On (04/08/16 11:15), Jakub Hrozek wrote: >On Thu, Aug 04, 2016 at 08:45:00AM +0200, Lukas Slebodnik wrote: >> On (03/08/16 18:56), Lukas Slebodnik wrote: >> >On (29/07/16 16:41), Jakub Hrozek wrote: >> >>On Thu, Jul 28, 2016 at 01:56:50PM +0200, Jakub Hrozek wrote: >> >>> On Thu, Jul 28, 2016 at 01:33:32PM +0200, Lukas Slebodnik wrote: >> >>> > On (28/07/16 12:06), thierry bordaz wrote: >> >>> > >On 07/28/2016 09:39 AM, Jakub Hrozek wrote: >> >>> > >> On Wed, Jul 27, 2016 at 04:09:07PM +0200, thierry bordaz wrote: >> >>> > >> > >> >>> > >> > On 07/27/2016 03:36 PM, Jakub Hrozek wrote: >> >>> > >> > > On Wed, Jul 27, 2016 at 02:55:37PM +0200, thierry bordaz wrote: >> >>> > >> > > > On 07/27/2016 01:56 PM, Jakub Hrozek wrote: >> >>> > >> > > > > On Wed, Jul 27, 2016 at 01:03:59PM +0200, Jakub Hrozek >> >>> > >> > > > > wrote: >> >>> > >> > > > > > On Wed, Jul 27, 2016 at 12:22:46PM +0200, Lukas Slebodnik >> >>> > >> > > > > > wrote: >> >>> > >> > > > > > > On (27/07/16 12:08), Jakub Hrozek wrote: >> >>> > >> > > > > > > > On Wed, Jul 27, 2016 at 12:02:24PM +0200, Jakub >> >>> > >> > > > > > > > Hrozek wrote: >> >>> > >> > > > > > > > > On Wed, Jul 27, 2016 at 11:54:16AM +0200, Lukas >> >>> > >> > > > > > > > > Slebodnik wrote: >> >>> > >> > > > > > > > > > ehlo, >> >>> > >> > > > > > > > > > >> >>> > >> > > > > > > > > > attached patch fixes acces denied after >> >>> > >> > > > > > > > > > activating user in 389ds. >> >>> > >> > > > > > > > > > Jakub had some comments/ideas in ticket but I >> >>> > >> > > > > > > > > > think it's better to discuss >> >>> > >> > > > > > > > > > about virtual attributes and timestamp cache on >> >>> > >> > > > > > > > > > mailing list. >> >>> > >> > > > > > > > > Yes, so the comment I have is that while this >> >>> > >> > > > > > > > > works, it might break some >> >>> > >> > > > > > > > > strange LDAP servers. >> >>> > >> > > > > > > > > >> >>> > >> > > > > > > > > We use modifyTimestamp as a 'positive' indicator >> >>> > >> > > > > > > > > that the entry has not >> >>> > >> > > > > > > > > changed -- if the modifyTimestamp didn't change, we >> >>> > >> > > > > > > > > consider the cached >> >>> > >> > > > > > > > > entry the same as what is on the server and only >> >>> > >> > > > > > > > > bump the timestamp >> >>> > >> > > > > > > > > cache. If the timestamp is different, we do a >> >>> > >> > > > > > > > > deep-comparison of cached >> >>> > >> > > > > > > > > attribute values with what is on the LDAP server >> >>> > >> > > > > > > > > and write the sysdb >> >>> > >> > > > > > > > > cache entry only if the attributes differ. >> >>> > >> > > > > > > > > >> >>> > >> > > > > > > > > I was wondering if we can use the modifyTimestamp >> >>> > >> > > > > > > > > at all, then, because >> >>> > >> > > > > > > > > even if it's the same, we might want to check the >> >>> > >> > > > > > > > > attributes to see if >> >>> > >> > > > > > > > > some of the values are different because some of >> >>> > >> > > > > > > > > the attributes might be >> >>> > >> > > > > > > > > this operational/virtual attribute.. >> >>> > >> > > > > > > > Sorry, sent too soon. >> >>> > >> > > > > > > > >> >>> > >> > > > > > > > I think the questions are -- 1) can we enumerate the >> >>> > >> > > > > > > > virtual attributes? >> >>> > >> > > > > > > That might be a question for 389-ds developers. >> >>> > >> > > > > > > But it's very likely it will be different on other LDAP >> >>> > >> > > > > > > servers. >> >>> > >> > > > > > > >> >>> > >> > > > > > > > 2) Would different LDAP servers have different >> >>> > >> > > > > > > > virtual attributes. >> >>> > >> > > > > > > > >> >>> > >> > > > > > > > For 2) maybe a possible solution might be to set a >> >>> > >> > > > > > > > non-existing >> >>> > >> > > > > > > > modifyTimestamp attribute value, but I would consider >> >>> > >> > > > > > > > that only a >> >>> > >> > > > > > > > kludge, we shouldn't break existing setups.. >> >>> > >> > > > > > > I am not satisfied with this POC solution either. >> >>> > >> > > > > > > >> >>> > >> > > > > > > So should we remove usage of modifyTimestamp for >> >>> > >> > > > > > > detecting changes? >> >>> > >> > > > > > I would prefer to ask the DS developers before removing >> >>> > >> > > > > > it completely. >> >>> > >> > > > > > >> >>> > >> > > > > > At least for large groups it might take a long time to >> >>> > >> > > > > > compare all attribute >> >>> > >> > > > > > values and IIRC we don't depend on any virtual attributes >> >>> > >> > > > > > for groups. Maybe >> >>> > >> > > > > > we could parametrize that part of the code and enable the >> >>> > >> > > > > > fast way with >> >>> > >> > > > > > modifyTimestamps for 'known' server types, that is for >> >>> > >> > > > > > setups with AD and >> >>> > >> > > > > > IPA providers. >> >>> > >> > > > > > >> >>> > >> > > > > > For users, there is typically not as many attributes so >> >>> > >> > > > > > we should be >> >>> > >> > > > > > fine deep-comparing all attributes. >> >>> > >> > > > > I'm adding Thierry (so please reply-to-all to keep him in >> >>> > >> > > > > the thread). >> >>> > >> > > > > >> >>> > >> > > > > Thierry, in the latest sssd version we tried to add a >> >>> > >> > > > > performance >> >>> > >> > > > > improvement related to how we store SSSD entries in the >> >>> > >> > > > > cache. The short >> >>> > >> > > > > version is that we store the modifyTimestamp attribute in >> >>> > >> > > > > the cache and >> >>> > >> > > > > when we fetch an entry, we compare the entry >> >>> > >> > > > > modifyTimestamp with what >> >>> > >> > > > > is on the server. When the two are the same, we say that >> >>> > >> > > > > the entry did >> >>> > >> > > > > not change and don't update the cache. >> >>> > >> > > > > >> >>> > >> > > > > This works fine for most attributes, but not for attributes >> >>> > >> > > > > like >> >>> > >> > > > > nsAccountLock which do not change modifyTimestamp when they >> >>> > >> > > > > are >> >>> > >> > > > > modified. So when an entry was already cached but then >> >>> > >> > > > > nsAccountLock >> >>> > >> > > > > changed, we treated the entry as the same and never read >> >>> > >> > > > > the new >> >>> > >> > > > > nsAccountLock value. >> >>> > >> > > > > >> >>> > >> > > > > To fix this, I think we have several options: >> >>> > >> > > > > 1) special-case the nsAccountLock. This seems a bit >> >>> > >> > > > > dangerous, >> >>> > >> > > > > because I'm not sure we can say that some other >> >>> > >> > > > > attribute we are >> >>> > >> > > > > interested in behaves the same as nsAccountLock. >> >>> > >> > > > > 2) drop the modifyTimestamp optimization completely. >> >>> > >> > > > > Then we fall >> >>> > >> > > > > back to comparing the attribute values, which might >> >>> > >> > > > > work, but for >> >>> > >> > > > > huge objects like groups with thousands of members, >> >>> > >> > > > > this might be >> >>> > >> > > > > too expensive. >> >>> > >> > > > > 3) only use the modifyTimestamp optimization for >> >>> > >> > > > > cases where we know >> >>> > >> > > > > we don't read any virtual attributes. >> >>> > >> > > > > >> >>> > >> > > > > And my question is -- can we, in general, know if the >> >>> > >> > > > > modifyTimestamp >> >>> > >> > > > > way of detecting changes is realiable for all LDAP servers? >> >>> > >> > > > > Or do you >> >>> > >> > > > > think it should only be used for cases where we know we are >> >>> > >> > > > > not >> >>> > >> > > > > interested in any virtual attributes (that would mostly be >> >>> > >> > > > > storing >> >>> > >> > > > > groups from servers where we know exactly what is on the >> >>> > >> > > > > server side, >> >>> > >> > > > > like IPA or AD). >> >>> > >> > > > Hello, >> >>> > >> > > > >> >>> > >> > > > Relying on modifytimestamp looks a good idea. Any MOD/MODRDN >> >>> > >> > > > will update it, >> >>> > >> > > > except I think it is unchanged when updating some password >> >>> > >> > > > policy >> >>> > >> > > > attributes. >> >>> > >> > > > >> >>> > >> > > > Regarding virtual attribute, the only one I know in IPA is >> >>> > >> > > > nsaccountlock. >> >>> > >> > > > nsaccountlock is an operational attribute (you need to >> >>> > >> > > > request it to see it) >> >>> > >> > > > and is also a virtual attribute BUT only for 'staged' and >> >>> > >> > > > 'deleted' users. >> >>> > >> > > > It is a stored attribute for regular users and we should >> >>> > >> > > > update >> >>> > >> > > > modifytimestamp when it is set. >> >>> > >> > > > >> >>> > >> > > > thanks >> >>> > >> > > > thierry >> >>> > >> > > OK, in that case it seems like we can special-case it. But do >> >>> > >> > > you know >> >>> > >> > > about any other attributes in any other LDAP servers? >> >>> > >> > Any LDAP server following standard should provide modifytimestamp >> >>> > >> > that >> >>> > >> > reflect the last update of the entry. Now virtual attribute >> >>> > >> > values may be >> >>> > >> > "attached" to the entry and its value change without modification >> >>> > >> > of >> >>> > >> > modifytimestamp. >> >>> > >> > For 389-ds and IPA it is fine as virtual value of nsaccountlock >> >>> > >> > is changed >> >>> > >> > only when the DN change. >> >>> > >> > For others LDAP servers I suppose it exists the same ability to >> >>> > >> > define >> >>> > >> > service providers that return virtual attribute values. The >> >>> > >> > difficulty is >> >>> > >> > that the schema may not give any hint if the retrieved attributes >> >>> > >> > values >> >>> > >> > were stored or computed and consequently trust modifytimestamp to >> >>> > >> > know if >> >>> > >> > the values changed or not. >> >>> > >> > For example in ODSEE, memberof is a virtual attribute. >> >>> > >> Thank you, for the explanation Thierry. >> >>> > >> >> >>> > >> Then to be on the safe side I propose: >> >>> > >> 1) We add an (probably undocumented?) flag that says whether >> >>> > >> to use >> >>> > >> modifyTimestamp to detect entry changes or not >> >>> > >> 2) for the generic LDAP provider we always really compare the >> >>> > >> attribute values, in other words the option would be set to >> >>> > >> false. If there is anyone with performance issues with a >> >>> > >> generic >> >>> > >> setup, we tell them to flip the option. >> >>> > >> 3) For the IPA and AD providers, we set this option to true >> >>> > >> and use >> >>> > >> the modifyTimestamp value to detect changes >> >>> > >> 4) We special case nsAccountLock >> >>> > >> >> >>> > >> Lukas, do you agree? >> >>> > >Hi Jakub, >> >>> > > >> >>> > >digging further into the server, it appears that a DS plugin >> >>> > >'acctpolicy' >> >>> > >updates an entry without changing the mofidytimestamp. >> >>> > >The updated attribute is 'lastlogintime' (by default) but i think can >> >>> > >be any >> >>> > >attribute configured in the entry account policy. >> >>> > >I need to do further tests to confirm this. >> >>> > > >> >>> > >> >>> > IMHO, the problems with nsAccountLock just revealed the fact that >> >>> > it might happen that the attribute modifyTimestamp/whenChanged needn't >> >>> > be >> >>> > a reliable way how to determine change in entry for any LDAP Server. >> >>> > >> >>> > We improved the performance but there might be other corner cases with >> >>> > other LDAP servers. >> >>> > >> >>> > Jakub proosed in 2) that we should always really compare the the >> >>> > attibutes >> >>> > from sssd cache and from LDAP search. But it would mean that we would >> >>> > not >> >>> > improve a performance for generic LDAP providers. >> >>> >> >>> We would still avoid the cache writes, "only" after comparing the >> >>> attribute values. So essentially by using the modifyTimestamp we save a >> >>> single LDB base search and a number of attribute-value comparisons, >> >>> depending on how large the object is. >> >>> >> >>> > >> >>> > We cannot generally detect virtual attributes for any LDAP server. >> >>> > What about adding an option where user could list virtual attributes. >> >>> > It would be a kind of proposed solution 4) but it would not be a >> >>> > special case for nsAccountLock but for more attributes which could be >> >>> > changed >> >>> > in configuration. >> >>> >> >>> OK, so your proposal is to keep the more aggressive cache optimization? >> >>> I think I'm mostly afraid about the more exotic LDAP servers, like IBM >> >>> Tivoli or Novell eDirectory which I already know from experience don't >> >>> follow the established standards closely. I guess I'm fine with that, we >> >>> can always flip the default back. Worst case for people who start using >> >>> 1.14, the admin can always define modifyTimestamp to some non-existing >> >>> attribute and force the attribute value comparison check. >> >>> >> >>> Yes, we can make the list configurable. We also need to be >> >>> very careful about printing the reason for (not) updating the cache to >> >>> the admin (#3060). >> >> >> >>OK, so after some discussion with Simo on IRC, there is a different >> >>proposal - let responder control the optimization level, so that PAM >> >>responder would always trigger a full cache write, or at least >> >>deep-compare the attributes and NSS responder would rely on >> >>modifyTimestamp. >> >> >> >>But that's a larger fix, so for short-term fix I propose to only use >> >>modifyTimestamp for group objects and always compare attributes for >> >>users. Then later, as another patch we can let the responder send a flag >> >>to control the optimization (would probably be done as a flag for a >> >>sysdb transaction). >> >> >> >>If you agree, I would file a ticket for the second part and you can >> >>instead write a patch to disable modifyTimestamp checks for users. >> > >> >As you wish. >> >The updated patch is attached. >> > >> >LS >> >> >From ae01ffdbbc74c5b43c2b644f8847d856cd2bf997 Mon Sep 17 00:00:00 2001 >> >From: Lukas Slebodnik <[email protected]> >> >Date: Wed, 3 Aug 2016 18:48:04 +0200 >> >Subject: [PATCH] SYSDB: Avoid optimisation with modifyTimestamp for users >> > >> >The usage of modifyTimestamp needn't be a reliable way >> >for detecting of changes in user entry in LDAP. >> >The authorisation need to rely current data from LDAP >> >and therefore we will temporary disable optimisation with >> >modifyTimestamp and we will rather rely on deep comparison >> >of attributes. In he future, it might be changed and >> >responders might control the optimization level. >> > >> And now with version witout failures in unit test and without compiler >> warnings >> :-) >> >> LS > >Hi, > >this patch doesn't apply atop origin/master, do I need some patches >before this one?
I looks like I created patch on top of your patch [SSSD] [PATCH] SYSDB: Fix setting dataExpireTimestamp if sysdb is supposed to set the current time If you want I can create on origin/master but you would need to rebase your patch. So it depends on wich patch will be pushed the first LS _______________________________________________ sssd-devel mailing list [email protected] https://lists.fedorahosted.org/admin/lists/[email protected]
