Fixes to rpc-grind

NSE: rpc-grind Connect(): RPC library does not support: nil protocol
NSE: rpc-grind Connect(): RPC library does not support: rpcbind version
81578896

These errors caused by ChkProgram and ChkVersion called from
rpc.Comm.Connect. Added a dummy program in rpc-grind and a check for
self.checkprogver in ChkVersion, and everything works great.

Also fixed portrule to only fail if the non-rpcbind service name was not
the result of table lookup. Was failing on port 2049 (in nmap-services
as "nfs") without -sV.

nselib/rpc.lua

@@ -231,6 +231,7 @@ Comm = {
     -- @return status boolean true on success, false on failure
     -- @return string containing error message (if status is false)
     ChkVersion = function(self)
+      if not self.checkprogver then return true end
       if ( self.version > RPC_version[self.program].max or
       self.version < RPC_version[self.program].min ) then
         return false, string.format("RPC library does not support: %s version %d",

scripts/rpc-grind.nse

@@ -41,7 +41,7 @@ categories = {"version"}
 
 
 portrule = function(host, port)
-    if port.service ~= nil and port.service ~= 'rpcbind' then
+    if port.service ~= nil and port.version.service_dtype ~= "table" and port.service ~= 'rpcbind' then
         -- Exclude services that have already been detected as something
         -- different than rpcbind.
         return false
@@ -157,9 +157,8 @@ local rpcGrinder = function(host, port, iterator, result)
       -- We use a random, most likely unsupported version so that
     -- we also trigger min and max version disclosure for the target service.
     version = math.random(12345, 123456789)
-    rpcConn = rpc.Comm:new()
+    rpcConn = rpc.Comm:new("rpcbind", version)
     rpcConn:SetCheckProgVer(false)
-    rpcConn:SetVersion(version)
     status, err = rpcConn:Connect(host, port)
 
     if not status then