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dns-answer: preserve shared aliases when removing records

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dns_answer_remove_by_rr() mutats the backing OrderedSet even when the answer
has multiple references. Callers such as trust-anchor revocation could thus
change snapshots held elsewhere in the resolver.

Clone a shared answer before removal.

Follow-up for 71aee23dba
This commit is contained in:
Luca Boccassi
2026-07-13 15:04:35 +01:00
parent 3734b69f03
commit e509a6a4cb
2 changed files with 32 additions and 1 deletions
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17
src/resolve/test-dns-answer.c
View File

@@ -371,6 +371,23 @@ TEST(dns_answer_remove_by_rr) {
ASSERT_NULL(answer);
}
TEST(dns_answer_remove_shared) {
_cleanup_(dns_answer_unrefp) DnsAnswer *answer = prepare_answer(), *alias = NULL;
_cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
alias = dns_answer_ref(answer);
ASSERT_PTR_EQ(alias, answer);
rr = ASSERT_NOT_NULL(dns_resource_record_new_full(DNS_CLASS_IN, DNS_TYPE_A, "b.example.com"));
rr->a.in_addr.s_addr = htobe32(0xc0a8017f);
ASSERT_OK_POSITIVE(dns_answer_remove_by_rr(&answer, rr));
ASSERT_EQ(dns_answer_size(answer), 2u);
ASSERT_EQ(dns_answer_size(alias), 3u);
ASSERT_FALSE(dns_answer_contains(answer, rr));
ASSERT_TRUE(dns_answer_contains(alias, rr));
}
TEST(dns_answer_remove_by_answer_keys) {
_cleanup_(dns_answer_unrefp) DnsAnswer *a = prepare_answer(), *b = prepare_answer();
DnsResourceKey *key;

16
src/shared/dns-answer.c
View File

@@ -555,14 +555,28 @@ int dns_answer_remove_by_rr(DnsAnswer **a, DnsResourceRecord *rr) {
if (r < 0)
return r;
if (r > 0) {
dns_answer_item_unref(ordered_set_remove((*a)->items, item));
found = true;
break;
}
}
if (!found)
return 0;
if ((*a)->n_ref > 1) {
r = dns_answer_reserve_or_clone(a, 1);
if (r < 0)
return r;
}
DNS_ANSWER_FOREACH_ITEM(item, *a) {
r = dns_resource_record_equal(item->rr, rr);
if (r < 0)
return r;
if (r > 0)
dns_answer_item_unref(ordered_set_remove((*a)->items, item));
}
if (dns_answer_isempty(*a))
*a = dns_answer_unref(*a); /* Return NULL for the empty answer */