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# -*- test-case-name: twisted.conch.test.test_checkers -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.
"""
Provide L{ICredentialsChecker} implementations to be used in Conch protocols.
"""
import binascii
import errno
import sys
from base64 import decodebytes
from typing import IO, Any, Callable, Iterable, Iterator, Mapping, Optional, Tuple, cast
from zope.interface import Interface, implementer, providedBy
from incremental import Version
from typing import Literal, Protocol
from twisted.conch import error
from twisted.conch.ssh import keys
from twisted.cred.checkers import ICredentialsChecker
from twisted.cred.credentials import ISSHPrivateKey, IUsernamePassword
from twisted.cred.error import UnauthorizedLogin, UnhandledCredentials
from twisted.internet import defer
from twisted.logger import Logger
from twisted.plugins.cred_unix import verifyCryptedPassword
from twisted.python import failure, reflect
from twisted.python.deprecate import deprecatedModuleAttribute
from twisted.python.filepath import FilePath
from twisted.python.util import runAsEffectiveUser
_log = Logger()
class UserRecord(Tuple[str, str, int, int, str, str, str]):
"""
A record in a UNIX-style password database. See L{pwd} for field details.
This corresponds to the undocumented type L{pwd.struct_passwd}, but lacks named
field accessors.
"""
@property
def pw_dir(self) -> str: # type: ignore[empty-body]
...
class UserDB(Protocol):
"""
A database of users by name, like the stdlib L{pwd} module.
See L{twisted.python.fakepwd} for an in-memory implementation.
"""
def getpwnam(self, username: str) -> UserRecord:
"""
Lookup a user record by name.
@raises KeyError: when no such user exists
"""
pwd: Optional[UserDB]
try:
import pwd as _pwd
except ImportError:
pwd = None
else:
pwd = cast(UserDB, _pwd)
try:
import spwd as _spwd
except ImportError:
spwd = None
else:
spwd = _spwd
class CryptedPasswordRecord(Protocol):
"""
A sequence where the item at index 1 may be a crypted password.
Both L{pwd.struct_passwd} and L{spwd.struct_spwd} conform to this protocol.
"""
def __getitem__(self, index: Literal[1]) -> str:
"""
Get the crypted password.
"""
def _lookupUser(userdb: UserDB, username: bytes) -> UserRecord:
"""
Lookup a user by name in a L{pwd}-style database.
@param userdb: The user database.
@param username: Identifying name in bytes. This will be decoded according
to the filesystem encoding, as the L{pwd} module does internally.
@raises KeyError: when the user doesn't exist
"""
return userdb.getpwnam(username.decode(sys.getfilesystemencoding()))
def _pwdGetByName(username: str) -> Optional[CryptedPasswordRecord]:
"""
Look up a user in the /etc/passwd database using the pwd module. If the
pwd module is not available, return None.
@param username: the username of the user to return the passwd database
information for.
@returns: A L{pwd.struct_passwd}, where field 1 may contain a crypted
password, or L{None} when the L{pwd} database is unavailable.
@raises KeyError: when no such user exists
"""
if pwd is None:
return None
return cast(CryptedPasswordRecord, pwd.getpwnam(username))
def _shadowGetByName(username: str) -> Optional[CryptedPasswordRecord]:
"""
Look up a user in the /etc/shadow database using the spwd module. If it is
not available, return L{None}.
@param username: the username of the user to return the shadow database
information for.
@type username: L{str}
@returns: A L{spwd.struct_spwd}, where field 1 may contain a crypted
password, or L{None} when the L{spwd} database is unavailable.
@raises KeyError: when no such user exists
"""
if spwd is not None:
f = spwd.getspnam
else:
return None
return cast(CryptedPasswordRecord, runAsEffectiveUser(0, 0, f, username))
@implementer(ICredentialsChecker)
class UNIXPasswordDatabase:
"""
A checker which validates users out of the UNIX password databases, or
databases of a compatible format.
@ivar _getByNameFunctions: a C{list} of functions which are called in order
to validate a user. The default value is such that the C{/etc/passwd}
database will be tried first, followed by the C{/etc/shadow} database.
"""
credentialInterfaces = (IUsernamePassword,)
def __init__(self, getByNameFunctions=None):
if getByNameFunctions is None:
getByNameFunctions = [_pwdGetByName, _shadowGetByName]
self._getByNameFunctions = getByNameFunctions
def requestAvatarId(self, credentials):
# We get bytes, but the Py3 pwd module uses str. So attempt to decode
# it using the same method that CPython does for the file on disk.
username = credentials.username.decode(sys.getfilesystemencoding())
password = credentials.password.decode(sys.getfilesystemencoding())
for func in self._getByNameFunctions:
try:
pwnam = func(username)
except KeyError:
return defer.fail(UnauthorizedLogin("invalid username"))
else:
if pwnam is not None:
crypted = pwnam[1]
if crypted == "":
continue
if verifyCryptedPassword(crypted, password):
return defer.succeed(credentials.username)
# fallback
return defer.fail(UnauthorizedLogin("unable to verify password"))
@implementer(ICredentialsChecker)
class SSHPublicKeyDatabase:
"""
Checker that authenticates SSH public keys, based on public keys listed in
authorized_keys and authorized_keys2 files in user .ssh/ directories.
"""
credentialInterfaces = (ISSHPrivateKey,)
_userdb: UserDB = cast(UserDB, pwd)
def requestAvatarId(self, credentials):
d = defer.maybeDeferred(self.checkKey, credentials)
d.addCallback(self._cbRequestAvatarId, credentials)
d.addErrback(self._ebRequestAvatarId)
return d
def _cbRequestAvatarId(self, validKey, credentials):
"""
Check whether the credentials themselves are valid, now that we know
if the key matches the user.
@param validKey: A boolean indicating whether or not the public key
matches a key in the user's authorized_keys file.
@param credentials: The credentials offered by the user.
@type credentials: L{ISSHPrivateKey} provider
@raise UnauthorizedLogin: (as a failure) if the key does not match the
user in C{credentials}. Also raised if the user provides an invalid
signature.
@raise ValidPublicKey: (as a failure) if the key matches the user but
the credentials do not include a signature. See
L{error.ValidPublicKey} for more information.
@return: The user's username, if authentication was successful.
"""
if not validKey:
return failure.Failure(UnauthorizedLogin("invalid key"))
if not credentials.signature:
return failure.Failure(error.ValidPublicKey())
else:
try:
pubKey = keys.Key.fromString(credentials.blob)
if pubKey.verify(credentials.signature, credentials.sigData):
return credentials.username
except Exception: # any error should be treated as a failed login
_log.failure("Error while verifying key")
return failure.Failure(UnauthorizedLogin("error while verifying key"))
return failure.Failure(UnauthorizedLogin("unable to verify key"))
def getAuthorizedKeysFiles(self, credentials):
"""
Return a list of L{FilePath} instances for I{authorized_keys} files
which might contain information about authorized keys for the given
credentials.
On OpenSSH servers, the default location of the file containing the
list of authorized public keys is
U{$HOME/.ssh/authorized_keys<http://www.openbsd.org/cgi-bin/man.cgi?query=sshd_config>}.
I{$HOME/.ssh/authorized_keys2} is also returned, though it has been
U{deprecated by OpenSSH since
2001<http://marc.info/?m=100508718416162>}.
@return: A list of L{FilePath} instances to files with the authorized keys.
"""
pwent = _lookupUser(self._userdb, credentials.username)
root = FilePath(pwent.pw_dir).child(".ssh")
files = ["authorized_keys", "authorized_keys2"]
return [root.child(f) for f in files]
def checkKey(self, credentials):
"""
Retrieve files containing authorized keys and check against user
credentials.
"""
ouid, ogid = _lookupUser(self._userdb, credentials.username)[2:4]
for filepath in self.getAuthorizedKeysFiles(credentials):
if not filepath.exists():
continue
try:
lines = filepath.open()
except OSError as e:
if e.errno == errno.EACCES:
lines = runAsEffectiveUser(ouid, ogid, filepath.open)
else:
raise
with lines:
for l in lines:
l2 = l.split()
if len(l2) < 2:
continue
try:
if decodebytes(l2[1]) == credentials.blob:
return True
except binascii.Error:
continue
return False
def _ebRequestAvatarId(self, f):
if not f.check(UnauthorizedLogin):
_log.error(
"Unauthorized login due to internal error: {error}", error=f.value
)
return failure.Failure(UnauthorizedLogin("unable to get avatar id"))
return f
@implementer(ICredentialsChecker)
class SSHProtocolChecker:
"""
SSHProtocolChecker is a checker that requires multiple authentications
to succeed. To add a checker, call my registerChecker method with
the checker and the interface.
After each successful authenticate, I call my areDone method with the
avatar id. To get a list of the successful credentials for an avatar id,
use C{SSHProcotolChecker.successfulCredentials[avatarId]}. If L{areDone}
returns True, the authentication has succeeded.
"""
def __init__(self):
self.checkers = {}
self.successfulCredentials = {}
@property
def credentialInterfaces(self):
return list(self.checkers.keys())
def registerChecker(self, checker, *credentialInterfaces):
if not credentialInterfaces:
credentialInterfaces = checker.credentialInterfaces
for credentialInterface in credentialInterfaces:
self.checkers[credentialInterface] = checker
def requestAvatarId(self, credentials):
"""
Part of the L{ICredentialsChecker} interface. Called by a portal with
some credentials to check if they'll authenticate a user. We check the
interfaces that the credentials provide against our list of acceptable
checkers. If one of them matches, we ask that checker to verify the
credentials. If they're valid, we call our L{_cbGoodAuthentication}
method to continue.
@param credentials: the credentials the L{Portal} wants us to verify
"""
ifac = providedBy(credentials)
for i in ifac:
c = self.checkers.get(i)
if c is not None:
d = defer.maybeDeferred(c.requestAvatarId, credentials)
return d.addCallback(self._cbGoodAuthentication, credentials)
return defer.fail(
UnhandledCredentials(
"No checker for %s" % ", ".join(map(reflect.qual, ifac))
)
)
def _cbGoodAuthentication(self, avatarId, credentials):
"""
Called if a checker has verified the credentials. We call our
L{areDone} method to see if the whole of the successful authentications
are enough. If they are, we return the avatar ID returned by the first
checker.
"""
if avatarId not in self.successfulCredentials:
self.successfulCredentials[avatarId] = []
self.successfulCredentials[avatarId].append(credentials)
if self.areDone(avatarId):
del self.successfulCredentials[avatarId]
return avatarId
else:
raise error.NotEnoughAuthentication()
def areDone(self, avatarId):
"""
Override to determine if the authentication is finished for a given
avatarId.
@param avatarId: the avatar returned by the first checker. For
this checker to function correctly, all the checkers must
return the same avatar ID.
"""
return True
deprecatedModuleAttribute(
Version("Twisted", 15, 0, 0),
(
"Please use twisted.conch.checkers.SSHPublicKeyChecker, "
"initialized with an instance of "
"twisted.conch.checkers.UNIXAuthorizedKeysFiles instead."
),
__name__,
"SSHPublicKeyDatabase",
)
class IAuthorizedKeysDB(Interface):
"""
An object that provides valid authorized ssh keys mapped to usernames.
@since: 15.0
"""
def getAuthorizedKeys(avatarId):
"""
Gets an iterable of authorized keys that are valid for the given
C{avatarId}.
@param avatarId: the ID of the avatar
@type avatarId: valid return value of
L{twisted.cred.checkers.ICredentialsChecker.requestAvatarId}
@return: an iterable of L{twisted.conch.ssh.keys.Key}
"""
def readAuthorizedKeyFile(
fileobj: IO[bytes], parseKey: Callable[[bytes], keys.Key] = keys.Key.fromString
) -> Iterator[keys.Key]:
"""
Reads keys from an authorized keys file. Any non-comment line that cannot
be parsed as a key will be ignored, although that particular line will
be logged.
@param fileobj: something from which to read lines which can be parsed
as keys
@param parseKey: a callable that takes bytes and returns a
L{twisted.conch.ssh.keys.Key}, mainly to be used for testing. The
default is L{twisted.conch.ssh.keys.Key.fromString}.
@return: an iterable of L{twisted.conch.ssh.keys.Key}
@since: 15.0
"""
for line in fileobj:
line = line.strip()
if line and not line.startswith(b"#"): # for comments
try:
yield parseKey(line)
except keys.BadKeyError as e:
_log.error(
"Unable to parse line {line!r} as a key: {error!s}",
line=line,
error=e,
)
def _keysFromFilepaths(
filepaths: Iterable[FilePath[Any]], parseKey: Callable[[bytes], keys.Key]
) -> Iterable[keys.Key]:
"""
Helper function that turns an iterable of filepaths into a generator of
keys. If any file cannot be read, a message is logged but it is
otherwise ignored.
@param filepaths: iterable of L{twisted.python.filepath.FilePath}.
@type filepaths: iterable
@param parseKey: a callable that takes a string and returns a
L{twisted.conch.ssh.keys.Key}
@type parseKey: L{callable}
@return: generator of L{twisted.conch.ssh.keys.Key}
@since: 15.0
"""
for fp in filepaths:
if fp.exists():
try:
with fp.open() as f:
yield from readAuthorizedKeyFile(f, parseKey)
except OSError as e:
_log.error("Unable to read {path!r}: {error!s}", path=fp.path, error=e)
@implementer(IAuthorizedKeysDB)
class InMemorySSHKeyDB:
"""
Object that provides SSH public keys based on a dictionary of usernames
mapped to L{twisted.conch.ssh.keys.Key}s.
@since: 15.0
"""
def __init__(self, mapping: Mapping[bytes, Iterable[keys.Key]]) -> None:
"""
Initializes a new L{InMemorySSHKeyDB}.
@param mapping: mapping of usernames to iterables of
L{twisted.conch.ssh.keys.Key}s
"""
self._mapping = mapping
def getAuthorizedKeys(self, username: bytes) -> Iterable[keys.Key]:
"""
Look up the authorized keys for a user.
@param username: Name of the user
"""
return self._mapping.get(username, [])
@implementer(IAuthorizedKeysDB)
class UNIXAuthorizedKeysFiles:
"""
Object that provides SSH public keys based on public keys listed in
authorized_keys and authorized_keys2 files in UNIX user .ssh/ directories.
If any of the files cannot be read, a message is logged but that file is
otherwise ignored.
@since: 15.0
"""
_userdb: UserDB
def __init__(
self,
userdb: Optional[UserDB] = None,
parseKey: Callable[[bytes], keys.Key] = keys.Key.fromString,
):
"""
Initializes a new L{UNIXAuthorizedKeysFiles}.
@param userdb: access to the Unix user account and password database
(default is the Python module L{pwd}, if available)
@param parseKey: a callable that takes a string and returns a
L{twisted.conch.ssh.keys.Key}, mainly to be used for testing. The
default is L{twisted.conch.ssh.keys.Key.fromString}.
"""
if userdb is not None:
self._userdb = userdb
elif pwd is not None:
self._userdb = pwd
else:
raise ValueError("No pwd module found, and no userdb argument passed.")
self._parseKey = parseKey
def getAuthorizedKeys(self, username: bytes) -> Iterable[keys.Key]:
try:
passwd = _lookupUser(self._userdb, username)
except KeyError:
return ()
root = FilePath(passwd.pw_dir).child(".ssh")
files = ["authorized_keys", "authorized_keys2"]
return _keysFromFilepaths((root.child(f) for f in files), self._parseKey)
@implementer(ICredentialsChecker)
class SSHPublicKeyChecker:
"""
Checker that authenticates SSH public keys, based on public keys listed in
authorized_keys and authorized_keys2 files in user .ssh/ directories.
Initializing this checker with a L{UNIXAuthorizedKeysFiles} should be
used instead of L{twisted.conch.checkers.SSHPublicKeyDatabase}.
@since: 15.0
"""
credentialInterfaces = (ISSHPrivateKey,)
def __init__(self, keydb: IAuthorizedKeysDB) -> None:
"""
Initializes a L{SSHPublicKeyChecker}.
@param keydb: a provider of L{IAuthorizedKeysDB}
"""
self._keydb = keydb
def requestAvatarId(self, credentials):
d = defer.execute(self._sanityCheckKey, credentials)
d.addCallback(self._checkKey, credentials)
d.addCallback(self._verifyKey, credentials)
return d
def _sanityCheckKey(self, credentials):
"""
Checks whether the provided credentials are a valid SSH key with a
signature (does not actually verify the signature).
@param credentials: the credentials offered by the user
@type credentials: L{ISSHPrivateKey} provider
@raise ValidPublicKey: the credentials do not include a signature. See
L{error.ValidPublicKey} for more information.
@raise BadKeyError: The key included with the credentials is not
recognized as a key.
@return: the key in the credentials
@rtype: L{twisted.conch.ssh.keys.Key}
"""
if not credentials.signature:
raise error.ValidPublicKey()
return keys.Key.fromString(credentials.blob)
def _checkKey(self, pubKey, credentials):
"""
Checks the public key against all authorized keys (if any) for the
user.
@param pubKey: the key in the credentials (just to prevent it from
having to be calculated again)
@type pubKey:
@param credentials: the credentials offered by the user
@type credentials: L{ISSHPrivateKey} provider
@raise UnauthorizedLogin: If the key is not authorized, or if there
was any error obtaining a list of authorized keys for the user.
@return: C{pubKey} if the key is authorized
@rtype: L{twisted.conch.ssh.keys.Key}
"""
if any(
key == pubKey for key in self._keydb.getAuthorizedKeys(credentials.username)
):
return pubKey
raise UnauthorizedLogin("Key not authorized")
def _verifyKey(self, pubKey, credentials):
"""
Checks whether the credentials themselves are valid, now that we know
if the key matches the user.
@param pubKey: the key in the credentials (just to prevent it from
having to be calculated again)
@type pubKey: L{twisted.conch.ssh.keys.Key}
@param credentials: the credentials offered by the user
@type credentials: L{ISSHPrivateKey} provider
@raise UnauthorizedLogin: If the key signature is invalid or there
was any error verifying the signature.
@return: The user's username, if authentication was successful
@rtype: L{bytes}
"""
try:
if pubKey.verify(credentials.signature, credentials.sigData):
return credentials.username
except Exception as e: # Any error should be treated as a failed login
raise UnauthorizedLogin("Error while verifying key") from e
raise UnauthorizedLogin("Key signature invalid.")