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Merge pull request #18636 from poettering/resolved-different-server

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resolved: tweaks for switching to different DNS servers
This commit is contained in:
Lennart Poettering 2021-02-16 20:27:09 +01:00 committed by GitHub
commit a9a43d8aa2
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1 changed files with 38 additions and 15 deletions
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53
src/resolve/resolved-dns-transaction.c
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@ -502,7 +502,12 @@ static void dns_transaction_retry(DnsTransaction *t, bool next_server) {
assert(t);
log_debug("Retrying transaction %" PRIu16 ".", t->id);
/* Retries the transaction as it is, possibly on a different server */
if (next_server)
log_debug("Retrying transaction %" PRIu16 ", after switching servers.", t->id);
else
log_debug("Retrying transaction %" PRIu16 ".", t->id);
/* Before we try again, switch to a new server. */
if (next_server)
@ -513,12 +518,25 @@ static void dns_transaction_retry(DnsTransaction *t, bool next_server) {
dns_transaction_complete_errno(t, r);
}
static bool dns_transaction_limited_retry(DnsTransaction *t) {
assert(t);
/* If we haven't tried all different servers yet, let's try again with a different server */
if (t->n_picked_servers >= dns_scope_get_n_dns_servers(t->scope))
return false;
dns_transaction_retry(t, /* next_server= */ true);
return true;
}
static int dns_transaction_maybe_restart(DnsTransaction *t) {
int r;
assert(t);
/* Returns > 0 if the transaction was restarted, 0 if not */
/* Restarts the transaction, under a new ID if the feature level of the server changed since we first
* tried, without changing DNS server. Returns > 0 if the transaction was restarted, 0 if not. */
if (!t->server)
return 0;
@ -911,11 +929,8 @@ static void dns_transaction_process_dnssec(DnsTransaction *t) {
/* 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);
if (dns_transaction_limited_retry(t))
return;
}
/* OK, let's give up, apparently all servers we tried didn't work. */
dns_transaction_complete(t, DNS_TRANSACTION_DNSSEC_FAILED);
@ -1098,11 +1113,8 @@ void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p, bool encrypt
* 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);
if (dns_transaction_limited_retry(t))
return;
}
/* Give up, accept the rcode */
log_debug("Server returned error: %s", dns_rcode_to_string(DNS_PACKET_RCODE(p)));
@ -1133,8 +1145,11 @@ void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p, bool encrypt
if (DNS_PACKET_RCODE(p) == DNS_RCODE_REFUSED) {
/* This server refused our request? If so, try again, use a different server */
log_debug("Server returned REFUSED, switching servers, and retrying.");
dns_transaction_retry(t, true /* pick a new server */);
return;
if (dns_transaction_limited_retry(t))
return;
break;
}
if (DNS_PACKET_TC(p))
@ -1180,7 +1195,11 @@ void dns_transaction_process_reply(DnsTransaction *t, DnsPacket *p, bool encrypt
goto fail;
/* On DNS, couldn't send? Try immediately again, with a new server */
dns_transaction_retry(t, true);
if (dns_transaction_limited_retry(t))
return;
/* No new server to try, give up */
dns_transaction_complete(t, DNS_TRANSACTION_ATTEMPTS_MAX_REACHED);
}
return;
@ -1306,7 +1325,10 @@ static int on_dns_packet(sd_event_source *s, int fd, uint32_t revents, void *use
dns_transaction_close_connection(t, /* use_graveyard = */ false);
dns_transaction_retry(t, true);
if (dns_transaction_limited_retry(t)) /* Try a different server */
return 0;
dns_transaction_complete_errno(t, r);
return 0;
}
if (r < 0) {
@ -1425,7 +1447,8 @@ static int on_transaction_timeout(sd_event_source *s, usec_t usec, void *userdat
log_debug("Timeout reached on transaction %" PRIu16 ".", t->id);
dns_transaction_retry(t, true);
dns_transaction_retry(t, true); /* try a different server, but given this means packet loss, let's do
* so even if we already tried a bunch */
return 0;
}