Handle libssh2 errors on connect. Closes #2616. Fixes #1014

CHANGELOG

@@ -1,5 +1,9 @@
 #Nmap Changelog ($Id$); -*-text-*-
 
+o [NSE][GH#1014][GH#2616] SSH NSE scripts now catch connection errors thrown by
+  the libssh2 Lua binding, providing useful output instead of a backtrace.
+  [Joshua Rogers, Daniel Miller]
+
 o Nmap will now allow targets to be specified both on the command line and in
   an input file with -iL. Previously, if targets were provided in both places,
   only the targets in the input file would be scanned, and no notice was given

scripts/ssh-auth-methods.nse

@@ -41,8 +41,9 @@ portrule = shortport.ssh
 function action (host, port)
   local result = stdnse.output_table()
   local helper = libssh2_util.SSHConnection:new()
-  if not helper:connect(host, port) then
+  local status, err = helper:connect_pcall(host, port)
-    return "Failed to connect to ssh server"
+  if not status then
+    return "Failed to connect to ssh server: " .. err
   end
 
   local authmethods = helper:list(username)

scripts/ssh-brute.nse

@@ -82,9 +82,7 @@ Driver = {
 
 local function password_auth_allowed (host, port)
   local helper = libssh2_util.SSHConnection:new()
-  if not helper:connect(host, port) then
+  helper:connect(host, port) -- throws error on failure
-    return "Failed to connect to ssh server"
-  end
   local methods = helper:list "root"
   if methods then
     for _, value in pairs(methods) do
@@ -99,7 +97,11 @@ end
 function action (host, port)
   local timems = stdnse.parse_timespec(arg_timeout) --todo: use this!
   local ssh_timeout = 1000 * timems
-  if password_auth_allowed(host, port) then
+  local connected, auth_status = pcall(password_auth_allowed, host, port)
+  if not connected then
+    return "Failed to connect to ssh server: " .. auth_status
+  end
+  if auth_status then
     local options = {
       ssh_timeout = ssh_timeout,
     }

scripts/ssh-publickey-acceptance.nse

@@ -61,12 +61,12 @@ function action (host, port)
         local status, result = helper:read_publickey(publickeys[i])
         if not status then
           stdnse.verbose("Error reading key: " .. result)
-        elseif helper:connect(host, port) then
+        elseif helper:connect_pcall(host, port) then
           successes = successes + 1
           local status, err = helper:publickey_canauth(usernames[j], result)
           if status then
             table.insert(r, "Key " .. publickeys[i] .. " accepted for user " .. usernames[j])
-            stdnse.verbose("Found accepted key: " .. publickeys[i] .. " for user " .. usernames[j])
+            stdnse.verbose("Found accepted key: " .. publickeys[i] .. " for user " .. usernames[j] .. " on host " .. host.ip .. ":" .. port.number)
           elseif err then
             stdnse.debug("Error in publickey_canauth: %s", err)
           end
@@ -100,7 +100,7 @@ function action (host, port)
       local msg = sections[3]
       stdnse.debug("Checking key: " .. key .. " for user " .. user)
       key = base64.dec(key)
-      if helper:connect(host, port) then
+      if helper:connect_pcall(host, port) then
         successes = successes + 1
         if helper:publickey_canauth(user, key) then
           table.insert(r, msg)
@@ -128,14 +128,13 @@ function action (host, port)
     for j = 1, #usernames do
       for i = 1, #privatekeys do
         stdnse.debug("Checking key: " .. privatekeys[i] .. " for user " .. usernames[j])
-        if helper:connect(host, port) then
+        if helper:connect_pcall(host, port) then
           successes = successes + 1
           if not helper:publickey_auth(usernames[j], privatekeys[i], passphrases[i] or "") then
-            stdnse.verbose "Failed to authenticate"
+            stdnse.verbose("Failed to authenticate key " .. privatekeys[i] .. " for user " .. usernames[j] .. " on host " .. host.ip .. ":" .. port.number)
           else
             table.insert(r, "Key " .. privatekeys[i] .. " accepted for user " .. usernames[j])
-            stdnse.verbose("Found accepted key: " .. privatekeys[i] .. " for user " .. usernames[j])
+            stdnse.verbose("Found accepted key: " .. privatekeys[i] .. " for user " .. usernames[j] .. " on host " .. host.ip .. ":" .. port.number)
-
           end
           helper:disconnect()
         else

scripts/ssh-run.nse

@@ -61,8 +61,9 @@ end
 
 function action (host, port)
   local conn = libssh2_util.SSHConnection:new()
-  if not conn:connect(host, port) then
+  local status, err = helper:connect_pcall(host, port)
-    return "Failed to connect to ssh server"
+  if not status then
+    return "Failed to connect to ssh server: " .. err
   end
   if username and password and cmd then
     if not conn:password_auth(username, password) then