openssh unix dev - Nov 2003 - AIX KRB5CCNAME problem

I believe there is a bug in how AIX handles the KRB5CCNAME environment 
variable.  The symptom occurs when a root user restarts sshd while they 
have KRB5CCNAME set; all of the resulting client connections will inherit 
the same KRB5CCNAME variable.  This can occur if the admin uses 'ksu' or
some other kerberized method of obtaining root privileges.

Investigating this problem, I stumbled across some code in session.c that 
confused me a bit.  This code exists in the OpenSSH source from at least 
as far back as 3.1 to the current source tree.

On about line 1087 of session.c we see this:
#ifdef _AIX
        {
                char *cp;

                if ((cp = getenv("AUTHSTATE")) != NULL)
                        child_set_env(&env, &envsize,
"AUTHSTATE", cp);
                if ((cp = getenv("KRB5CCNAME")) != NULL)
                        child_set_env(&env, &envsize,
"KRB5CCNAME", cp);
                read_environment_file(&env, &envsize,
"/etc/environment");
        }
#endif

It seems to me that this section of code takes the KRB5CCNAME from sshd 
(if it exists) and hands it off to the child.  My question is, why would 
you ever want to do this?

The next section of code is what confused me:
#ifdef KRB5
        if (s->authctxt->krb5_ticket_file)
                child_set_env(&env, &envsize, "KRB5CCNAME",
                    s->authctxt->krb5_ticket_file);
#endif

This would appear to overwrite KRB5CCNAME with (I'm assuming) the correct 
value.  For some reason it doesn't.  Any thoughts on what I'm missing?

-Mike

Mike Dopheide wrote:
> 
> I believe there is a bug in how AIX handles the KRB5CCNAME environment
> variable.  The symptom occurs when a root user restarts sshd while they
> have KRB5CCNAME set; all of the resulting client connections will inherit
> the same KRB5CCNAME variable.  This can occur if the admin uses
'ksu' or
> some other kerberized method of obtaining root privileges.
[snip]
> On about line 1087 of session.c we see this:
[snip code]
> It seems to me that this section of code takes the KRB5CCNAME from sshd
> (if it exists) and hands it off to the child.  My question is, why would
> you ever want to do this?
I've never used Kerberos on AIX but I would guess that this is to handle
the case where KRB5CCNAME is set by one of the modules called by the AIX's
authenticate() function.

It would seem that KRB5CCNAME should be cleared from the sshd's
environment when it starts up to prevent the situation you're describing.

-- 
Darren Tucker (dtucker at zip.com.au)
GPG key 8FF4FA69 / D9A3 86E9 7EEE AF4B B2D4  37C9 C982 80C7 8FF4 FA69
    Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.