/usr/lib/maas/maas-write-file is in maas-common 2.4.0~beta2-6865-gec43e47e6-0ubuntu1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 | #!/usr/bin/env python3
# Copyright 2017 Canonical Ltd. This software is licensed under the
# GNU Affero General Public License version 3 (see the file LICENSE).
"""Atomically write a file.
Reads the byte content from standard-in and writes to the specified file. The
filename is checked against an internal white list. As such it's intended to
be used behind `sudo`.
"""
import argparse
import os
import pipes
import sys
from provisioningserver.utils.fs import atomic_write
whitelist = {
"/etc/chrony/chrony.conf",
"/etc/chrony/maas.conf",
"/var/lib/maas/dhcpd-interfaces",
"/var/lib/maas/dhcpd.conf",
"/var/lib/maas/dhcpd6-interfaces",
"/var/lib/maas/dhcpd6.conf",
}
# For DEVELOPMENT ONLY update the paths in the white list to all be prefixed
# with MAAS_ROOT, if defined. Check real and effective UIDs to be super extra
# paranoid (only the latter actually matters).
if os.getuid() != 0 and os.geteuid() != 0:
root = os.environ.get("MAAS_ROOT")
if root is not None:
whitelist = {
os.path.abspath(root + os.sep + path)
for path in whitelist
}
def octal(string):
"""Parse `string` as an octal number."""
return int(string, 8)
arg_parser = argparse.ArgumentParser(description=__doc__)
arg_parser.add_argument("filename", help="The file to write.")
arg_parser.add_argument("mode", type=octal, help="The octal file mode.")
def main(args, fin):
# Validate the filename here because using a `choices` argument in the
# parser results in ugly help and error text.
if args.filename not in whitelist:
arg_parser.error(
"Given filename %s is not in the white list. "
"Choose from: %s." % (
pipes.quote(args.filename), ", ".join(
map(pipes.quote, sorted(whitelist)))))
# Do not allow "high" bits in the mode, especially setuid and setgid.
elif args.mode & 0o777 != args.mode:
arg_parser.error(
"Given file mode 0o%o is not permitted; only "
"permission bits may be set." % args.mode)
# Okay, good to go.
else:
atomic_write(
fin.read(), args.filename, overwrite=True,
mode=args.mode)
if __name__ == "__main__":
main(arg_parser.parse_args(), sys.stdin.buffer)
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