Add nat-like method using nftables instead of iptables

sshuttle/linux.py

+import re
 import os
 import socket
 import subprocess as ssubprocess
@@ -49,6 +50,39 @@ def ipt(family, table, *args):
         raise Fatal('%r returned %d' % (argv, rv))
 
 
+def nft(family, table, action, *args):
+    if family == socket.AF_INET:
+        argv = ['nft', action, 'ip', table] + list(args)
+    elif family == socket.AF_INET6:
+        argv = ['nft', action, 'ip6', table] + list(args)
+    else:
+        raise Exception('Unsupported family "%s"' % family_to_string(family))
+    debug1('>> %s\n' % ' '.join(argv))
+    env = {
+        'PATH': os.environ['PATH'],
+        'LC_ALL': "C",
+    }
+    rv = ssubprocess.call(argv, env=env)
+    if rv:
+        raise Fatal('%r returned %d' % (argv, rv))
+
+
+def nft_get_handle(expression, chain):
+    cmd = 'nft'
+    argv = [cmd, 'list', expression, '-a']
+    env = {
+        'PATH': os.environ['PATH'],
+        'LC_ALL': "C",
+    }
+    p = ssubprocess.Popen(argv, stdout=ssubprocess.PIPE, env=env)
+    for line in p.stdout:
+        if (b'jump %s' % chain.encode('utf-8')) in line:
+            return re.sub('.*# ', '', line.decode('utf-8'))
+    rv = p.wait()
+    if rv:
+        raise Fatal('%r returned %d' % (argv, rv))
+
+
 _no_ttl_module = False
 
 

sshuttle/methods/__init__.py

@@ -102,12 +102,14 @@ def get_method(method_name):
 def get_auto_method():
     if _program_exists('iptables'):
         method_name = "nat"
+    elif _program_exists('nft'):
+        method_name = "nft"
     elif _program_exists('pfctl'):
         method_name = "pf"
     elif _program_exists('ipfw'):
         method_name = "ipfw"
     else:
         raise Fatal(
-            "can't find either iptables or pfctl; check your PATH")
+            "can't find either iptables, nft or pfctl; check your PATH")
 
     return get_method(method_name)

sshuttle/methods/nft.py

+import socket
+from sshuttle.firewall import subnet_weight
+from sshuttle.linux import nft, nft_get_handle, nonfatal
+from sshuttle.methods import BaseMethod
+
+
+class Method(BaseMethod):
+
+    # We name the chain based on the transproxy port number so that it's
+    # possible to run multiple copies of sshuttle at the same time.  Of course,
+    # the multiple copies shouldn't have overlapping subnets, or only the most-
+    # recently-started one will win (because we use "-I OUTPUT 1" instead of
+    # "-A OUTPUT").
+    def setup_firewall(self, port, dnsport, nslist, family, subnets, udp,
+                       user):
+        if udp:
+            raise Exception("UDP not supported by nft")
+
+        table = "nat"
+
+        def _nft(action, *args):
+            return nft(family, table, action, *args)
+
+        chain = 'sshuttle-%s' % port
+
+        # basic cleanup/setup of chains
+        _nft('add table', '')
+        _nft('add chain', 'prerouting',
+             '{ type nat hook prerouting priority -100; policy accept; }')
+        _nft('add chain', 'postrouting',
+             '{ type nat hook postrouting priority 100; policy accept; }')
+        _nft('add chain', 'output',
+             '{ type nat hook output priority -100; policy accept; }')
+        _nft('add chain', chain)
+        _nft('flush chain', chain)
+        _nft('add rule', 'output jump %s' % chain)
+        _nft('add rule', 'prerouting jump %s' % chain)
+
+        # create new subnet entries.
+        for _, swidth, sexclude, snet, fport, lport \
+                in sorted(subnets, key=subnet_weight, reverse=True):
+            tcp_ports = ('ip', 'protocol', 'tcp')
+            if fport:
+                tcp_ports = tcp_ports + ('dport { %d-%d }' % (fport, lport))
+
+            if sexclude:
+                _nft('add rule', chain, *(tcp_ports + (
+                     'ip daddr %s/%s' % (snet, swidth), 'return')))
+            else:
+                _nft('add rule', chain, *(tcp_ports + (
+                     'ip daddr %s/%s' % (snet, swidth), 'ip ttl != 42',
+                     ('redirect to :' + str(port)))))
+
+        for _, ip in [i for i in nslist if i[0] == family]:
+            if family == socket.AF_INET:
+                _nft('add rule', chain, 'ip protocol udp ip daddr %s' % ip,
+                     'udp dport { 53 }', 'ip ttl != 42',
+                     ('redirect to :' + str(dnsport)))
+            elif family == socket.AF_INET6:
+                _nft('add rule', chain, 'ip6 protocol udp ip6 daddr %s' % ip,
+                     'udp dport { 53 }', 'ip ttl != 42',
+                     ('redirect to :' + str(dnsport)))
+
+    def restore_firewall(self, port, family, udp, user):
+        if udp:
+            raise Exception("UDP not supported by nft method_name")
+
+        table = "nat"
+
+        def _nft(action, *args):
+            return nft(family, table, action, *args)
+
+        chain = 'sshuttle-%s' % port
+
+        # basic cleanup/setup of chains
+        handle = nft_get_handle('chain ip nat output', chain)
+        nonfatal(_nft, 'delete rule', 'output', handle)
+        handle = nft_get_handle('chain ip nat prerouting', chain)
+        nonfatal(_nft, 'delete rule', 'prerouting', handle)
+        nonfatal(_nft, 'delete chain', chain)

sshuttle/options.py

@@ -160,7 +160,7 @@ parser.add_argument(
 
 parser.add_argument(
     "--method",
-    choices=["auto", "nat", "tproxy", "pf", "ipfw"],
+    choices=["auto", "nat", "nft", "tproxy", "pf", "ipfw"],
     metavar="TYPE",
     default="auto",
     help="""
@@ -230,7 +230,7 @@ parser.add_argument(
     metavar="HOSTNAME[,HOSTNAME]",
     default=[],
     help="""
-    comma-separated list of hostnames for initial scan (may be used with 
+    comma-separated list of hostnames for initial scan (may be used with
     or without --auto-hosts)
     """
 )