Thank you Willian,
So far your scenario (entry found when reading base entry but no more
existing when computing the candidates) is the only one that matches the
symptoms.
And that triggered a thought:
We cannot do anything for SUBTREE and ONE_LEVEL searches
because the fact that the base entry id is not in the candidate may be
normal
but IMHO we should improve the BASE search case.
In this case the candidate list is directly set to the base entry id
==> if the candidate entry (in ldbm_back_next_search_entry) is not found
and the scope is BASE then we should return a LDAP_NO_SUCH_ENTRY error ..
Pierre
On Wed, Jan 13, 2021 at 1:45 AM William Brown <[email protected]> wrote:
> Hey there,
>
> https://github.com/389ds/389-ds-base/pull/4525/files
>
> I had a look and I can see a few possible contributing factors, but
> without a core and the exact state I can't be sure if this is correct. It's
> all just hypothetical from reading the code.
>
>
> The crash is in deref_do_deref_attr() which is called as part of
> deref_pre_entry(). This is the SLAPI_PLUGIN_PRE_ENTRY_FN which is called by
> "./ldap/servers/slapd/result.c:1488: rc = plugin_call_plugins(pb,
> SLAPI_PLUGIN_PRE_ENTRY_FN);"
>
>
> I think what's important here is that the search is conducted in
> ./ldap/servers/slapd/opshared.c:818 rc = (*be->be_search)(pb); Is *not*
> in a transaction. That means that while the single search in be_search() is
> consistent due to an implied transaction, the subsequent search in
> deref_pre_entry() is likely conducted in a seperate transaction. This
> allows for other operations to potentially interleave and cause changes -
> modrdn or delete would certainly be candidates to cause a DN to be remove
> between these two points. It would be extremely hard to reproduce as a race
> condition of course.
>
>
> A question you asked is why don't we get a "no such entry" error or
> similar? I think that this is because build_candidate_list in ldbm_search.c
> doesn't actually create an error if the base_candidates list is empty,
> because an IDL is allocated with a value of 0 (no matching entries). this
> allows the search to proceed, and there are no errors, and the result set
> is set to NULL with size 0. I can't see where LDAP_NO_SUCH_OBJECT is set in
> this process, but without looking further into it, my suspicion is that
> entries of size 0 WONT return an error condition to internal_search_pb, so
> it's valid for this to be empty.
>
> Anyway, again, this is just reading the code for 20 minutes, and is not a
> complete in depth investigation, but maybe it's some ideas about what
> happened?
>
> Hope it helps :)
>
>
>
> —
> Sincerely,
>
> William Brown
>
> Senior Software Engineer, 389 Directory Server
> SUSE Labs, Australia
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