resolved: when caching negative responses, honour NSEC/NSEC3 TTLs

When storing negative responses, clamp the SOA minimum TTL (as suggested
by RFC2308) to the TTL of the NSEC/NSEC3 RRs we used to prove
non-existance, if it there is any.

This is necessary since otherwise an attacker might put together a faked
negative response for one of our question including a high-ttl SOA RR
for any parent zone, and we'd use trust the TTL.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/resolve/resolved-dns-dnssec.h b/src/resolve/resolved-dns-dnssec.h
index df377c8016..94d0b23f80 100644
--- a/src/resolve/resolved-dns-dnssec.h
+++ b/src/resolve/resolved-dns-dnssec.h
@@ -99,7 +99,7 @@ typedef enum DnssecNsecResult {
         DNSSEC_NSEC_OPTOUT,
 } DnssecNsecResult;
 
-int dnssec_test_nsec(DnsAnswer *answer, DnsResourceKey *key, DnssecNsecResult *result, bool *authenticated);
+int dnssec_test_nsec(DnsAnswer *answer, DnsResourceKey *key, DnssecNsecResult *result, bool *authenticated, uint32_t *ttl);
 
 const char* dnssec_mode_to_string(DnssecMode m) _const_;
 DnssecMode dnssec_mode_from_string(const char *s) _pure_;