Hello Ludovic,

thanks for pointing that out.  IIRC, I saw this kind of errors during
testing but I thought I fixed them.  What Guile-SSH version do you use?

Here's 'free_session' procedure from Guile-SSH version 0.10.0:

--8<---------------cut here---------------start------------->8---
size_t
free_session (SCM session_smob)
{
  if (! SCM_SMOB_PREDICATE (session_tag, session_smob))
    {
      _ssh_log (SSH_LOG_FUNCTIONS, "free_session", "%s", "already freed");
      return 0;
    }
  struct session_data *data = _scm_to_session_data (session_smob);

  [...]

  return 0;
}
--8<---------------cut here---------------end--------------->8---

As you can see, there's additional smob check before accessing the
smob's data.

Please let me know if the problem manifest itself in the latest
Guile-SSH version.

Thanks!

- Artyom

-- 
Artyom V. Poptsov <poptsov.artyom@gmail.com>;  GPG Key: 0898A02F
Home page: http://poptsov-artyom.narod.ru/