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resolved: when restarting a transaction make sure to not touch it anymore (#3553) 

dns_transaction_maybe_restart() is supposed to return 1 if the the transaction
has been restarted and 0 otherwise. dns_transaction_process_dnssec() relies on
this behaviour. Before this change in case of restart we'd call
dns_transaction_go() when restarting the lookup, returning its return value
unmodified. This is wrong however, as that function returns 1 if the
transaction is pending, and 0 if it completed immediately, which is a very
different set of return values. Fix this, by always returning 1 on redirection.

The wrong return value resulted in all kinds of bad memory accesses as we might
continue processing a transaction that was redirected and completed immediately
(and thus freed).

This patch also adds comments to the two functions to clarify the return values
for the future.

Most likely fixes: #2942 #3475 #3484
This commit is contained in:
Lennart Poettering 2016-06-16 18:37:11 +02:00 committed by GitHub
parent 79e21f7a71
commit 5278bbfe0c
1 changed files with 13 additions and 1 deletions
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14
src/resolve/resolved-dns-transaction.c
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@ -404,8 +404,12 @@ static void dns_transaction_retry(DnsTransaction *t) {
}
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;
@ -420,7 +424,12 @@ static int dns_transaction_maybe_restart(DnsTransaction *t) {
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);
r = dns_transaction_go(t);
if (r < 0)
return r;
return 1;
}
static int on_stream_complete(DnsStream *s, int error) {
@ -1421,6 +1430,9 @@ int dns_transaction_go(DnsTransaction *t) {
assert(t);
/* Returns > 0 if the transaction is now pending, returns 0 if could be processed immediately and has finished
* now. */
assert_se(sd_event_now(t->scope->manager->event, clock_boottime_or_monotonic(), &ts) >= 0);
r = dns_transaction_prepare(t, ts);