(ITS#8064) SIGSEGV in monitor-shutdown code

Full_Name: Leonid Yuriev Version: 2.4-HEAD OS: RHEL7 URL: ftp://ftp.openldap.org/incoming/ Submission from: (NULL) (31.130.36.33)

Monitor-backend shutdown code could call a callback from registered subsystem after it is already destroyed.

For instance, currently ldap-backend frees its own registered context (lmi_mss from ldap_monitor_info_t) before than monitor_back_db_destroy() will be called.

Therefore SIGSEGV would be occur on monitor shutdown if any ldap-backend database is configured and such freed context will be overwrited.

This bug could be reproduced by a filling-memory-with-non-zero before calling free() from glibc.