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resolved: when restarting a transaction pick a new ID 

When we restart a transaction because of an incompatible server, pick a new transaction ID.

This should increase compatibility with DNS servers that don't like if they get different requests with the same
transaction ID.
This commit is contained in:
Lennart Poettering 2016-01-18 23:27:16 +01:00
parent b214dc0f68
commit 4dd15077f3
1 changed files with 35 additions and 6 deletions
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41
src/resolve/resolved-dns-transaction.c
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@ -137,6 +137,22 @@ bool dns_transaction_gc(DnsTransaction *t) {
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;
@ -177,11 +193,7 @@ int dns_transaction_new(DnsTransaction **ret, DnsScope *s, DnsResourceKey *key)
t->key = dns_resource_key_ref(key);
t->current_feature_level = _DNS_SERVER_FEATURE_LEVEL_INVALID;
/* Find a fresh, unused transaction id */
do
random_bytes(&t->id, sizeof(t->id));
while (t->id == 0 ||
hashmap_get(s->manager->dns_transactions, UINT_TO_PTR(t->id)));
t->id = pick_new_id(s->manager);
r = hashmap_put(s->manager->dns_transactions, UINT_TO_PTR(t->id), t);
if (r < 0) {
@ -208,6 +220,22 @@ int dns_transaction_new(DnsTransaction **ret, DnsScope *s, DnsResourceKey *key)
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;
DnsZoneItem *z;
@ -382,7 +410,8 @@ static int dns_transaction_maybe_restart(DnsTransaction *t) {
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.");
log_debug("Server feature level is now lower than when we began our transaction. Restarting with new ID.");
dns_transaction_shuffle_id(t);
return dns_transaction_go(t);
}