openldap-bugs August 2007

openldap-bugs@openldap.org

42 participants
211 discussions

Re: (ITS#5114) pcache cache results for searches that hit size/timelimit
by ando＠sys-net.it 29 Aug '07

29 Aug '07

rhafer(a)suse.de wrote: > On Wednesday 29 August 2007 18:48, ando(a)sys-net.it wrote: >> rhafer(a)suse.de wrote: >>> But a malicous client can then just send requests with sizelimit 1. Those >>> query will get cached and the database is of no real use anymore (IMO). >> Well, in this case, the proxycache should either change the sizelimit >> (and the timelimit) to unlimited, and deal with client-requested limits >> locally, > This seems like the nicest approach to solve the problem. But seems to be a > bit more effort. I'd go this way, yes. > My suggest for a quick fix for this issue would be to just not cache queries > that return one off the _LIMIT_EXCEEDED error codes. Probably with checking > if it was a client-requested limit or a limit of the server side (in which > case we could probably cache the results). Then please make a clear statement in the code that it's a temporary workaround, so it is easier to spot and remove, eventually. >> or consider uncacheable those requests that specify a time or a >> size limit. > Well that would cause even those queries being uncachable that would not hit > the requested limit. If I understand you correctly. Right. Well, I understand if no limit was hit the request would become cacheable. In this case, the approach you suggest would be fine. p. Ing. Pierangelo Masarati OpenLDAP Core Team SysNet s.r.l. via Dossi, 8 - 27100 Pavia - ITALIA http://www.sys-net.it --------------------------------------- Office: +39 02 23998309 Mobile: +39 333 4963172 Email: pierangelo.masarati(a)sys-net.it ---------------------------------------

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Re: (ITS#5114) pcache cache results for searches that hit size/timelimit
by rhafer＠suse.de 29 Aug '07

29 Aug '07

On Wednesday 29 August 2007 18:48, ando(a)sys-net.it wrote: > rhafer(a)suse.de wrote: > > But a malicous client can then just send requests with sizelimit 1. Those > > query will get cached and the database is of no real use anymore (IMO). > > Well, in this case, the proxycache should either change the sizelimit > (and the timelimit) to unlimited, and deal with client-requested limits > locally, This seems like the nicest approach to solve the problem. But seems to be a bit more effort. My suggest for a quick fix for this issue would be to just not cache queries that return one off the _LIMIT_EXCEEDED error codes. Probably with checking if it was a client-requested limit or a limit of the server side (in which case we could probably cache the results). > or consider uncacheable those requests that specify a time or a > size limit. Well that would cause even those queries being uncachable that would not hit the requested limit. If I understand you correctly. > On the contrary, they should be considered answerable if a > corresponding request is cached, and the limits should be checked locally. -- Ralf

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Re: (ITS#5112) memory leak in pcache overlay
by hyc＠symas.com 29 Aug '07

29 Aug '07

Pierangelo Masarati wrote: > hyc(a)symas.com wrote: > >> Ah yes, that's correct. I misspoke - the DB is written when the cache has >> received an LDAP_RESULT from the remote server. The client gets this result >> when the cache has finished writing. We could move the DB write to a separate >> cleanup handler instead of running it in the response handler, which would free >> up the client sooner. > > I also noticed that > <http://www.openldap.org/lists/openldap-devel/200708/msg00033.html>, and > I wanted to do something similar, but considering Ralf's observations, > multiple clients concurrently running the same search request would > cause it to be cached multiple times, because until the first one is not > cached the others will not find it. OTOH, letting the others know it's > being cached, and making them wait until caching is done would imply > some delay, which could be long based on how many entries are being > cached. However, given the purpose of a proxy cache, and considering > that so many identical searches are not likely to occur simultaneously, > I'd prefer to queue requests that are being cached. Agreed. Even with a delay it ought to be faster than making the remote search again. But this is probably not worth changing at this moment. Let's get 2.4.5 out first. -- -- Howard Chu Chief Architect, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/

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Re: (ITS#5112) memory leak in pcache overlay
by ando＠sys-net.it 29 Aug '07

29 Aug '07

hyc(a)symas.com wrote: > Ah yes, that's correct. I misspoke - the DB is written when the cache has > received an LDAP_RESULT from the remote server. The client gets this result > when the cache has finished writing. We could move the DB write to a separate > cleanup handler instead of running it in the response handler, which would free > up the client sooner. I also noticed that <http://www.openldap.org/lists/openldap-devel/200708/msg00033.html>, and I wanted to do something similar, but considering Ralf's observations, multiple clients concurrently running the same search request would cause it to be cached multiple times, because until the first one is not cached the others will not find it. OTOH, letting the others know it's being cached, and making them wait until caching is done would imply some delay, which could be long based on how many entries are being cached. However, given the purpose of a proxy cache, and considering that so many identical searches are not likely to occur simultaneously, I'd prefer to queue requests that are being cached. p. Ing. Pierangelo Masarati OpenLDAP Core Team SysNet s.r.l. via Dossi, 8 - 27100 Pavia - ITALIA http://www.sys-net.it --------------------------------------- Office: +39 02 23998309 Mobile: +39 333 4963172 Email: pierangelo.masarati(a)sys-net.it ---------------------------------------

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Re: (ITS#5112) memory leak in pcache overlay
by hyc＠symas.com 29 Aug '07

29 Aug '07

rhafer(a)suse.de wrote: > On Wednesday 29 August 2007 18:10, Howard Chu wrote: >> Ralf Haferkamp wrote: >>> On Wednesday 29 August 2007 17:36, Howard Chu wrote: >>>> rhafer(a)suse.de wrote: >>>>> Full_Name: Ralf Haferkamp >>>>> Version: RE23, HEAD >>>>> >>>>> Valgrind gives me the log pasted below when I abort an ldapsearch >>>>> command (CTRL-C) that is running against a back-ldap database that uses >>>>> the pcache overlay. >>>> Makes sense. We need to use the cleanup handler and free the saved query >>>> info if op->o_abandon is set. Do you want to code this up? >>> I am still working on that, but checking for op->o_abandon doesn't seem >>> to be enough. E.g. if I abort the ldapsearch while slapd is updating its >>> cache (all entries have been returned, but the final LDAP_RESULT to the >>> client is still missing) a filter_free in the cleanup handler will >>> invalidly free the filter. >>> >>> We somehow need to make sure that the query is only free'd if nothing has >>> been written to the cache database. >> I don't understand the problem. Nothing can get written to the DB until the >> LDAP_RESULT has been sent. I.e., rs->sr_result == REP_RESULT. > Hm, but the ldapsearch command only returns after the complete query result > has been written to the cache (at least here it behaves so), which can take > quite a while. So it seems to me that the client has not received the > LDAP_RESULT. Ah yes, that's correct. I misspoke - the DB is written when the cache has received an LDAP_RESULT from the remote server. The client gets this result when the cache has finished writing. We could move the DB write to a separate cleanup handler instead of running it in the response handler, which would free up the client sooner. -- -- Howard Chu Chief Architect, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/

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Re: (ITS#5114) pcache cache results for searches that hit size/timelimit
by ando＠sys-net.it 29 Aug '07

29 Aug '07

rhafer(a)suse.de wrote: > But a malicous client can then just send requests with sizelimit 1. Those > query will get cached and the database is of no real use anymore (IMO). Well, in this case, the proxycache should either change the sizelimit (and the timelimit) to unlimited, and deal with client-requested limits locally, or consider uncacheable those requests that specify a time or a size limit. On the contrary, they should be considered answerable if a corresponding request is cached, and the limits should be checked locally. p. Ing. Pierangelo Masarati OpenLDAP Core Team SysNet s.r.l. via Dossi, 8 - 27100 Pavia - ITALIA http://www.sys-net.it --------------------------------------- Office: +39 02 23998309 Mobile: +39 333 4963172 Email: pierangelo.masarati(a)sys-net.it ---------------------------------------

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Re: (ITS#5114) pcache cache results for searches that hit size/timelimit
by rhafer＠suse.de 29 Aug '07

29 Aug '07

On Wednesday 29 August 2007 18:36, Pierangelo Masarati wrote: > hyc(a)symas.com wrote: > >> pcache currently cache the results of search that hit server- or > >> clientside size- or timelimits. That means that subsequent search will > >> get the (incomplete) results from the cache. I guess pcache should only > >> cache operations that returned LDAP_SUCCESS. > > > > Makes sense... > > Well, I agree for timelimit, but sizelimit might be questionable. In > fact, the only reason not to cache searches ending in sizelimit exceeded > is that the size limit may depend on the client's identity. But this is > true in general also for access to entries and to entry data, but we > don't cache based on the identity of the client, so data cached with one > identity (set A) might differ from data that would be returned by > another identity for the very same search (set B), and both the relative > complement of A in B and of B in A may be not empty. So, if we accept > this for ACLs (no differences between the results returned for requests > with different identities) I don't see why we should differentiate with > respect to the size limit. But a malicous client can then just send requests with sizelimit 1. Those query will get cached and the database is of no real use anymore (IMO). -- Ralf

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Re: (ITS#5114) pcache cache results for searches that hit size/timelimit
by ando＠sys-net.it 29 Aug '07

29 Aug '07

hyc(a)symas.com wrote: >> pcache currently cache the results of search that hit server- or clientside >> size- or timelimits. That means that subsequent search will get the (incomplete) >> results from the cache. I guess pcache should only cache operations that >> returned LDAP_SUCCESS. > > Makes sense... Well, I agree for timelimit, but sizelimit might be questionable. In fact, the only reason not to cache searches ending in sizelimit exceeded is that the size limit may depend on the client's identity. But this is true in general also for access to entries and to entry data, but we don't cache based on the identity of the client, so data cached with one identity (set A) might differ from data that would be returned by another identity for the very same search (set B), and both the relative complement of A in B and of B in A may be not empty. So, if we accept this for ACLs (no differences between the results returned for requests with different identities) I don't see why we should differentiate with respect to the size limit. p. Ing. Pierangelo Masarati OpenLDAP Core Team SysNet s.r.l. via Dossi, 8 - 27100 Pavia - ITALIA http://www.sys-net.it --------------------------------------- Office: +39 02 23998309 Mobile: +39 333 4963172 Email: pierangelo.masarati(a)sys-net.it ---------------------------------------

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Re: (ITS#5112) memory leak in pcache overlay
by rhafer＠suse.de 29 Aug '07

29 Aug '07

On Wednesday 29 August 2007 18:10, Howard Chu wrote: > Ralf Haferkamp wrote: > > On Wednesday 29 August 2007 17:36, Howard Chu wrote: > >> rhafer(a)suse.de wrote: > >>> Full_Name: Ralf Haferkamp > >>> Version: RE23, HEAD > >>> > >>> Valgrind gives me the log pasted below when I abort an ldapsearch > >>> command (CTRL-C) that is running against a back-ldap database that uses > >>> the pcache overlay. > >> > >> Makes sense. We need to use the cleanup handler and free the saved query > >> info if op->o_abandon is set. Do you want to code this up? > > > > I am still working on that, but checking for op->o_abandon doesn't seem > > to be enough. E.g. if I abort the ldapsearch while slapd is updating its > > cache (all entries have been returned, but the final LDAP_RESULT to the > > client is still missing) a filter_free in the cleanup handler will > > invalidly free the filter. > > > > We somehow need to make sure that the query is only free'd if nothing has > > been written to the cache database. > > I don't understand the problem. Nothing can get written to the DB until the > LDAP_RESULT has been sent. I.e., rs->sr_result == REP_RESULT. Hm, but the ldapsearch command only returns after the complete query result has been written to the cache (at least here it behaves so), which can take quite a while. So it seems to me that the client has not received the LDAP_RESULT. With the suggested fix I get this, if I abort the ldapsearch during that time, as the op->o_abandon is set in cleanup handler: ==26949== Invalid free() / delete / delete[] ==26949== at 0x4C226DB: free (in /usr/lib64/valgrind/amd64-linux/vgpreload_memcheck.so) ==26949== by 0x508A819: ber_memfree_x (memory.c:152) ==26949== by 0x4AC9D7: slap_sl_free (sl_malloc.c:455) ==26949== by 0x44797D: filter_free_x (filter.c:526) ==26949== by 0x4478C9: filter_free_x (filter.c:509) ==26949== by 0x4479D9: filter_free (filter.c:538) ==26949== by 0x5A7794: free_query (pcache.c:1126) ==26949== by 0x5AF9B0: pcache_db_close (pcache.c:3282) ==26949== by 0x4C2F87: over_db_close (backover.c:192) ==26949== by 0x452658: backend_shutdown (backend.c:365) ==26949== by 0x47C03E: slap_shutdown (init.c:253) ==26949== by 0x422D65: main (main.c:943) ==26949== Address 0xA533A68 is 0 bytes inside a block of size 24 free'd ==26949== at 0x4C226DB: free (in /usr/lib64/valgrind/amd64-linux/vgpreload_memcheck.so) ==26949== by 0x508A819: ber_memfree_x (memory.c:152) ==26949== by 0x4AC9D7: slap_sl_free (sl_malloc.c:455) ==26949== by 0x44797D: filter_free_x (filter.c:526) ==26949== by 0x4478C9: filter_free_x (filter.c:509) ==26949== by 0x4479D9: filter_free (filter.c:538) ==26949== by 0x5A9F7F: pcache_op_cleanup (pcache.c:1886) ==26949== by 0x456A69: slap_cleanup_play (result.c:344) ==26949== by 0x4571DC: send_ldap_response (result.c:526) ==26949== by 0x457935: slap_send_ldap_result (result.c:632) ==26949== by 0x4F7AE4: ldap_back_search (search.c:528) ==26949== by 0x4C3FD0: overlay_op_walk (backover.c:652) -- Ralf

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Re: (ITS#5114) pcache cache results for searches that hit size/timelimit
by hyc＠symas.com 29 Aug '07

29 Aug '07

rhafer(a)suse.de wrote: > Full_Name: Ralf Haferkamp > Version: RE23, HEAD > OS: - > URL: ftp://ftp.openldap.org/incoming/ > Submission from: (NULL) (89.166.180.39) > > > pcache currently cache the results of search that hit server- or clientside > size- or timelimits. That means that subsequent search will get the (incomplete) > results from the cache. I guess pcache should only cache operations that > returned LDAP_SUCCESS. Makes sense... -- -- Howard Chu Chief Architect, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/

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openldap-bugs August 2007