Auto clear DNS cache on set

secdev · Feb 13, 2024 · d612454 · d612454
1 parent bb36cec
commit d612454
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diff --git a/scapy/layers/dns.py b/scapy/layers/dns.py
@@ -325,6 +325,13 @@ class DNSStrField(StrLenField):
     """
 
     def h2i(self, pkt, x):
+        # Setting a DNSStrField manually (h2i) means any current compression will break
+        if (
+            pkt and
+            isinstance(pkt.parent, DNSCompressedPacket) and
+            pkt.parent.raw_packet_cache
+        ):
+            pkt.parent.clear_cache()
         if not x:
             return b"."
         x = bytes_encode(x)

diff --git a/test/scapy/layers/dns.uts b/test/scapy/layers/dns.uts
@@ -164,6 +164,15 @@ recompressed.an[3].rdlen = None
 
 assert raw(recompressed) == raw(pkt)
 
+= DNS cache clearance on sub change
+~ dns
+
+# GH4216
+p = DNS(b'\x00\x00\x01\x00\x00\x00\x00\x02\x00\x00\x00\x00\x03H-1\x05local\x00\x00\x05\x00\x01\x00\x00\x00\x00\x00\x06\x03H-2\xc0\x10\xc0!\x00\x05\x00\x01\x00\x00\x00\x00\x00\x02\xc0\x0c')
+p[DNS].an[0].rrname = 'H'
+assert p.raw_packet_cache is None
+assert bytes(p) == b'\x00\x00\x01\x00\x00\x00\x00\x02\x00\x00\x00\x00\x01H\x00\x00\x05\x00\x01\x00\x00\x00\x00\x00\x0b\x03H-2\x05local\x00\x03H-2\x05local\x00\x00\x05\x00\x01\x00\x00\x00\x00\x00\x0b\x03H-1\x05local\x00'
+
 = DNS frames with MX records
 ~ dns