[LLMNR] tolerate malformed queries/responses (#4381)

when showing summaries.

Now that the question and answer sections are PacketListFields they can
contain Raw instances without the qname/rrname attributes. This patch
prevents `mysummary` from throwing the AttributeError exception when it
encounters queries/responses like that.

It's a follow-up to dda902e.

Fixes:
```
  File "scapy/scapy/sendrecv.py", line 1439, in tshark
    sniff(prn=_cb, store=False, *args, **kargs)
  File "scapy/scapy/sendrecv.py", line 1311, in sniff
    sniffer._run(*args, **kwargs)
  File "scapy/scapy/sendrecv.py", line 1254, in _run
    session.on_packet_received(p)
  File "scapy/scapy/sessions.py", line 109, in on_packet_received
    result = self.prn(pkt)
  File "scapy/scapy/sendrecv.py", line 1436, in _cb
    print("%5d\t%s" % (i[0], pkt.summary()))
  File "scapy/scapy/packet.py", line 1650, in summary
    return self._do_summary()[1]
  File "scapy/scapy/packet.py", line 1624, in _do_summary
    found, s, needed = self.payload._do_summary()
  File "scapy/scapy/packet.py", line 1624, in _do_summary
    found, s, needed = self.payload._do_summary()
  File "scapy/scapy/packet.py", line 1624, in _do_summary
    found, s, needed = self.payload._do_summary()
  File "scapy/scapy/packet.py", line 1627, in _do_summary
    ret = self.mysummary()
  File "scapy/scapy/layers/llmnr.py", line 60, in mysummary
    self.qd[0].qname.decode(errors="backslashreplace"),
  File "scapy/scapy/packet.py", line 469, in __getattr__
    return self.payload.__getattr__(attr)
  File "scapy/scapy/packet.py", line 467, in __getattr__
    fld, v = self.getfield_and_val(attr)
  File "scapy/scapy/packet.py", line 1793, in getfield_and_val
    raise AttributeError(attr)
AttributeError: qname. Did you mean: '_name'?
```

scapy/layers/llmnr.py

@@ -28,6 +28,8 @@
     DNSCompressedPacket,
     DNS_am,
     DNS,
+    DNSQR,
+    DNSRR,
 )
 
 
@@ -57,15 +59,22 @@ def hashret(self):
         return struct.pack("!H", self.id)
 
     def mysummary(self):
-        if self.an:
-            return "LLMNRResponse '%s' is at '%s'" % (
-                self.an[0].rrname.decode(errors="backslashreplace"),
-                self.an[0].rdata,
-            ), [UDP]
-        if self.qd:
-            return "LLMNRQuery who has '%s'" % (
+        s = self.__class__.__name__
+        if self.qr:
+            if self.an and isinstance(self.an[0], DNSRR):
+                s += " '%s' is at '%s'" % (
+                    self.an[0].rrname.decode(errors="backslashreplace"),
+                    self.an[0].rdata,
+                )
+            else:
+                s += " [malformed]"
+        elif self.qd and isinstance(self.qd[0], DNSQR):
+            s += " who has '%s'" % (
                 self.qd[0].qname.decode(errors="backslashreplace"),
-            ), [UDP]
+            )
+        else:
+            s += " [malformed]"
+        return s, [UDP]
 
 
 class LLMNRResponse(LLMNRQuery):

test/scapy/layers/llmnr.uts

@@ -42,8 +42,22 @@ assert b.answers(a)
 assert not a.answers(b)
 
 = Summary
+q = LLMNRQuery(b'\xd5\xd5\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x07example\x00\x00\x01\x00\x01')
+assert q.mysummary()[0] == r"LLMNRQuery who has 'example.'"
+
 q = LLMNRQuery(b'Yy\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x01\xff\x00\x00\x01\x00\x01')
 assert q.mysummary()[0] == r"LLMNRQuery who has '\xff.'"
 
+with no_debug_dissector():
+    q = LLMNRQuery(b'@@\x00\x1b\xed7\x96J\x00\x00\x00\x01\x00\x00')
+    assert q.mysummary()[0] == r"LLMNRQuery [malformed]"
+
+r = LLMNRResponse(b'e\xcc\x80\x00\x00\x01\x00\x01\x00\x00\x00\x00\x07example\x00\x00\x01\x00\x01\x07example\x00\x00\x01\x00\x01\x00\x00\x00\x1e\x00\x04\xc0\x00\x02\x01')
+assert r.mysummary()[0] == r"LLMNRResponse 'example.' is at '192.0.2.1'"
+
 r = LLMNRResponse(b'\n\xe6\x80\x00\x00\x01\x00\x01\x00\x00\x00\x00\x01\xff\x00\x00\x1c\x00\x01\xc0\x0c\x00\x1c\x00\x01\x00\x00\x00\x1e\x00\x10\xfe\x80\x00\x00\x00\x00\x00\x00xu\x17\xff\xfe\xbc\xac\xcb')
 assert r.mysummary()[0] == r"LLMNRResponse '\xff.' is at 'fe80::7875:17ff:febc:accb'"
+
+with no_debug_dissector():
+    r = LLMNRResponse(b'\xd3<\x80\x00\x00\x01\x00\x01\x00\x00\x00\x00\x04H\x00\x00\x01\x00\x01\xc0\x0c\x00\x01\x00\x01\x00\x00\x00\x1e\x00\x04\xc0\xa88\x04')
+    assert r.mysummary()[0] == r"LLMNRResponse [malformed]"