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-rw-r--r--src/resolve/resolved-dns-answer.c24
1 files changed, 21 insertions, 3 deletions
diff --git a/src/resolve/resolved-dns-answer.c b/src/resolve/resolved-dns-answer.c
index 399b518644..445999f545 100644
--- a/src/resolve/resolved-dns-answer.c
+++ b/src/resolve/resolved-dns-answer.c
@@ -125,10 +125,13 @@ int dns_answer_add(DnsAnswer *a, DnsResourceRecord *rr, int ifindex, DnsAnswerFl
if (r < 0)
return r;
if (r > 0) {
- /* Entry already exists, keep the entry with
- * the higher RR, or the one with TTL 0 */
+ /* Don't mix contradicting TTLs (see below) */
+ if ((rr->ttl == 0) != (a->items[i].rr->ttl == 0))
+ return -EINVAL;
- if (rr->ttl == 0 || (rr->ttl > a->items[i].rr->ttl && a->items[i].rr->ttl != 0)) {
+ /* Entry already exists, keep the entry with
+ * the higher RR. */
+ if (rr->ttl > a->items[i].rr->ttl) {
dns_resource_record_ref(rr);
dns_resource_record_unref(a->items[i].rr);
a->items[i].rr = rr;
@@ -137,6 +140,21 @@ int dns_answer_add(DnsAnswer *a, DnsResourceRecord *rr, int ifindex, DnsAnswerFl
a->items[i].flags |= flags;
return 0;
}
+
+ r = dns_resource_key_equal(a->items[i].rr->key, rr->key);
+ if (r < 0)
+ return r;
+ if (r > 0) {
+ /* There's already an RR of the same RRset in
+ * place! Let's see if the TTLs more or less
+ * match. We don't really care if they match
+ * precisely, but we do care whether one is 0
+ * and the other is not. See RFC 2181, Section
+ * 5.2.*/
+
+ if ((rr->ttl == 0) != (a->items[i].rr->ttl == 0))
+ return -EINVAL;
+ }
}
return dns_answer_add_raw(a, rr, ifindex, flags);