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resolve.py
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resolve.py
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#!/usr/bin/env python
"""
resolve.py
Perform an iterative resolution of a DNS name, type, class,
starting from the root DNS servers.
Author: Shumon Huque <shuque - @ - gmail.com>
"""
import os, sys, getopt, time, random
import dns.message, dns.query, dns.rdatatype, dns.rcode, dns.dnssec
PROGNAME = os.path.basename(sys.argv[0])
VERSION = "0.14"
TIMEOUT = 3 # Query timeout in seconds
RETRY = 1 # of full list (not implemented yet)
MAX_CNAME = 10 # Max #CNAME indirections
MAX_QUERY = 300 # Max number of queries
MAX_DELEG = 26 # Max number of delegations
# root server names and addresses
ROOTHINTS = [
("a.root-servers.net.", "198.41.0.4"),
("a.root-servers.net.", "2001:503:ba3e::2:30"),
("b.root-servers.net.", "192.228.79.201"),
("b.root-servers.net.", "2001:500:200::b"),
("c.root-servers.net.", "192.33.4.12"),
("c.root-servers.net.", "2001:500:2::c"),
("d.root-servers.net.", "199.7.91.13"),
("d.root-servers.net.", "2001:500:2d::d"),
("e.root-servers.net.", "192.203.230.10"),
("e.root-servers.net.", "2001:500:a8::e"),
("f.root-servers.net.", "192.5.5.241"),
("f.root-servers.net.", "2001:500:2f::f"),
("g.root-servers.net.", "192.112.36.4"),
("g.root-servers.net.", "2001:500:12::d0d"),
("h.root-servers.net.", "198.97.190.53"),
("h.root-servers.net.", "2001:500:1::53"),
("i.root-servers.net.", "192.36.148.17"),
("i.root-servers.net.", "2001:7fe::53"),
("j.root-servers.net.", "192.58.128.30"),
("j.root-servers.net.", "2001:503:c27::2:30"),
("k.root-servers.net.", "193.0.14.129"),
("k.root-servers.net.", "2001:7fd::1"),
("l.root-servers.net.", "199.7.83.42"),
("l.root-servers.net.", "2001:500:9f::42"),
("m.root-servers.net.", "2001:dc3::35"),
("m.root-servers.net.", "202.12.27.33"),
]
# RootZone object
RootZone = None # Populated by get_root_zone()
class Prefs:
"""Preferences"""
DEBUG = False # -d: Print debugging output?
MINIMIZE = False # -m: Do qname minimization?
TCPONLY = False # -t: Use TCP only
VERBOSE = False # -v: Trace query->zone path
VIOLATE = False # -x: ENT nxdomain workaround
STATS = False # -s: Print statistics
NSRESOLVE = False # -n: Resolve all NS addresses
BATCHFILE = None # -b: batch file mode
class Stats:
"""Statistics counters"""
cnt_cname = 0
cnt_query1 = 0 # regular queries
cnt_query2 = 0 # NS address queries
cnt_fail = 0
cnt_tcp = 0
cnt_deleg = 0
delegation_depth = 0
class Cache:
"""Cache of Zone & NameServer objects"""
ZoneDict = dict() # dns.name.Name -> Zone
NSDict = dict() # dns.name.Name -> NameServer
def printCache():
"""Print zone and NS cache contents - for debugging"""
print("---------------------------- Zone Cache ----------------")
for zname, zobj in Cache.ZoneDict.items():
print("Zone: %s" % zname)
for ns in zobj.nslist:
print(" NS: %s" % Cache.NSDict[ns].name)
print("---------------------------- NS Cache ----------------")
for nsname, nsobj in Cache.NSDict.items():
ipstring_list = " ".join([x.addr for x in nsobj.iplist])
print("%s %s" % (nsname, ipstring_list))
return
def usage():
print("""
{0} version {1}
Usage: {0} [-dmtvsnx] <qname> [<qtype>] [<qclass>]
{0} [-dmtvsnx] -b <batchfile>
-d: print debugging output
-m: do qname minimization
-t: use TCP only
-v: verbose - trace query & zone path
-s: print summary statistics
-n: resolve all non-glue NS addresses in referrals
-x: workaround NXDOMAIN on empty non-terminals
-b <batchfile>: batch file mode
When using -b, <batchfile> contains one (space separated) query name, type,
class per line.
""".format(PROGNAME, VERSION))
sys.exit(1)
def dprint(msg):
if Prefs.DEBUG: print(">> DEBUG: %s" % msg)
return
class Query:
"""Query name class"""
def __init__(self, qname, qtype, qclass, minimize=False):
if isinstance(qname, dns.name.Name):
self.qname = qname
else:
self.qname = dns.name.from_text(qname)
self.orig_qname = self.qname
self.qtype = qtype
self.qclass = qclass
self.minimize = minimize
self.quiet = False # don't print anything
self.rcode = None
self.got_answer = False
self.cname_chain = []
self.answer_rrset = []
self.full_answer_rrset = []
def print_full_answer(self):
if self.full_answer_rrset:
print("\n".join([x.to_text() for x in self.full_answer_rrset]))
def get_answer_ip_list(self):
iplist = []
for rrset in self.answer_rrset:
if rrset.rdtype in [dns.rdatatype.A, dns.rdatatype.AAAA]:
for rr in rrset:
iplist.append(rr.to_text())
return iplist
def set_minimized(self, zone):
labels_qname = self.orig_qname.labels
labels_zone = zone.name.labels
minLabels = len(labels_zone) + 1
self.qname = dns.name.Name(labels_qname[-minLabels:])
def prepend_label(self):
numLabels = len(self.qname) + 1
self.qname = dns.name.Name(self.orig_qname[-numLabels:])
def __repr__(self):
return "<Query: %s,%s,%s>" % (self.qname, self.qtype, self.qclass)
class IPaddress:
"""IPaddress class"""
def __init__(self, ip):
self.addr = ip
self.addrtype = None
self.rtt = float('inf') # RTT for UDP
self.query_count = 0
def __repr__(self):
return "<IPaddress: %s>" % self.addr
class NameServer:
"""NameServer class"""
def __init__(self, name):
self.name = name # dns.name.Name
self.iplist = [] # list of IPaddress
def has_ip(self, ipstring):
if ipstring in [x.addr for x in self.iplist]:
return True
else:
return False
def install_ip(self, ipstring):
if not self.has_ip(ipstring):
self.iplist.append(IPaddress(ipstring))
return
def __repr__(self):
return "<NS: %s>" % self.name
class Zone:
"""Zone class"""
def __init__(self, zone):
self.name = zone # dns.name.Name
self.nslist = [] # list of dns.name.Name
Cache.ZoneDict[zone] = self
def has_ns(self, ns):
if ns in self.nslist:
return True
else:
return False
def install_ns(self, nsname, clobber=False):
"""Install a nameserver record for this zone"""
if nsname not in self.nslist:
self.nslist.append(nsname)
if clobber or (nsname not in Cache.NSDict):
Cache.NSDict[nsname] = NameServer(nsname)
return Cache.NSDict[nsname]
def iplist(self):
result = []
for ns in self.nslist:
result += Cache.NSDict[ns].iplist
return result
def iplist_sorted_by_rtt(self):
return sorted(self.iplist(), key = lambda ip: ip.rtt)
def print_details(self):
print("ZONE: %s" % self.name)
for nsname in self.nslist:
nsobj = Cache.NSDict[nsname]
addresses = [x.addr for x in nsobj.iplist]
print("%s %s %s" % (self.name, nsobj.name, addresses))
return
def __repr__(self):
return "<Zone: %s>" % self.name
def get_root_zone():
"""populate the Root Zone object from hints file"""
z = Zone(dns.name.root)
for name, addr in ROOTHINTS:
name = dns.name.from_text(name)
nsobj = z.install_ns(name, clobber=False)
nsobj.install_ip(addr)
return z
def closest_zone(qname):
"""given query name, find closest enclosing zone object in Cache"""
for z in reversed(sorted(Cache.ZoneDict.keys())):
if qname.is_subdomain(z):
return Cache.ZoneDict[z]
else:
return Cache.ZoneDict[dns.name.root]
def get_ns_addrs(zone, message):
"""
Populate nameserver addresses for zone.
Note: by default, we only save and use NS record addresses we can find
in the additional section of the referral. To be complete, we should
really explicitly resolve all non-glue NS addresses, which results in a
large number of additional queries and corresponding latency. This
complete mode can be turned on with -n (NSRESOLVE). If no NS addresses
can be found in the additional section, we resort to NSRESOLVE mode.
"""
global Prefs
needsGlue = []
for nsname in zone.nslist:
if nsname.is_subdomain(zone.name):
needsGlue.append(nsname)
needToResolve = list(set(zone.nslist) - set(needsGlue))
for rrset in message.additional:
if rrset.rdtype in [dns.rdatatype.A, dns.rdatatype.AAAA]:
name = rrset.name
for rr in rrset:
if not zone.has_ns(name):
continue
if (not Prefs.NSRESOLVE) or (name in needsGlue):
nsobj = Cache.NSDict[name]
nsobj.install_ip(rr.address)
if not zone.iplist() or Prefs.NSRESOLVE:
for name in needToResolve:
nsobj = Cache.NSDict[name]
if nsobj.iplist:
continue
for addrtype in ['A', 'AAAA']:
nsquery = Query(name, addrtype, 'IN', Prefs.MINIMIZE)
nsquery.quiet = True
resolve_name(nsquery, closest_zone(nsquery.qname), inPath=False, nsQuery=True)
for ip in nsquery.get_answer_ip_list():
nsobj.install_ip(ip)
return
def process_referral(message, query):
"""Process referral. Returns a zone object for the referred zone"""
global Prefs
for rrset in message.authority:
if rrset.rdtype == dns.rdatatype.NS:
break
else:
print("ERROR: unable to find NS RRset in referral response")
return None
zonename = rrset.name
if Prefs.VERBOSE and not query.quiet:
print(">> [Got Referral to zone: %s]" % zonename)
if zonename in Cache.ZoneDict:
zone = Cache.ZoneDict[zonename]
else:
zone = Zone(zonename)
for rr in rrset:
nsobj = zone.install_ns(rr.target)
get_ns_addrs(zone, message)
return zone
def process_answer(response, query, addResults=None):
"""Process answer section, chasing aliases when needed"""
global Stats, Prefs
answer = response.answer
# If minimizing, then we ignore answers for intermediate query names.
if query.qname != query.orig_qname:
return answer
empty_answer = (len(answer) == 0)
if empty_answer:
if not query.quiet:
print("ERROR: NODATA: %s of type %s not found" % \
(query.qname, query.qtype))
for rrset in answer:
if rrset.rdtype == dns.rdatatype.from_text(query.qtype) and \
rrset.name == query.qname:
query.answer_rrset.append(rrset)
addResults and addResults.full_answer_rrset.append(rrset)
query.got_answer = True
elif rrset.rdtype == dns.rdatatype.DNAME:
query.answer_rrset.append(rrset)
addResults and addResults.full_answer_rrset.append(rrset)
if Prefs.VERBOSE:
print(rrset.to_text())
elif rrset.rdtype == dns.rdatatype.CNAME:
query.answer_rrset.append(rrset)
addResults and addResults.full_answer_rrset.append(rrset)
if Prefs.VERBOSE:
print(rrset.to_text())
cname = rrset[0].target
Stats.cnt_cname += 1
if Stats.cnt_cname >= MAX_CNAME:
print("ERROR: Too many (%d) CNAME indirections." % MAX_CNAME)
return None
else:
dprint("CNAME found, resolving canonical name %s" % cname)
cname_query = Query(cname, query.qtype, query.qclass, Prefs.MINIMIZE)
addResults and addResults.cname_chain.append(cname_query)
resolve_name(cname_query, closest_zone(cname),
inPath=False, addResults=addResults)
return answer
def process_response(response, query, addResults=None):
"""process a DNS response. Returns rcode, answer message, zone referral"""
rc = None; ans = None; referral = None
if not response:
return (rc, ans, z)
rc = response.rcode()
query.rcode = rc
aa = (response.flags & dns.flags.AA == dns.flags.AA)
if rc == dns.rcode.NOERROR:
answerlen = len(response.answer)
if answerlen == 0 and not aa: # Referral
referral = process_referral(response, query)
if referral:
dprint("Obtained referral to zone: %s" % referral.name)
else:
print("ERROR: processing referral")
else: # Answer
ans = process_answer(response, query, addResults=addResults)
elif rc == dns.rcode.NXDOMAIN: # NXDOMAIN
if not query.quiet:
print("ERROR: NXDOMAIN: %s not found" % query.qname)
return (rc, ans, referral)
def update_query_counts(ip, nsQuery=False, tcp=False):
"""Update query counts in Statistics"""
global Stats
ip.query_count += 1
if tcp:
Stats.cnt_tcp += 1
else:
if nsQuery:
Stats.cnt_query2 += 1
else:
Stats.cnt_query1 += 1
return
def send_query(query, zone, nsQuery=False):
"""send DNS query to nameservers of given zone"""
global Prefs, Stats
response = None
if Prefs.DEBUG or (Prefs.VERBOSE and not query.quiet):
print("\n>> Query: %s %s %s at zone %s" % \
(query.qname, query.qtype, query.qclass, zone.name))
msg = dns.message.make_query(query.qname, query.qtype, rdclass=query.qclass)
msg.flags ^= dns.flags.RD
nsaddr_list = zone.iplist_sorted_by_rtt();
if len(nsaddr_list) == 0:
print("ERROR: No nameserver addresses found for zone: %s." % zone.name)
return response
for nsaddr in nsaddr_list:
if Stats.cnt_query1 + Stats.cnt_query2 >= MAX_QUERY:
print("ERROR: Max number of queries (%d) exceeded." % MAX_QUERY)
return response
dprint("Querying zone %s at address %s" % (zone.name, nsaddr.addr))
try:
update_query_counts(ip=nsaddr, nsQuery=nsQuery)
msg.id = random.randint(1,65535) # randomize txid
truncated = False
if not Prefs.TCPONLY:
t1 = time.time()
response = dns.query.udp(msg, nsaddr.addr, timeout=TIMEOUT,
ignore_unexpected=True)
t2 = time.time()
nsaddr.rtt = (t2 - t1)
truncated = (response.flags & dns.flags.TC == dns.flags.TC)
if Prefs.TCPONLY or truncated:
update_query_counts(ip=nsaddr, nsQuery=nsQuery, tcp=True)
if truncated:
dprint("WARNING: Truncated response; Retrying with TCP ..")
response = dns.query.tcp(msg, nsaddr.addr, timeout=TIMEOUT)
except Exception as e:
print("Query failed: %s (%s, %s)" % (nsaddr.addr, type(e).__name__, e))
Stats.cnt_fail += 1
pass
else:
rc = response.rcode()
if rc not in [dns.rcode.NOERROR, dns.rcode.NXDOMAIN]:
Stats.cnt_fail += 1
print("WARNING: response %s from %s" % (dns.rcode.to_text(rc), nsaddr.addr))
else:
break
else:
print("ERROR: Queries to all servers for zone %s failed." % zone.name)
return response
def resolve_name(query, zone, inPath=True, nsQuery=False, addResults=None):
"""resolve a DNS query. addResults is an optional Query object to
which the answer results are to be added."""
global Prefs, Stats
curr_zone = zone
repeatZone = False
while Stats.cnt_deleg < MAX_DELEG:
if Prefs.DEBUG:
print("\n>> Current Zone: %s" % curr_zone.name)
curr_zone.print_details()
if query.minimize:
if repeatZone:
query.prepend_label()
repeatZone = False
else:
query.set_minimized(curr_zone)
response = send_query(query, curr_zone, nsQuery=nsQuery)
if not response:
return
rc, ans, referral = process_response(response, query, addResults=addResults)
if rc == dns.rcode.NXDOMAIN:
# for broken servers that give NXDOMAIN for empty non-terminals
if Prefs.VIOLATE and (query.minimize) and (query.qname != query.orig_qname):
repeatZone = True
else:
break
if not referral:
if (not query.minimize) or (query.qname == query.orig_qname):
break
elif query.minimize:
repeatZone = True
else:
Stats.cnt_deleg += 1
if inPath:
Stats.delegation_depth += 1
if not referral.name.is_subdomain(curr_zone.name):
print("ERROR: Upward referral: %s is not subdomain of %s" %
(referral.name, curr_zone.name))
break
curr_zone = referral
if Stats.cnt_deleg >= MAX_DELEG:
print("ERROR: Max levels of delegation (%d) reached." % MAX_DELEG)
return
def do_batchmode(infile, cmdline):
"""Execute batch mode on input file supplied to -b"""
global Prefs, Stats
print("### resolve.py: Batch Mode file: %s" % Prefs.BATCHFILE)
print("### command: %s" % ' '.join(cmdline))
linenum = 0
for line in open(infile):
linenum += 1
line = line.rstrip('\n')
parts = line.split()
if len(parts) == 1:
qname, = parts
qtype = 'A'
qclass = 'IN'
elif len(parts) == 2:
qname, qtype = parts
qclass = 'IN'
elif len(parts) == 3:
qname, qtype, qclass = parts
else:
print("\nERROR input line %d: %s" % (linenum, line))
continue
Stats.cnt_cname = 0
Stats.cnt_deleg = 0
Stats.cnt_query1 = 0
Stats.cnt_query2 = 0
Stats.cnt_fail = 0
Stats.cnt_tcp = 0
print("\n### INPUT: %s, %s, %s" % (qname, qtype, qclass))
query = Query(qname, qtype, qclass, minimize=Prefs.MINIMIZE)
starting_zone = closest_zone(query.qname)
print("### Query: %s" % query)
print("### Starting at zone: %s" % starting_zone)
resolve_name(query, starting_zone, addResults=query)
if Prefs.VERBOSE:
print('')
query.print_full_answer()
print("\n### End Batch Mode.")
return
def print_stats():
"""Print some statistics"""
global Stats
print('')
cnt_query_total = Stats.cnt_query1 + Stats.cnt_query2
print("Qname Delegation depth: %d" % Stats.delegation_depth)
print("Number of delegations traversed: %d" % Stats.cnt_deleg)
print("Number of queries performed (regular): %d" % Stats.cnt_query1)
print("Number of queries performed:(nsaddr) %d" % Stats.cnt_query2)
if Stats.cnt_tcp:
print("Number of TCP fallbacks: %d" % Stats.cnt_tcp)
if Stats.cnt_fail:
print("Number of queries failed: %d (%.2f%%)" %
(Stats.cnt_fail, (100.0 * Stats.cnt_fail/cnt_query_total)))
if Stats.cnt_cname:
print("Number of CNAME indirections: %d" % Stats.cnt_cname)
return
def exit_status(query):
"""Obtain final exit status code"""
if query.cname_chain:
last_cname = query.cname_chain.pop()
rcode = last_cname.rcode
got_answer = last_cname.got_answer
else:
rcode = query.rcode
got_answer = query.got_answer
if rcode == 0 and got_answer:
return 0
else:
return 1
def process_args(arguments):
"""Process all command line arguments"""
global Prefs
try:
(options, args) = getopt.getopt(arguments, 'dmtvsnxb:')
except getopt.GetoptError:
usage()
for (opt, optval) in options:
if opt == "-d":
Prefs.DEBUG = True
elif opt == "-m":
Prefs.MINIMIZE = True
elif opt == "-t":
Prefs.TCPONLY = True
elif opt == "-v":
Prefs.VERBOSE = True
elif opt == "-s":
Prefs.STATS = True
elif opt == "-n":
Prefs.NSRESOLVE = True
elif opt == "-x":
Prefs.VIOLATE = True
elif opt == "-b":
Prefs.BATCHFILE = optval
if Prefs.BATCHFILE:
if not args:
return (None, None, None)
else:
usage()
numargs = len(args)
if numargs == 1:
qname, = args
qtype = 'A'
qclass = 'IN'
elif numargs == 2:
qname, qtype = args
qclass = 'IN'
elif numargs == 3:
qname, qtype, qclass = args
else:
usage()
return (qname, qtype, qclass)
if __name__ == '__main__':
random.seed(os.urandom(64))
qname, qtype, qclass = process_args(sys.argv[1:])
RootZone = get_root_zone()
if Prefs.BATCHFILE:
do_batchmode(infile=Prefs.BATCHFILE, cmdline=sys.argv)
sys.exit(0)
else:
query = Query(qname, qtype, qclass, minimize=Prefs.MINIMIZE)
resolve_name(query, RootZone, addResults=query)
if Prefs.VERBOSE:
print('')
query.print_full_answer()
if Prefs.DEBUG or Prefs.STATS:
print_stats()
sys.exit(exit_status(query))