netgroup / passwd

2007-12-25 7:26:00

>> I was just asked to enforce security on our network by selecting

>> users on hosts. I thought using the +@ / -@ feature in /etc/passwd.

>> And I did:

>> tail /etc/passwd

>> sysdiag:*:0:1:Old System Diagnostic:/usr/diag/sysdiag:/usr/diag/sysdiag/sysdi

>> sundiag:*:0:1:System Diagnostic:/usr/diag/sundiag:/usr/diag/sundiag/sundiag

>> -@u_students:

>> +::::::

>> Since the manual pages passwd(5) says:

>> -@netgroup means

>> to disallow any subsequent entries for all members of the

>> network group netgroup.

>> I thought that no students can log in this host.(because of the word

>> "subsequent"). But it fails. Why?

1. Some people told me this is a reverse order: I disallow students,

then I allow everyone. So they told me to write:

+::::::

-@u_students:

It doesn't work.

2. Some people told:

+@u_students::0:0::/no/home:/some/prog

I didn't test this. But doing this, people have

an account, of course with no login/rlogin/telnet.

But there are a lot of ways to execute commands: .forward,

rsh, on, ftp, etc. (yes, I know how to protect these first 4

but not how to protect the fifth...)

3. AN ANSWER IS to set a regular passwd line:

-@u_students::0:0::::

+::::::

Without the two '0', it doesn't work.

It's not quite normal because to allow people you just

have to say:

+@u_students:

So there is a dissymetry between allowing/disallowing.

And DEC/Ultrix undertand the short form (-@u_students:).

So I think there is a bug...

Thanks to:

        brent@curie.ssctr.bcm.tmc.edu

        paul@Concour.cs.Concordia.CA

        jstewart@mailbox.syr.edu

        trinkle@cs.purdue.edu

        canuck@rice.edu

        stern@sunne.East.Sun.COM

        bernards@ECN.NL

        tom@sees.bangor.ac.uk

        mdl@cypress.com

        matt@oddjob.uchicago.edu

        butzer@cis.ohio-state.edu

        stanonik@nprdc.navy.mil

        phil@pex.eecs.nwu.edu

  --Jacques Beigbeder

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