diff options
Diffstat (limited to 'src/resolve/resolved-manager.c')
| -rw-r--r-- | src/resolve/resolved-manager.c | 1775 |
1 files changed, 1775 insertions, 0 deletions
diff --git a/src/resolve/resolved-manager.c b/src/resolve/resolved-manager.c new file mode 100644 index 0000000..34b785e --- /dev/null +++ b/src/resolve/resolved-manager.c @@ -0,0 +1,1775 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <fcntl.h> +#include <netinet/in.h> +#include <poll.h> +#include <sys/ioctl.h> +#include <sys/stat.h> +#include <sys/types.h> +#include <unistd.h> + +#include "af-list.h" +#include "alloc-util.h" +#include "bus-polkit.h" +#include "dirent-util.h" +#include "dns-domain.h" +#include "event-util.h" +#include "fd-util.h" +#include "fileio.h" +#include "hostname-util.h" +#include "idn-util.h" +#include "io-util.h" +#include "missing_network.h" +#include "missing_socket.h" +#include "netlink-util.h" +#include "ordered-set.h" +#include "parse-util.h" +#include "random-util.h" +#include "resolved-bus.h" +#include "resolved-conf.h" +#include "resolved-dns-stub.h" +#include "resolved-dnssd.h" +#include "resolved-etc-hosts.h" +#include "resolved-llmnr.h" +#include "resolved-manager.h" +#include "resolved-mdns.h" +#include "resolved-resolv-conf.h" +#include "resolved-util.h" +#include "resolved-varlink.h" +#include "socket-util.h" +#include "string-table.h" +#include "string-util.h" +#include "utf8.h" + +#define SEND_TIMEOUT_USEC (200 * USEC_PER_MSEC) + +static int manager_process_link(sd_netlink *rtnl, sd_netlink_message *mm, void *userdata) { + Manager *m = ASSERT_PTR(userdata); + uint16_t type; + Link *l; + int ifindex, r; + + assert(rtnl); + assert(mm); + + r = sd_netlink_message_get_type(mm, &type); + if (r < 0) + goto fail; + + r = sd_rtnl_message_link_get_ifindex(mm, &ifindex); + if (r < 0) + goto fail; + + l = hashmap_get(m->links, INT_TO_PTR(ifindex)); + + switch (type) { + + case RTM_NEWLINK:{ + bool is_new = !l; + + if (!l) { + r = link_new(m, &l, ifindex); + if (r < 0) + goto fail; + } + + r = link_process_rtnl(l, mm); + if (r < 0) + goto fail; + + r = link_update(l); + if (r < 0) + goto fail; + + if (is_new) + log_debug("Found new link %i/%s", ifindex, l->ifname); + + break; + } + + case RTM_DELLINK: + if (l) { + log_debug("Removing link %i/%s", l->ifindex, l->ifname); + link_remove_user(l); + link_free(l); + } + + break; + } + + return 0; + +fail: + log_warning_errno(r, "Failed to process RTNL link message: %m"); + return 0; +} + +static int manager_process_address(sd_netlink *rtnl, sd_netlink_message *mm, void *userdata) { + Manager *m = ASSERT_PTR(userdata); + union in_addr_union address; + uint16_t type; + int r, ifindex, family; + LinkAddress *a; + Link *l; + + assert(rtnl); + assert(mm); + + r = sd_netlink_message_get_type(mm, &type); + if (r < 0) + goto fail; + + r = sd_rtnl_message_addr_get_ifindex(mm, &ifindex); + if (r < 0) + goto fail; + + l = hashmap_get(m->links, INT_TO_PTR(ifindex)); + if (!l) + return 0; + + r = sd_rtnl_message_addr_get_family(mm, &family); + if (r < 0) + goto fail; + + switch (family) { + + case AF_INET: + r = sd_netlink_message_read_in_addr(mm, IFA_LOCAL, &address.in); + if (r < 0) { + r = sd_netlink_message_read_in_addr(mm, IFA_ADDRESS, &address.in); + if (r < 0) + goto fail; + } + + break; + + case AF_INET6: + r = sd_netlink_message_read_in6_addr(mm, IFA_LOCAL, &address.in6); + if (r < 0) { + r = sd_netlink_message_read_in6_addr(mm, IFA_ADDRESS, &address.in6); + if (r < 0) + goto fail; + } + + break; + + default: + return 0; + } + + a = link_find_address(l, family, &address); + + switch (type) { + + case RTM_NEWADDR: + + if (!a) { + r = link_address_new(l, &a, family, &address); + if (r < 0) + return r; + } + + r = link_address_update_rtnl(a, mm); + if (r < 0) + return r; + + break; + + case RTM_DELADDR: + link_address_free(a); + break; + } + + return 0; + +fail: + log_warning_errno(r, "Failed to process RTNL address message: %m"); + return 0; +} + +static int manager_rtnl_listen(Manager *m) { + _cleanup_(sd_netlink_message_unrefp) sd_netlink_message *req = NULL, *reply = NULL; + int r; + + assert(m); + + /* First, subscribe to interfaces coming and going */ + r = sd_netlink_open(&m->rtnl); + if (r < 0) + return r; + + r = sd_netlink_attach_event(m->rtnl, m->event, SD_EVENT_PRIORITY_IMPORTANT); + if (r < 0) + return r; + + r = sd_netlink_add_match(m->rtnl, NULL, RTM_NEWLINK, manager_process_link, NULL, m, "resolve-NEWLINK"); + if (r < 0) + return r; + + r = sd_netlink_add_match(m->rtnl, NULL, RTM_DELLINK, manager_process_link, NULL, m, "resolve-DELLINK"); + if (r < 0) + return r; + + r = sd_netlink_add_match(m->rtnl, NULL, RTM_NEWADDR, manager_process_address, NULL, m, "resolve-NEWADDR"); + if (r < 0) + return r; + + r = sd_netlink_add_match(m->rtnl, NULL, RTM_DELADDR, manager_process_address, NULL, m, "resolve-DELADDR"); + if (r < 0) + return r; + + /* Then, enumerate all links */ + r = sd_rtnl_message_new_link(m->rtnl, &req, RTM_GETLINK, 0); + if (r < 0) + return r; + + r = sd_netlink_message_set_request_dump(req, true); + if (r < 0) + return r; + + r = sd_netlink_call(m->rtnl, req, 0, &reply); + if (r < 0) + return r; + + for (sd_netlink_message *i = reply; i; i = sd_netlink_message_next(i)) { + r = manager_process_link(m->rtnl, i, m); + if (r < 0) + return r; + } + + req = sd_netlink_message_unref(req); + reply = sd_netlink_message_unref(reply); + + /* Finally, enumerate all addresses, too */ + r = sd_rtnl_message_new_addr(m->rtnl, &req, RTM_GETADDR, 0, AF_UNSPEC); + if (r < 0) + return r; + + r = sd_netlink_message_set_request_dump(req, true); + if (r < 0) + return r; + + r = sd_netlink_call(m->rtnl, req, 0, &reply); + if (r < 0) + return r; + + for (sd_netlink_message *i = reply; i; i = sd_netlink_message_next(i)) { + r = manager_process_address(m->rtnl, i, m); + if (r < 0) + return r; + } + + return r; +} + +static int on_network_event(sd_event_source *s, int fd, uint32_t revents, void *userdata) { + Manager *m = ASSERT_PTR(userdata); + Link *l; + int r; + + sd_network_monitor_flush(m->network_monitor); + + HASHMAP_FOREACH(l, m->links) { + r = link_update(l); + if (r < 0) + log_warning_errno(r, "Failed to update monitor information for %i: %m", l->ifindex); + } + + (void) manager_write_resolv_conf(m); + (void) manager_send_changed(m, "DNS"); + + return 0; +} + +static int manager_network_monitor_listen(Manager *m) { + int r, fd, events; + + assert(m); + + r = sd_network_monitor_new(&m->network_monitor, NULL); + if (r < 0) + return r; + + fd = sd_network_monitor_get_fd(m->network_monitor); + if (fd < 0) + return fd; + + events = sd_network_monitor_get_events(m->network_monitor); + if (events < 0) + return events; + + r = sd_event_add_io(m->event, &m->network_event_source, fd, events, &on_network_event, m); + if (r < 0) + return r; + + r = sd_event_source_set_priority(m->network_event_source, SD_EVENT_PRIORITY_IMPORTANT+5); + if (r < 0) + return r; + + (void) sd_event_source_set_description(m->network_event_source, "network-monitor"); + + return 0; +} + +static int manager_clock_change_listen(Manager *m); + +static int on_clock_change(sd_event_source *source, int fd, uint32_t revents, void *userdata) { + Manager *m = ASSERT_PTR(userdata); + + /* The clock has changed, let's flush all caches. Why that? That's because DNSSEC validation takes + * the system clock into consideration, and if the clock changes the old validations might have been + * wrong. Let's redo all validation with the new, correct time. + * + * (Also, this is triggered after system suspend, which is also a good reason to drop caches, since + * we might be connected to a different network now without this being visible in a dropped link + * carrier or so.) */ + + log_info("Clock change detected. Flushing caches."); + manager_flush_caches(m, LOG_DEBUG /* downgrade the functions own log message, since we already logged here at LOG_INFO level */); + + /* The clock change timerfd is unusable after it triggered once, create a new one. */ + return manager_clock_change_listen(m); +} + +static int manager_clock_change_listen(Manager *m) { + int r; + + assert(m); + + m->clock_change_event_source = sd_event_source_disable_unref(m->clock_change_event_source); + + r = event_add_time_change(m->event, &m->clock_change_event_source, on_clock_change, m); + if (r < 0) + return log_error_errno(r, "Failed to create clock change event source: %m"); + + return 0; +} + +static int determine_hostnames(char **full_hostname, char **llmnr_hostname, char **mdns_hostname) { + _cleanup_free_ char *h = NULL, *n = NULL; + int r; + + assert(full_hostname); + assert(llmnr_hostname); + assert(mdns_hostname); + + r = resolve_system_hostname(&h, &n); + if (r < 0) + return r; + + r = dns_name_concat(n, "local", 0, mdns_hostname); + if (r < 0) + return log_error_errno(r, "Failed to determine mDNS hostname: %m"); + + *llmnr_hostname = TAKE_PTR(n); + *full_hostname = TAKE_PTR(h); + + return 0; +} + +static char* fallback_hostname(void) { + + /* Determine the fall back hostname. For exposing this system to the outside world, we cannot have it + * to be "localhost" even if that's the default hostname. In this case, let's revert to "linux" + * instead. */ + + _cleanup_free_ char *n = get_default_hostname(); + if (!n) + return NULL; + + if (is_localhost(n)) + return strdup("linux"); + + return TAKE_PTR(n); +} + +static int make_fallback_hostnames(char **full_hostname, char **llmnr_hostname, char **mdns_hostname) { + _cleanup_free_ char *h = NULL, *n = NULL, *m = NULL; + char label[DNS_LABEL_MAX]; + const char *p; + int r; + + assert(full_hostname); + assert(llmnr_hostname); + assert(mdns_hostname); + + p = h = fallback_hostname(); + if (!h) + return log_oom(); + + r = dns_label_unescape(&p, label, sizeof label, 0); + if (r < 0) + return log_error_errno(r, "Failed to unescape fallback hostname: %m"); + + assert(r > 0); /* The fallback hostname must have at least one label */ + + r = dns_label_escape_new(label, r, &n); + if (r < 0) + return log_error_errno(r, "Failed to escape fallback hostname: %m"); + + r = dns_name_concat(n, "local", 0, &m); + if (r < 0) + return log_error_errno(r, "Failed to concatenate mDNS hostname: %m"); + + *llmnr_hostname = TAKE_PTR(n); + *mdns_hostname = TAKE_PTR(m); + *full_hostname = TAKE_PTR(h); + + return 0; +} + +static int on_hostname_change(sd_event_source *es, int fd, uint32_t revents, void *userdata) { + _cleanup_free_ char *full_hostname = NULL, *llmnr_hostname = NULL, *mdns_hostname = NULL; + Manager *m = ASSERT_PTR(userdata); + bool llmnr_hostname_changed; + int r; + + r = determine_hostnames(&full_hostname, &llmnr_hostname, &mdns_hostname); + if (r < 0) { + log_warning_errno(r, "Failed to determine the local hostname and LLMNR/mDNS names, ignoring: %m"); + return 0; /* ignore invalid hostnames */ + } + + llmnr_hostname_changed = !streq(llmnr_hostname, m->llmnr_hostname); + if (streq(full_hostname, m->full_hostname) && + !llmnr_hostname_changed && + streq(mdns_hostname, m->mdns_hostname)) + return 0; + + log_info("System hostname changed to '%s'.", full_hostname); + + free_and_replace(m->full_hostname, full_hostname); + free_and_replace(m->llmnr_hostname, llmnr_hostname); + free_and_replace(m->mdns_hostname, mdns_hostname); + + manager_refresh_rrs(m); + (void) manager_send_changed(m, "LLMNRHostname"); + + return 0; +} + +static int manager_watch_hostname(Manager *m) { + int r; + + assert(m); + + m->hostname_fd = open("/proc/sys/kernel/hostname", + O_RDONLY|O_CLOEXEC|O_NONBLOCK|O_NOCTTY); + if (m->hostname_fd < 0) { + log_warning_errno(errno, "Failed to watch hostname: %m"); + return 0; + } + + r = sd_event_add_io(m->event, &m->hostname_event_source, m->hostname_fd, 0, on_hostname_change, m); + if (r < 0) { + if (r == -EPERM) + /* kernels prior to 3.2 don't support polling this file. Ignore the failure. */ + m->hostname_fd = safe_close(m->hostname_fd); + else + return log_error_errno(r, "Failed to add hostname event source: %m"); + } + + (void) sd_event_source_set_description(m->hostname_event_source, "hostname"); + + r = determine_hostnames(&m->full_hostname, &m->llmnr_hostname, &m->mdns_hostname); + if (r < 0) { + _cleanup_free_ char *d = NULL; + + d = fallback_hostname(); + if (!d) + return log_oom(); + + log_info("Defaulting to hostname '%s'.", d); + + r = make_fallback_hostnames(&m->full_hostname, &m->llmnr_hostname, &m->mdns_hostname); + if (r < 0) + return r; + } else + log_info("Using system hostname '%s'.", m->full_hostname); + + return 0; +} + +static int manager_sigusr1(sd_event_source *s, const struct signalfd_siginfo *si, void *userdata) { + _cleanup_free_ char *buffer = NULL; + _cleanup_fclose_ FILE *f = NULL; + Manager *m = ASSERT_PTR(userdata); + size_t size = 0; + Link *l; + + assert(s); + assert(si); + + f = open_memstream_unlocked(&buffer, &size); + if (!f) + return log_oom(); + + LIST_FOREACH(scopes, scope, m->dns_scopes) + dns_scope_dump(scope, f); + + LIST_FOREACH(servers, server, m->dns_servers) + dns_server_dump(server, f); + LIST_FOREACH(servers, server, m->fallback_dns_servers) + dns_server_dump(server, f); + HASHMAP_FOREACH(l, m->links) + LIST_FOREACH(servers, server, l->dns_servers) + dns_server_dump(server, f); + + if (fflush_and_check(f) < 0) + return log_oom(); + + log_dump(LOG_INFO, buffer); + return 0; +} + +static int manager_sigusr2(sd_event_source *s, const struct signalfd_siginfo *si, void *userdata) { + Manager *m = ASSERT_PTR(userdata); + + assert(s); + assert(si); + + manager_flush_caches(m, LOG_INFO); + + return 0; +} + +static int manager_sigrtmin1(sd_event_source *s, const struct signalfd_siginfo *si, void *userdata) { + Manager *m = ASSERT_PTR(userdata); + + assert(s); + assert(si); + + manager_reset_server_features(m); + return 0; +} + +int manager_new(Manager **ret) { + _cleanup_(manager_freep) Manager *m = NULL; + int r; + + assert(ret); + + m = new(Manager, 1); + if (!m) + return -ENOMEM; + + *m = (Manager) { + .llmnr_ipv4_udp_fd = -1, + .llmnr_ipv6_udp_fd = -1, + .llmnr_ipv4_tcp_fd = -1, + .llmnr_ipv6_tcp_fd = -1, + .mdns_ipv4_fd = -1, + .mdns_ipv6_fd = -1, + .hostname_fd = -1, + + .llmnr_support = DEFAULT_LLMNR_MODE, + .mdns_support = DEFAULT_MDNS_MODE, + .dnssec_mode = DEFAULT_DNSSEC_MODE, + .dns_over_tls_mode = DEFAULT_DNS_OVER_TLS_MODE, + .enable_cache = DNS_CACHE_MODE_YES, + .dns_stub_listener_mode = DNS_STUB_LISTENER_YES, + .read_resolv_conf = true, + .need_builtin_fallbacks = true, + .etc_hosts_last = USEC_INFINITY, + .read_etc_hosts = true, + }; + + r = dns_trust_anchor_load(&m->trust_anchor); + if (r < 0) + return r; + + r = manager_parse_config_file(m); + if (r < 0) + log_warning_errno(r, "Failed to parse configuration file: %m"); + +#if ENABLE_DNS_OVER_TLS + r = dnstls_manager_init(m); + if (r < 0) + return r; +#endif + + r = sd_event_default(&m->event); + if (r < 0) + return r; + + (void) sd_event_add_signal(m->event, NULL, SIGTERM, NULL, NULL); + (void) sd_event_add_signal(m->event, NULL, SIGINT, NULL, NULL); + + (void) sd_event_set_watchdog(m->event, true); + + r = manager_watch_hostname(m); + if (r < 0) + return r; + + r = dnssd_load(m); + if (r < 0) + log_warning_errno(r, "Failed to load DNS-SD configuration files: %m"); + + r = dns_scope_new(m, &m->unicast_scope, NULL, DNS_PROTOCOL_DNS, AF_UNSPEC); + if (r < 0) + return r; + + r = manager_network_monitor_listen(m); + if (r < 0) + return r; + + r = manager_rtnl_listen(m); + if (r < 0) + return r; + + r = manager_clock_change_listen(m); + if (r < 0) + return r; + + r = manager_connect_bus(m); + if (r < 0) + return r; + + (void) sd_event_add_signal(m->event, &m->sigusr1_event_source, SIGUSR1, manager_sigusr1, m); + (void) sd_event_add_signal(m->event, &m->sigusr2_event_source, SIGUSR2, manager_sigusr2, m); + (void) sd_event_add_signal(m->event, &m->sigrtmin1_event_source, SIGRTMIN+1, manager_sigrtmin1, m); + + manager_cleanup_saved_user(m); + + *ret = TAKE_PTR(m); + + return 0; +} + +int manager_start(Manager *m) { + int r; + + assert(m); + + r = manager_dns_stub_start(m); + if (r < 0) + return r; + + r = manager_varlink_init(m); + if (r < 0) + return r; + + return 0; +} + +Manager *manager_free(Manager *m) { + Link *l; + DnssdService *s; + + if (!m) + return NULL; + + dns_server_unlink_all(m->dns_servers); + dns_server_unlink_all(m->fallback_dns_servers); + dns_search_domain_unlink_all(m->search_domains); + + while ((l = hashmap_first(m->links))) + link_free(l); + + while (m->dns_queries) + dns_query_free(m->dns_queries); + + m->stub_queries_by_packet = hashmap_free(m->stub_queries_by_packet); + + dns_scope_free(m->unicast_scope); + + /* At this point only orphaned streams should remain. All others should have been freed already by their + * owners */ + while (m->dns_streams) + dns_stream_unref(m->dns_streams); + +#if ENABLE_DNS_OVER_TLS + dnstls_manager_free(m); +#endif + + hashmap_free(m->links); + hashmap_free(m->dns_transactions); + + sd_event_source_unref(m->network_event_source); + sd_network_monitor_unref(m->network_monitor); + + sd_netlink_unref(m->rtnl); + sd_event_source_unref(m->rtnl_event_source); + sd_event_source_unref(m->clock_change_event_source); + + manager_llmnr_stop(m); + manager_mdns_stop(m); + manager_dns_stub_stop(m); + manager_varlink_done(m); + + manager_socket_graveyard_clear(m); + + ordered_set_free(m->dns_extra_stub_listeners); + + bus_verify_polkit_async_registry_free(m->polkit_registry); + + sd_bus_flush_close_unref(m->bus); + + sd_event_source_unref(m->sigusr1_event_source); + sd_event_source_unref(m->sigusr2_event_source); + sd_event_source_unref(m->sigrtmin1_event_source); + + dns_resource_key_unref(m->llmnr_host_ipv4_key); + dns_resource_key_unref(m->llmnr_host_ipv6_key); + dns_resource_key_unref(m->mdns_host_ipv4_key); + dns_resource_key_unref(m->mdns_host_ipv6_key); + + sd_event_source_unref(m->hostname_event_source); + safe_close(m->hostname_fd); + + sd_event_unref(m->event); + + free(m->full_hostname); + free(m->llmnr_hostname); + free(m->mdns_hostname); + + while ((s = hashmap_first(m->dnssd_services))) + dnssd_service_free(s); + hashmap_free(m->dnssd_services); + + dns_trust_anchor_flush(&m->trust_anchor); + manager_etc_hosts_flush(m); + + return mfree(m); +} + +int manager_recv(Manager *m, int fd, DnsProtocol protocol, DnsPacket **ret) { + _cleanup_(dns_packet_unrefp) DnsPacket *p = NULL; + CMSG_BUFFER_TYPE(CMSG_SPACE(MAXSIZE(struct in_pktinfo, struct in6_pktinfo)) + + CMSG_SPACE(int) /* ttl/hoplimit */ + + EXTRA_CMSG_SPACE /* kernel appears to require extra buffer space */) control; + union sockaddr_union sa; + struct iovec iov; + struct msghdr mh = { + .msg_name = &sa.sa, + .msg_namelen = sizeof(sa), + .msg_iov = &iov, + .msg_iovlen = 1, + .msg_control = &control, + .msg_controllen = sizeof(control), + }; + struct cmsghdr *cmsg; + ssize_t ms, l; + int r; + + assert(m); + assert(fd >= 0); + assert(ret); + + ms = next_datagram_size_fd(fd); + if (ms < 0) + return ms; + + r = dns_packet_new(&p, protocol, ms, DNS_PACKET_SIZE_MAX); + if (r < 0) + return r; + + iov = IOVEC_MAKE(DNS_PACKET_DATA(p), p->allocated); + + l = recvmsg_safe(fd, &mh, 0); + if (l < 0) { + if (ERRNO_IS_TRANSIENT(l)) + return 0; + return l; + } + if (l == 0) + return 0; + + assert(!(mh.msg_flags & MSG_TRUNC)); + + p->size = (size_t) l; + + p->family = sa.sa.sa_family; + p->ipproto = IPPROTO_UDP; + if (p->family == AF_INET) { + p->sender.in = sa.in.sin_addr; + p->sender_port = be16toh(sa.in.sin_port); + } else if (p->family == AF_INET6) { + p->sender.in6 = sa.in6.sin6_addr; + p->sender_port = be16toh(sa.in6.sin6_port); + p->ifindex = sa.in6.sin6_scope_id; + } else + return -EAFNOSUPPORT; + + p->timestamp = now(CLOCK_BOOTTIME); + + CMSG_FOREACH(cmsg, &mh) { + + if (cmsg->cmsg_level == IPPROTO_IPV6) { + assert(p->family == AF_INET6); + + switch (cmsg->cmsg_type) { + + case IPV6_PKTINFO: { + struct in6_pktinfo *i = (struct in6_pktinfo*) CMSG_DATA(cmsg); + + if (p->ifindex <= 0) + p->ifindex = i->ipi6_ifindex; + + p->destination.in6 = i->ipi6_addr; + break; + } + + case IPV6_HOPLIMIT: + p->ttl = *(int *) CMSG_DATA(cmsg); + break; + + case IPV6_RECVFRAGSIZE: + p->fragsize = *(int *) CMSG_DATA(cmsg); + break; + } + } else if (cmsg->cmsg_level == IPPROTO_IP) { + assert(p->family == AF_INET); + + switch (cmsg->cmsg_type) { + + case IP_PKTINFO: { + struct in_pktinfo *i = (struct in_pktinfo*) CMSG_DATA(cmsg); + + if (p->ifindex <= 0) + p->ifindex = i->ipi_ifindex; + + p->destination.in = i->ipi_addr; + break; + } + + case IP_TTL: + p->ttl = *(int *) CMSG_DATA(cmsg); + break; + + case IP_RECVFRAGSIZE: + p->fragsize = *(int *) CMSG_DATA(cmsg); + break; + } + } + } + + /* The Linux kernel sets the interface index to the loopback + * device if the packet came from the local host since it + * avoids the routing table in such a case. Let's unset the + * interface index in such a case. */ + if (p->ifindex == LOOPBACK_IFINDEX) + p->ifindex = 0; + + if (protocol != DNS_PROTOCOL_DNS) { + /* If we don't know the interface index still, we look for the + * first local interface with a matching address. Yuck! */ + if (p->ifindex <= 0) + p->ifindex = manager_find_ifindex(m, p->family, &p->destination); + } + + log_debug("Received %s UDP packet of size %zu, ifindex=%i, ttl=%u, fragsize=%zu, sender=%s, destination=%s", + dns_protocol_to_string(protocol), p->size, p->ifindex, p->ttl, p->fragsize, + IN_ADDR_TO_STRING(p->family, &p->sender), + IN_ADDR_TO_STRING(p->family, &p->destination)); + + *ret = TAKE_PTR(p); + return 1; +} + +static int sendmsg_loop(int fd, struct msghdr *mh, int flags) { + int r; + + assert(fd >= 0); + assert(mh); + + for (;;) { + if (sendmsg(fd, mh, flags) >= 0) + return 0; + if (errno == EINTR) + continue; + if (errno != EAGAIN) + return -errno; + + r = fd_wait_for_event(fd, POLLOUT, SEND_TIMEOUT_USEC); + if (r < 0) + return r; + if (r == 0) + return -ETIMEDOUT; + } +} + +static int write_loop(int fd, void *message, size_t length) { + int r; + + assert(fd >= 0); + assert(message); + + for (;;) { + if (write(fd, message, length) >= 0) + return 0; + if (errno == EINTR) + continue; + if (errno != EAGAIN) + return -errno; + + r = fd_wait_for_event(fd, POLLOUT, SEND_TIMEOUT_USEC); + if (r < 0) + return r; + if (r == 0) + return -ETIMEDOUT; + } +} + +int manager_write(Manager *m, int fd, DnsPacket *p) { + int r; + + log_debug("Sending %s%s packet with id %" PRIu16 " of size %zu.", + DNS_PACKET_TC(p) ? "truncated (!) " : "", + DNS_PACKET_QR(p) ? "response" : "query", + DNS_PACKET_ID(p), + p->size); + + r = write_loop(fd, DNS_PACKET_DATA(p), p->size); + if (r < 0) + return r; + + return 0; +} + +static int manager_ipv4_send( + Manager *m, + int fd, + int ifindex, + const struct in_addr *destination, + uint16_t port, + const struct in_addr *source, + DnsPacket *p) { + + CMSG_BUFFER_TYPE(CMSG_SPACE(sizeof(struct in_pktinfo))) control = {}; + union sockaddr_union sa; + struct iovec iov; + struct msghdr mh = { + .msg_iov = &iov, + .msg_iovlen = 1, + .msg_name = &sa.sa, + .msg_namelen = sizeof(sa.in), + }; + + assert(m); + assert(fd >= 0); + assert(destination); + assert(port > 0); + assert(p); + + iov = IOVEC_MAKE(DNS_PACKET_DATA(p), p->size); + + sa = (union sockaddr_union) { + .in.sin_family = AF_INET, + .in.sin_addr = *destination, + .in.sin_port = htobe16(port), + }; + + if (ifindex > 0) { + struct cmsghdr *cmsg; + struct in_pktinfo *pi; + + mh.msg_control = &control; + mh.msg_controllen = sizeof(control); + + cmsg = CMSG_FIRSTHDR(&mh); + cmsg->cmsg_len = CMSG_LEN(sizeof(struct in_pktinfo)); + cmsg->cmsg_level = IPPROTO_IP; + cmsg->cmsg_type = IP_PKTINFO; + + pi = (struct in_pktinfo*) CMSG_DATA(cmsg); + pi->ipi_ifindex = ifindex; + + if (source) + pi->ipi_spec_dst = *source; + } + + return sendmsg_loop(fd, &mh, 0); +} + +static int manager_ipv6_send( + Manager *m, + int fd, + int ifindex, + const struct in6_addr *destination, + uint16_t port, + const struct in6_addr *source, + DnsPacket *p) { + + CMSG_BUFFER_TYPE(CMSG_SPACE(sizeof(struct in6_pktinfo))) control = {}; + union sockaddr_union sa; + struct iovec iov; + struct msghdr mh = { + .msg_iov = &iov, + .msg_iovlen = 1, + .msg_name = &sa.sa, + .msg_namelen = sizeof(sa.in6), + }; + + assert(m); + assert(fd >= 0); + assert(destination); + assert(port > 0); + assert(p); + + iov = IOVEC_MAKE(DNS_PACKET_DATA(p), p->size); + + sa = (union sockaddr_union) { + .in6.sin6_family = AF_INET6, + .in6.sin6_addr = *destination, + .in6.sin6_port = htobe16(port), + .in6.sin6_scope_id = ifindex, + }; + + if (ifindex > 0) { + struct cmsghdr *cmsg; + struct in6_pktinfo *pi; + + mh.msg_control = &control; + mh.msg_controllen = sizeof(control); + + cmsg = CMSG_FIRSTHDR(&mh); + cmsg->cmsg_len = CMSG_LEN(sizeof(struct in6_pktinfo)); + cmsg->cmsg_level = IPPROTO_IPV6; + cmsg->cmsg_type = IPV6_PKTINFO; + + pi = (struct in6_pktinfo*) CMSG_DATA(cmsg); + pi->ipi6_ifindex = ifindex; + + if (source) + pi->ipi6_addr = *source; + } + + return sendmsg_loop(fd, &mh, 0); +} + +static int dns_question_to_json(DnsQuestion *q, JsonVariant **ret) { + _cleanup_(json_variant_unrefp) JsonVariant *l = NULL; + DnsResourceKey *key; + int r; + + assert(ret); + + DNS_QUESTION_FOREACH(key, q) { + _cleanup_(json_variant_unrefp) JsonVariant *v = NULL; + + r = dns_resource_key_to_json(key, &v); + if (r < 0) + return r; + + r = json_variant_append_array(&l, v); + if (r < 0) + return r; + } + + *ret = TAKE_PTR(l); + return 0; +} + +int manager_monitor_send( + Manager *m, + int state, + int rcode, + int error, + DnsQuestion *question_idna, + DnsQuestion *question_utf8, + DnsPacket *question_bypass, + DnsQuestion *collected_questions, + DnsAnswer *answer) { + + _cleanup_(json_variant_unrefp) JsonVariant *jquestion = NULL, *jcollected_questions = NULL, *janswer = NULL; + _cleanup_(dns_question_unrefp) DnsQuestion *merged = NULL; + Varlink *connection; + DnsAnswerItem *rri; + int r; + + assert(m); + + if (set_isempty(m->varlink_subscription)) + return 0; + + /* Merge all questions into one */ + r = dns_question_merge(question_idna, question_utf8, &merged); + if (r < 0) + return log_error_errno(r, "Failed to merge UTF8/IDNA questions: %m"); + + if (question_bypass) { + _cleanup_(dns_question_unrefp) DnsQuestion *merged2 = NULL; + + r = dns_question_merge(merged, question_bypass->question, &merged2); + if (r < 0) + return log_error_errno(r, "Failed to merge UTF8/IDNA questions and DNS packet question: %m"); + + dns_question_unref(merged); + merged = TAKE_PTR(merged2); + } + + /* Convert the current primary question to JSON */ + r = dns_question_to_json(merged, &jquestion); + if (r < 0) + return log_error_errno(r, "Failed to convert question to JSON: %m"); + + /* Generate a JSON array of the questions preceding the current one in the CNAME chain */ + r = dns_question_to_json(collected_questions, &jcollected_questions); + if (r < 0) + return log_error_errno(r, "Failed to convert question to JSON: %m"); + + DNS_ANSWER_FOREACH_ITEM(rri, answer) { + _cleanup_(json_variant_unrefp) JsonVariant *v = NULL, *w = NULL; + + r = dns_resource_record_to_json(rri->rr, &v); + if (r < 0) + return log_error_errno(r, "Failed to convert answer resource record to JSON: %m"); + + r = dns_resource_record_to_wire_format(rri->rr, /* canonical= */ false); /* don't use DNSSEC canonical format, since it removes casing, but we want that for DNS_SD compat */ + if (r < 0) + return log_error_errno(r, "Failed to generate RR wire format: %m"); + + r = json_build(&w, JSON_BUILD_OBJECT( + JSON_BUILD_PAIR_CONDITION(v, "rr", JSON_BUILD_VARIANT(v)), + JSON_BUILD_PAIR("raw", JSON_BUILD_BASE64(rri->rr->wire_format, rri->rr->wire_format_size)), + JSON_BUILD_PAIR_CONDITION(rri->ifindex > 0, "ifindex", JSON_BUILD_INTEGER(rri->ifindex)))); + if (r < 0) + return log_error_errno(r, "Failed to make answer RR object: %m"); + + r = json_variant_append_array(&janswer, w); + if (r < 0) + return log_debug_errno(r, "Failed to append notification entry to array: %m"); + } + + SET_FOREACH(connection, m->varlink_subscription) { + r = varlink_notifyb(connection, + JSON_BUILD_OBJECT(JSON_BUILD_PAIR("state", JSON_BUILD_STRING(dns_transaction_state_to_string(state))), + JSON_BUILD_PAIR_CONDITION(state == DNS_TRANSACTION_RCODE_FAILURE, "rcode", JSON_BUILD_INTEGER(rcode)), + JSON_BUILD_PAIR_CONDITION(state == DNS_TRANSACTION_ERRNO, "errno", JSON_BUILD_INTEGER(error)), + JSON_BUILD_PAIR("question", JSON_BUILD_VARIANT(jquestion)), + JSON_BUILD_PAIR_CONDITION(jcollected_questions, "collectedQuestions", JSON_BUILD_VARIANT(jcollected_questions)), + JSON_BUILD_PAIR_CONDITION(janswer, "answer", JSON_BUILD_VARIANT(janswer)))); + if (r < 0) + log_debug_errno(r, "Failed to send monitor event, ignoring: %m"); + } + + return 0; +} + +int manager_send( + Manager *m, + int fd, + int ifindex, + int family, + const union in_addr_union *destination, + uint16_t port, + const union in_addr_union *source, + DnsPacket *p) { + + assert(m); + assert(fd >= 0); + assert(destination); + assert(port > 0); + assert(p); + + /* For mDNS, it is natural that the packet have truncated flag when we have many known answers. */ + bool truncated = DNS_PACKET_TC(p) && (p->protocol != DNS_PROTOCOL_MDNS || !p->more); + + log_debug("Sending %s%s packet with id %" PRIu16 " on interface %i/%s of size %zu.", + truncated ? "truncated (!) " : "", + DNS_PACKET_QR(p) ? "response" : "query", + DNS_PACKET_ID(p), + ifindex, af_to_name(family), + p->size); + + if (family == AF_INET) + return manager_ipv4_send(m, fd, ifindex, &destination->in, port, source ? &source->in : NULL, p); + if (family == AF_INET6) + return manager_ipv6_send(m, fd, ifindex, &destination->in6, port, source ? &source->in6 : NULL, p); + + return -EAFNOSUPPORT; +} + +uint32_t manager_find_mtu(Manager *m) { + uint32_t mtu = 0; + Link *l; + + /* If we don't know on which link a DNS packet would be delivered, let's find the largest MTU that + * works on all interfaces we know of that have an IP address associated */ + + HASHMAP_FOREACH(l, m->links) { + /* Let's filter out links without IP addresses (e.g. AF_CAN links and suchlike) */ + if (!l->addresses) + continue; + + /* Safety check: MTU shorter than what we need for the absolutely shortest DNS request? Then + * let's ignore this link. */ + if (l->mtu < MIN(UDP4_PACKET_HEADER_SIZE + DNS_PACKET_HEADER_SIZE, + UDP6_PACKET_HEADER_SIZE + DNS_PACKET_HEADER_SIZE)) + continue; + + if (mtu <= 0 || l->mtu < mtu) + mtu = l->mtu; + } + + if (mtu == 0) /* found nothing? then let's assume the typical Ethernet MTU for lack of anything more precise */ + return 1500; + + return mtu; +} + +int manager_find_ifindex(Manager *m, int family, const union in_addr_union *in_addr) { + LinkAddress *a; + + assert(m); + + if (!IN_SET(family, AF_INET, AF_INET6)) + return 0; + + if (!in_addr) + return 0; + + a = manager_find_link_address(m, family, in_addr); + if (a) + return a->link->ifindex; + + return 0; +} + +void manager_refresh_rrs(Manager *m) { + Link *l; + DnssdService *s; + + assert(m); + + m->llmnr_host_ipv4_key = dns_resource_key_unref(m->llmnr_host_ipv4_key); + m->llmnr_host_ipv6_key = dns_resource_key_unref(m->llmnr_host_ipv6_key); + m->mdns_host_ipv4_key = dns_resource_key_unref(m->mdns_host_ipv4_key); + m->mdns_host_ipv6_key = dns_resource_key_unref(m->mdns_host_ipv6_key); + + HASHMAP_FOREACH(l, m->links) + link_add_rrs(l, true); + + if (m->mdns_support == RESOLVE_SUPPORT_YES) + HASHMAP_FOREACH(s, m->dnssd_services) + if (dnssd_update_rrs(s) < 0) + log_warning("Failed to refresh DNS-SD service '%s'", s->name); + + HASHMAP_FOREACH(l, m->links) + link_add_rrs(l, false); +} + +static int manager_next_random_name(const char *old, char **ret_new) { + const char *p; + uint64_t u, a; + char *n; + + p = strchr(old, 0); + assert(p); + + while (p > old) { + if (!ascii_isdigit(p[-1])) + break; + + p--; + } + + if (*p == 0 || safe_atou64(p, &u) < 0 || u <= 0) + u = 1; + + /* Add a random number to the old value. This way we can avoid + * that two hosts pick the same hostname, win on IPv4 and lose + * on IPv6 (or vice versa), and pick the same hostname + * replacement hostname, ad infinitum. We still want the + * numbers to go up monotonically, hence we just add a random + * value 1..10 */ + + random_bytes(&a, sizeof(a)); + u += 1 + a % 10; + + if (asprintf(&n, "%.*s%" PRIu64, (int) (p - old), old, u) < 0) + return -ENOMEM; + + *ret_new = n; + + return 0; +} + +int manager_next_hostname(Manager *m) { + _cleanup_free_ char *h = NULL, *k = NULL; + int r; + + assert(m); + + r = manager_next_random_name(m->llmnr_hostname, &h); + if (r < 0) + return r; + + r = dns_name_concat(h, "local", 0, &k); + if (r < 0) + return r; + + log_info("Hostname conflict, changing published hostname from '%s' to '%s'.", m->llmnr_hostname, h); + + free_and_replace(m->llmnr_hostname, h); + free_and_replace(m->mdns_hostname, k); + + manager_refresh_rrs(m); + (void) manager_send_changed(m, "LLMNRHostname"); + + return 0; +} + +LinkAddress* manager_find_link_address(Manager *m, int family, const union in_addr_union *in_addr) { + Link *l; + + assert(m); + + if (!IN_SET(family, AF_INET, AF_INET6)) + return NULL; + + if (!in_addr) + return NULL; + + HASHMAP_FOREACH(l, m->links) { + LinkAddress *a; + + a = link_find_address(l, family, in_addr); + if (a) + return a; + } + + return NULL; +} + +bool manager_packet_from_local_address(Manager *m, DnsPacket *p) { + assert(m); + assert(p); + + /* Let's see if this packet comes from an IP address we have on any local interface */ + + return !!manager_find_link_address(m, p->family, &p->sender); +} + +bool manager_packet_from_our_transaction(Manager *m, DnsPacket *p) { + DnsTransaction *t; + + assert(m); + assert(p); + + /* Let's see if we have a transaction with a query message with the exact same binary contents as the + * one we just got. If so, it's almost definitely a packet loop of some kind. */ + + t = hashmap_get(m->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p))); + if (!t) + return false; + + return t->sent && dns_packet_equal(t->sent, p); +} + +DnsScope* manager_find_scope(Manager *m, DnsPacket *p) { + Link *l; + + assert(m); + assert(p); + + l = hashmap_get(m->links, INT_TO_PTR(p->ifindex)); + if (!l) + return NULL; + + switch (p->protocol) { + case DNS_PROTOCOL_LLMNR: + if (p->family == AF_INET) + return l->llmnr_ipv4_scope; + else if (p->family == AF_INET6) + return l->llmnr_ipv6_scope; + + break; + + case DNS_PROTOCOL_MDNS: + if (p->family == AF_INET) + return l->mdns_ipv4_scope; + else if (p->family == AF_INET6) + return l->mdns_ipv6_scope; + + break; + + default: + break; + } + + return NULL; +} + +void manager_verify_all(Manager *m) { + assert(m); + + LIST_FOREACH(scopes, s, m->dns_scopes) + dns_zone_verify_all(&s->zone); +} + +int manager_is_own_hostname(Manager *m, const char *name) { + int r; + + assert(m); + assert(name); + + if (m->llmnr_hostname) { + r = dns_name_equal(name, m->llmnr_hostname); + if (r != 0) + return r; + } + + if (m->mdns_hostname) { + r = dns_name_equal(name, m->mdns_hostname); + if (r != 0) + return r; + } + + if (m->full_hostname) + return dns_name_equal(name, m->full_hostname); + + return 0; +} + +int manager_compile_dns_servers(Manager *m, OrderedSet **dns) { + Link *l; + int r; + + assert(m); + assert(dns); + + r = ordered_set_ensure_allocated(dns, &dns_server_hash_ops); + if (r < 0) + return r; + + /* First add the system-wide servers and domains */ + LIST_FOREACH(servers, s, m->dns_servers) { + r = ordered_set_put(*dns, s); + if (r == -EEXIST) + continue; + if (r < 0) + return r; + } + + /* Then, add the per-link servers */ + HASHMAP_FOREACH(l, m->links) { + LIST_FOREACH(servers, s, l->dns_servers) { + r = ordered_set_put(*dns, s); + if (r == -EEXIST) + continue; + if (r < 0) + return r; + } + } + + /* If we found nothing, add the fallback servers */ + if (ordered_set_isempty(*dns)) { + LIST_FOREACH(servers, s, m->fallback_dns_servers) { + r = ordered_set_put(*dns, s); + if (r == -EEXIST) + continue; + if (r < 0) + return r; + } + } + + return 0; +} + +/* filter_route is a tri-state: + * < 0: no filtering + * = 0 or false: return only domains which should be used for searching + * > 0 or true: return only domains which are for routing only + */ +int manager_compile_search_domains(Manager *m, OrderedSet **domains, int filter_route) { + Link *l; + int r; + + assert(m); + assert(domains); + + r = ordered_set_ensure_allocated(domains, &dns_name_hash_ops); + if (r < 0) + return r; + + LIST_FOREACH(domains, d, m->search_domains) { + + if (filter_route >= 0 && + d->route_only != !!filter_route) + continue; + + r = ordered_set_put(*domains, d->name); + if (r == -EEXIST) + continue; + if (r < 0) + return r; + } + + HASHMAP_FOREACH(l, m->links) { + + LIST_FOREACH(domains, d, l->search_domains) { + + if (filter_route >= 0 && + d->route_only != !!filter_route) + continue; + + r = ordered_set_put(*domains, d->name); + if (r == -EEXIST) + continue; + if (r < 0) + return r; + } + } + + return 0; +} + +DnssecMode manager_get_dnssec_mode(Manager *m) { + assert(m); + + if (m->dnssec_mode != _DNSSEC_MODE_INVALID) + return m->dnssec_mode; + + return DNSSEC_NO; +} + +bool manager_dnssec_supported(Manager *m) { + DnsServer *server; + Link *l; + + assert(m); + + if (manager_get_dnssec_mode(m) == DNSSEC_NO) + return false; + + server = manager_get_dns_server(m); + if (server && !dns_server_dnssec_supported(server)) + return false; + + HASHMAP_FOREACH(l, m->links) + if (!link_dnssec_supported(l)) + return false; + + return true; +} + +DnsOverTlsMode manager_get_dns_over_tls_mode(Manager *m) { + assert(m); + + if (m->dns_over_tls_mode != _DNS_OVER_TLS_MODE_INVALID) + return m->dns_over_tls_mode; + + return DNS_OVER_TLS_NO; +} + +void manager_dnssec_verdict(Manager *m, DnssecVerdict verdict, const DnsResourceKey *key) { + + assert(verdict >= 0); + assert(verdict < _DNSSEC_VERDICT_MAX); + + if (DEBUG_LOGGING) { + char s[DNS_RESOURCE_KEY_STRING_MAX]; + + log_debug("Found verdict for lookup %s: %s", + dns_resource_key_to_string(key, s, sizeof s), + dnssec_verdict_to_string(verdict)); + } + + m->n_dnssec_verdict[verdict]++; +} + +bool manager_routable(Manager *m) { + Link *l; + + assert(m); + + /* Returns true if the host has at least one interface with a routable address (regardless if IPv4 or IPv6) */ + + HASHMAP_FOREACH(l, m->links) + if (link_relevant(l, AF_UNSPEC, false)) + return true; + + return false; +} + +void manager_flush_caches(Manager *m, int log_level) { + assert(m); + + LIST_FOREACH(scopes, scope, m->dns_scopes) + dns_cache_flush(&scope->cache); + + log_full(log_level, "Flushed all caches."); +} + +void manager_reset_server_features(Manager *m) { + Link *l; + + dns_server_reset_features_all(m->dns_servers); + dns_server_reset_features_all(m->fallback_dns_servers); + + HASHMAP_FOREACH(l, m->links) + dns_server_reset_features_all(l->dns_servers); + + log_info("Resetting learnt feature levels on all servers."); +} + +void manager_cleanup_saved_user(Manager *m) { + _cleanup_closedir_ DIR *d = NULL; + + assert(m); + + /* Clean up all saved per-link files in /run/systemd/resolve/netif/ that don't have a matching interface + * anymore. These files are created to persist settings pushed in by the user via the bus, so that resolved can + * be restarted without losing this data. */ + + d = opendir("/run/systemd/resolve/netif/"); + if (!d) { + if (errno == ENOENT) + return; + + log_warning_errno(errno, "Failed to open interface directory: %m"); + return; + } + + FOREACH_DIRENT_ALL(de, d, log_error_errno(errno, "Failed to read interface directory: %m")) { + _cleanup_free_ char *p = NULL; + int ifindex; + Link *l; + + if (!IN_SET(de->d_type, DT_UNKNOWN, DT_REG)) + continue; + + if (dot_or_dot_dot(de->d_name)) + continue; + + ifindex = parse_ifindex(de->d_name); + if (ifindex < 0) /* Probably some temporary file from a previous run. Delete it */ + goto rm; + + l = hashmap_get(m->links, INT_TO_PTR(ifindex)); + if (!l) /* link vanished */ + goto rm; + + if (l->is_managed) /* now managed by networkd, hence the bus settings are useless */ + goto rm; + + continue; + + rm: + p = path_join("/run/systemd/resolve/netif", de->d_name); + if (!p) { + log_oom(); + return; + } + + (void) unlink(p); + } +} + +bool manager_next_dnssd_names(Manager *m) { + DnssdService *s; + bool tried = false; + int r; + + assert(m); + + HASHMAP_FOREACH(s, m->dnssd_services) { + _cleanup_free_ char * new_name = NULL; + + if (!s->withdrawn) + continue; + + r = manager_next_random_name(s->name_template, &new_name); + if (r < 0) { + log_warning_errno(r, "Failed to get new name for service '%s': %m", s->name); + continue; + } + + free_and_replace(s->name_template, new_name); + + s->withdrawn = false; + + tried = true; + } + + if (tried) + manager_refresh_rrs(m); + + return tried; +} + +bool manager_server_is_stub(Manager *m, DnsServer *s) { + DnsStubListenerExtra *l; + + assert(m); + assert(s); + + /* Safety check: we generally already skip the main stub when parsing configuration. But let's be + * extra careful, and check here again */ + if (s->family == AF_INET && + s->address.in.s_addr == htobe32(INADDR_DNS_STUB) && + dns_server_port(s) == 53) + return true; + + /* Main reason to call this is to check server data against the extra listeners, and filter things + * out. */ + ORDERED_SET_FOREACH(l, m->dns_extra_stub_listeners) + if (s->family == l->family && + in_addr_equal(s->family, &s->address, &l->address) && + dns_server_port(s) == dns_stub_listener_extra_port(l)) + return true; + + return false; +} + +int socket_disable_pmtud(int fd, int af) { + int r; + + assert(fd >= 0); + + if (af == AF_UNSPEC) { + af = socket_get_family(fd); + if (af < 0) + return af; + } + + switch (af) { + + case AF_INET: { + /* Turn off path MTU discovery, let's rather fragment on the way than to open us up against + * PMTU forgery vulnerabilities. + * + * There appears to be no documentation about IP_PMTUDISC_OMIT, but it has the effect that + * the "Don't Fragment" bit in the IPv4 header is turned off, thus enforcing fragmentation if + * our datagram size exceeds the MTU of a router in the path, and turning off path MTU + * discovery. + * + * This helps mitigating the PMTUD vulnerability described here: + * + * https://blog.apnic.net/2019/07/12/its-time-to-consider-avoiding-ip-fragmentation-in-the-dns/ + * + * Similar logic is in place in most DNS servers. + * + * There are multiple conflicting goals: we want to allow the largest datagrams possible (for + * efficiency reasons), but not have fragmentation (for security reasons), nor use PMTUD (for + * security reasons, too). Our strategy to deal with this is: use large packets, turn off + * PMTUD, but watch fragmentation taking place, and then size our packets to the max of the + * fragments seen — and if we need larger packets always go to TCP. + */ + + r = setsockopt_int(fd, IPPROTO_IP, IP_MTU_DISCOVER, IP_PMTUDISC_OMIT); + if (r < 0) + return r; + + return 0; + } + + case AF_INET6: { + /* On IPv6 fragmentation only is done by the sender — never by routers on the path. PMTUD is + * mandatory. If we want to turn off PMTUD, the only way is by sending with minimal MTU only, + * so that we apply maximum fragmentation locally already, and thus PMTUD doesn't happen + * because there's nothing that could be fragmented further anymore. */ + + r = setsockopt_int(fd, IPPROTO_IPV6, IPV6_MTU, IPV6_MIN_MTU); + if (r < 0) + return r; + + return 0; + } + + default: + return -EAFNOSUPPORT; + } +} |