Add a --exclude option for excluding subnets from routing.

Also, add 127.0.0.0/8 to the default list of excludes.  If you want to route
0/0, you almost certainly *don't* want to route localhost to the remote ssh
server's localhost!

Thanks to Edward for the suggestion.

client.py

@@ -20,10 +20,11 @@ def original_dst(sock):
 
 
 class FirewallClient:
-    def __init__(self, port, subnets):
+    def __init__(self, port, subnets_include, subnets_exclude):
         self.port = port
         self.auto_nets = []
-        self.subnets = subnets
+        self.subnets_include = subnets_include
+        self.subnets_exclude = subnets_exclude
         argvbase = ([sys.argv[0]] +
                     ['-v'] * (helpers.verbose or 0) +
                     ['--firewall', str(port)])
@@ -67,8 +68,10 @@ class FirewallClient:
 
     def start(self):
         self.pfile.write('ROUTES\n')
-        for (ip,width) in self.subnets+self.auto_nets:
-            self.pfile.write('%s,%d\n' % (ip, width))
+        for (ip,width) in self.subnets_include+self.auto_nets:
+            self.pfile.write('%d,0,%s\n' % (width, ip))
+        for (ip,width) in self.subnets_exclude:
+            self.pfile.write('%d,1,%s\n' % (width, ip))
         self.pfile.write('GO\n')
         self.pfile.flush()
         line = self.pfile.readline()
@@ -185,7 +188,8 @@ def _main(listener, fw, use_server, remotename, seed_hosts, auto_nets):
             mux.check_fullness()
 
 
-def main(listenip, use_server, remotename, seed_hosts, auto_nets, subnets):
+def main(listenip, use_server, remotename, seed_hosts, auto_nets,
+         subnets_include, subnets_exclude):
     debug1('Starting sshuttle proxy.\n')
     listener = socket.socket()
     listener.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
@@ -212,7 +216,7 @@ def main(listenip, use_server, remotename, seed_hosts, auto_nets, subnets):
     listenip = listener.getsockname()
     debug1('Listening on %r.\n' % (listenip,))
 
-    fw = FirewallClient(listenip[1], subnets)
+    fw = FirewallClient(listenip[1], subnets_include, subnets_exclude)
     
     try:
         return _main(listener, fw, use_server, remotename,

firewall.py

@@ -43,14 +43,23 @@ def do_iptables(port, subnets):
         ipt('-I', 'OUTPUT', '1', '-j', chain)
         ipt('-I', 'PREROUTING', '1', '-j', chain)
 
-        # create new subnet entries
-        for snet,swidth in subnets:
-            ipt('-A', chain, '-j', 'REDIRECT',
-                '--dest', '%s/%s' % (snet,swidth),
-                '-p', 'tcp',
-                '--to-ports', str(port),
-                '-m', 'ttl', '!', '--ttl', '42'  # to prevent infinite loops
-                )
+        # create new subnet entries.  Note that we're sorting in a very
+        # particular order: we need to go from most-specific (largest swidth)
+        # to least-specific, and at any given level of specificity, we want
+        # excludes to come first.  That's why the columns are in such a non-
+        # intuitive order.
+        for swidth,sexclude,snet in sorted(subnets, reverse=True):
+            if sexclude:
+                ipt('-A', chain, '-j', 'RETURN',
+                    '--dest', '%s/%s' % (snet,swidth),
+                    '-p', 'tcp')
+            else:
+                ipt('-A', chain, '-j', 'REDIRECT',
+                    '--dest', '%s/%s' % (snet,swidth),
+                    '-p', 'tcp',
+                    '--to-ports', str(port),
+                    '-m', 'ttl', '!', '--ttl', '42'  # to prevent infinite loops
+                    )
 
 
 def ipfw_rule_exists(n):
@@ -103,6 +112,7 @@ def ipfw(*args):
 
 def do_ipfw(port, subnets):
     sport = str(port)
+    xsport = str(port+1)
 
     # cleanup any existing rules
     if ipfw_rule_exists(port):
@@ -120,11 +130,16 @@ def do_ipfw(port, subnets):
              'from', 'any', 'to', 'any', 'established')
         
         # create new subnet entries
-        for snet,swidth in subnets:
-            ipfw('add', sport, 'fwd', '127.0.0.1,%d' % port,
-                 'log', 'tcp',
-                 'from', 'any', 'to', '%s/%s' % (snet,swidth),
-                 'not', 'ipttl', '42')
+        for swidth,sexclude,snet in sorted(subnets, reverse=True):
+            if sexclude:
+                ipfw('add', sport, 'skipto', xsport,
+                     'log', 'tcp',
+                     'from', 'any', 'to', '%s/%s' % (snet,swidth))
+            else:
+                ipfw('add', sport, 'fwd', '127.0.0.1,%d' % port,
+                     'log', 'tcp',
+                     'from', 'any', 'to', '%s/%s' % (snet,swidth),
+                     'not', 'ipttl', '42')
 
 
 def program_exists(name):
@@ -228,10 +243,11 @@ def main(port):
         elif line == 'GO\n':
             break
         try:
-            (ip,width) = line.strip().split(',', 1)
+            (width,exclude,ip) = line.strip().split(',', 2)
         except:
             raise Fatal('firewall: expected route or GO but got %r' % line)
-        subnets.append((ip, int(width)))
+        subnets.append((int(width), bool(int(exclude)), ip))
+        
     try:
         if line:
             debug1('firewall manager: starting transproxy.\n')
@@ -258,7 +274,6 @@ def main(port):
                 raise Fatal('expected EOF, got %r' % line)
             else:
                 break
-
     finally:
         try:
             debug1('firewall manager: undoing changes.\n')

main.py

@@ -53,6 +53,7 @@ l,listen=  transproxy to this ip address and port number [default=0]
 H,auto-hosts scan for remote hostnames and update local /etc/hosts
 N,auto-nets  automatically determine subnets to route
 r,remote=  ssh hostname (and optional username) of remote sshuttle server
+x,exclude= exclude this subnet (can be used more than once)
 v,verbose  increase debug message verbosity
 seed-hosts= with -H, use these hostnames for initial scan (comma-separated)
 noserver   don't use a separate server process (mostly for debugging)
@@ -79,6 +80,11 @@ try:
     else:
         if len(extra) < 1 and not opt.auto_nets:
             o.fatal('at least one subnet (or -N) expected')
+        includes = extra
+        excludes = ['127.0.0.0/8']
+        for k,v in flags:
+            if k in ('-x','--exclude'):
+                excludes.append(v)
         remotename = opt.remote
         if remotename == '' or remotename == '-':
             remotename = None
@@ -95,7 +101,8 @@ try:
                              remotename,
                              sh,
                              opt.auto_nets,
-                             parse_subnets(extra)))
+                             parse_subnets(includes),
+                             parse_subnets(excludes)))
 except Fatal, e:
     log('fatal: %s\n' % e)
     sys.exit(99)