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Re: Login PAM interaction suspect



Quoting Tomas Mraz <tmraz redhat com>:

On Thu, 2011-11-17 at 16:59 +0100, Thorsten Kukuk wrote:
On Thu, Nov 17, David Mitton wrote:


> Which was the first thing I saw login do wrong.  It calls pam_open_session
> before pam_setcred.  I'm waiting for someone to explain that.

As I think somebody wrote already here: it's a bug in login where
I did send already a patch upstream.

Note that the original PAM RFC has an example where the pam_setcred() is
called AFTER the pam_open_session(). This conflict with the manual page
was never resolved one way or another. Some applications prefer calling
pam_setcred() twice with PAM_ESTABLISH_CRED before pam_open_session()
and with PAM_REINITIALIZE_CRED after pam_open_session().

Also for David, I'd really say, that what you want to do is really a
hack as the correct thing would be to write a proper nsswitch module or
to use an existing one. And if you insist on such a hack you should
really use pam_acct_mgmt() call to put the user into the
local /etc/passwd instead of relying on pam_setcred() behavior in one
way or another.

I'm sorry, if you read my earlier messages, I am writting an nsswitch module, the issue was _when_ my nsswitch got the information _relative_ to the PAM processing. My first read of the documentation was that it would make sense to do that at pam_setcred() time. My read of login has convinced me otherwise.

Now, I'm not really sure what the purpose of pam_setcred is. Though the point of the setting of UID before calling is telling. I have no need to store any credentials using the user's privs. I can see that if you need to store a proof of authentication credential (Kerberos ticket) or are doing some sort of SSO. But that's never explained.

Dave.

--
Tomas Mraz
No matter how far down the wrong road you've gone, turn back.
                                              Turkish proverb


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