Fix rapid7#4711 - Errno::EINVA (getpeername(2)) BrowserAutoPwn Fix

This patch fixes rapid7#4711.

The problem here is that the browser sometimes will shutdown some of our
exploit's connections (in my testing, all Java), and that will cause Ruby
to call a rb_sys_fail with "getpeername(2)". The error goes all the
way to Rex::IO::StreamServer's monitor_listener method, which triggers a
"break" to quit monitoring. And then this causes another chain of reactions
that eventually forces BrowserAutoPwn to quit completely (while the
JavaScript on the browser is still running)

Author: wchen-r7

lib/rex/socket.rb

@@ -732,7 +732,15 @@ def getlocalname
   # Return peer connection information.
   #
   def getpeername
-    return Socket.from_sockaddr(super)
+    peer_name = nil
+    begin
+      peer_name = Socket.from_sockaddr(super)
+    rescue ::Exception => e
+      # Ruby's getpeername method may call rb_sys_fail("getpeername(2)")
+      elog("#{e.message} (#{e.class})#{e.backtrace * "\n"}\n", 'core', LEV_3)
+    end
+
+    return peer_name
   end
 
   #

lib/rex/socket/tcp_server.rb

@@ -56,6 +56,9 @@ def accept(opts = {})
 
       pn = t.getpeername
 
+      # We hit a "getpeername(2)" from Ruby
+      return nil unless pn
+
       t.peerhost = pn[1]
       t.peerport = pn[2]
     end