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Merge pull request #634 from skuhl/systemd-dns-flush

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Flush systemd DNS cache on startup and exit.
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Brian May 2021-05-18 15:40:56 +10:00 committed by GitHub
commit f376674941
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1 changed files with 34 additions and 0 deletions
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34
sshuttle/firewall.py
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@ -5,6 +5,7 @@ import sys
import os
import platform
import traceback
import subprocess as ssubprocess
import sshuttle.ssyslog as ssyslog
import sshuttle.helpers as helpers
@ -89,6 +90,29 @@ def subnet_weight(s):
return (-s[-1] + (s[-2] or -65535), s[1], s[2])
def flush_systemd_dns_cache():
# If the user is using systemd-resolve for DNS resolution, it is
# possible for the request to go through systemd-resolve before we
# see it...and it may use a cached result instead of sending a
# request that we can intercept. When sshuttle starts and stops,
# this means that we should clear the cache!
#
# The command to do this was named systemd-resolve, but changed to
# resolvectl in systemd 239.
# https://github.com/systemd/systemd/blob/f8eb41003df1a4eab59ff9bec67b2787c9368dbd/NEWS#L3816
if helpers.which("resolvectl"):
debug2("Flushing systemd's DNS resolver cache: "
"resolvectl flush-caches")
ssubprocess.Popen(["resolvectl", "flush-caches"],
stdout=ssubprocess.PIPE, env=helpers.get_env())
elif helpers.which("systemd-resolve"):
debug2("Flushing systemd's DNS resolver cache: "
"systemd-resolve --flush-caches")
ssubprocess.Popen(["systemd-resolve", "--flush-caches"],
stdout=ssubprocess.PIPE, env=helpers.get_env())
# This is some voodoo for setting up the kernel's transparent
# proxying stuff. If subnets is empty, we just delete our sshuttle rules;
# otherwise we delete it, then make them from scratch.
@ -227,6 +251,7 @@ def main(method_name, syslog, ttl):
socket.AF_INET, subnets_v4, udp,
user, ttl)
flush_systemd_dns_cache()
stdout.write('STARTED\n')
try:
@ -288,3 +313,12 @@ def main(method_name, syslog, ttl):
debug1(traceback.format_exc())
except BaseException:
debug2('An error occurred, ignoring it.')
try:
flush_systemd_dns_cache()
except BaseException:
try:
debug1("Error trying to flush systemd dns cache.")
debug1(traceback.format_exc())
except BaseException:
debug2("An error occurred, ignoring it.")