resolved: add infrastructure for mDNS related sockets

Just hook up mDNS listeners with an empty packet dispather function,
introduce a config directive, man page updates etc.

1 files changed, 231 insertions, 0 deletions

diff --git a/src/resolve/resolved-mdns.c b/src/resolve/resolved-mdns.c
new file mode 100644
index 0000000000..6767706f6e
--- /dev/null
+++ b/src/resolve/resolved-mdns.c
@@ -0,0 +1,231 @@
+/*-*- 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) {
+        /* TODO */
+        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;
+}