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# Copyright (C) 2012 Canonical Ltd.
# Copyright (C) 2012 Hewlett-Packard Development Company, L.P.
#
# Author: Scott Moser <scott.moser@canonical.com>
# Author: Juerg Hafliger <juerg.haefliger@hp.com>
#
# This file is part of cloud-init. See LICENSE file for license information.
import logging
import os
import pwd
from contextlib import suppress
from typing import List, Sequence, Tuple
from cloudinit import lifecycle, subp, util
LOG = logging.getLogger(__name__)
# See: man sshd_config
DEF_SSHD_CFG = "/etc/ssh/sshd_config"
# this list has been filtered out from keytypes of OpenSSH source
# openssh-8.3p1/sshkey.c:
# static const struct keytype keytypes[] = {
# filter out the keytypes with the sigonly flag, eg:
# { "rsa-sha2-256", "RSA", NULL, KEY_RSA, 0, 0, 1 },
# refer to the keytype struct of OpenSSH in the same file, to see
# if the position of the sigonly flag has been moved.
#
# rsa, ecdsa and ed25519 are added for legacy, as they are valid
# public keys in some old distros. They can possibly be removed
# in the future when support for the older distros is dropped
#
# When updating the list, also update the _is_printable_key list in
# cloudinit/config/cc_ssh_authkey_fingerprints.py
VALID_KEY_TYPES = (
"rsa",
"ecdsa",
"ed25519",
"ecdsa-sha2-nistp256-cert-v01@openssh.com",
"ecdsa-sha2-nistp256",
"ecdsa-sha2-nistp384-cert-v01@openssh.com",
"ecdsa-sha2-nistp384",
"ecdsa-sha2-nistp521-cert-v01@openssh.com",
"ecdsa-sha2-nistp521",
"sk-ecdsa-sha2-nistp256-cert-v01@openssh.com",
"sk-ecdsa-sha2-nistp256@openssh.com",
"sk-ssh-ed25519-cert-v01@openssh.com",
"sk-ssh-ed25519@openssh.com",
"ssh-ed25519-cert-v01@openssh.com",
"ssh-ed25519",
"ssh-rsa-cert-v01@openssh.com",
"ssh-rsa",
"ssh-xmss-cert-v01@openssh.com",
"ssh-xmss@openssh.com",
)
_DISABLE_USER_SSH_EXIT = 142
DISABLE_USER_OPTS = (
"no-port-forwarding,no-agent-forwarding,"
'no-X11-forwarding,command="echo \'Please login as the user \\"$USER\\"'
' rather than the user \\"$DISABLE_USER\\".\';echo;sleep 10;'
"exit " + str(_DISABLE_USER_SSH_EXIT) + '"'
)
class AuthKeyLine:
def __init__(
self, source, keytype=None, base64=None, comment=None, options=None
):
self.base64 = base64
self.comment = comment
self.options = options
self.keytype = keytype
self.source = source
def valid(self):
return self.base64 and self.keytype
def __str__(self):
toks = []
if self.options:
toks.append(self.options)
if self.keytype:
toks.append(self.keytype)
if self.base64:
toks.append(self.base64)
if self.comment:
toks.append(self.comment)
if not toks:
return self.source
else:
return " ".join(toks)
class AuthKeyLineParser:
"""
AUTHORIZED_KEYS FILE FORMAT
AuthorizedKeysFile specifies the file containing public keys for public
key authentication; if none is specified, the default is
~/.ssh/authorized_keys. Each line of the file contains one key (empty
(because of the size of the public key encoding) up to a limit of 8 kilo-
bytes, which permits DSA keys up to 8 kilobits and RSA keys up to 16
kilobits. You don't want to type them in; instead, copy the
identity.pub or the id_rsa.pub file and edit it.
sshd enforces a minimum RSA key modulus size for protocol 1 and protocol
2 keys of 768 bits.
The options (if present) consist of comma-separated option specifica-
tions. No spaces are permitted, except within double quotes. The fol-
lowing option specifications are supported (note that option keywords are
case-insensitive):
"""
def _extract_options(self, ent):
"""
The options (if present) consist of comma-separated option specifica-
tions. No spaces are permitted, except within double quotes.
Note that option keywords are case-insensitive.
"""
quoted = False
i = 0
while i < len(ent) and ((quoted) or (ent[i] not in (" ", "\t"))):
curc = ent[i]
if i + 1 >= len(ent):
i = i + 1
break
nextc = ent[i + 1]
if curc == "\\" and nextc == '"':
i = i + 1
elif curc == '"':
quoted = not quoted
i = i + 1
options = ent[0:i]
# Return the rest of the string in 'remain'
remain = ent[i:].lstrip()
return (options, remain)
def parse(self, src_line, options=None):
# modeled after opensshes auth2-pubkey.c:user_key_allowed2
line = src_line.rstrip("\r\n")
if line.startswith("#") or line.strip() == "":
return AuthKeyLine(src_line)
def parse_ssh_key(ent):
# return ketype, key, [comment]
toks = ent.split(None, 2)
if len(toks) < 2:
raise TypeError("To few fields: %s" % len(toks))
if toks[0] not in VALID_KEY_TYPES:
raise TypeError("Invalid keytype %s" % toks[0])
# valid key type and 2 or 3 fields:
if len(toks) == 2:
# no comment in line
toks.append("")
return toks
ent = line.strip()
try:
(keytype, base64, comment) = parse_ssh_key(ent)
except TypeError:
(keyopts, remain) = self._extract_options(ent)
if options is None:
options = keyopts
try:
(keytype, base64, comment) = parse_ssh_key(remain)
except TypeError:
return AuthKeyLine(src_line)
return AuthKeyLine(
src_line,
keytype=keytype,
base64=base64,
comment=comment,
options=options,
)
def parse_authorized_keys(fnames):
lines = []
parser = AuthKeyLineParser()
contents = []
for fname in fnames:
try:
if os.path.isfile(fname):
lines = util.load_text_file(fname).splitlines()
for line in lines:
contents.append(parser.parse(line))
except (IOError, OSError):
util.logexc(LOG, "Error reading lines from %s", fname)
return contents
def update_authorized_keys(old_entries, keys):
to_add = list([k for k in keys if k.valid()])
for i in range(len(old_entries)):
ent = old_entries[i]
if not ent.valid():
continue
# Replace those with the same base64
for k in keys:
if k.base64 == ent.base64:
# Replace it with our better one
ent = k
# Don't add it later
if k in to_add:
to_add.remove(k)
old_entries[i] = ent
# Now append any entries we did not match above
for key in to_add:
old_entries.append(key)
# Now format them back to strings...
lines = [str(b) for b in old_entries]
# Ensure it ends with a newline
lines.append("")
return "\n".join(lines)
def users_ssh_info(username):
pw_ent = pwd.getpwnam(username)
if not pw_ent or not pw_ent.pw_dir:
raise RuntimeError("Unable to get SSH info for user %r" % (username))
return (os.path.join(pw_ent.pw_dir, ".ssh"), pw_ent)
def render_authorizedkeysfile_paths(value, homedir, username):
# The 'AuthorizedKeysFile' may contain tokens
# of the form %T which are substituted during connection set-up.
# The following tokens are defined: %% is replaced by a literal
# '%', %h is replaced by the home directory of the user being
# authenticated and %u is replaced by the username of that user.
macros = (("%h", homedir), ("%u", username), ("%%", "%"))
if not value:
value = "%h/.ssh/authorized_keys"
paths = value.split()
rendered = []
for path in paths:
for macro, field in macros:
path = path.replace(macro, field)
if not path.startswith("/"):
path = os.path.join(homedir, path)
rendered.append(path)
return rendered
# Inspired from safe_path() in openssh source code (misc.c).
def check_permissions(username, current_path, full_path, is_file, strictmodes):
"""Check if the file/folder in @current_path has the right permissions.
We need to check that:
1. If StrictMode is enabled, the owner is either root or the user
2. the user can access the file/folder, otherwise ssh won't use it
3. If StrictMode is enabled, no write permission is given to group
and world users (022)
"""
# group/world can only execute the folder (access)
minimal_permissions = 0o711
if is_file:
# group/world can only read the file
minimal_permissions = 0o644
# 1. owner must be either root or the user itself
owner = util.get_owner(current_path)
if strictmodes and owner != username and owner != "root":
LOG.debug(
"Path %s in %s must be own by user %s or"
" by root, but instead is own by %s. Ignoring key.",
current_path,
full_path,
username,
owner,
)
return False
parent_permission = util.get_permissions(current_path)
# 2. the user can access the file/folder, otherwise ssh won't use it
if owner == username:
# need only the owner permissions
minimal_permissions &= 0o700
else:
group_owner = util.get_group(current_path)
user_groups = util.get_user_groups(username)
if group_owner in user_groups:
# need only the group permissions
minimal_permissions &= 0o070
else:
# need only the world permissions
minimal_permissions &= 0o007
if parent_permission & minimal_permissions == 0:
LOG.debug(
"Path %s in %s must be accessible by user %s,"
" check its permissions",
current_path,
full_path,
username,
)
return False
# 3. no write permission (w) is given to group and world users (022)
# Group and world user can still have +rx.
if strictmodes and (parent_permission & 0o022):
LOG.debug(
"Path %s in %s must not give write"
"permission to group or world users. Ignoring key.",
current_path,
full_path,
)
return False
return True
def check_create_path(username, filename, strictmodes):
user_pwent = users_ssh_info(username)[1]
root_pwent = users_ssh_info("root")[1]
try:
# check the directories first
directories = filename.split("/")[1:-1]
# scan in order, from root to file name
parent_folder = ""
# this is to comply also with unit tests, and
# strange home directories
home_folder = os.path.dirname(user_pwent.pw_dir)
for directory in directories:
parent_folder += "/" + directory
# security check, disallow symlinks in the AuthorizedKeysFile path.
if os.path.islink(parent_folder):
LOG.debug(
"Invalid directory. Symlink exists in path: %s",
parent_folder,
)
return False
if os.path.isfile(parent_folder):
LOG.debug(
"Invalid directory. File exists in path: %s", parent_folder
)
return False
if (
home_folder.startswith(parent_folder)
or parent_folder == user_pwent.pw_dir
):
continue
if not os.path.exists(parent_folder):
# directory does not exist, and permission so far are good:
# create the directory, and make it accessible by everyone
# but owned by root, as it might be used by many users.
with util.SeLinuxGuard(parent_folder):
mode = 0o755
uid = root_pwent.pw_uid
gid = root_pwent.pw_gid
if parent_folder.startswith(user_pwent.pw_dir):
mode = 0o700
uid = user_pwent.pw_uid
gid = user_pwent.pw_gid
os.makedirs(parent_folder, mode=mode, exist_ok=True)
util.chownbyid(parent_folder, uid, gid)
permissions = check_permissions(
username, parent_folder, filename, False, strictmodes
)
if not permissions:
return False
if os.path.islink(filename) or os.path.isdir(filename):
LOG.debug("%s is not a file!", filename)
return False
# check the file
if not os.path.exists(filename):
# if file does not exist: we need to create it, since the
# folders at this point exist and have right permissions
util.write_file(filename, "", mode=0o600, ensure_dir_exists=True)
util.chownbyid(filename, user_pwent.pw_uid, user_pwent.pw_gid)
permissions = check_permissions(
username, filename, filename, True, strictmodes
)
if not permissions:
return False
except (IOError, OSError) as e:
util.logexc(LOG, str(e))
return False
return True
def extract_authorized_keys(username, sshd_cfg_file=DEF_SSHD_CFG):
(ssh_dir, pw_ent) = users_ssh_info(username)
default_authorizedkeys_file = os.path.join(ssh_dir, "authorized_keys")
user_authorizedkeys_file = default_authorizedkeys_file
auth_key_fns = []
with util.SeLinuxGuard(ssh_dir, recursive=True):
try:
ssh_cfg = parse_ssh_config_map(sshd_cfg_file)
key_paths = ssh_cfg.get(
"authorizedkeysfile", "%h/.ssh/authorized_keys"
)
strictmodes = ssh_cfg.get("strictmodes", "yes")
auth_key_fns = render_authorizedkeysfile_paths(
key_paths, pw_ent.pw_dir, username
)
except (IOError, OSError):
# Give up and use a default key filename
auth_key_fns[0] = default_authorizedkeys_file
util.logexc(
LOG,
"Failed extracting 'AuthorizedKeysFile' in SSH "
"config from %r, using 'AuthorizedKeysFile' file "
"%r instead",
DEF_SSHD_CFG,
auth_key_fns[0],
)
# check if one of the keys is the user's one and has the right permissions
for key_path, auth_key_fn in zip(key_paths.split(), auth_key_fns):
if any(
[
"%u" in key_path,
"%h" in key_path,
auth_key_fn.startswith("{}/".format(pw_ent.pw_dir)),
]
):
permissions_ok = check_create_path(
username, auth_key_fn, strictmodes == "yes"
)
if permissions_ok:
user_authorizedkeys_file = auth_key_fn
break
if user_authorizedkeys_file != default_authorizedkeys_file:
LOG.debug(
"AuthorizedKeysFile has an user-specific authorized_keys, "
"using %s",
user_authorizedkeys_file,
)
return (
user_authorizedkeys_file,
parse_authorized_keys([user_authorizedkeys_file]),
)
def setup_user_keys(keys, username, options=None):
# Turn the 'update' keys given into actual entries
parser = AuthKeyLineParser()
key_entries = []
for k in keys:
key_entries.append(parser.parse(str(k), options=options))
# Extract the old and make the new
(auth_key_fn, auth_key_entries) = extract_authorized_keys(username)
ssh_dir = os.path.dirname(auth_key_fn)
with util.SeLinuxGuard(ssh_dir, recursive=True):
content = update_authorized_keys(auth_key_entries, key_entries)
util.write_file(auth_key_fn, content, preserve_mode=True)
class SshdConfigLine:
def __init__(self, line, k=None, v=None):
self.line = line
self._key = k
self.value = v
@property
def key(self):
if self._key is None:
return None
# Keywords are case-insensitive
return self._key.lower()
def __str__(self):
if self._key is None:
return str(self.line)
else:
v = str(self._key)
if self.value:
v += " " + str(self.value)
return v
def parse_ssh_config(fname) -> List[SshdConfigLine]:
if not os.path.isfile(fname):
return []
return parse_ssh_config_lines(util.load_text_file(fname).splitlines())
def parse_ssh_config_lines(lines) -> List[SshdConfigLine]:
# See: man sshd_config
# The file contains keyword-argument pairs, one per line.
# Lines starting with '#' and empty lines are interpreted as comments.
# Note: key-words are case-insensitive and arguments are case-sensitive
ret: List[SshdConfigLine] = []
for line in lines:
line = line.strip()
if not line or line.startswith("#"):
ret.append(SshdConfigLine(line))
continue
try:
key, val = line.split(None, 1)
except ValueError:
try:
key, val = line.split("=", 1)
except ValueError:
LOG.debug(
'sshd_config: option "%s" has no key/value pair,'
" skipping it",
line,
)
continue
ret.append(SshdConfigLine(line, key, val))
return ret
def parse_ssh_config_map(fname):
lines = parse_ssh_config(fname)
if not lines:
return {}
ret = {}
for line in lines:
if not line.key:
continue
ret[line.key] = line.value
return ret
def _includes_dconf(fname: str) -> bool:
if not os.path.isfile(fname):
return False
for line in util.load_text_file(fname).splitlines():
if line.startswith(f"Include {fname}.d/*.conf"):
return True
return False
def _ensure_cloud_init_ssh_config_file(fname):
if _includes_dconf(fname):
if not os.path.isdir(f"{fname}.d"):
util.ensure_dir(f"{fname}.d", mode=0o755)
fname = os.path.join(f"{fname}.d", "50-cloud-init.conf")
if not os.path.isfile(fname):
# Ensure root read-only:
util.ensure_file(fname, 0o600)
return fname
def update_ssh_config(updates, fname=DEF_SSHD_CFG):
"""Read fname, and update if changes are necessary.
@param updates: dictionary of desired values {Option: value}
@return: boolean indicating if an update was done."""
fname = _ensure_cloud_init_ssh_config_file(fname)
lines = parse_ssh_config(fname)
changed = update_ssh_config_lines(lines=lines, updates=updates)
if changed:
util.write_file(
fname,
"\n".join([str(line) for line in lines]) + "\n",
preserve_mode=True,
)
return len(changed) != 0
def update_ssh_config_lines(lines, updates):
"""Update the SSH config lines per updates.
@param lines: array of SshdConfigLine. This array is updated in place.
@param updates: dictionary of desired values {Option: value}
@return: A list of keys in updates that were changed."""
found = set()
changed = []
# Keywords are case-insensitive and arguments are case-sensitive
casemap = dict([(k.lower(), k) for k in updates.keys()])
for i, line in enumerate(lines, start=1):
if not line.key:
continue
if line.key in casemap:
key = casemap[line.key]
value = updates[key]
found.add(key)
if line.value == value:
LOG.debug(
"line %d: option %s already set to %s", i, key, value
)
else:
changed.append(key)
LOG.debug(
"line %d: option %s updated %s -> %s",
i,
key,
line.value,
value,
)
line.value = value
if len(found) != len(updates):
for key, value in updates.items():
if key in found:
continue
changed.append(key)
lines.append(SshdConfigLine("", key, value))
LOG.debug(
"line %d: option %s added with %s", len(lines), key, value
)
return changed
def append_ssh_config(lines: Sequence[Tuple[str, str]], fname=DEF_SSHD_CFG):
if not lines:
return
fname = _ensure_cloud_init_ssh_config_file(fname)
content = (f"{k} {v}" for k, v in lines)
util.write_file(
fname,
"\n".join(content) + "\n",
omode="ab",
preserve_mode=True,
)
def get_opensshd_version():
"""Get the full version of the OpenSSH sshd daemon on the system.
On an ubuntu system, this would look something like:
1.2p1 Ubuntu-1ubuntu0.1
If we can't find `sshd` or parse the version number, return None.
"""
# -V isn't actually a valid argument, but it will cause sshd to print
# out its version number to stderr.
err = ""
with suppress(subp.ProcessExecutionError):
_, err = subp.subp(["sshd", "-V"], rcs=[0, 1])
prefix = "OpenSSH_"
for line in err.split("\n"):
if line.startswith(prefix):
return line[len(prefix) : line.find(",")]
return None
def get_opensshd_upstream_version():
"""Get the upstream version of the OpenSSH sshd daemon on the system.
This will NOT include the portable number, so if the Ubuntu version looks
like `1.2p1 Ubuntu-1ubuntu0.1`, then this function would return
`1.2`
"""
# The default version of openssh is not less than 9.0
upstream_version = "9.0"
full_version = get_opensshd_version()
if full_version is None:
return lifecycle.Version.from_str(upstream_version)
if "p" in full_version:
upstream_version = full_version[: full_version.find("p")]
elif " " in full_version:
upstream_version = full_version[: full_version.find(" ")]
else:
upstream_version = full_version
try:
upstream_version = lifecycle.Version.from_str(upstream_version)
return upstream_version
except (ValueError, TypeError):
LOG.warning("Could not parse sshd version: %s", upstream_version)