[Samba] SSH - Winbind and Keybased Auth

[Nathan Frankish]

Hi Team,

We have a weird issue that we are trying to understand. We have winbind set up and working successfully for user authentication with passwords via ssh. We have pam.d/system-auth-ac and password-auth-ac (symlinked) set to require membership of a group which works great via password authentication.

However, if the user has a ssh key set up, they seem to bypass the group membership requirement. The user isnt defined on the box in either shadow or passwd, they are only defined in AD, but are successfully able to authenticate as shown in the log below.

Some logs below:

/var/log/secure
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] ENTER: pam_sm_acct_mgmt (flags: 0x0000)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_SERVICE) = "sshd" (0x7f6b826837d0)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_USER) = "nathan" (0x7f6b826837f0)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_TTY) = "ssh" (0x7f6b8268dbd0)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_RHOST) = "mycomputer.domain.local" (0x7f6b82684610)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_CONV) = 0x7f6b82683810
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): user 'nathan' granted access
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] LEAVE: pam_sm_acct_mgmt returning 0 (PAM_SUCCESS)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_SERVICE) = "sshd" (0x7f6b826837d0)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_USER) = "nathan" (0x7f6b826837f0)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_TTY) = "ssh" (0x7f6b8268dbd0)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_RHOST) = "mycomputer.domain.local" (0x7f6b82684610)
Nov 28 17:34:58 testbox01 sshd[26078]: pam_winbind(sshd:account): [pamh: 0x7f6b82683650] STATE: ITEM(PAM_CONV) = 0x7f6b82683810
Nov 28 17:34:58 testbox01 sshd[26078]: Accepted publickey for nathan from 1.2.3.4 port 61767 ssh2

System-auth-ac:
[root at testbox01 pam.d]# cat system-auth-ac
auth required /lib/security/$ISA/pam_env.so
auth sufficient /lib/security/$ISA/pam_unix.so likeauth nullok
auth sufficient /lib/security/$ISA/pam_winbind.so debug debug_state use_first_pass require_membership_of=testbox02_access_sg, testbox02_2_access_sg
auth required /lib/security/$ISA/pam_deny.so

account required /lib/security/$ISA/pam_unix.so
account sufficient /lib/security/$ISA/pam_succeed_if.so uid < 100 quiet
account required /lib/security/$ISA/pam_winbind.so debug debug_state require_membership_of= testbox_access_sg,testbox02_2_access_sg
account required /lib/security/$ISA/pam_permit.so

password requisite /lib/security/$ISA/pam_cracklib.so retry=3 type=
password sufficient /lib/security/$ISA/pam_unix.so nullok use_authtok md5 shadow
password sufficient /lib/security/$ISA/pam_winbind.so use_first_pass
password required /lib/security/$ISA/pam_deny.so

session required /lib/security/$ISA/pam_limits.so
session required /lib/security/$ISA/pam_unix.so
session required pam_mkhomedir.so skel=/etc/skel umask=0022
session required /lib/security/$ISA/pam_winbind.so

/etc/pam.d/sshd: #%PAM-1.0
auth       required     pam_sepermit.so
auth       include      password-auth
account    required     pam_nologin.so
account    include      password-auth
password   include      password-auth
# pam_selinux.so close should be the first session rule
session    required     pam_selinux.so close
session    required     pam_loginuid.so
# pam_selinux.so open should only be followed by sessions to be executed in the user context
session    required     pam_selinux.so open env_params
session    optional     pam_keyinit.so force revoke
session    include      password-auth


System information:
Linux testbox01 2.6.32-431.el6.x86_64 #1 SMP Sun Nov 10 22:19:54 EST 2013 x86_64 x86_64 x86_64 GNU/Linux
Red Hat Enterprise Linux Server release 6.5 (Santiago)
Samba packages: 3.6.9-164.el6

Not sure where to go next, or what else to provide.


Nathan Frankish  |  Network & Systems Team Lead


Queensland Motorways Pty Limited