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Make server and client handle resolv.conf differently.

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The server should just read from resolv.conf to find DNS servers to
use. This restores this behavior after the previous commit changed it.

The client now reads both /etc/resolv.conf and
/run/systemd/resolve/resolv.conf. The latter is required to more
reliably intercept regular DNS requests that systemd-resolved makes.
This commit is contained in:
Scott Kuhl 2020-11-03 20:27:57 -05:00
parent 502960d796
commit 8461e08bc3
4 changed files with 29 additions and 15 deletions
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2
sshuttle/client.py
View File

@ -589,7 +589,7 @@ def main(listenip_v6, listenip_v4,
# redirect packets outgoing to this server to the remote host
# instead.
if dns:
nslist += resolvconf_nameservers()
nslist += resolvconf_nameservers(True)
if to_nameserver is not None:
to_nameserver = "%s@%s" % tuple(to_nameserver[1:])
else:

36
sshuttle/helpers.py
View File

@ -48,10 +48,18 @@ class Fatal(Exception):
pass
def resolvconf_nameservers():
"""Retrieves a list of tuples (address type, address as a string) that
the current system uses to resolve hostnames from /etc/resolv.conf
and possibly other files.
def resolvconf_nameservers(systemd_resolved):
"""Retrieves a list of tuples (address type, address as a string) of
the DNS servers used by the system to resolve hostnames.
If parameter is False, DNS servers are retrieved from only
/etc/resolv.conf. This behavior makes sense for the sshuttle
server.
If parameter is True, we retrieve information from both
/etc/resolv.conf and /run/systemd/resolve/resolv.conf (if it
exists). This behavior makes sense for the sshuttle client.
"""
# Historically, we just needed to read /etc/resolv.conf.
@ -59,10 +67,10 @@ def resolvconf_nameservers():
# If systemd-resolved is active, /etc/resolv.conf will point to
# localhost and the actual DNS servers that systemd-resolved uses
# are stored in /run/systemd/resolve/resolv.conf. For programs
# that use the localhost DNS server, only reading /etc/resolv.conf
# is sufficient. However, resolved provides other ways of
# resolving hostnames (such as via dbus) that may not route
# requests through localhost. So, we retrieve a list of DNS
# that use the localhost DNS server, having sshuttle read
# /etc/resolv.conf is sufficient. However, resolved provides other
# ways of resolving hostnames (such as via dbus) that may not
# route requests through localhost. So, we retrieve a list of DNS
# servers that resolved uses so we can intercept those as well.
#
# For more information about systemd-resolved, see:
@ -70,7 +78,9 @@ def resolvconf_nameservers():
#
# On machines without systemd-resolved, we expect opening the
# second file will fail.
files = ['/etc/resolv.conf', '/run/systemd/resolve/resolv.conf']
files = ['/etc/resolv.conf']
if systemd_resolved:
files += ['/run/systemd/resolve/resolv.conf']
nsservers = []
for f in files:
@ -90,8 +100,12 @@ def resolvconf_nameservers():
return nsservers
def resolvconf_random_nameserver():
lines = resolvconf_nameservers()
def resolvconf_random_nameserver(systemd_resolved):
"""Return a random nameserver selected from servers produced by
resolvconf_nameservers(). See documentation for
resolvconf_nameservers() for a description of the parameter.
"""
lines = resolvconf_nameservers(systemd_resolved)
if lines:
if len(lines) > 1:
# don't import this unless we really need it

2
sshuttle/server.py
View File

@ -205,7 +205,7 @@ class DnsProxy(Handler):
self.tries += 1
if self.to_nameserver is None:
_, peer = resolvconf_random_nameserver()
_, peer = resolvconf_random_nameserver(False)
port = 53
else:
peer = self.to_ns_peer

4
tests/client/test_helpers.py
View File

@ -131,7 +131,7 @@ nameserver 2404:6800:4004:80c::3
nameserver 2404:6800:4004:80c::4
""")
ns = sshuttle.helpers.resolvconf_nameservers()
ns = sshuttle.helpers.resolvconf_nameservers(False)
assert ns == [
(AF_INET, u'192.168.1.1'), (AF_INET, u'192.168.2.1'),
(AF_INET, u'192.168.3.1'), (AF_INET, u'192.168.4.1'),
@ -156,7 +156,7 @@ nameserver 2404:6800:4004:80c::2
nameserver 2404:6800:4004:80c::3
nameserver 2404:6800:4004:80c::4
""")
ns = sshuttle.helpers.resolvconf_random_nameserver()
ns = sshuttle.helpers.resolvconf_random_nameserver(False)
assert ns in [
(AF_INET, u'192.168.1.1'), (AF_INET, u'192.168.2.1'),
(AF_INET, u'192.168.3.1'), (AF_INET, u'192.168.4.1'),