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 <lsleb...@redhat.com> > >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? _______________________________________________ sssd-devel mailing list sssd-devel@lists.fedorahosted.org https://lists.fedorahosted.org/admin/lists/sssd-devel@lists.fedorahosted.org