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# $Id: dns.py 27 2006-11-21 01:22:52Z dahelder $
"""Domain Name System."""
import struct
import dpkt
DNS_Q = 0
DNS_R = 1
# Opcodes
DNS_QUERY = 0
DNS_IQUERY = 1
DNS_STATUS = 2
DNS_NOTIFY = 4
DNS_UPDATE = 5
# Flags
DNS_CD = 0x0010 # checking disabled
DNS_AD = 0x0020 # authenticated data
DNS_Z = 0x0040 # unused
DNS_RA = 0x0080 # recursion available
DNS_RD = 0x0100 # recursion desired
DNS_TC = 0x0200 # truncated
DNS_AA = 0x0400 # authoritative answer
DNS_QR = 0x8000 # response ( query / response )
# Response codes
DNS_RCODE_NOERR = 0
DNS_RCODE_FORMERR = 1
DNS_RCODE_SERVFAIL = 2
DNS_RCODE_NXDOMAIN = 3
DNS_RCODE_NOTIMP = 4
DNS_RCODE_REFUSED = 5
DNS_RCODE_YXDOMAIN = 6
DNS_RCODE_YXRRSET = 7
DNS_RCODE_NXRRSET = 8
DNS_RCODE_NOTAUTH = 9
DNS_RCODE_NOTZONE = 10
# RR types
DNS_A = 1
DNS_NS = 2
DNS_CNAME = 5
DNS_SOA = 6
DNS_PTR = 12
DNS_HINFO = 13
DNS_MX = 15
DNS_TXT = 16
DNS_AAAA = 28
DNS_SRV = 33
# RR classes
DNS_IN = 1
DNS_CHAOS = 3
DNS_HESIOD = 4
DNS_ANY = 255
def pack_name(name, off, label_ptrs):
if name:
labels = name.split('.')
else:
labels = []
labels.append('')
buf = ''
for i, label in enumerate(labels):
key = '.'.join(labels[i:]).upper()
ptr = label_ptrs.get(key)
if not ptr:
if len(key) > 1:
ptr = off + len(buf)
if ptr < 0xc000:
label_ptrs[key] = ptr
i = len(label)
buf += chr(i) + label
else:
buf += struct.pack('>H', (0xc000 | ptr))
break
return buf
def unpack_name(buf, off):
name = ''
saved_off = 0
for i in range(100): # XXX
n = ord(buf[off])
if n == 0:
off += 1
break
elif (n & 0xc0) == 0xc0:
ptr = struct.unpack('>H', buf[off:off+2])[0] & 0x3fff
off += 2
if not saved_off:
saved_off = off
# XXX - don't use recursion!@#$
name = name + unpack_name(buf, ptr)[0] + '.'
break
else:
off += 1
name = name + buf[off:off+n] + '.'
if len(name) > 255:
raise dpkt.UnpackError('name longer than 255 bytes')
off += n
return name.strip('.'), off
class DNS(dpkt.Packet):
__hdr__ = (
('id', 'H', 0),
('op', 'H', DNS_RD), # recursive query
# XXX - lists of query, RR objects
('qd', 'H', []),
('an', 'H', []),
('ns', 'H', []),
('ar', 'H', [])
)
def get_qr(self):
return int((self.op & DNS_QR) == DNS_QR)
def set_qr(self, v):
if v: self.op |= DNS_QR
else: self.op &= ~DNS_QR
qr = property(get_qr, set_qr)
def get_opcode(self):
return (self.op >> 11) & 0xf
def set_opcode(self, v):
self.op = (self.op & ~0x7800) | ((v & 0xf) << 11)
opcode = property(get_opcode, set_opcode)
def get_aa(self):
return int((self.op & DNS_AA) == DNS_AA)
def set_aa(self, v):
if v: self.op |= DNS_AA
else: self.op &= ~DNS_AA
aa = property(get_aa, set_aa)
def get_rd(self):
return int((self.op & DNS_RD) == DNS_RD)
def set_rd(self,v):
if v: self.op |= DNS_RD
else: self.op &= ~DNS_RD
rd = property(get_rd, set_rd)
def get_ra(self):
return int((self.op & DNS_RA) == DNS_RA)
def set_ra(self,v):
if v: self.op |= DNS_RA
else: self.op &= ~DNS_RA
ra = property(get_ra, set_ra)
def get_zero(self):
return int((self.op & DNS_Z) == DNS_Z)
def set_zero(self, v):
if v: self.op |= DNS_Z
else: self.op &= ~DNS_Z
zero = property(get_zero, set_zero)
def get_rcode(self):
return self.op & 0xf
def set_rcode(self, v):
self.op = (self.op & ~0xf) | (v & 0xf)
rcode = property(get_rcode, set_rcode)
class Q(dpkt.Packet):
"""DNS question."""
__hdr__ = (
('name', '1025s', ''),
('type', 'H', DNS_A),
('cls', 'H', DNS_IN)
)
# XXX - suk
def __len__(self):
raise NotImplementedError
__str__ = __len__
def unpack(self, buf):
raise NotImplementedError
class RR(Q):
"""DNS resource record."""
__hdr__ = (
('name', '1025s', ''),
('type', 'H', DNS_A),
('cls', 'H', DNS_IN),
('ttl', 'I', 0),
('rlen', 'H', 4),
('rdata', 's', '')
)
def pack_rdata(self, off, label_ptrs):
# XXX - yeah, this sux
if self.rdata:
return self.rdata
if self.type == DNS_A:
return self.ip
elif self.type == DNS_NS:
return pack_name(self.nsname, off, label_ptrs)
elif self.type == DNS_CNAME:
return pack_name(self.cname, off, label_ptrs)
elif self.type == DNS_PTR:
return pack_name(self.ptrname, off, label_ptrs)
elif self.type == DNS_SOA:
l = []
l.append(pack_name(self.mname, off, label_ptrs))
l.append(pack_name(self.rname, off + len(l[0]), label_ptrs))
l.append(struct.pack('>IIIII', self.serial, self.refresh,
self.retry, self.expire, self.minimum))
return ''.join(l)
elif self.type == DNS_MX:
return struct.pack('>H', self.preference) + \
pack_name(self.mxname, off + 2, label_ptrs)
elif self.type == DNS_TXT or self.type == DNS_HINFO:
return ''.join([ '%s%s' % (chr(len(x)), x)
for x in self.text ])
elif self.type == DNS_AAAA:
return self.ip6
elif self.type == DNS_SRV:
return struct.pack('>HHH', self.priority, self.weight, self.port) + \
pack_name(self.srvname, off + 6, label_ptrs)
def unpack_rdata(self, buf, off):
if self.type == DNS_A:
self.ip = self.rdata
elif self.type == DNS_NS:
self.nsname, off = unpack_name(buf, off)
elif self.type == DNS_CNAME:
self.cname, off = unpack_name(buf, off)
elif self.type == DNS_PTR:
self.ptrname, off = unpack_name(buf, off)
elif self.type == DNS_SOA:
self.mname, off = unpack_name(buf, off)
self.rname, off = unpack_name(buf, off)
self.serial, self.refresh, self.retry, self.expire, \
self.minimum = struct.unpack('>IIIII', buf[off:off+20])
elif self.type == DNS_MX:
self.preference = struct.unpack('>H', self.rdata[:2])
self.mxname, off = unpack_name(buf, off+2)
elif self.type == DNS_TXT or self.type == DNS_HINFO:
self.text = []
buf = self.rdata
while buf:
n = ord(buf[0])
self.text.append(buf[1:1+n])
buf = buf[1+n:]
elif self.type == DNS_AAAA:
self.ip6 = self.rdata
elif self.type == DNS_SRV:
self.priority, self.weight, self.port = \
struct.unpack('>HHH', self.rdata[:6])
self.srvname, off = unpack_name(buf, off+6)
def pack_q(self, buf, q):
"""Append packed DNS question and return buf."""
return buf + pack_name(q.name, len(buf), self.label_ptrs) + \
struct.pack('>HH', q.type, q.cls)
def unpack_q(self, buf, off):
"""Return DNS question and new offset."""
q = self.Q()
q.name, off = unpack_name(buf, off)
q.type, q.cls = struct.unpack('>HH', buf[off:off+4])
off += 4
return q, off
def pack_rr(self, buf, rr):
"""Append packed DNS RR and return buf."""
name = pack_name(rr.name, len(buf), self.label_ptrs)
rdata = rr.pack_rdata(len(buf) + len(name) + 10, self.label_ptrs)
return buf + name + struct.pack('>HHIH', rr.type, rr.cls, rr.ttl,
len(rdata)) + rdata
def unpack_rr(self, buf, off):
"""Return DNS RR and new offset."""
rr = self.RR()
rr.name, off = unpack_name(buf, off)
rr.type, rr.cls, rr.ttl, rdlen = struct.unpack('>HHIH', buf[off:off+10])
off += 10
rr.rdata = buf[off:off+rdlen]
rr.unpack_rdata(buf, off)
off += rdlen
return rr, off
def unpack(self, buf):
dpkt.Packet.unpack(self, buf)
off = self.__hdr_len__
cnt = self.qd
self.qd = []
for i in range(cnt):
q, off = self.unpack_q(buf, off)
self.qd.append(q)
for x in ('an', 'ns', 'ar'):
cnt = getattr(self, x, 0)
setattr(self, x, [])
for i in range(cnt):
rr, off = self.unpack_rr(buf, off)
getattr(self, x).append(rr)
self.data = ''
def __len__(self):
# XXX - cop out
return len(str(self))
def __str__(self):
# XXX - compress names on the fly
self.label_ptrs = {}
buf = struct.pack(self.__hdr_fmt__, self.id, self.op, len(self.qd),
len(self.an), len(self.ns), len(self.ar))
for q in self.qd:
buf = self.pack_q(buf, q)
for x in ('an', 'ns', 'ar'):
for rr in getattr(self, x):
buf = self.pack_rr(buf, rr)
del self.label_ptrs
return buf
if __name__ == '__main__':
import unittest
from ip import IP
class DNSTestCase(unittest.TestCase):
def test_basic(self):
s = 'E\x00\x02\x08\xc15\x00\x00\x80\x11\x92aBk0\x01Bk0w\x005\xc07\x01\xf4\xda\xc2d\xd2\x81\x80\x00\x01\x00\x03\x00\x0b\x00\x0b\x03www\x06google\x03com\x00\x00\x01\x00\x01\xc0\x0c\x00\x05\x00\x01\x00\x00\x03V\x00\x17\x03www\x06google\x06akadns\x03net\x00\xc0,\x00\x01\x00\x01\x00\x00\x01\xa3\x00\x04@\xe9\xabh\xc0,\x00\x01\x00\x01\x00\x00\x01\xa3\x00\x04@\xe9\xabc\xc07\x00\x02\x00\x01\x00\x00KG\x00\x0c\x04usw5\x04akam\xc0>\xc07\x00\x02\x00\x01\x00\x00KG\x00\x07\x04usw6\xc0t\xc07\x00\x02\x00\x01\x00\x00KG\x00\x07\x04usw7\xc0t\xc07\x00\x02\x00\x01\x00\x00KG\x00\x08\x05asia3\xc0t\xc07\x00\x02\x00\x01\x00\x00KG\x00\x05\x02za\xc07\xc07\x00\x02\x00\x01\x00\x00KG\x00\x0f\x02zc\x06akadns\x03org\x00\xc07\x00\x02\x00\x01\x00\x00KG\x00\x05\x02zf\xc07\xc07\x00\x02\x00\x01\x00\x00KG\x00\x05\x02zh\xc0\xd5\xc07\x00\x02\x00\x01\x00\x00KG\x00\x07\x04eur3\xc0t\xc07\x00\x02\x00\x01\x00\x00KG\x00\x07\x04use2\xc0t\xc07\x00\x02\x00\x01\x00\x00KG\x00\x07\x04use4\xc0t\xc0\xc1\x00\x01\x00\x01\x00\x00\xfb4\x00\x04\xd0\xb9\x84\xb0\xc0\xd2\x00\x01\x00\x01\x00\x001\x0c\x00\x04?\xf1\xc76\xc0\xed\x00\x01\x00\x01\x00\x00\xfb4\x00\x04?\xd7\xc6S\xc0\xfe\x00\x01\x00\x01\x00\x001\x0c\x00\x04?\xd00.\xc1\x0f\x00\x01\x00\x01\x00\x00\n\xdf\x00\x04\xc1-\x01g\xc1"\x00\x01\x00\x01\x00\x00\x101\x00\x04?\xd1\xaa\x88\xc15\x00\x01\x00\x01\x00\x00\r\x1a\x00\x04PCC\xb6\xc0o\x00\x01\x00\x01\x00\x00\x10\x7f\x00\x04?\xf1I\xd6\xc0\x87\x00\x01\x00\x01\x00\x00\n\xdf\x00\x04\xce\x84dl\xc0\x9a\x00\x01\x00\x01\x00\x00\n\xdf\x00\x04A\xcb\xea\x1b\xc0\xad\x00\x01\x00\x01\x00\x00\x0b)\x00\x04\xc1l\x9a\t'
ip = IP(s)
dns = DNS(ip.udp.data)
self.failUnless(dns.qd[0].name == 'www.google.com' and
dns.an[1].name == 'www.google.akadns.net')
s = '\x05\xf5\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00\x03www\x03cnn\x03com\x00\x00\x01\x00\x01'
dns = DNS(s)
self.failUnless(s == str(dns))
def test_PTR(self):
s = 'g\x02\x81\x80\x00\x01\x00\x01\x00\x03\x00\x00\x011\x011\x03211\x03141\x07in-addr\x04arpa\x00\x00\x0c\x00\x01\xc0\x0c\x00\x0c\x00\x01\x00\x00\r6\x00$\x07default\nv-umce-ifs\x05umnet\x05umich\x03edu\x00\xc0\x0e\x00\x02\x00\x01\x00\x00\r6\x00\r\x06shabby\x03ifs\xc0O\xc0\x0e\x00\x02\x00\x01\x00\x00\r6\x00\x0f\x0cfish-license\xc0m\xc0\x0e\x00\x02\x00\x01\x00\x00\r6\x00\x0b\x04dns2\x03itd\xc0O'
dns = DNS(s)
self.failUnless(dns.qd[0].name == '1.1.211.141.in-addr.arpa' and
dns.an[0].ptrname == 'default.v-umce-ifs.umnet.umich.edu' and
dns.ns[0].nsname == 'shabby.ifs.umich.edu' and
dns.ns[1].ttl == 3382L and
dns.ns[2].nsname == 'dns2.itd.umich.edu')
self.failUnless(s == str(dns))
def test_pack_name(self):
# Empty name is \0
x = pack_name('', 0, {})
self.assertEqual(x, '\0')
unittest.main()
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