv6_fd = safe_close(m->mdns_ipv6_fd);
return r;
}
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