Re: Login PAM interaction suspect

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Quoting Tomas Mraz <tmraz@xxxxxxxxxx>:

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.


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

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