bug #10609: CVE-2014-0239 Don't reply to replies

Due to insufficient input checking, the DNS server will reply to a packet that
has the "reply" bit set. Over UDP, this allows to send a packet with a spoofed
sender address and have two servers DOS each other with circular replies.

This patch fixes bug #10609 and adds a test to make sure we don't regress.
CVE-2014-2039 has been assigned to this issue.
Bug: https://bugzilla.samba.org/show_bug.cgi?id=10609

Signed-off-by: Kai Blin <kai@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>

Autobuild-User(master): Kai Blin <kai@samba.org>
Autobuild-Date(master): Tue May 20 04:15:44 CEST 2014 on sn-devel-104

2 files changed, 35 insertions, 0 deletions

diff --git a/python/samba/tests/dns.py b/python/samba/tests/dns.py
index 9c0b27471a7..400321fe161 100644
--- a/python/samba/tests/dns.py
+++ b/python/samba/tests/dns.py
@@ -833,6 +833,35 @@ class TestInvalidQueries(DNSTest):
         self.assertEquals(response.answers[0].rdata,
                           os.getenv('SERVER_IP'))
 
+    def test_one_a_reply(self):
+        "send a reply instead of a query"
+
+        p = self.make_name_packet(dns.DNS_OPCODE_QUERY)
+        questions = []
+
+        name = "%s.%s" % ('fakefakefake', self.get_dns_domain())
+        q = self.make_name_question(name, dns.DNS_QTYPE_A, dns.DNS_QCLASS_IN)
+        print "asking for ", q.name
+        questions.append(q)
+
+        self.finish_name_packet(p, questions)
+        p.operation |= dns.DNS_FLAG_REPLY
+        s = None
+        try:
+            send_packet = ndr.ndr_pack(p)
+            s = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
+            host=os.getenv('SERVER_IP')
+            s.connect((host, 53))
+            tcp_packet = struct.pack('!H', len(send_packet))
+            tcp_packet += send_packet
+            s.send(tcp_packet, 0)
+            recv_packet = s.recv(0xffff + 2, 0)
+            self.assertEquals(0, len(recv_packet))
+        finally:
+            if s is not None:
+                s.close()
+
+
 if __name__ == "__main__":
     import unittest
     unittest.main()
diff --git a/source4/dns_server/dns_server.c b/source4/dns_server/dns_server.c
index 976774d020f..60ce27c6ff9 100644
--- a/source4/dns_server/dns_server.c
+++ b/source4/dns_server/dns_server.c
@@ -156,6 +156,12 @@ static struct tevent_req *dns_process_send(TALLOC_CTX *mem_ctx,
 		return tevent_req_post(req, ev);
 	}
 
+	if (state->in_packet.operation & DNS_FLAG_REPLY) {
+		DEBUG(1, ("Won't reply to replies.\n"));
+		tevent_req_werror(req, WERR_INVALID_PARAM);
+		return tevent_req_post(req, ev);
+	}
+
 	state->state.flags = state->in_packet.operation;
 	state->state.flags |= DNS_FLAG_REPLY;