[Swan] IKEv2 PAM auth failure - how it's done properly?

[Mirsad Goran Todorovac]

On 21.1.2022. 15:08, Paul Wouters wrote:

> Hello,
>>> I have installed the IKEv2 VPN connection at my colleague's laptop and he disappointingly noticed that there is no password authentication in addition to certificate.
>>> This is also akward because we would have to change all certificates if i.e. one laptop configured for the Faculty VPN was lost or stolen. :-(
>> I don't think this is right. The certificate system (in general, not libreswan's specifically) is explicitly designed so that you don't have to do that.
>> Ref CRL (Certificate Revocation List).
> Exactly. You only need to revoke the laptop certificate. The CA certificate is on the laptop too but not the CA certificate’s private key, only the public key.
>
> An additional password adds little security assuming there is already a login password, an automatic screen lock after a few minutes and whole disk encryption with a password.
>
> The libreswan pam option for IKEv2 is only meant for the server to check authorization of the client ID (usually a cert), not authentication. This is so you can temporary lock out a user without (irrevocably) revoking their certificate. This is often used when a customer hasn’t paid their bill for instance, or could be used if a laptop is missing but most likely will be found again.

1. I agree this opportunity to temporary disable the login with a 
certificate would be practical. I have generated the certificates as 
proposed on the link: 
https://libreswan.org/wiki/VPN_server_for_remote_clients_using_IKEv2#Example_certificate_generation_with_certutil

export PARM='--keyUsage digitalSignature,keyEncipherment --extKeyUsage 
serverAuth,clientAuth'
certutil -S -c "GRF-UNIZG CA" -n "laptop-marko.grf.hr" -s 
"O=GRF-UNIZG,CN=laptop-marko.grf.hr"  -k rsa -g 4096 -v 12 -d 
sql:${HOME}/tmpdb -t ",," ${PARM} -8 "laptop-marko.grf.hr"
pk12util -o laptop-marko.grf.hr.p12 -n "laptop-marko.grf.hr" -d 
sql:${HOME}/tmpdb/

I have imported the cert into Windows 10 certificate manager in the 
"Local Machine" keystore.

I can't seem to understand how to revoke such a local certificate. It is 
not generated by Letsencrypt or Sectigo, so where does ipsec check for 
revocation lists?

However, once it is revoked, the damage is done. I can't make it alive 
again, can I? So, there is a justified question:

2. Can I get a pointer to the username/password file for the 
certificates? I don't know if it should be in 
/etc/ipsec.d/hostname.secrets, and what is the syntax considering that 
the username contains spaces when expanded by certificate check facility 
of I think pluto.

As the username is as it appears in the pluto log, what is the location 
and syntax of the password file? And who would provide password? Windows 
10 client or else?

Jan 20 09:45:03.533787: | PAM: #1: PAM-process completed for user 
'CN=pc-mtodorov.alu.hr, O=ALU-UNIZG' with result FAILURE

This would be a great feature to have.
However, the manual ipsec.conf (5) only says this:

    pam-authorize

    IKEv1 supports PAM authorization via XAUTH using xauthby=pam. IKEv2
    does not support receiving a plaintext username and password.
    Libreswan does not yet support EAP authentication methods for IKE.
    The pam-authorize=yes option performs an authorization call via PAM,
    but only includes the remote ID (not username or password). This
    allows for backends to disallow an ID based on non-password
    situations, such as "user disabled" or "user over quota". See also
    xauthby=pam

It is not clear to me which file should provide remote ID list with 
permissions? And the syntax.

My current /etc/pam.d/pluto looks like this:

root at domac:~# cat /etc/pam.d/pluto
#%PAM-1.0
auth       required     pam_unix.so
auth       required     pam_nologin.so
account    required     pam_unix.so
password   required     pam_unix.so
session    required     pam_unix.so
session    required     pam_loginuid.so
root at domac:~#

The 4.6 distribution original did not work for me either: it said simply 
this:

Jan 20 09:07:48.551340: "MYCONN-ikev2-cp"[4] 193.198.186.218 #2: IKEv2 
FAILED during pam_authenticate with 'Permission denied' for
state #2, MYCONN-ikev2-cp[4] user=CN=pc-mtodorov.alu.hr, O=ALU-UNIZG.
Jan 20 09:07:48.551600: | PAM: #2: PAM-process completed for user 
'CN=pc-mtodorov.alu.hr, O=ALU-UNIZG' with result FAILURE
Jan 20 09:07:48.552834: | processing signal PLUTO_SIGCHLD
Jan 20 09:07:48.552890: | waitpid returned pid 2652 (exited with status 1)
Jan 20 09:07:48.552903: | suspend: restoring MD at 0x55f56d8e5aa8 from 
state #2 (server_fork_sigchld_handler() +224 programs/pluto/ser
ver_fork.c)
Jan 20 09:07:48.552928: | #2 waited 0.010288 for 'pamauth' fork()
Jan 20 09:07:48.552941: "MYCONN-ikev2-cp"[4] 193.198.186.218 #2: PAM: 
authentication of user 'CN=pc-mtodorov.alu.hr, O=ALU-UNIZG' FAILED after 
0.01074 seconds

I would love this feature to work on my VPN server. Libreswan team is 
very motivational for experimenting. As I said before, I felt moved by 
the all-inclusive code of conduct for the project :-)

> The next version of libreswan will add EAPTLS authentication, so windows won’t require administrative rights to add the IKEv2 connection. Once that it is, perhaps another EAP method - mschapv2 - will be added that does add a user / password method that can be used without certificates.
This sounds great. Looking forward to testing it :-)

Kind regards,
Mirsad

-- 
Mirsad Todorovac
CARNet system engineer
Faculty of Graphic Arts | Academy of Fine Arts
University of Zagreb
Republic of Croatia, the European Union
--
CARNet sistem inženjer
Grafički fakultet | Akademija likovnih umjetnosti
Sveučilište u Zagrebu
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