Hi Sumit,
Thank you for the reply!
First of all, I assume you meant "shell" whenever you used "homedir"
previously. Please see my further replies below.
On 05/20/2016 02:50 PM, Sumit Bose wrote:
On Fri, May 20, 2016 at 01:54:33PM +0300, Nikolai Kondrashov wrote:
On 05/20/2016 01:39 PM, Sumit Bose wrote:
On Fri, May 20, 2016 at 12:53:51PM +0300, Nikolai Kondrashov wrote:
On 05/19/2016 02:41 PM, Sumit Bose wrote:
On Thu, May 12, 2016 at 04:29:07PM +0300, Nikolai Kondrashov wrote:
On 04/26/2016 11:32 AM, Sumit Bose wrote:
On Mon, Apr 25, 2016 at 09:16:22PM +0300, Nikolai Kondrashov wrote:
On 04/11/2016 07:44 PM, Sumit Bose wrote:
On Fri, Apr 08, 2016 at 07:31:59PM +0300, Nikolai Kondrashov wrote:
On 04/06/2016 02:06 PM, Sumit Bose wrote:
I wonder if it would makes sense to add the cached user object to preq
in pam_check_user_search() to avoid the lookup in
pam_reply_export_shell(). The data is already allocated on preq and as
far as I can see never freed explicitly, so it wouldn't even cost more
memory.
Sure, that would be nice. However it's really hard for me to tell where that
would come from, where it's actually retrieved and what's the lifetime would
be. I really miss documentation there.
Could you suggest the change, perhaps?
sure, please have a look at attached (untested) patch. With this you start in
pam_reply_export_shell() with
+ shell = ldb_msg_find_attr_as_string(preq->user_obj, SYSDB_SHELL, NULL);
+ if (shell == NULL) {
+ DEBUG(SSSDBG_CRIT_FAILURE, "user has no shell\n");
+ ret = ENOENT;
+ goto done;
+ }
Thanks a lot Sumit, this is very helpful! However, the problem is the non-UPN
case is requesting the user with sysdb_getpwnam_with_views and
pam_reply_export_shell needs the non-overridden shell to pass it to tlog-rec,
as local override is the mechanism used to enable tlog-rec at the moment.
So, it seems we need the second lookup in pam_reply_export_shell after all.
Or am I missing something?
The *_with_views() calls add the override data with the OVERRIDE_PREFIX,
so SYSDB_SHELL is still the original one while OVERRIDE_PREFIX SYSDB_SHELL
is the overridden one if there is any.
There is something special with AD users and the default view. If the
shell for an AD user is overridden in the default view it is already
applied and SYSDB_SHELL will show it. The original shell from AD can be
found in ORIGINALAD_PREFIX SYSDB_SHELL if it is needed here.
Thank you, Sumit.
I looked at this for a while and believe I can do it. However, do we really
want it done this way? It would create a tighter coupling between the code
adding these fields (SYSDB_SHELL with various prefixes) and the shell export
code, which would complicate maintenance.
I mean, as far as I see it, pam_reply_export_shell would have to check if it's
the AD case, if it is, it will have to use ORIGINALAD_PREFIX SYSDB_SHELL, if
it is not, the it will have to use SYSDB_SHELL. Now, if any of the condition
and names change, for example as the result of investigating those tickets you
created, it will break. Do we want to track another copy of the logic?
Is the optimization we're trying to achieve here worth it? Wouldn't it be
better to limit ourselves to a narrower and better-defined interface of
sysdb_getpwnam at least for now? Sure, there might be a performance penalty,
but we're just trying things out and we don't actually know how often this
feature will be used and in which conditions. I.e. we don't measure it yet.
What if we take the middle road and add an option enabling "session
recording", which would turn the original shell exporting on, which would
simply use sysdb_getpwnam?
I presume we will need such a switch anyway and for the start it can do just
this one thing (i.e. exporting the shell). When we implement central control,
it would also enable acting on the corresponding attributes from LDAP.
Then later, if performance would be a problem, we can optimize this.
Now, I'm not entirely sure adding such an option would be the best idea, as
perhaps we can avoid it. I.e. simply have the recording activated for a user
if there's corresponding data in LDAP, in the future when we implement it.
What do you think?
(sorry for the delay)
I think it is not so much about tight or not so tight coupling. The main
point is to determine the shell as the nss responder does. The nss
responder use sysdb_getpwnam_with_views() and get_homedir_override() to
get the right shell. The pam responder already uses
sysdb_getpwnam_with_views() so all needed data is already available, you
cannot use plain sysdb_getpwnam() because it won't contain the override
data if any.
So what is missing is to make get_homedir_override() public so that you
can use it in pam_reply_export_shell(). Unfortunately
get_homedir_override() depends on some nss responder specific options,
override_homedir, homedir_substring and fallback_homedir. Those options
must be read by the pam responder as well to make sure that the pam
responder puts the same shell in the environment as the nss responder
would return.
Thanks, Sumit, but now I'm confused :)
I think we understand this completely differently.
The "pam_reply_export_shell" needs the *original*, *not* overridden shell,
because the override is how we configure tlog-rec use (we set the shell
override to point to tlog-rec). Exporting the original shell lets tlog-rec
know what is the actual shell user needs, so it can start that.
ah, was thought tlog will be switched on differently, so you either can
have tlog or an overriden shell. And yes, in this case you do not have to
check the overriden shell.
But I think you still need an evaluation similar to
get_homedir_override() because e.g. if there are no POSIX attributes in
AD users from AD will not have a shell set at all and the shell might be
chosen based on SSSD's shell related config options.
Instead of sss_view_ldb_msg_find_attr_as_string() you should use
ldb_msg_find_attr_as_string() and if this is already tlog (this is the
case where the tlog shell is added to the default override) you should
check if ORIGINALAD_PREFIX SYSDB_SHELL exists.
I'm sorry, I don't quite understand this sentence. How can it already be
"tlog" and what is the "default override"?
Could you please elaborate on this piece of logic?
If you still have an empty shell at this point you should apply the SSSD
config options.
Finally if there is still no shell /bin/sh should be used. If
getpwnam() does not return a shell for the user login and sshd (and I
hope all other applications as well) use /bin/sh. The nss responder will
return an empty shell entry in this case as well letting the caller
decide. But in the case here we should add /bin/sh to the environment
variable if nothing else was found.
Thanks, Sumit! However, before I try to fully understand the above, isn't
there a function of some kind, that decides which shell the user should have
*without* applying the override? I mean, that logic should be implemented
somewhere already, and reimplementing it in pam_reply_export_shell would be a
bad form.
Unfortunately get_homedir_override() is the only one we have because
currently currently the only use-case was
get-the-effective-shell-for-the-user which of course includes overrides
and SSSD config option evaluation. But as said the main difference is in
the initial part where sss_view_ldb_msg_find_attr_as_string() is
currently used. I think you can just add a flag to
get_homedir_override() which indicates the tlog use case and the
ldb_msg_find_attr_as_string() for SYSDB_SHELL and eventually for
ORIGINALAD_PREFIX SYSDB_SHELL and continue with the option processing.
Since the struct nss_ctx argument is specific for the nss responder you
might want to replace this with the actual config options
homedir_substr, override_homedir and fallback_homedir as well.
This way you do not need to reimplement it but only extend what is
already available to your use-case.
Doesn't sysdb_getpwnam do that?
sysdb_getpwnam only reads data from the cache but the cache basically
has what is read from LDAP without additional processing, so the
SYSDB_SHELL might even already have the tlog shell in the default
override case. Since you do not need the additional override attributes
from other view it would be possible to use sysdb_getpwnam() the
additional processing is still needed.
Ah, after reading the source code for quite a while, I think I finally
understand what's going on and what you mean :)
Now, I think adding a special parameter to get_shell_override() to switch
between ldb_msg_find_attr_as_string() and
sss_view_ldb_msg_find_attr_as_string() will make the function more complex and
harder to understand. What if I simply make it accept a shell string and
retreive that outside the function? The only user of the function
(fill_pwent()) does a lot of that for the other attributes anyway.
For that matter, what if I do the similar thing for the other get_*_override
functions just to keep it uniform?
Regardless of that, what would be the proper way to expose these functions to
the pamsrv_cmd.c module (and I think they all should be exposed at once, as
they're doing a similar thing), since they're in nsssrv_cmd.c? Do I move them
to another module and rename (to which and rename how?), do I put them into a
header file (which and under which names), do I create a new header file,
something else? I can't quite catch the conventions here.
Btw, I just check which attributes are read by sysdb_getpwnam() and
sysdb_getpwnam_with_views() and found that ORIGINALAD_PREFIX SYSDB_SHELL
is missing. I think the easiest here is to add it to SYSDB_PW_ATTRS.
Alright, I'll do that.
Thanks for all your help, Sumit!
Nick
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