Hi SSSd team,
I was advised in IRC to send email to the group in order to discuss this
functionality.
I am thinking about taking on implementing it as I have a need in such
functionality. But I can also see that it would perhaps be interesting to
many other users as well.
Preamble:
Now SSSd's LDAP backend only provides ability to have a restriction via
host record to restrict access by verifying local hostname of machine (by
either explicitly allowing or denying access as hostname) using
ldap_access_order=host.
My thought is that it would be good to have ability to perform similar
access verification for rhost (IP or via DNS).
Why is it relevant to me - I am (as part of my work) managing 1k+ hosts
where we restrict ssh access to specific IP(s) using sshd_config AllowUsers
option using (*@ip_address) record to only allow logins from well protected
bastion server. It went pretty bad when IDC disaster happened and the
bastion was N/A - there was no way to access hosts until access to bastion
was restored. Meanwhile we manage ssh users and sudo access with LDAP, so
it would be perfect if we could manage this in there as well.
Why is it relevant to others - I've seen many cases when other
companies/individuals are doing similar - restrict access to bastion server
via either sshd_config or iptables (not even firewall as someone on IRC
suggested).
Proposal:
I am thinking of following implementation:
New sssd.conf option for ldap_access_order = rhost, which would enable
rhost verification.
New sssd.conf option ldap_user_authorized_rhost, which would carry similar
meaning as ldap_user_authorized_host (that is the name of field in LDAP
record containing rule).
LDAP entry field I am thinking could also be similar to the current host
field format - text Unicode field validated in order: explicit deny
(!host), explicit allow (host), allow all (*) ending with deny all (default
if no matching rule found).
Validation could happen as follows: If the rhost is an IP address first
lookup directly any matching rules, if none found attempt to fetch rDNS
record for rhost and lookup match for it. If rhost is a hostname first
lookup match directly, if none found fetch forward DNS record (that is A
and AAAA records) and try to match all elements from returned list (not
sure if sssd may receive hostname as rhost, but assume that as a
possibility).
Please let me know if this could be implemented as a part of LDAP backend
of SSSD. If this proposal is accepted I could start working on
implementation shortly.
Best regards,
akamenskiy
