Check the instance of ADDR_ENTRY[0] (#4565)

* Check the instance of ADDR_ENTRY[0]

* Update test/scapy/layers/netbios.uts

Co-authored-by: gpotter2 <10530980+gpotter2@users.noreply.github.com>

---------

Co-authored-by: gpotter2 <10530980+gpotter2@users.noreply.github.com>

Author: guedou

scapy/layers/netbios.py

@@ -185,7 +185,8 @@ class NBNSQueryResponse(Packet):
                    ]
 
     def mysummary(self):
-        if not self.ADDR_ENTRY:
+        if not self.ADDR_ENTRY or \
+           not isinstance(self.ADDR_ENTRY[0], NBNS_ADD_ENTRY):
             return "NBNSQueryResponse"
         return "NBNSQueryResponse '\\\\%s' is at %s" % (
             self.RR_NAME.decode(errors="backslashreplace"),

test/scapy/layers/netbios.uts

@@ -99,3 +99,11 @@ assert pkt[NBNSWackResponse].RR_NAME == b'SARAH'
 z = raw(TCP()/NBTSession())
 assert z == b'\x00\x8b\x00\x8b\x00\x00\x00\x00\x00\x00\x00\x00P\x02 \x00\x00\x00\x00\x00\x00\x00\x00\x00'
 assert NBTSession in TCP(z)
+
+= OSS-Fuzz Findings
+
+# Note: the packet is corrupted
+with no_debug_dissector():
+    raw_packet = b'E\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x05\x00\x00\x00'
+    packet = NBNSQueryResponse(raw_packet)
+    assert packet.summary() == "NBNSQueryResponse"