UNIX for Advanced &amp; Expert Users

View Public Profile for Scrutinizer

11-29-2016

Moderator

12,296, 3,792

Join Date: Nov 2008

Last Activity: 1 January 2021, 1:47 AM EST

Location: Amsterdam

Posts: 12,296

Thanks Given: 679

Thanked 3,792 Times in 3,282 Posts

Hi Robin,

What is in /etc/pam.d/system-auth ?

Scrutinizer

Find all posts by Scrutinizer

11-30-2016

Moderator

3,843, 841

Join Date: Jun 2007

Last Activity: 29 June 2020, 12:30 PM EDT

Location: Lancashire, UK

Posts: 3,843

Thanks Given: 2,004

Thanked 841 Times in 727 Posts

The content of /etc/pam.d/system-auth is below:-

Code:

#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth        required      pam_env.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth        sufficient    pam_winbind.so try_first_pass
auth        required      pam_deny.so

account     required      pam_unix.so broken_shadow
account     required      pam_access.so
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account     [default=bad success=ok user_unknown=ignore] pam_winbind.so
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3
password    sufficient    pam_unix.so md5 shadow nullok try_first_pass use_authtok
password    sufficient    pam_winbind.so use_authtok
password    required      pam_deny.so

session     required      pam_mkhomedir.so skel=/etc/skel/ umask=0022
session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so

Have we done something really bad? Well, I suppose it's bad enough to allow anyone with a valid account

I know it's designed to be flexible and allow applications to abstract the authentication/authorisation etc. , but it is very confusing!

Apologies,
Robin

rbatte1

12-06-2016

Moderator

3,843, 841

Join Date: Jun 2007

Last Activity: 29 June 2020, 12:30 PM EDT

Location: Lancashire, UK

Posts: 3,843

Thanks Given: 2,004

Thanked 841 Times in 727 Posts

So, limited testing options have just left me with the theory unless anyone can suggest how I could set up a couple of servers to match. Basically, no there servers have access to the public internet, so I'm a bit stuck how I can do this without asking the network people to expose my test server to the public side - and that's another headache all together.

Am I missing something simple? I'm concerned to prove to myself that I would actually drive through a proxy to a dummy sftp server I can set up internally.

Robin - very confused

rbatte1

https://www.unix.com/man-pages.php?qu...on=5&os=centos

12-06-2016

Moderator

12,296, 3,792

Join Date: Nov 2008

Last Activity: 1 January 2021, 1:47 AM EST

Location: Amsterdam

Posts: 12,296

Thanks Given: 679

Thanked 3,792 Times in 3,282 Posts

Hi Robin. Try putting

Code:

auth       required     pam_wheel.so use_uid group=SocksUsers

above:

Code:

auth       include      system-auth

Otherwise if

Code:

auth        sufficient    pam_winbind.so try_first_pass

succeeds, then no further modules will be called in the pam_stack..

Code:

       sufficient
           if such a module succeeds and no prior required module has failed the PAM framework returns success to the application or to the superior PAM stack immediately
           without calling any further modules in the stack. A failure of a sufficient module is ignored and processing of the PAM module stack continues unaffected.

Last edited by Scrutinizer; 12-06-2016 at 03:37 PM..

These 2 Users Gave Thanks to Scrutinizer For This Post:

Scrutinizer

View Public Profile for Scrutinizer

Find all posts by Scrutinizer

12-07-2016

Moderator

3,843, 841

Join Date: Jun 2007

Last Activity: 29 June 2020, 12:30 PM EDT

Location: Lancashire, UK

Posts: 3,843

Thanks Given: 2,004

Thanked 841 Times in 727 Posts

Thanks for the suggestion. I'd tried to read the manual pages but got rather goggle-eyed, so it is now smack-in-the-face obvious that we've got the order wrong.

I feel a fool for not spotting it

Mind you, I didn't do it in the first place, so it's not too bad.

I will see if I can get this put in sometime and report back.

Kind regards,
Robin

rbatte1

01-03-2017

Moderator

3,843, 841

Join Date: Jun 2007

Last Activity: 29 June 2020, 12:30 PM EDT

Location: Lancashire, UK

Posts: 3,843

Thanks Given: 2,004

Thanked 841 Times in 727 Posts

Thanks for the pointers. I am pleased to report that we have changed /etc/pam.d/ss5 from this:-

Code:

#%PAM-1.0
auth       include      system-auth
account    required     pam_nologin.so
auth       required     pam_wheel.so use_uid group=SocksUsers
account    include      system-auth
password   include      system-auth
session    optional     pam_keyinit.so force revoke
session    include      system-auth
session    required     pam_loginuid.so

.... to this (grouping all the auth statements together too):-

Code:

#%PAM-1.0
auth       requisite	pam_succeed_if.so debug user ingroup socksusers
auth       include      system-auth
account    required     pam_nologin.so
account    include      system-auth
password   include      system-auth
session    optional     pam_keyinit.so force revoke
session    include      system-auth
session    required     pam_loginuid.so

When we moved the rule up the order before the include statement, the use_uid meant that the rules were being applied to the account running the code, not the connecting user, i.e. it was testing the single account root for every connection.

Notes:-

I've set this to be requisite to just exit if the account does not have the required group.
I found that pam_succeed_if.so gave me the debug option for logging.
The pam_succeed_if.so also can be extended if multiple acceptance criteria were required.
The group appears to be case-insensitive, but shows as all lower case when running something like id rbatte1 | sed 's/) /)\n/g ; s/,/\n/g' | sort -nk1,1.5

I hope that this might be useful to someone else.

Robin

rbatte1