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Systemd/src/resolve/resolved-mdns.c
Daniel Mack 124602aea8 resolved: add mDNS packet dispatcher 
Add the packet dispatching routine for mDNS.

It differs to what LLMNR and DNS dispatchers do in the way it matches
incoming packets. In mDNS, we actually handle all incoming packets,
regardless whether we asked for them earlier or not.
2015-12-08 16:51:40 +01:00

289 lines
8.7 KiB
C
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/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
/***
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 == 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("There appears to be another mDNS responder running. Turning off mDNS support.");
m->mdns_support = SUPPORT_NO;
manager_mdns_stop(m);
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;
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) {
unsigned i;
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);
for (i = 0; i < p->answer->n_rrs; i++) {
DnsResourceRecord *rr;
DnsTransaction *t;
rr = p->answer->items[i].rr;
t = dns_scope_find_transaction(scope, rr->key, false);
if (t)
dns_transaction_process_reply(t, p);
}
dns_cache_put(&scope->cache, NULL, DNS_PACKET_RCODE(p), p->answer,
p->answer->n_rrs, false, 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));
dns_scope_process_query(scope, NULL, p);
} 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 -errno;
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_TTL, &ttl, sizeof(ttl));
if (r < 0) {
r = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_MULTICAST_TTL, &ttl, sizeof(ttl));
if (r < 0) {
r = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_MULTICAST_LOOP, &one, sizeof(one));
if (r < 0) {
r = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv4_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
if (r < 0) {
r = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_PKTINFO, &one, sizeof(one));
if (r < 0) {
r = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv4_fd, IPPROTO_IP, IP_RECVTTL, &one, sizeof(one));
if (r < 0) {
r = -errno;
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 = -errno;
goto fail;
}
r = bind(m->mdns_ipv4_fd, &sa.sa, sizeof(sa.in));
if (r < 0) {
r = -errno;
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 -errno;
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_UNICAST_HOPS, &ttl, sizeof(ttl));
if (r < 0) {
r = -errno;
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 = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, &one, sizeof(one));
if (r < 0) {
r = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
if (r < 0) {
r = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv6_fd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));
if (r < 0) {
r = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_RECVPKTINFO, &one, sizeof(one));
if (r < 0) {
r = -errno;
goto fail;
}
r = setsockopt(m->mdns_ipv6_fd, IPPROTO_IPV6, IPV6_RECVHOPLIMIT, &one, sizeof(one));
if (r < 0) {
r = -errno;
goto fail;
}
r = bind(m->mdns_ipv6_fd, &sa.sa, sizeof(sa.in6));
if (r < 0) {
r = -errno;
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) {
r = -errno;
goto fail;
}
return m->mdns_ipv6_fd;
fail:
m->mdns_ipv6_fd = safe_close(m->mdns_ipv6_fd);
return r;
}
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