I've been fighting with this problem for a couple of days now and
thought it was time to appeal to the experts...
I'm using RHEL4 with pam_ldap to authenticate users who do not have
local accounts. This works. I'm also using pam_check_host_attr in
ldap.conf to limit who is allowed to log into a host based on their host
attribute in ldap. This also works, mostly.
When users log in using their ldap password, that is, when ssh prompts
them for their password, the host-based access control provided by
pam_check_host_attr works. Users who don't have the proper ldap host
attribute are denied access.
But as soon as a user puts a public key in ~/.ssh/authorized_keys,
pam_check_host_attr stops working. Regardless of what is in their ldap
host attribute, openssh lets them in. I want to allow (and encourage)
the use of authorized_keys files for logging into the machines, but I
also want to retain control of which machines they can log into by using
the host attribute in their ldap entry.
I've tried changing ChallengeResponseAuthentication to 'yes', but then
users are always prompted for their password. I've also tried adding
the 'debug' option to pam_ldap.so and directing all *.debug messages in
syslog to /var/log/debug, but I don't see anything appear from pam_ldap.
Is it possible to allow ssh key-based authentication, but still prohibit
logins based on the ldap host attribute?
--Mike
sshd_config contains:
Protocol 2
SyslogFacility AUTHPRIV
ChallengeResponseAuthentication no
GSSAPIAuthentication yes
GSSAPICleanupCredentials yes
UsePAM yes
X11Forwarding yes
Subsystem sftp /usr/libexec/openssh/sftp-server
/etc/pam.d/system-auth contains:
#%PAM-1.0
# This file is auto-generated.
# User changes will be destroyed the next time authconfig is run.
auth required /lib/security/$ISA/pam_env.so
auth sufficient /lib/security/$ISA/pam_unix.so likeauth nullok
auth sufficient /lib/security/$ISA/pam_ldap.so use_first_pass
auth required /lib/security/$ISA/pam_deny.so
account required /lib/security/$ISA/pam_unix.so broken_shadow
account sufficient /lib/security/$ISA/pam_succeed_if.so uid < 100
quiet
account [default=bad success=ok user_unknown=ignore]
/lib/security/$ISA/pam_ldap.so
account required /lib/security/$ISA/pam_permit.so
password requisite /lib/security/$ISA/pam_cracklib.so retry=3
password sufficient /lib/security/$ISA/pam_unix.so nullok
use_authtok md5 shadow
password sufficient /lib/security/$ISA/pam_ldap.so use_authtok
password required /lib/security/$ISA/pam_deny.so
session required /lib/security/$ISA/pam_mkhomedir.so
skel=/etc/skel/ umask=0022
session required /lib/security/$ISA/pam_limits.so
session required /lib/security/$ISA/pam_unix.so
session optional /lib/security/$ISA/pam_ldap.so
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