memory leak in callback_sshauth_publickey_default in libnetconf #258

Hi,

I'm seeing couple of issues with regard to password based authentication in libnetconf.
Can these issues be fixed ?
Thanks in advance.

1. Memory leak in callback_sshauth_publickey_default
   We are allocating memory at line 162, but are returning NULL at some places on error without freeing the memory.
   buf = malloc (buflen * sizeof(char));
   if (buf == NULL) {
   ERROR("Memory allocation failed (%s:%d - %s).", FILE, LINE, strerror(errno));
   return (NULL);
   }
   if ((tty = fopen("/dev/tty", "r+")) == NULL) {
   ERROR("Unable to open the current terminal (%s:%d - %s).", FILE, LINE, strerror(errno));
   return (NULL);
   }
   if (tcgetattr(fileno(tty), &oldterm) != 0) {
   ERROR("Unable to get terminal settings (%d: %s).", LINE, strerror(errno));
   return (NULL);
   }

2. nc_session_connect_libssh_socket doesn't handle the NULL returned by callback_sshauth_publickey_default
   In ssh.c line 297, we don't do NULL check and start using returned value , resulting in a crash in libssh eventually.
   s = callbacks.sshauth_password(username, host);
   while ((ret_auth = ssh_userauth_password(retval->ssh_sess, username, s)) == SSH_AUTH_AGAIN) {

Best regards,
Parameswaran