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 <aaronhaslett@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>

diff --git a/python/samba/tests/dns.py b/python/samba/tests/dns.py
index 56609769a4f6abccf05ac378fca7a85e84a92399..e35cded7b8c0ce4c777d7ae795164dbfcfc09c07 100644 (file)
--- a/python/samba/tests/dns.py
+++ b/python/samba/tests/dns.py
@@ -846,6 +846,28 @@ 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):

diff --git a/selftest/knownfail.d/dns b/selftest/knownfail.d/dns
index 0f6caba8916e3bb3d55088c0778263f1f513259d..39b337ed6bb73f1fbbdaf46bb39781c2fefc3365 100644 (file)
--- a/selftest/knownfail.d/dns
+++ b/selftest/knownfail.d/dns
@@ -71,3 +71,9 @@ samba.tests.dns.__main__.TestSimpleQueries.test_qtype_all_query\(rodc:local\)
 
 # The SOA override should not pass against the RODC, it must not overstamp
 samba.tests.dns.__main__.TestSimpleQueries.test_one_SOA_query\(rodc:local\)
+
+#
+# rodc and vampire_dc require signed dns updates, so the test setup
+# fails, but the test does run on fl2003dc
+^samba.tests.dns.__main__.TestComplexQueries.test_cname_loop\(rodc:local\)
+^samba.tests.dns.__main__.TestComplexQueries.test_cname_loop\(vampire_dc:local\)

diff --git a/source4/dns_server/dns_query.c b/source4/dns_server/dns_query.c
index 923f7233eb995baaa524621567a75e981a0f32c5..65faeac3b6a4c89657e33122ebfe493d41b9efb7 100644 (file)
--- 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;
@@ -419,6 +420,11 @@ 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)));