zulip/zerver/lib/ccache.py

198 lines
7.5 KiB
Python

from typing import Any, Dict, List, Optional, Text
# This file is adapted from samples/shellinabox/ssh-krb-wrapper in
# https://github.com/davidben/webathena, which has the following
# license:
#
# Copyright (c) 2013 David Benjamin and Alan Huang
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
from zerver.lib.str_utils import force_bytes
import base64
import struct
# Some DER encoding stuff. Bleh. This is because the ccache contains a
# DER-encoded krb5 Ticket structure, whereas Webathena deserializes
# into the various fields. Re-encoding in the client would be easy as
# there is already an ASN.1 implementation, but in the interest of
# limiting MIT Kerberos's exposure to malformed ccaches, encode it
# ourselves. To that end, here's the laziest DER encoder ever.
def der_encode_length(length):
# type: (int) -> bytes
if length <= 127:
return struct.pack('!B', length)
out = b""
while length > 0:
out = struct.pack('!B', length & 0xff) + out
length >>= 8
out = struct.pack('!B', len(out) | 0x80) + out
return out
def der_encode_tlv(tag, value):
# type: (int, bytes) -> bytes
return struct.pack('!B', tag) + der_encode_length(len(value)) + value
def der_encode_integer_value(val):
# type: (int) -> bytes
if not isinstance(val, int):
raise TypeError("int")
# base 256, MSB first, two's complement, minimum number of octets
# necessary. This has a number of annoying edge cases:
# * 0 and -1 are 0x00 and 0xFF, not the empty string.
# * 255 is 0x00 0xFF, not 0xFF
# * -256 is 0xFF 0x00, not 0x00
# Special-case to avoid an empty encoding.
if val == 0:
return b"\x00"
sign = 0 # What you would get if you sign-extended the current high bit.
out = b""
# We can stop once sign-extension matches the remaining value.
while val != sign:
byte = val & 0xff
out = struct.pack('!B', byte) + out
sign = -1 if byte & 0x80 == 0x80 else 0
val >>= 8
return out
def der_encode_integer(val):
# type: (int) -> bytes
return der_encode_tlv(0x02, der_encode_integer_value(val))
def der_encode_int32(val):
# type: (int) -> bytes
if val < -2147483648 or val > 2147483647:
raise ValueError("Bad value")
return der_encode_integer(val)
def der_encode_uint32(val):
# type: (int) -> bytes
if val < 0 or val > 4294967295:
raise ValueError("Bad value")
return der_encode_integer(val)
def der_encode_string(val):
# type: (Text) -> bytes
if not isinstance(val, Text):
raise TypeError("unicode")
return der_encode_tlv(0x1b, val.encode("utf-8"))
def der_encode_octet_string(val):
# type: (bytes) -> bytes
if not isinstance(val, bytes):
raise TypeError("bytes")
return der_encode_tlv(0x04, val)
def der_encode_sequence(tlvs, tagged=True):
# type: (List[Optional[bytes]], Optional[bool]) -> bytes
body = []
for i, tlv in enumerate(tlvs):
# Missing optional elements represented as None.
if tlv is None:
continue
if tagged:
# Assume kerberos-style explicit tagging of components.
tlv = der_encode_tlv(0xa0 | i, tlv)
body.append(tlv)
return der_encode_tlv(0x30, b"".join(body))
def der_encode_ticket(tkt):
# type: (Dict[str, Any]) -> bytes
return der_encode_tlv(
0x61, # Ticket
der_encode_sequence(
[der_encode_integer(5), # tktVno
der_encode_string(tkt["realm"]),
der_encode_sequence( # PrincipalName
[der_encode_int32(tkt["sname"]["nameType"]),
der_encode_sequence([der_encode_string(c)
for c in tkt["sname"]["nameString"]],
tagged=False)]),
der_encode_sequence( # EncryptedData
[der_encode_int32(tkt["encPart"]["etype"]),
(der_encode_uint32(tkt["encPart"]["kvno"])
if "kvno" in tkt["encPart"]
else None),
der_encode_octet_string(
base64.b64decode(tkt["encPart"]["cipher"]))])]))
# Kerberos ccache writing code. Using format documentation from here:
# http://www.gnu.org/software/shishi/manual/html_node/The-Credential-Cache-Binary-File-Format.html
def ccache_counted_octet_string(data):
# type: (bytes) -> bytes
if not isinstance(data, bytes):
raise TypeError("bytes")
return struct.pack("!I", len(data)) + data
def ccache_principal(name, realm):
# type: (Dict[str, str], str) -> bytes
header = struct.pack("!II", name["nameType"], len(name["nameString"]))
return (header + ccache_counted_octet_string(force_bytes(realm)) +
b"".join(ccache_counted_octet_string(force_bytes(c))
for c in name["nameString"]))
def ccache_key(key):
# type: (Dict[str, str]) -> bytes
return (struct.pack("!H", key["keytype"]) +
ccache_counted_octet_string(base64.b64decode(key["keyvalue"])))
def flags_to_uint32(flags):
# type: (List[str]) -> int
ret = 0
for i, v in enumerate(flags):
if v:
ret |= 1 << (31 - i)
return ret
def ccache_credential(cred):
# type: (Dict[str, Any]) -> bytes
out = ccache_principal(cred["cname"], cred["crealm"])
out += ccache_principal(cred["sname"], cred["srealm"])
out += ccache_key(cred["key"])
out += struct.pack("!IIII",
cred["authtime"] // 1000,
cred.get("starttime", cred["authtime"]) // 1000,
cred["endtime"] // 1000,
cred.get("renewTill", 0) // 1000)
out += struct.pack("!B", 0)
out += struct.pack("!I", flags_to_uint32(cred["flags"]))
# TODO: Care about addrs or authdata? Former is "caddr" key.
out += struct.pack("!II", 0, 0)
out += ccache_counted_octet_string(der_encode_ticket(cred["ticket"]))
# No second_ticket.
out += ccache_counted_octet_string(b"")
return out
def make_ccache(cred):
# type: (Dict[str, Any]) -> bytes
# Do we need a DeltaTime header? The ccache I get just puts zero
# in there, so do the same.
out = struct.pack("!HHHHII",
0x0504, # file_format_version
12, # headerlen
1, # tag (DeltaTime)
8, # taglen (two uint32_ts)
0, 0, # time_offset / usec_offset
)
out += ccache_principal(cred["cname"], cred["crealm"])
out += ccache_credential(cred)
return out