Rewrite ICMP extensions (#4332)

Author: gpotter2

scapy/contrib/icmp_extensions.py

@@ -2,186 +2,29 @@
 # This file is part of Scapy
 # See https://scapy.net/ for more information
 
-# scapy.contrib.description = ICMP Extensions
-# scapy.contrib.status = loads
-
-import struct
-
-import scapy
-from scapy.compat import chb
-from scapy.packet import Packet, bind_layers
-from scapy.fields import BitField, ByteField, ConditionalField, \
-    FieldLenField, IPField, IntField, PacketListField, ShortField, \
-    StrLenField
-from scapy.layers.inet import IP, ICMP, checksum
-from scapy.layers.inet6 import IP6Field
-from scapy.error import warning
-from scapy.contrib.mpls import MPLS
-from scapy.config import conf
-
-
-class ICMPExtensionObject(Packet):
-    name = 'ICMP Extension Object'
-    fields_desc = [ShortField('len', None),
-                   ByteField('classnum', 0),
-                   ByteField('classtype', 0)]
-
-    def post_build(self, p, pay):
-        if self.len is None:
-            tmp_len = len(p) + len(pay)
-            p = struct.pack('!H', tmp_len) + p[2:]
-        return p + pay
-
-
-class ICMPExtensionHeader(Packet):
-    name = 'ICMP Extension Header (RFC4884)'
-    fields_desc = [BitField('version', 2, 4),
-                   BitField('reserved', 0, 12),
-                   BitField('chksum', None, 16)]
-
-    _min_ieo_len = len(ICMPExtensionObject())
-
-    def post_build(self, p, pay):
-        if self.chksum is None:
-            ck = checksum(p)
-            p = p[:2] + chb(ck >> 8) + chb(ck & 0xff) + p[4:]
-        return p + pay
-
-    def guess_payload_class(self, payload):
-        if len(payload) < self._min_ieo_len:
-            return Packet.guess_payload_class(self, payload)
-
-        # Look at fields of the generic ICMPExtensionObject to determine which
-        # bound extension type to use.
-        ieo = ICMPExtensionObject(payload)
-        if ieo.len < self._min_ieo_len:
-            return Packet.guess_payload_class(self, payload)
-
-        for fval, cls in self.payload_guess:
-            if all(hasattr(ieo, k) and v == ieo.getfieldval(k)
-                   for k, v in fval.items()):
-                return cls
-        return ICMPExtensionObject
-
-
-def ICMPExtension_post_dissection(self, pkt):
-    # RFC4884 section 5.2 says if the ICMP packet length
-    # is >144 then ICMP extensions start at byte 137.
-
-    lastlayer = pkt.lastlayer()
-    if not isinstance(lastlayer, conf.padding_layer):
-        return
-
-    if IP in pkt:
-        if (ICMP in pkt and
-            pkt[ICMP].type in [3, 11, 12] and
-                pkt.len > 144):
-            bytes = pkt[ICMP].build()[136:]
-        else:
-            return
-    elif scapy.layers.inet6.IPv6 in pkt:
-        if ((scapy.layers.inet6.ICMPv6TimeExceeded in pkt or
-             scapy.layers.inet6.ICMPv6DestUnreach in pkt) and
-                pkt.plen > 144):
-            bytes = pkt[scapy.layers.inet6.ICMPv6TimeExceeded].build()[136:]
-        else:
-            return
-    else:
-        return
-
-    # validate checksum
-    ieh = ICMPExtensionHeader(bytes)
-    if checksum(ieh.build()):
-        return  # failed
-
-    lastlayer.load = lastlayer.load[:-len(ieh)]
-    lastlayer.add_payload(ieh)
-
-
-class ICMPExtensionMPLS(ICMPExtensionObject):
-    name = 'ICMP Extension Object - MPLS (RFC4950)'
-
-    fields_desc = [ShortField('len', None),
-                   ByteField('classnum', 1),
-                   ByteField('classtype', 1),
-                   PacketListField('stack', [], MPLS,
-                                   length_from=lambda pkt: pkt.len - 4)]
-
-
-class ICMPExtensionInterfaceInformation(ICMPExtensionObject):
-    name = 'ICMP Extension Object - Interface Information Object (RFC5837)'
-
-    fields_desc = [ShortField('len', None),
-                   ByteField('classnum', 2),
-                   BitField('interface_role', 0, 2),
-                   BitField('reserved', 0, 2),
-                   BitField('has_ifindex', 0, 1),
-                   BitField('has_ipaddr', 0, 1),
-                   BitField('has_ifname', 0, 1),
-                   BitField('has_mtu', 0, 1),
-
-                   ConditionalField(
-        IntField('ifindex', None),
-        lambda pkt: pkt.has_ifindex == 1),
-
-        ConditionalField(
-        ShortField('afi', None),
-        lambda pkt: pkt.has_ipaddr == 1),
-        ConditionalField(
-        ShortField('reserved2', 0),
-        lambda pkt: pkt.has_ipaddr == 1),
-        ConditionalField(
-        IPField('ip4', None),
-        lambda pkt: pkt.afi == 1),
-        ConditionalField(
-        IP6Field('ip6', None),
-        lambda pkt: pkt.afi == 2),
-
-        ConditionalField(
-        FieldLenField('ifname_len', None, fmt='B',
-                      length_of='ifname'),
-        lambda pkt: pkt.has_ifname == 1),
-        ConditionalField(
-        StrLenField('ifname', None,
-                    length_from=lambda pkt: pkt.ifname_len),
-        lambda pkt: pkt.has_ifname == 1),
-
-        ConditionalField(
-        IntField('mtu', None),
-        lambda pkt: pkt.has_mtu == 1)]
-
-    def self_build(self, **kwargs):
-        if self.afi is None:
-            if self.ip4 is not None:
-                self.afi = 1
-            elif self.ip6 is not None:
-                self.afi = 2
-
-        if self.has_ifindex and self.ifindex is None:
-            warning('has_ifindex set but ifindex is not set.')
-        if self.has_ipaddr and self.afi is None:
-            warning('has_ipaddr set but afi is not set.')
-        if self.has_ipaddr and self.ip4 is None and self.ip6 is None:
-            warning('has_ipaddr set but ip4 or ip6 is not set.')
-        if self.has_ifname and self.ifname is None:
-            warning('has_ifname set but ifname is not set.')
-        if self.has_mtu and self.mtu is None:
-            warning('has_mtu set but mtu is not set.')
-
-        return ICMPExtensionObject.self_build(self, **kwargs)
-
-
-# Add the post_dissection() method to the existing ICMPv4 and
-# ICMPv6 error messages
-scapy.layers.inet.ICMPerror.post_dissection = ICMPExtension_post_dissection
-scapy.layers.inet.TCPerror.post_dissection = ICMPExtension_post_dissection
-scapy.layers.inet.UDPerror.post_dissection = ICMPExtension_post_dissection
-
-scapy.layers.inet6.ICMPv6DestUnreach.post_dissection = ICMPExtension_post_dissection  # noqa: E501
-scapy.layers.inet6.ICMPv6TimeExceeded.post_dissection = ICMPExtension_post_dissection  # noqa: E501
-
-
-# ICMPExtensionHeader looks at fields from the upper layer object when
-# determining which upper layer to use.
-bind_layers(ICMPExtensionHeader, ICMPExtensionMPLS, classnum=1, classtype=1)
-bind_layers(ICMPExtensionHeader, ICMPExtensionInterfaceInformation, classnum=2)
+# scapy.contrib.description = ICMP Extensions (deprecated)
+# scapy.contrib.status = deprecated
+
+__all__ = [
+    "ICMPExtensionObject",
+    "ICMPExtensionHeader",
+    "ICMPExtensionInterfaceInformation",
+    "ICMPExtensionMPLS",
+]
+
+import warnings
+
+from scapy.layers.inet import (
+    ICMPExtension_Object as ICMPExtensionObject,
+    ICMPExtension_Header as ICMPExtensionHeader,
+    ICMPExtension_InterfaceInformation as ICMPExtensionInterfaceInformation,
+)
+from scapy.contrib.mpls import (
+    ICMPExtension_MPLS as ICMPExtensionMPLS,
+)
+
+warnings.warn(
+    "scapy.contrib.icmp_extensions is deprecated. Behavior has changed ! "
+    "Use scapy.layers.inet",
+    DeprecationWarning
+)

scapy/contrib/mpls.py

@@ -6,12 +6,24 @@
 # scapy.contrib.status = loads
 
 from scapy.packet import Packet, bind_layers, Padding
-from scapy.fields import BitField, ByteField, ShortField
-from scapy.layers.inet import IP, UDP
-from scapy.contrib.bier import BIER
+from scapy.fields import (
+    BitField,
+    ByteField,
+    ByteEnumField,
+    PacketListField,
+    ShortField,
+)
+
+from scapy.layers.inet import (
+    _ICMP_classnums,
+    ICMPExtension_Object,
+    IP,
+    UDP,
+)
 from scapy.layers.inet6 import IPv6
 from scapy.layers.l2 import Ether, GRE
-from scapy.compat import orb
+
+from scapy.contrib.bier import BIER
 
 
 class EoMCW(Packet):
@@ -37,21 +49,36 @@ def guess_payload_class(self, payload):
         if len(payload) >= 1:
             if not self.s:
                 return MPLS
-            ip_version = (orb(payload[0]) >> 4) & 0xF
+            ip_version = (payload[0] >> 4) & 0xF
             if ip_version == 4:
                 return IP
             elif ip_version == 5:
                 return BIER
             elif ip_version == 6:
                 return IPv6
             else:
-                if orb(payload[0]) == 0 and orb(payload[1]) == 0:
+                if payload[0] == 0 and payload[1] == 0:
                     return EoMCW
                 else:
                     return Ether
         return Padding
 
 
+# ICMP Extension
+
+class ICMPExtension_MPLS(ICMPExtension_Object):
+    name = "ICMP Extension Object - MPLS (RFC4950)"
+
+    fields_desc = [
+        ShortField("len", None),
+        ByteEnumField("classnum", 1, _ICMP_classnums),
+        ByteField("classtype", 1),
+        PacketListField("stack", [], MPLS, length_from=lambda pkt: pkt.len - 4),
+    ]
+
+
+# Bindings
+
 bind_layers(Ether, MPLS, type=0x8847)
 bind_layers(IP, MPLS, proto=137)
 bind_layers(IPv6, MPLS, nh=137)

scapy/fields.py

@@ -1893,6 +1893,8 @@ def i2repr(self,
     def getfield(self, pkt, s):
         # type: (Packet, bytes) -> Tuple[bytes, bytes]
         len_pkt = self.length_from(pkt)
+        if len_pkt == 0:
+            return s, b""
         return s[len_pkt:], self.m2i(pkt, s[:len_pkt])
 
     def addfield(self, pkt, s, val):