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resolved-dns-transaction.c
3258 lines (2526 loc) · 124 KB
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resolved-dns-transaction.c
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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include "sd-messages.h"
#include "af-list.h"
#include "alloc-util.h"
#include "dns-domain.h"
#include "errno-list.h"
#include "errno-util.h"
#include "fd-util.h"
#include "random-util.h"
#include "resolved-dns-cache.h"
#include "resolved-dns-transaction.h"
#include "resolved-dnstls.h"
#include "resolved-llmnr.h"
#include "string-table.h"
#define TRANSACTIONS_MAX 4096
#define TRANSACTION_TCP_TIMEOUT_USEC (10U*USEC_PER_SEC)
/* After how much time to repeat classic DNS requests */
#define DNS_TIMEOUT_USEC (SD_RESOLVED_QUERY_TIMEOUT_USEC / DNS_TRANSACTION_ATTEMPTS_MAX)
static void dns_transaction_reset_answer(DnsTransaction *t) {
assert(t);
t->received = dns_packet_unref(t->received);
t->answer = dns_answer_unref(t->answer);
t->answer_rcode = 0;
t->answer_dnssec_result = _DNSSEC_RESULT_INVALID;
t->answer_source = _DNS_TRANSACTION_SOURCE_INVALID;
t->answer_authenticated = false;
t->answer_nsec_ttl = (uint32_t) -1;
t->answer_errno = 0;
}
static void dns_transaction_flush_dnssec_transactions(DnsTransaction *t) {
DnsTransaction *z;
assert(t);
while ((z = set_steal_first(t->dnssec_transactions))) {
set_remove(z->notify_transactions, t);
set_remove(z->notify_transactions_done, t);
dns_transaction_gc(z);
}
}
static void dns_transaction_close_connection(DnsTransaction *t) {
assert(t);
if (t->stream) {
/* Let's detach the stream from our transaction, in case something else keeps a reference to it. */
LIST_REMOVE(transactions_by_stream, t->stream->transactions, t);
/* Remove packet in case it's still in the queue */
dns_packet_unref(ordered_set_remove(t->stream->write_queue, t->sent));
t->stream = dns_stream_unref(t->stream);
}
t->dns_udp_event_source = sd_event_source_unref(t->dns_udp_event_source);
t->dns_udp_fd = safe_close(t->dns_udp_fd);
}
static void dns_transaction_stop_timeout(DnsTransaction *t) {
assert(t);
t->timeout_event_source = sd_event_source_unref(t->timeout_event_source);
}
DnsTransaction* dns_transaction_free(DnsTransaction *t) {
DnsQueryCandidate *c;
DnsZoneItem *i;
DnsTransaction *z;
if (!t)
return NULL;
log_debug("Freeing transaction %" PRIu16 ".", t->id);
dns_transaction_close_connection(t);
dns_transaction_stop_timeout(t);
dns_packet_unref(t->sent);
dns_transaction_reset_answer(t);
dns_server_unref(t->server);
if (t->scope) {
hashmap_remove_value(t->scope->transactions_by_key, t->key, t);
LIST_REMOVE(transactions_by_scope, t->scope->transactions, t);
if (t->id != 0)
hashmap_remove(t->scope->manager->dns_transactions, UINT_TO_PTR(t->id));
}
while ((c = set_steal_first(t->notify_query_candidates)))
set_remove(c->transactions, t);
set_free(t->notify_query_candidates);
while ((c = set_steal_first(t->notify_query_candidates_done)))
set_remove(c->transactions, t);
set_free(t->notify_query_candidates_done);
while ((i = set_steal_first(t->notify_zone_items)))
i->probe_transaction = NULL;
set_free(t->notify_zone_items);
while ((i = set_steal_first(t->notify_zone_items_done)))
i->probe_transaction = NULL;
set_free(t->notify_zone_items_done);
while ((z = set_steal_first(t->notify_transactions)))
set_remove(z->dnssec_transactions, t);
set_free(t->notify_transactions);
while ((z = set_steal_first(t->notify_transactions_done)))
set_remove(z->dnssec_transactions, t);
set_free(t->notify_transactions_done);
dns_transaction_flush_dnssec_transactions(t);
set_free(t->dnssec_transactions);
dns_answer_unref(t->validated_keys);
dns_resource_key_unref(t->key);
return mfree(t);
}
DEFINE_TRIVIAL_CLEANUP_FUNC(DnsTransaction*, dns_transaction_free);
bool dns_transaction_gc(DnsTransaction *t) {
assert(t);
if (t->block_gc > 0)
return true;
if (set_isempty(t->notify_query_candidates) &&
set_isempty(t->notify_query_candidates_done) &&
set_isempty(t->notify_zone_items) &&
set_isempty(t->notify_zone_items_done) &&
set_isempty(t->notify_transactions) &&
set_isempty(t->notify_transactions_done)) {
dns_transaction_free(t);
return false;
}
return true;
}
static uint16_t pick_new_id(Manager *m) {
uint16_t new_id;
/* Find a fresh, unused transaction id. Note that this loop is bounded because there's a limit on the
* number of transactions, and it's much lower than the space of IDs. */
assert_cc(TRANSACTIONS_MAX < 0xFFFF);
do
random_bytes(&new_id, sizeof(new_id));
while (new_id == 0 ||
hashmap_get(m->dns_transactions, UINT_TO_PTR(new_id)));
return new_id;
}
int dns_transaction_new(DnsTransaction **ret, DnsScope *s, DnsResourceKey *key) {
_cleanup_(dns_transaction_freep) DnsTransaction *t = NULL;
int r;
assert(ret);
assert(s);
assert(key);
/* Don't allow looking up invalid or pseudo RRs */
if (!dns_type_is_valid_query(key->type))
return -EINVAL;
if (dns_type_is_obsolete(key->type))
return -EOPNOTSUPP;
/* We only support the IN class */
if (!IN_SET(key->class, DNS_CLASS_IN, DNS_CLASS_ANY))
return -EOPNOTSUPP;
if (hashmap_size(s->manager->dns_transactions) >= TRANSACTIONS_MAX)
return -EBUSY;
r = hashmap_ensure_allocated(&s->manager->dns_transactions, NULL);
if (r < 0)
return r;
r = hashmap_ensure_allocated(&s->transactions_by_key, &dns_resource_key_hash_ops);
if (r < 0)
return r;
t = new(DnsTransaction, 1);
if (!t)
return -ENOMEM;
*t = (DnsTransaction) {
.dns_udp_fd = -1,
.answer_source = _DNS_TRANSACTION_SOURCE_INVALID,
.answer_dnssec_result = _DNSSEC_RESULT_INVALID,
.answer_nsec_ttl = (uint32_t) -1,
.key = dns_resource_key_ref(key),
.current_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID,
.clamp_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID,
.id = pick_new_id(s->manager),
};
r = hashmap_put(s->manager->dns_transactions, UINT_TO_PTR(t->id), t);
if (r < 0) {
t->id = 0;
return r;
}
r = hashmap_replace(s->transactions_by_key, t->key, t);
if (r < 0) {
hashmap_remove(s->manager->dns_transactions, UINT_TO_PTR(t->id));
return r;
}
LIST_PREPEND(transactions_by_scope, s->transactions, t);
t->scope = s;
s->manager->n_transactions_total++;
if (ret)
*ret = t;
t = NULL;
return 0;
}
static void dns_transaction_shuffle_id(DnsTransaction *t) {
uint16_t new_id;
assert(t);
/* Pick a new ID for this transaction. */
new_id = pick_new_id(t->scope->manager);
assert_se(hashmap_remove_and_put(t->scope->manager->dns_transactions, UINT_TO_PTR(t->id), UINT_TO_PTR(new_id), t) >= 0);
log_debug("Transaction %" PRIu16 " is now %" PRIu16 ".", t->id, new_id);
t->id = new_id;
/* Make sure we generate a new packet with the new ID */
t->sent = dns_packet_unref(t->sent);
}
static void dns_transaction_tentative(DnsTransaction *t, DnsPacket *p) {
_cleanup_free_ char *pretty = NULL;
char key_str[DNS_RESOURCE_KEY_STRING_MAX];
DnsZoneItem *z;
assert(t);
assert(p);
if (manager_our_packet(t->scope->manager, p) != 0)
return;
(void) in_addr_to_string(p->family, &p->sender, &pretty);
log_debug("Transaction %" PRIu16 " for <%s> on scope %s on %s/%s got tentative packet from %s.",
t->id,
dns_resource_key_to_string(t->key, key_str, sizeof key_str),
dns_protocol_to_string(t->scope->protocol),
t->scope->link ? t->scope->link->ifname : "*",
af_to_name_short(t->scope->family),
strnull(pretty));
/* RFC 4795, Section 4.1 says that the peer with the
* lexicographically smaller IP address loses */
if (memcmp(&p->sender, &p->destination, FAMILY_ADDRESS_SIZE(p->family)) >= 0) {
log_debug("Peer has lexicographically larger IP address and thus lost in the conflict.");
return;
}
log_debug("We have the lexicographically larger IP address and thus lost in the conflict.");
t->block_gc++;
while ((z = set_first(t->notify_zone_items))) {
/* First, make sure the zone item drops the reference
* to us */
dns_zone_item_probe_stop(z);
/* Secondly, report this as conflict, so that we might
* look for a different hostname */
dns_zone_item_conflict(z);
}
t->block_gc--;
dns_transaction_gc(t);
}
void dns_transaction_complete(DnsTransaction *t, DnsTransactionState state) {
DnsQueryCandidate *c;
DnsZoneItem *z;
DnsTransaction *d;
const char *st;
char key_str[DNS_RESOURCE_KEY_STRING_MAX];
assert(t);
assert(!DNS_TRANSACTION_IS_LIVE(state));
if (state == DNS_TRANSACTION_DNSSEC_FAILED) {
dns_resource_key_to_string(t->key, key_str, sizeof key_str);
log_struct(LOG_NOTICE,
"MESSAGE_ID=" SD_MESSAGE_DNSSEC_FAILURE_STR,
LOG_MESSAGE("DNSSEC validation failed for question %s: %s", key_str, dnssec_result_to_string(t->answer_dnssec_result)),
"DNS_TRANSACTION=%" PRIu16, t->id,
"DNS_QUESTION=%s", key_str,
"DNSSEC_RESULT=%s", dnssec_result_to_string(t->answer_dnssec_result),
"DNS_SERVER=%s", strna(dns_server_string_full(t->server)),
"DNS_SERVER_FEATURE_LEVEL=%s", dns_server_feature_level_to_string(t->server->possible_feature_level));
}
/* Note that this call might invalidate the query. Callers
* should hence not attempt to access the query or transaction
* after calling this function. */
if (state == DNS_TRANSACTION_ERRNO)
st = errno_to_name(t->answer_errno);
else
st = dns_transaction_state_to_string(state);
log_debug("Transaction %" PRIu16 " for <%s> on scope %s on %s/%s now complete with <%s> from %s (%s).",
t->id,
dns_resource_key_to_string(t->key, key_str, sizeof key_str),
dns_protocol_to_string(t->scope->protocol),
t->scope->link ? t->scope->link->ifname : "*",
af_to_name_short(t->scope->family),
st,
t->answer_source < 0 ? "none" : dns_transaction_source_to_string(t->answer_source),
t->answer_authenticated ? "authenticated" : "unsigned");
t->state = state;
dns_transaction_close_connection(t);
dns_transaction_stop_timeout(t);
/* Notify all queries that are interested, but make sure the
* transaction isn't freed while we are still looking at it */
t->block_gc++;
SET_FOREACH_MOVE(c, t->notify_query_candidates_done, t->notify_query_candidates)
dns_query_candidate_notify(c);
SWAP_TWO(t->notify_query_candidates, t->notify_query_candidates_done);
SET_FOREACH_MOVE(z, t->notify_zone_items_done, t->notify_zone_items)
dns_zone_item_notify(z);
SWAP_TWO(t->notify_zone_items, t->notify_zone_items_done);
if (t->probing && t->state == DNS_TRANSACTION_ATTEMPTS_MAX_REACHED)
(void) dns_scope_announce(t->scope, false);
SET_FOREACH_MOVE(d, t->notify_transactions_done, t->notify_transactions)
dns_transaction_notify(d, t);
SWAP_TWO(t->notify_transactions, t->notify_transactions_done);
t->block_gc--;
dns_transaction_gc(t);
}
static void dns_transaction_complete_errno(DnsTransaction *t, int error) {
assert(t);
assert(error != 0);
t->answer_errno = abs(error);
dns_transaction_complete(t, DNS_TRANSACTION_ERRNO);
}
static int dns_transaction_pick_server(DnsTransaction *t) {
DnsServer *server;
assert(t);
assert(t->scope->protocol == DNS_PROTOCOL_DNS);
/* Pick a DNS server and a feature level for it. */
server = dns_scope_get_dns_server(t->scope);
if (!server)
return -ESRCH;
/* If we changed the server invalidate the feature level clamping, as the new server might have completely
* different properties. */
if (server != t->server)
t->clamp_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID;
t->current_feature_level = dns_server_possible_feature_level(server);
/* Clamp the feature level if that is requested. */
if (t->clamp_feature_level != _DNS_SERVER_FEATURE_LEVEL_INVALID &&
t->current_feature_level > t->clamp_feature_level)
t->current_feature_level = t->clamp_feature_level;
log_debug("Using feature level %s for transaction %u.", dns_server_feature_level_to_string(t->current_feature_level), t->id);
if (server == t->server)
return 0;
dns_server_unref(t->server);
t->server = dns_server_ref(server);
t->n_picked_servers ++;
log_debug("Using DNS server %s for transaction %u.", strna(dns_server_string_full(t->server)), t->id);
return 1;
}
static void dns_transaction_retry(DnsTransaction *t, bool next_server) {
int r;
assert(t);
log_debug("Retrying transaction %" PRIu16 ".", t->id);
/* Before we try again, switch to a new server. */
if (next_server)
dns_scope_next_dns_server(t->scope);
r = dns_transaction_go(t);
if (r < 0)
dns_transaction_complete_errno(t, r);
}
static int dns_transaction_maybe_restart(DnsTransaction *t) {
int r;
assert(t);
/* Returns > 0 if the transaction was restarted, 0 if not */
if (!t->server)
return 0;
if (t->current_feature_level <= dns_server_possible_feature_level(t->server))
return 0;
/* The server's current feature level is lower than when we sent the original query. We learnt something from
the response or possibly an auxiliary DNSSEC response that we didn't know before. We take that as reason to
restart the whole transaction. This is a good idea to deal with servers that respond rubbish if we include
OPT RR or DO bit. One of these cases is documented here, for example:
https://open.nlnetlabs.nl/pipermail/dnssec-trigger/2014-November/000376.html */
log_debug("Server feature level is now lower than when we began our transaction. Restarting with new ID.");
dns_transaction_shuffle_id(t);
r = dns_transaction_go(t);
if (r < 0)
return r;
return 1;
}
static void on_transaction_stream_error(DnsTransaction *t, int error) {
assert(t);
dns_transaction_close_connection(t);
if (ERRNO_IS_DISCONNECT(error)) {
if (t->scope->protocol == DNS_PROTOCOL_LLMNR) {
/* If the LLMNR/TCP connection failed, the host doesn't support LLMNR, and we cannot answer the
* question on this scope. */
dns_transaction_complete(t, DNS_TRANSACTION_NOT_FOUND);
return;
}
dns_transaction_retry(t, true);
return;
}
if (error != 0)
dns_transaction_complete_errno(t, error);
}
static int dns_transaction_on_stream_packet(DnsTransaction *t, DnsPacket *p) {
assert(t);
assert(p);
dns_transaction_close_connection(t);
if (dns_packet_validate_reply(p) <= 0) {
log_debug("Invalid TCP reply packet.");
dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
return 0;
}
dns_scope_check_conflicts(t->scope, p);
t->block_gc++;
dns_transaction_process_reply(t, p);
t->block_gc--;
/* If the response wasn't useful, then complete the transition
* now. After all, we are the worst feature set now with TCP
* sockets, and there's really no point in retrying. */
if (t->state == DNS_TRANSACTION_PENDING)
dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
else
dns_transaction_gc(t);
return 0;
}
static int on_stream_complete(DnsStream *s, int error) {
assert(s);
if (ERRNO_IS_DISCONNECT(error) && s->protocol != DNS_PROTOCOL_LLMNR) {
log_debug_errno(error, "Connection failure for DNS TCP stream: %m");
if (s->transactions) {
DnsTransaction *t;
t = s->transactions;
dns_server_packet_lost(t->server, IPPROTO_TCP, t->current_feature_level);
}
}
if (error != 0) {
DnsTransaction *t, *n;
LIST_FOREACH_SAFE(transactions_by_stream, t, n, s->transactions)
on_transaction_stream_error(t, error);
}
return 0;
}
static int on_stream_packet(DnsStream *s) {
_cleanup_(dns_packet_unrefp) DnsPacket *p = NULL;
DnsTransaction *t;
assert(s);
/* Take ownership of packet to be able to receive new packets */
p = dns_stream_take_read_packet(s);
assert(p);
t = hashmap_get(s->manager->dns_transactions, UINT_TO_PTR(DNS_PACKET_ID(p)));
if (t)
return dns_transaction_on_stream_packet(t, p);
/* Ignore incorrect transaction id as an old transaction can have been canceled. */
log_debug("Received unexpected TCP reply packet with id %" PRIu16 ", ignoring.", DNS_PACKET_ID(p));
return 0;
}
static uint16_t dns_transaction_port(DnsTransaction *t) {
if (t->server->port > 0)
return t->server->port;
return DNS_SERVER_FEATURE_LEVEL_IS_TLS(t->current_feature_level) ? 853 : 53;
}
static int dns_transaction_emit_tcp(DnsTransaction *t) {
_cleanup_(dns_stream_unrefp) DnsStream *s = NULL;
_cleanup_close_ int fd = -1;
union sockaddr_union sa;
DnsStreamType type;
int r;
assert(t);
dns_transaction_close_connection(t);
switch (t->scope->protocol) {
case DNS_PROTOCOL_DNS:
r = dns_transaction_pick_server(t);
if (r < 0)
return r;
if (!dns_server_dnssec_supported(t->server) && dns_type_is_dnssec(t->key->type))
return -EOPNOTSUPP;
r = dns_server_adjust_opt(t->server, t->sent, t->current_feature_level);
if (r < 0)
return r;
if (t->server->stream && (DNS_SERVER_FEATURE_LEVEL_IS_TLS(t->current_feature_level) == t->server->stream->encrypted))
s = dns_stream_ref(t->server->stream);
else
fd = dns_scope_socket_tcp(t->scope, AF_UNSPEC, NULL, t->server, dns_transaction_port(t), &sa);
type = DNS_STREAM_LOOKUP;
break;
case DNS_PROTOCOL_LLMNR:
/* When we already received a reply to this (but it was truncated), send to its sender address */
if (t->received)
fd = dns_scope_socket_tcp(t->scope, t->received->family, &t->received->sender, NULL, t->received->sender_port, &sa);
else {
union in_addr_union address;
int family = AF_UNSPEC;
/* Otherwise, try to talk to the owner of a
* the IP address, in case this is a reverse
* PTR lookup */
r = dns_name_address(dns_resource_key_name(t->key), &family, &address);
if (r < 0)
return r;
if (r == 0)
return -EINVAL;
if (family != t->scope->family)
return -ESRCH;
fd = dns_scope_socket_tcp(t->scope, family, &address, NULL, LLMNR_PORT, &sa);
}
type = DNS_STREAM_LLMNR_SEND;
break;
default:
return -EAFNOSUPPORT;
}
if (!s) {
if (fd < 0)
return fd;
r = dns_stream_new(t->scope->manager, &s, type, t->scope->protocol, fd, &sa);
if (r < 0)
return r;
fd = -1;
#if ENABLE_DNS_OVER_TLS
if (t->scope->protocol == DNS_PROTOCOL_DNS &&
DNS_SERVER_FEATURE_LEVEL_IS_TLS(t->current_feature_level)) {
assert(t->server);
r = dnstls_stream_connect_tls(s, t->server);
if (r < 0)
return r;
}
#endif
if (t->server) {
dns_server_unref_stream(t->server);
s->server = dns_server_ref(t->server);
t->server->stream = dns_stream_ref(s);
}
s->complete = on_stream_complete;
s->on_packet = on_stream_packet;
/* The interface index is difficult to determine if we are
* connecting to the local host, hence fill this in right away
* instead of determining it from the socket */
s->ifindex = dns_scope_ifindex(t->scope);
}
t->stream = TAKE_PTR(s);
LIST_PREPEND(transactions_by_stream, t->stream->transactions, t);
r = dns_stream_write_packet(t->stream, t->sent);
if (r < 0) {
dns_transaction_close_connection(t);
return r;
}
dns_transaction_reset_answer(t);
t->tried_stream = true;
return 0;
}
static void dns_transaction_cache_answer(DnsTransaction *t) {
assert(t);
/* For mDNS we cache whenever we get the packet, rather than
* in each transaction. */
if (!IN_SET(t->scope->protocol, DNS_PROTOCOL_DNS, DNS_PROTOCOL_LLMNR))
return;
/* Caching disabled? */
if (t->scope->manager->enable_cache == DNS_CACHE_MODE_NO)
return;
/* We never cache if this packet is from the local host, under
* the assumption that a locally running DNS server would
* cache this anyway, and probably knows better when to flush
* the cache then we could. */
if (!DNS_PACKET_SHALL_CACHE(t->received))
return;
dns_cache_put(&t->scope->cache,
t->scope->manager->enable_cache,
t->key,
t->answer_rcode,
t->answer,
t->answer_authenticated,
t->answer_nsec_ttl,
0,
t->received->family,
&t->received->sender);
}
static bool dns_transaction_dnssec_is_live(DnsTransaction *t) {
DnsTransaction *dt;
assert(t);
SET_FOREACH(dt, t->dnssec_transactions)
if (DNS_TRANSACTION_IS_LIVE(dt->state))
return true;
return false;
}
static int dns_transaction_dnssec_ready(DnsTransaction *t) {
DnsTransaction *dt;
assert(t);
/* Checks whether the auxiliary DNSSEC transactions of our transaction have completed, or are still
* ongoing. Returns 0, if we aren't ready for the DNSSEC validation, positive if we are. */
SET_FOREACH(dt, t->dnssec_transactions) {
switch (dt->state) {
case DNS_TRANSACTION_NULL:
case DNS_TRANSACTION_PENDING:
case DNS_TRANSACTION_VALIDATING:
/* Still ongoing */
return 0;
case DNS_TRANSACTION_RCODE_FAILURE:
if (!IN_SET(dt->answer_rcode, DNS_RCODE_NXDOMAIN, DNS_RCODE_SERVFAIL)) {
log_debug("Auxiliary DNSSEC RR query failed with rcode=%s.", dns_rcode_to_string(dt->answer_rcode));
goto fail;
}
/* Fall-through: NXDOMAIN/SERVFAIL is good enough for us. This is because some DNS servers
* erroneously return NXDOMAIN/SERVFAIL for empty non-terminals (Akamai...) or missing DS
* records (Facebook), and we need to handle that nicely, when asking for parent SOA or similar
* RRs to make unsigned proofs. */
case DNS_TRANSACTION_SUCCESS:
/* All good. */
break;
case DNS_TRANSACTION_DNSSEC_FAILED:
/* We handle DNSSEC failures different from other errors, as we care about the DNSSEC
* validationr result */
log_debug("Auxiliary DNSSEC RR query failed validation: %s", dnssec_result_to_string(dt->answer_dnssec_result));
t->answer_dnssec_result = dt->answer_dnssec_result; /* Copy error code over */
dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
return 0;
default:
log_debug("Auxiliary DNSSEC RR query failed with %s", dns_transaction_state_to_string(dt->state));
goto fail;
}
}
/* All is ready, we can go and validate */
return 1;
fail:
t->answer_dnssec_result = DNSSEC_FAILED_AUXILIARY;
dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
return 0;
}
static void dns_transaction_process_dnssec(DnsTransaction *t) {
int r;
assert(t);
/* Are there ongoing DNSSEC transactions? If so, let's wait for them. */
r = dns_transaction_dnssec_ready(t);
if (r < 0)
goto fail;
if (r == 0) /* We aren't ready yet (or one of our auxiliary transactions failed, and we shouldn't validate now */
return;
/* See if we learnt things from the additional DNSSEC transactions, that we didn't know before, and better
* restart the lookup immediately. */
r = dns_transaction_maybe_restart(t);
if (r < 0)
goto fail;
if (r > 0) /* Transaction got restarted... */
return;
/* All our auxiliary DNSSEC transactions are complete now. Try
* to validate our RRset now. */
r = dns_transaction_validate_dnssec(t);
if (r == -EBADMSG) {
dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
return;
}
if (r < 0)
goto fail;
if (t->answer_dnssec_result == DNSSEC_INCOMPATIBLE_SERVER &&
t->scope->dnssec_mode == DNSSEC_YES) {
/* We are not in automatic downgrade mode, and the server is bad. Let's try a different server, maybe
* that works. */
if (t->n_picked_servers < dns_scope_get_n_dns_servers(t->scope)) {
/* We tried fewer servers on this transaction than we know, let's try another one then */
dns_transaction_retry(t, true);
return;
}
/* OK, let's give up, apparently all servers we tried didn't work. */
dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
return;
}
if (!IN_SET(t->answer_dnssec_result,
_DNSSEC_RESULT_INVALID, /* No DNSSEC validation enabled */
DNSSEC_VALIDATED, /* Answer is signed and validated successfully */
DNSSEC_UNSIGNED, /* Answer is right-fully unsigned */
DNSSEC_INCOMPATIBLE_SERVER)) { /* Server does not do DNSSEC (Yay, we are downgrade attack vulnerable!) */
dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
return;
}
if (t->answer_dnssec_result == DNSSEC_INCOMPATIBLE_SERVER)
dns_server_warn_downgrade(t->server);
dns_transaction_cache_answer(t);
if (t->answer_rcode == DNS_RCODE_SUCCESS)
dns_transaction_complete(t, DNS_TRANSACTION_SUCCESS);
else
dns_transaction_complete(t, DNS_TRANSACTION_RCODE_FAILURE);
return;
fail:
dns_transaction_complete_errno(t, r);
}
static int dns_transaction_has_positive_answer(DnsTransaction *t, DnsAnswerFlags *flags) {
int r;
assert(t);
/* Checks whether the answer is positive, i.e. either a direct
* answer to the question, or a CNAME/DNAME for it */
r = dns_answer_match_key(t->answer, t->key, flags);
if (r != 0)
return r;
r = dns_answer_find_cname_or_dname(t->answer, t->key, NULL, flags);
if (r != 0)
return r;
return false;
}
static int dns_transaction_fix_rcode(DnsTransaction *t) {
int r;
assert(t);
/* Fix up the RCODE to SUCCESS if we get at least one matching RR in a response. Note that this contradicts the
* DNS RFCs a bit. Specifically, RFC 6604 Section 3 clarifies that the RCODE shall say something about a
* CNAME/DNAME chain element coming after the last chain element contained in the message, and not the first
* one included. However, it also indicates that not all DNS servers implement this correctly. Moreover, when
* using DNSSEC we usually only can prove the first element of a CNAME/DNAME chain anyway, hence let's settle
* on always processing the RCODE as referring to the immediate look-up we do, i.e. the first element of a
* CNAME/DNAME chain. This way, we uniformly handle CNAME/DNAME chains, regardless if the DNS server
* incorrectly implements RCODE, whether DNSSEC is in use, or whether the DNS server only supplied us with an
* incomplete CNAME/DNAME chain.
*
* Or in other words: if we get at least one positive reply in a message we patch NXDOMAIN to become SUCCESS,
* and then rely on the CNAME chasing logic to figure out that there's actually a CNAME error with a new
* lookup. */
if (t->answer_rcode != DNS_RCODE_NXDOMAIN)
return 0;
r = dns_transaction_has_positive_answer(t, NULL);
if (r <= 0)
return r;
t->answer_rcode = DNS_RCODE_SUCCESS;
return 0;
}
void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p) {
usec_t ts;
int r;
assert(t);
assert(p);
assert(t->scope);
assert(t->scope->manager);
if (t->state != DNS_TRANSACTION_PENDING)
return;
/* Note that this call might invalidate the query. Callers
* should hence not attempt to access the query or transaction
* after calling this function. */
log_debug("Processing incoming packet on transaction %" PRIu16" (rcode=%s).",
t->id, dns_rcode_to_string(DNS_PACKET_RCODE(p)));
switch (t->scope->protocol) {
case DNS_PROTOCOL_LLMNR:
/* For LLMNR we will not accept any packets from other interfaces */
if (p->ifindex != dns_scope_ifindex(t->scope))
return;
if (p->family != t->scope->family)
return;
/* Tentative packets are not full responses but still
* useful for identifying uniqueness conflicts during
* probing. */
if (DNS_PACKET_LLMNR_T(p)) {
dns_transaction_tentative(t, p);
return;
}
break;
case DNS_PROTOCOL_MDNS:
/* For mDNS we will not accept any packets from other interfaces */
if (p->ifindex != dns_scope_ifindex(t->scope))
return;
if (p->family != t->scope->family)
return;
break;
case DNS_PROTOCOL_DNS:
/* Note that we do not need to verify the
* addresses/port numbers of incoming traffic, as we
* invoked connect() on our UDP socket in which case
* the kernel already does the needed verification for
* us. */
break;
default:
assert_not_reached("Invalid DNS protocol.");
}
if (t->received != p) {
dns_packet_unref(t->received);
t->received = dns_packet_ref(p);
}
t->answer_source = DNS_TRANSACTION_NETWORK;
if (p->ipproto == IPPROTO_TCP) {
if (DNS_PACKET_TC(p)) {
/* Truncated via TCP? Somebody must be fucking with us */
dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
return;
}
if (DNS_PACKET_ID(p) != t->id) {
/* Not the reply to our query? Somebody must be fucking with us */
dns_transaction_complete(t, DNS_TRANSACTION_INVALID_REPLY);
return;
}
}
assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
switch (t->scope->protocol) {
case DNS_PROTOCOL_DNS:
assert(t->server);
if (IN_SET(DNS_PACKET_RCODE(p), DNS_RCODE_FORMERR, DNS_RCODE_SERVFAIL, DNS_RCODE_NOTIMP)) {
/* Request failed, immediately try again with reduced features */
if (t->current_feature_level <= DNS_SERVER_FEATURE_LEVEL_UDP) {
/* This was already at UDP feature level? If so, it doesn't make sense to downgrade
* this transaction anymore, but let's see if it might make sense to send the request
* to a different DNS server instead. If not let's process the response, and accept the
* rcode. Note that we don't retry on TCP, since that's a suitable way to mitigate
* packet loss, but is not going to give us better rcodes should we actually have
* managed to get them already at UDP level. */
if (t->n_picked_servers < dns_scope_get_n_dns_servers(t->scope)) {
/* We tried fewer servers on this transaction than we know, let's try another one then */
dns_transaction_retry(t, true);