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# Copyright (c) 2022 Alvar Penning <post@0x21.biz>
#
# Permission to use, copy, modify, and distribute this software for any
# purpose with or without fee is hereby granted, provided that the above
# copyright notice and this permission notice appear in all copies.
#
# THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
# WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
# ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
# WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
# ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
# OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
# The openbsd_privdrop.py script tries to achieve the principle of least
# privilege for a WeeChat running on OpenBSD by restricting both the available
# system operations as well as the available file system paths by pledge(2) and
# unveil(2). As those functions are OpenBSD-specific, this script does not work
# on any other operating system.
#
# The respective filters are set by configuration variables. On first run or in
# the absence of configuration entries, sane defaults are set. These should be
# sufficient for a normal WeeChat installation, but would have to be adjusted,
# for example, when using other scripts or plugins. So the default does not
# allow the execution of other programs and assumes a home directory under
# /home/$USERNAME for unveil(2).
#
# - https://man.openbsd.org/pledge.2
# - https://man.openbsd.org/unveil.2
# History:
#
# 2022-09-18, Alvar Penning <post@0x21.biz>
# version 0.1.0: initial release
import ctypes
import os
import sys
import weechat
SCRIPT_NAME = "openbsd_privdrop"
SCRIPT_AUTHOR = "Alvar Penning <post@0x21.biz>"
SCRIPT_VERSION = "0.1.0"
SCRIPT_LICENSE = "ISC"
SCRIPT_DESC = "Drop WeeChat's privileges through OpenBSD's pledge(2) and unveil(2)."
SETTINGS = {
"pledge_promises": (
"stdio rpath wpath cpath dpath inet flock unix dns sendfd recvfd tty proc error",
"List of promises for pledge(2).",
),
"pledge_execpromises": (
"",
"List of promises to executed processes; requires exec in pledge_promises.",
),
"unveil": (
"~:rwc;/home:r;/usr/local/lib:r", # WeeChat `stat`s /home while building the path to /home/$USER/...
"List of path and permissions for unveil(2). Format: /a/path:rwc;/another/path:rw",
),
}
def libc_func(name):
""" Returns a libc function, e.g., pledge or unveil.
Inspired by https://nullprogram.com/blog/2021/09/15/
"""
f = ctypes.CDLL(None, use_errno=True)[name]
def _call_f(*args):
weechat.prnt("", f"*\t{name}{args}")
if f(*args) == -1:
errno = ctypes.get_errno()
raise OSError(errno, os.strerror(errno))
return _call_f
def config_get(key):
""" Fetch a stored configuration value and normalize the returned string
for libc usage by replacing empty strings through None and converting
non-empty strings to bytes.
"""
value = weechat.config_get_plugin(key)
return value.encode() if value != "" else None
def weechat_pledge():
""" Execute pledge(2) for the configured promise.
"""
pledge = libc_func("pledge")
promises = config_get("pledge_promises")
execpromises = config_get("pledge_execpromises")
pledge(promises, execpromises)
def weechat_unveil():
""" Execute unveil(2) for the configured paths.
Unveil should be called before pledge unless "unveil" is promised.
"""
unveil = libc_func("unveil")
for path_part in config_get("unveil").split(b";"):
path, permissions = path_part.split(b":")
path = weechat.string_eval_path_home(path.decode(), {}, {}, {}).encode()
unveil(path, permissions)
unveil(None, None)
def main():
""" Main function to load the script and apply the restrictions.
"""
reg = weechat.register(
SCRIPT_NAME,
SCRIPT_AUTHOR,
SCRIPT_VERSION,
SCRIPT_LICENSE,
SCRIPT_DESC,
"", "")
if not reg:
return
if not sys.platform.startswith("openbsd"):
weechat.prnt("", f"{SCRIPT_NAME} is only supported on OpenBSD")
return
for key, value in SETTINGS.items():
if not weechat.config_is_set_plugin(key):
weechat.config_set_plugin(key, value[0])
weechat.config_set_desc_plugin(key, f"{value[1]} (default: \"{value[0]}\")")
weechat_unveil()
weechat_pledge()
if __name__ == "__main__":
main()
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