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systemd/src/resolve/resolved-llmnr.c
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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <resolv.h>
#include "errno-util.h"
#include "fd-util.h"
#include "resolved-llmnr.h"
#include "resolved-manager.h"
void manager_llmnr_stop(Manager *m) {
assert(m);
m->llmnr_ipv4_udp_event_source = sd_event_source_disable_unref(m->llmnr_ipv4_udp_event_source);
m->llmnr_ipv4_udp_fd = safe_close(m->llmnr_ipv4_udp_fd);
m->llmnr_ipv6_udp_event_source = sd_event_source_disable_unref(m->llmnr_ipv6_udp_event_source);
m->llmnr_ipv6_udp_fd = safe_close(m->llmnr_ipv6_udp_fd);
m->llmnr_ipv4_tcp_event_source = sd_event_source_disable_unref(m->llmnr_ipv4_tcp_event_source);
m->llmnr_ipv4_tcp_fd = safe_close(m->llmnr_ipv4_tcp_fd);
m->llmnr_ipv6_tcp_event_source = sd_event_source_disable_unref(m->llmnr_ipv6_tcp_event_source);
m->llmnr_ipv6_tcp_fd = safe_close(m->llmnr_ipv6_tcp_fd);
}
int manager_llmnr_start(Manager *m) {
int r;
assert(m);
if (m->llmnr_support == RESOLVE_SUPPORT_NO)
return 0;
r = manager_llmnr_ipv4_udp_fd(m);
if (r == -EADDRINUSE)
goto eaddrinuse;
if (r < 0)
return r;
r = manager_llmnr_ipv4_tcp_fd(m);
if (r == -EADDRINUSE)
goto eaddrinuse;
if (r < 0)
return r;
if (socket_ipv6_is_enabled()) {
r = manager_llmnr_ipv6_udp_fd(m);
if (r == -EADDRINUSE)
goto eaddrinuse;
if (r < 0)
return r;
r = manager_llmnr_ipv6_tcp_fd(m);
if (r == -EADDRINUSE)
goto eaddrinuse;
if (r < 0)
return r;
}
return 0;
eaddrinuse:
log_warning("Another LLMNR responder prohibits binding the socket to the same port. Turning off LLMNR support.");
m->llmnr_support = RESOLVE_SUPPORT_NO;
manager_llmnr_stop(m);
return 0;
}
static int on_llmnr_packet(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
DnsTransaction *t = NULL;
Manager *m = ASSERT_PTR(userdata);
DnsScope *scope;
int r;
assert(s);
assert(fd >= 0);
r = manager_recv(m, fd, DNS_PROTOCOL_LLMNR, &p);
if (r <= 0)
return r;
if (manager_packet_from_local_address(m, p))
return 0;
scope = manager_find_scope(m, p);
if (!scope) {
log_debug("Got LLMNR UDP packet on unknown scope. Ignoring.");
return 0;
}
if (dns_packet_validate_reply(p) > 0) {
log_debug("Got LLMNR UDP reply packet for id %u", DNS_PACKET_ID(p));
dns_scope_check_conflicts(scope, p);
t = hashmap_get(m->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p)));
if (t)
dns_transaction_process_reply(t, p, false);
} else if (dns_packet_validate_query(p) > 0) {
log_debug("Got LLMNR UDP query packet for id %u", DNS_PACKET_ID(p));
dns_scope_process_query(scope, NULL, p);
} else
log_debug("Invalid LLMNR UDP packet, ignoring.");
return 0;
}
static int set_llmnr_common_socket_options(int fd, int family) {
int r;
r = socket_set_recvpktinfo(fd, family, true);
if (r < 0)
return r;
r = socket_set_recvttl(fd, family, true);
if (r < 0)
return r;
return 0;
}
static int set_llmnr_common_udp_socket_options(int fd, int family) {
int r;
/* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
r = socket_set_ttl(fd, family, 255);
if (r < 0)
return r;
return 0;
}
int manager_llmnr_ipv4_udp_fd(Manager *m) {
union sockaddr_union sa = {
.in.sin_family = AF_INET,
.in.sin_port = htobe16(LLMNR_PORT),
};
_cleanup_close_ int s = -EBADF;
int r;
assert(m);
if (m->llmnr_ipv4_udp_fd >= 0)
return m->llmnr_ipv4_udp_fd;
s = socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
if (s < 0)
return log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to create socket: %m");
r = set_llmnr_common_socket_options(s, AF_INET);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(UDP): Failed to set common socket options: %m");
r = set_llmnr_common_udp_socket_options(s, AF_INET);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(UDP): Failed to set common UDP socket options: %m");
r = setsockopt_int(s, IPPROTO_IP, IP_MULTICAST_TTL, 255);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_TTL: %m");
r = setsockopt_int(s, IPPROTO_IP, IP_MULTICAST_LOOP, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(UDP): Failed to set IP_MULTICAST_LOOP: %m");
/* Disable Don't-Fragment bit in the IP header */
r = setsockopt_int(s, IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_DONT);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(UDP): Failed to set IP_MTU_DISCOVER: %m");
/* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
r = bind(s, &sa.sa, sizeof(sa.in));
if (r < 0) {
if (errno != EADDRINUSE)
return log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
log_warning("LLMNR-IPv4(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
/* try again with SO_REUSEADDR */
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
r = bind(s, &sa.sa, sizeof(sa.in));
if (r < 0)
return log_error_errno(errno, "LLMNR-IPv4(UDP): Failed to bind socket: %m");
} else {
/* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(UDP): Failed to set SO_REUSEADDR: %m");
}
r = sd_event_add_io(m->event, &m->llmnr_ipv4_udp_event_source, s, EPOLLIN, on_llmnr_packet, m);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(UDP): Failed to create event source: %m");
(void) sd_event_source_set_description(m->llmnr_ipv4_udp_event_source, "llmnr-ipv4-udp");
return m->llmnr_ipv4_udp_fd = TAKE_FD(s);
}
int manager_llmnr_ipv6_udp_fd(Manager *m) {
union sockaddr_union sa = {
.in6.sin6_family = AF_INET6,
.in6.sin6_port = htobe16(LLMNR_PORT),
};
_cleanup_close_ int s = -EBADF;
int r;
assert(m);
if (m->llmnr_ipv6_udp_fd >= 0)
return m->llmnr_ipv6_udp_fd;
s = socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
if (s < 0)
return log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to create socket: %m");
r = set_llmnr_common_socket_options(s, AF_INET6);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(UDP): Failed to set common socket options: %m");
r = set_llmnr_common_udp_socket_options(s, AF_INET6);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(UDP): Failed to set common UDP socket options: %m");
/* RFC 4795, section 2.5 recommends setting the TTL of UDP packets to 255. */
r = setsockopt_int(s, IPPROTO_IPV6, IPV6_MULTICAST_HOPS, 255);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_HOPS: %m");
r = setsockopt_int(s, IPPROTO_IPV6, IPV6_MULTICAST_LOOP, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(UDP): Failed to set IPV6_MULTICAST_LOOP: %m");
r = setsockopt_int(s, IPPROTO_IPV6, IPV6_V6ONLY, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(UDP): Failed to set IPV6_V6ONLY: %m");
/* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
r = bind(s, &sa.sa, sizeof(sa.in6));
if (r < 0) {
if (errno != EADDRINUSE)
return log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
log_warning("LLMNR-IPv6(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
/* try again with SO_REUSEADDR */
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
r = bind(s, &sa.sa, sizeof(sa.in6));
if (r < 0)
return log_error_errno(errno, "LLMNR-IPv6(UDP): Failed to bind socket: %m");
} else {
/* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(UDP): Failed to set SO_REUSEADDR: %m");
}
r = sd_event_add_io(m->event, &m->llmnr_ipv6_udp_event_source, s, EPOLLIN, on_llmnr_packet, m);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(UDP): Failed to create event source: %m");
(void) sd_event_source_set_description(m->llmnr_ipv6_udp_event_source, "llmnr-ipv6-udp");
return m->llmnr_ipv6_udp_fd = TAKE_FD(s);
}
static int on_llmnr_stream_packet(DnsStream *s, DnsPacket *p) {
DnsScope *scope;
assert(s);
assert(s->manager);
assert(p);
scope = manager_find_scope(s->manager, p);
if (!scope)
log_debug("Got LLMNR TCP packet on unknown scope. Ignoring.");
else if (dns_packet_validate_query(p) > 0) {
log_debug("Got LLMNR TCP query packet for id %u", DNS_PACKET_ID(p));
dns_scope_process_query(scope, s, p);
} else
log_debug("Invalid LLMNR TCP packet, ignoring.");
return 0;
}
static int on_llmnr_stream(sd_event_source *s, int fd, uint32_t revents, void *userdata) {
DnsStream *stream;
Manager *m = userdata;
int cfd, r;
cfd = accept4(fd, NULL, NULL, SOCK_NONBLOCK|SOCK_CLOEXEC);
if (cfd < 0) {
if (ERRNO_IS_ACCEPT_AGAIN(errno))
return 0;
return -errno;
}
/* We don't configure a "complete" handler here, we rely on the default handler, thus freeing it */
r = dns_stream_new(m, &stream, DNS_STREAM_LLMNR_RECV, DNS_PROTOCOL_LLMNR, cfd, NULL,
on_llmnr_stream_packet, NULL, DNS_STREAM_DEFAULT_TIMEOUT_USEC);
if (r < 0) {
safe_close(cfd);
return r;
}
return 0;
}
static int set_llmnr_common_tcp_socket_options(int fd, int family) {
int r;
/* RFC 4795, section 2.5. requires setting the TTL of TCP streams to 1 */
r = socket_set_ttl(fd, family, 1);
if (r < 0)
return r;
r = setsockopt_int(fd, IPPROTO_TCP, TCP_FASTOPEN, 5); /* Everybody appears to pick qlen=5, let's do the same here. */
if (r < 0)
log_debug_errno(r, "Failed to enable TCP_FASTOPEN on TCP listening socket, ignoring: %m");
r = setsockopt_int(fd, IPPROTO_TCP, TCP_NODELAY, true);
if (r < 0)
log_debug_errno(r, "Failed to enable TCP_NODELAY mode, ignoring: %m");
return 0;
}
int manager_llmnr_ipv4_tcp_fd(Manager *m) {
union sockaddr_union sa = {
.in.sin_family = AF_INET,
.in.sin_port = htobe16(LLMNR_PORT),
};
_cleanup_close_ int s = -EBADF;
int r;
assert(m);
if (m->llmnr_ipv4_tcp_fd >= 0)
return m->llmnr_ipv4_tcp_fd;
s = socket(AF_INET, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
if (s < 0)
return log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to create socket: %m");
r = set_llmnr_common_socket_options(s, AF_INET);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(TCP): Failed to set common socket options: %m");
r = set_llmnr_common_tcp_socket_options(s, AF_INET);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(TCP): Failed to set common TCP socket options: %m");
/* Disable Don't-Fragment bit in the IP header */
r = setsockopt_int(s, IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_DONT);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(TCP): Failed to set IP_MTU_DISCOVER: %m");
/* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
r = bind(s, &sa.sa, sizeof(sa.in));
if (r < 0) {
if (errno != EADDRINUSE)
return log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
log_warning("LLMNR-IPv4(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
/* try again with SO_REUSEADDR */
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
r = bind(s, &sa.sa, sizeof(sa.in));
if (r < 0)
return log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to bind socket: %m");
} else {
/* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(TCP): Failed to set SO_REUSEADDR: %m");
}
r = listen(s, SOMAXCONN_DELUXE);
if (r < 0)
return log_error_errno(errno, "LLMNR-IPv4(TCP): Failed to listen the stream: %m");
r = sd_event_add_io(m->event, &m->llmnr_ipv4_tcp_event_source, s, EPOLLIN, on_llmnr_stream, m);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv4(TCP): Failed to create event source: %m");
(void) sd_event_source_set_description(m->llmnr_ipv4_tcp_event_source, "llmnr-ipv4-tcp");
return m->llmnr_ipv4_tcp_fd = TAKE_FD(s);
}
int manager_llmnr_ipv6_tcp_fd(Manager *m) {
union sockaddr_union sa = {
.in6.sin6_family = AF_INET6,
.in6.sin6_port = htobe16(LLMNR_PORT),
};
_cleanup_close_ int s = -EBADF;
int r;
assert(m);
if (m->llmnr_ipv6_tcp_fd >= 0)
return m->llmnr_ipv6_tcp_fd;
s = socket(AF_INET6, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
if (s < 0)
return log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to create socket: %m");
r = setsockopt_int(s, IPPROTO_IPV6, IPV6_V6ONLY, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(TCP): Failed to set IPV6_V6ONLY: %m");
r = set_llmnr_common_socket_options(s, AF_INET6);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(TCP): Failed to set common socket options: %m");
r = set_llmnr_common_tcp_socket_options(s, AF_INET6);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(TCP): Failed to set common TCP socket options: %m");
/* first try to bind without SO_REUSEADDR to detect another LLMNR responder */
r = bind(s, &sa.sa, sizeof(sa.in6));
if (r < 0) {
if (errno != EADDRINUSE)
return log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
log_warning("LLMNR-IPv6(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.");
/* try again with SO_REUSEADDR */
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
r = bind(s, &sa.sa, sizeof(sa.in6));
if (r < 0)
return log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to bind socket: %m");
} else {
/* enable SO_REUSEADDR for the case that the user really wants multiple LLMNR responders */
r = setsockopt_int(s, SOL_SOCKET, SO_REUSEADDR, true);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(TCP): Failed to set SO_REUSEADDR: %m");
}
r = listen(s, SOMAXCONN_DELUXE);
if (r < 0)
return log_error_errno(errno, "LLMNR-IPv6(TCP): Failed to listen the stream: %m");
r = sd_event_add_io(m->event, &m->llmnr_ipv6_tcp_event_source, s, EPOLLIN, on_llmnr_stream, m);
if (r < 0)
return log_error_errno(r, "LLMNR-IPv6(TCP): Failed to create event source: %m");
(void) sd_event_source_set_description(m->llmnr_ipv6_tcp_event_source, "llmnr-ipv6-tcp");
return m->llmnr_ipv6_tcp_fd = TAKE_FD(s);
}
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