From 5cca15faf08b62bf6e8c3ae0d5d52f12aaab7dd6 Mon Sep 17 00:00:00 2001 From: Aaron Haslett Date: Tue, 23 Oct 2018 17:25:51 +1300 Subject: [PATCH] CVE-2018-14629 dns: CNAME loop prevention using counter Count number of answers generated by internal DNS query routine and stop at 20 to match Microsoft's loop prevention mechanism. BUG: https://bugzilla.samba.org/show_bug.cgi?id=13600 Signed-off-by: Aaron Haslett Reviewed-by: Andrew Bartlett Reviewed-by: Garming Sam --- python/samba/tests/dns.py | 24 ++++++++++++++++++++++++ source4/dns_server/dns_query.c | 6 ++++++ 2 files changed, 30 insertions(+) diff --git a/python/samba/tests/dns.py b/python/samba/tests/dns.py index 1b5b64da3a4..3390a3990c9 100644 --- a/python/samba/tests/dns.py +++ b/python/samba/tests/dns.py @@ -798,6 +798,30 @@ class TestComplexQueries(DNSTest): self.assertEquals(response.answers[1].name, name2) self.assertEquals(response.answers[1].rdata, name0) + def test_cname_loop(self): + cname1 = "cnamelooptestrec." + self.get_dns_domain() + cname2 = "cnamelooptestrec2." + self.get_dns_domain() + cname3 = "cnamelooptestrec3." + self.get_dns_domain() + self.make_dns_update(cname1, cname2, dnsp.DNS_TYPE_CNAME) + self.make_dns_update(cname2, cname3, dnsp.DNS_TYPE_CNAME) + self.make_dns_update(cname3, cname1, dnsp.DNS_TYPE_CNAME) + + p = self.make_name_packet(dns.DNS_OPCODE_QUERY) + questions = [] + + q = self.make_name_question(cname1, + dns.DNS_QTYPE_A, + dns.DNS_QCLASS_IN) + questions.append(q) + self.finish_name_packet(p, questions) + + (response, response_packet) =\ + self.dns_transaction_udp(p, host=self.server_ip) + + max_recursion_depth = 20 + self.assertEquals(len(response.answers), max_recursion_depth) + + class TestInvalidQueries(DNSTest): def setUp(self): super(TestInvalidQueries, self).setUp() diff --git a/source4/dns_server/dns_query.c b/source4/dns_server/dns_query.c index e8de304c8bb..fafadb6ac6f 100644 --- a/source4/dns_server/dns_query.c +++ b/source4/dns_server/dns_query.c @@ -40,6 +40,7 @@ #undef DBGC_CLASS #define DBGC_CLASS DBGC_DNS +#define MAX_Q_RECURSION_DEPTH 20 struct forwarder_string { const char *forwarder; @@ -470,6 +471,11 @@ static struct tevent_req *handle_dnsrpcrec_send( state->answers = answers; state->nsrecs = nsrecs; + if (talloc_array_length(*answers) >= MAX_Q_RECURSION_DEPTH) { + tevent_req_done(req); + return tevent_req_post(req, ev); + } + resolve_cname = ((rec->wType == DNS_TYPE_CNAME) && ((question->question_type == DNS_QTYPE_A) || (question->question_type == DNS_QTYPE_AAAA))); -- 2.11.0