----- Original Message -----
On Wed, Jul 02, 2014 at 01:45:00AM -0400, Yassir Elley wrote:
>
>
> ----- Original Message -----
> > On Tue, 2014-07-01 at 01:50 -0400, Yassir Elley wrote:
> > >
> > > ----- Original Message -----
> > > > On Sat, 2014-06-28 at 18:01 -0400, Yassir Elley wrote:
> > > > >
> > > > > ----- Original Message -----
> > > > > > On Sat, 2014-06-28 at 01:20 -0400, Yassir Elley wrote:
> > > > > > >
> > > > > > > ----- Original Message -----
> > > > > > > > On Thu, 2014-06-26 at 04:54 -0400, Yassir Elley
wrote:
> > > > > > > > > Hi Simo,
> > > > > > > > >
> > > > > > > > > I'd like to wrap up this discussion. I
propose that we
> > > > > > > > > support
> > > > > > > > > only
> > > > > > > > > the InteractiveLogonRight (for the pam
services you
> > > > > > > > > mentioned:
> > > > > > > > > "login", "*dm,
"su*"), and on the
> > > > > > > > > RemoteInteractiveLogonRight
> > > > > > > > > (for
> > > > > > > > > the
> > > > > > > > > "ssh" pam service). We should not
support the
> > > > > > > > > NetworkLogonRight
> > > > > > > > > since
> > > > > > > > > it is difficult to implement. Do you agree
with this
> > > > > > > > > proposal?
> > > > > > > >
> > > > > > > > Well I guess the answer depends on what do you
plan to do for
> > > > > > > > pam
> > > > > > > > services that are not listed ?
> > > > > > > > Do you always deny access ? Always permit ?
> > > > > > >
> > > > > > > Since we would only support the InteractiveLogonRight
and
> > > > > > > RemoteInteractiveLogonRight, we would always permit
access for
> > > > > > > other
> > > > > > > pam
> > > > > > > services (because they would not be governed by
gpo-based
> > > > > > > access
> > > > > > > control,
> > > > > > > and this would be clearly documented).
> > > > > > >
> > > > > > > >
> > > > > > > > I think a more reasonable workaround is to define
a default
> > > > > > > > type,
> > > > > > > > and
> > > > > > > > a
> > > > > > > > list of mappings.
> > > > > > > >
> > > > > > > > If a PAM service is explicitly mapped you use
that Right to
> > > > > > > > decide,
> > > > > > > > otherwise the decision falls back to the
"default" Right.
> > > > > > > > Actually the default right could well be
actually
> > > > > > > > NetworkLogonRight
> > > > > > > > or
> > > > > > > > InteractiveLogonRight or something else. As long
as you can
> > > > > > > > change
> > > > > > > > the
> > > > > > > > mappings locally through some configuration that
would allow
> > > > > > > > the
> > > > > > > > admin
> > > > > > > > to add mappings according to their needs. Of
course strong
> > > > > > > > guidance
> > > > > > > > on which mappings should be used for specific
type of
> > > > > > > > services
> > > > > > > > should
> > > > > > > > be
> > > > > > > > provided.
> > > > > > > >
> > > > > > > > Simo.
> > > > > > > >
> > > > > > >
> > > > > > > I would prefer an approach which is more predictable
for the AD
> > > > > > > admin.
> > > > > > > If
> > > > > > > we limit ourselves to InteractiveLogonRight and
> > > > > > > RemoteInteractiveLogonRight, the semantics are very
clear
> > > > > > > (console
> > > > > > > login
> > > > > > > and remote login), allowing the AD Admin to be
confident that
> > > > > > > any
> > > > > > > existing
> > > > > > > or future policy files containing those rights would
be applied
> > > > > > > correctly
> > > > > > > and consistently, regardless of whether the machine is
running
> > > > > > > Linux or
> > > > > > > Windows.
> > > > > > >
> > > > > > > Also, I suspect AD admins would not like per-machine
service
> > > > > > > mappings
> > > > > > > to be
> > > > > > > enforced, since that would defeat the purpose of
enforcing a
> > > > > > > centralized
> > > > > > > policy in a consistent manner. When an AD admin made a
change
> > > > > > > to a
> > > > > > > LogonRight policy setting, he would have to keep in
mind that
> > > > > > > Linux
> > > > > > > machines may use the policy settings in ways that were
not
> > > > > > > intended
> > > > > > > by
> > > > > > > the
> > > > > > > AD admin. For example, it would be problematic if a
local admin
> > > > > > > decided
> > > > > > > to
> > > > > > > map "login" to NetworkLogonRight, or if some
local admins
> > > > > > > mapped
> > > > > > > "ftp"
> > > > > > > to
> > > > > > > some LogonRight (but other local admins stayed with
the
> > > > > > > default).
> > > > > > > This
> > > > > > > would result in inconsistent behavior between
different Linux
> > > > > > > machines,
> > > > > > > and between Linux machines and Windows machines.
Indeed, in the
> > > > > > > Windows
> > > > > > > world, the "local" per-machine GPO is given
least priority in
> > > > > > > case
> > > > > > > of
> > > > > > > conflict (i.e. ou overrides domain, which overrides
site, which
> > > > > > > overrides
> > > > > > > local). A solution to this problem of consistency
would be to
> > > > > > > have
> > > > > > > a
> > > > > > > centralized GPO that maps pam services to LogonRights,
but I
> > > > > > > don't
> > > > > > > think
> > > > > > > we need to implement that in the first release.
> > > > > > >
> > > > > > > I think limiting ourselves to InteractiveLogonRight
and
> > > > > > > RemoteInteractiveLogonRight would be less confusing
and more
> > > > > > > predictable
> > > > > > > for AD admins (resulting in a greater likelihood of
them
> > > > > > > deploying
> > > > > > > gpo-based access control). They would know that these
two
> > > > > > > LogonRights
> > > > > > > would be enforced with the same semantics on Windows
and Linux
> > > > > > > machines.
> > > > > > > They would also know that other LogonRights would not
be
> > > > > > > enforced
> > > > > > > on
> > > > > > > Linux
> > > > > > > machines. Clean and crisp.
> > > > > > >
> > > > > > > What do you think?
> > > > > >
> > > > > > You make a good argument, but I am not entirely convinced
you can
> > > > > > avoid
> > > > > > a local mapping unless you provide a GPO mapping, because
the
> > > > > > admin
> > > > > > must
> > > > > > be able to adjust mappings for new services installed on
the box
> > > > > > that
> > > > > > were not included in the upstream provided lists.
> > > > > >
> > > > > > So if you already need to provide a way to augment
mappings, you
> > > > > > may
> > > > > > as
> > > > > > well handle all rights with reasonable defaults, and let
the
> > > > > > admin
> > > > > > decide whether they need to change stuff around.
> > > > > >
> > > > > > Simo.
> > > > > >
> > > > >
> > > > > Allowing local admins to change stuff from underneath the AD
> > > > > admin's
> > > > > directives seems to violate the GPO philosophy of centralized,
> > > > > consistent application of policy. I don't think AD admins
will find
> > > > > the gpo-based access control feature compelling, if it does not
fit
> > > > > with their mental model of how GPO is supposed to work.
> > > >
> > > > Sorry but I do not buy this argument. The whole GPO policy can be
> > > > turned
> > > > on or off in sssd, so if admins do not control the boxes'
sssd.conf
> > > > file
> > > > they already know their policies are, at best, advisory.
> > > >
> > > > > As you know, LogonRights are existing Windows policy settings
(not
> > > > > Linux-specific settings), so we really do have to honor the
intent
> > > > > of
> > > > > the settings and the GPO framework.
> > > >
> > > > Indeed, and in order to do that you need to be able to appropriately
> > > > map
> > > > arbitrary services.
> > > >
> > > > > Having said that, I don't think we necessarily need to have
a
> > > > > comprehensive implementation in the first release, especially if
we
> > > > > think the GPO mapping is the correct solution (and if we think
that
> > > > > we
> > > > > may implement that in a subsequent release).
> > > >
> > > > We do not need the support as a GPO deliverable policy, but you need
> > > > a
> > > > local mapping for the feature to be usable/testable IMO.
> > > >
> > > > > I think the centralized mapping offered by a future GPO mapping
> > > > > would
> > > > > certainly allay the concerns of AD admins, as the power would
> > > > > remain
> > > > > in their hands and it would be applied consistently.
Implementing
> > > > > local mapping now, and then adding a centralized mapping later
> > > > > would
> > > > > delay deployment and would add too much complexity IMO.
> > > >
> > > > Why ? This is exactly the same as overlaying global policy on top of
> > > > local policy, I honestly do not see it as any more complex than
> > > > needed.
> > > >
> > > > > As for how to deal with new services (in the initial
> > > > > implementation),
> > > > > two ideas come to mind:
> > > > > 1) My preference would be that only services included in the
> > > > > upstream
> > > > > provided lists will be affected by gpo-based access control.
Not
> > > > > very
> > > > > extensible, but that's OK if we intend on adding a GPO
mapping in a
> > > > > future release.
> > > >
> > > > Upstream runs on multiple OSs and Linux distributions, within those
> > > > there is already, I bet, enough conflict to make a single upstream
> > > > list
> > > > unfeasible, as pam service names are somewhat arbitrary and
> > > > customized
> > > > in different way especially for very distro-specific services like
> > > > login
> > > > and graphical session managers.
> > > >
> > > > > 2) Alternatively, we could go with a completely different
proposal
> > > > > that would affect all pam services. Specifically, since remote
> > > > > login
> > > > > seems to be an uncommon pam service (we could only come up with
> > > > > "ssh"), we could declare that "ssh" maps to
> > > > > RemoteInteractiveLogonRight, and that *all* other services
> > > > > (including
> > > > > new services, custom services, etc), map to
InteractiveLogonRight.
> > > >
> > > > That would be wrong. I suspect one of the services you really want
to
> > > > control, as a windows admin, is samba file services, and those must
> > > > be
> > > > mapped to NetworkLogonRight.
> > > > And NEtworkLogonRight seem to be generally the most sensible default
> > > > once you exclude the services you know are interactive login shells.
> > > >
> > > > > While certainly not ideal (and not my preference), I think AD
> > > > > admins
> > > > > would find this easier to grok than local mappings, as it would
be
> > > > > predictable and would allow policy authority to remain
centralized,
> > > > > without central directives being manipulated by local admins.
> > > >
> > > > If the admin doesn't grok what services run on a Linux box, they
are
> > > > already doomed I would think. You need at least a passing
> > > > understanding
> > > > of the policies you are going to set. We can *definitely* provide a
> > > > good
> > > > default set, admins should not be required to provide explicit
> > > > mappings
> > > > if the default works for them, but an unchangeable list will
severely
> > > > reduce the utility of the feature.
> > > >
> > >
> > > OK. I forgot that local admins can disable gpo processing, so although
> > > AD admins may want centralized control over all domain computers
> > > (whether Windows or Linux), they may not be able to get it with this
> > > feature. Whether this will be a show-stopper for them remains to be
> > > seen. With that in mind, I agree that it makes sense to allow pam
> > > services to be mapped to logon rights.
> > >
> > > With regard to the default set of mappings, I propose the following
> > > (based on previous emails).
> > > login/*dm/su* maps to InteractiveLogonRight
> > > ssh maps to RemoteInteractiveLogonRight
> > > explicit mappings are honored
> > > if the service is still unmapped, map it to NetworkLogonRight
> >
> > I think we can take a page from FreeIPA's configuration, this is the
> > original list of services we provide by default for HBAC:
> >
> > sshd
> > ftp
> > su
> > login
> > su-l
> > sudo
> > sudo-i
> > gdm
> > gdm-password
> > kdm
> >
> > To which later updates added:
> > crond
> > vsftpd
> > proftpd
> > pure-ftpd
> > gssftp
> >
> > Keep in mind that FreeIPA uses also service groups so all the ftp
> > services are grouped under a ftp group.
> >
> > I think that we can add crond and samba to the first list and use that
> > as the default list.
> >
> > > A few questions for you:
> > > * Does this list make sense?
> >
> > Mostly, yes.
> >
> > > * Should there be anything special about the default set, or can an
> > > admin re-map services from the default set (i.e. map "ssh" to
> > > NetworkLogonRight)?
> >
> > I would use the following mappings.
> >
> > InteractiveLogonRight:
> > su, login, su-l, sudo, sudo-i, gdm, gdm-password, kdm
> > RemoteInteractiveLogonRight:
> > sshd
> > NetworkLogonRight:
> > ftp
> > samba
> > BatchLogonRight (?):
> > crond
> >
> > I am not sure what to use as default fallback for any service that do
> > not match these.
> >
> > There is a default "remote" service in Fedora, and there is a
"other"
> > service which matches any unrecognized service IIRC.
> >
> > Maybe we could map unknown stuff to ServiceLogonRight which poorly
> > translates to anything useful on Linux I think.
> >
> > > * Should an admin be able to map a service to NULL (indicating that
> > > they don't want this service to be enforced by GPO policy)
> >
> > So your suggestion would be the unrecognized services would simply be
> > ignored when it comes to GPO enforcing ?
> >
>
> Yes. By essentially providing an opt-in model for pam services (with
> respect to gpo enforcement), we would be requiring someone to make an
> informed decision about the service-to-Right mapping (rather than for us
> to make an arbitrary decision). When an unmapped service is encountered,
> we would emit a log message (so that the admin can add an explicit
> mapping, if he forgot to add one). I suspect the distros would be savvy
> enough to pre-populate the sssd.conf file with distro-specific service
> mappings, but an individual admin using their own custom pam service might
> need a nudge.
>
> For example, if an admin forgets to explicitly map a custom service (or
> doesn't even know he needs to), it would be better for him to receive an
> "unrecognized service" message in the logs (which would hopefully remind
> him to add an explicit mapping, after giving it some thought), than for us
> to arbitrarily map the custom service to some default (which might even
> result in unintended access denials).
>
> This would be in line with the opt-in model we are using for overall
> gpo-enforcement (b/c the default is "permissive"). An admin would have to
> intentionally set the mode to "enforcing", and would have to
intentionally
> provide explicit mappings for non-default services (or even to change a
> default service mapping).
>
> What do you think?
Explaining on the logs why access to a service was granted or denied is
always a good idea. I guess those messages will fell in the
audit-messages category but currently SSSD does not treat audit messages
specially. Maybe we should start simple and just add an alias to the
DEBUG macro called AUDIT? Later on we can start handling them differently
than other debug messages but we will already have (at least for newer
code) a label in the code where audit information originates.
Can't we just use the sss_log_ext() function that I introduced recently (in util.h).
It is currently used only in ad_gpo.c (to deal with gpo permissive mode). Note that this
function emits a syslog message to the security log (with or without journald). It does
not emit a message to the debug log (although the code separately emits a debug log
message).
from ad_gpo.c:
sss_log_ext(SSS_LOG_WARNING, LOG_AUTHPRIV, "Warning: user would " \
"have been denied GPO-based logon access if the " \
"ad_gpo_access_control option were set to enforcing " \
"mode.");
(Sorry for hijacking this tread, I'll return now to the gpo and
services
discussion :-)
I'd like to try to summarize the discussion with a hypothetical man page
section of new config options:
ad_gpo_map_interactive (string)
A comma-separated list of PAM service names for which access control
is evaluated with the help of the AD Interactive Logon Right.
Default: su, login, su-l, sudo, sudo-i, gdm, gdm-password, kdm
ad_gpo_map_remote_interactive (string)
A comma-separated list of PAM service names for which access control
is evaluated with the help of the AD Remote Interactive Logon Right.
Default: sshd
ad_gpo_map_network (string)
A comma-separated list of PAM service names for which access control
is evaluated with the help of the AD Network Logon Right.
Default: ftp
ad_gpo_map_batch (string)
A comma-separated list of PAM service names for which access control
is evaluated with the help of the AD Batch Logon Right.
Default: crond
ad_gpo_map_service (string)
A comma-separated list of PAM service names for which access control
is evaluated with the help of the AD Service Logon Right.
Default: Not set
ad_gpo_default_rights (string)
This option defines how access control is evaluated for PAM
services which are not explicitly listed in one of the ad_gpo_map_*
options. Allowed values are 'interactive', 'remote_interactive',
'network', 'batch' and 'service' to do the evaluation based
on the
corresponding AD Logon Right. Additionally 'permit' and 'deny' can
be used to either always grant or reject access for those PAM
services.
Default: deny
bye,
Sumit
Thanks!! This is a great start! Very helpful.
A few comments:
1. We should tweak the wording a bit (and also mention the corresponding Deny Rights). For
example, "A comma-separated list of PAM service names for which access control is
evaluated based on the AD BatchLogonRight and DenyBatchLogonRight policy settings."
2. We should make the option names describe the contents of the option. For example,
"ad_gpo_service_names_interactive"
3. The default for ad_gpo_map_network should also include "samba" (in addition
to "ftp")
4. Should we add the various gdm-* service names as interactive: gdm-autologin,
gdm-fingerprint, gdm-launch-environment, gdm-pin, gdm-smartcard
5. Should we add the screen savers as interactive: gnome-screensaver, kscreensaver
6. I don't like overloading the ad_gpo_default_rights option so as to include either a
Right or a permit/deny. In fact, I don't think a default Right is needed at all (but
the permit/deny might be useful). Assuming there are only a handful of unrecognized
rights, there is already a convenient mechanism to specify explicit mappings. We can use a
non-overloaded option that can be used to specify permit/deny semantics for unmapped
service names. I think this would be more understandable. For example:
"ad_gpo_service_names_unmapped_action (string): This option defines how access
control is evaluated for PAM services which are not explicitly listed in one of the
ad_gpo_service_names_* options. Values of 'permit' and 'deny' can be used
to either always grant or always reject access for those PAM services."
7. I think the default for the default/unmapped option should be "permit" rather
than "deny" (to be consistent with the opt-in model for overall gpo processing)
Comments?
Regards,
Yassir