s3/lib: Prevent use after free of messaging_ctdb_fde_ev structs

s3/lib: Prevent use after free of messaging_ctdb_fde_ev structs

In a cluster setup samba-bgqd async callback
cups_pcap_load_async can access messaging_ctdb_fde_ev associated
with already destructed global_ctdb_ctx_destructor

==26053== Invalid read of size 8
==26053==    at 0x71692E1: messaging_ctdb_fde_ev_destructor (messages_ctdb.c:181)
==26053==    by 0x40B2309: _tc_free_internal (talloc.c:1158)
==26053==    by 0x40B3539: _tc_free_children_internal (talloc.c:1669)
==26053==    by 0x40B24C4: _tc_free_internal (talloc.c:1184)
==26053==    by 0x40B3539: _tc_free_children_internal (talloc.c:1669)
==26053==    by 0x40B24C4: _tc_free_internal (talloc.c:1184)
==26053==    by 0x40B2685: _talloc_free_internal (talloc.c:1248)
==26053==    by 0x40B3963: _talloc_free (talloc.c:1792)
==26053==    by 0x4056BCA: tevent_req_received (tevent_req.c:301)
==26053==    by 0x405673D: tevent_req_destructor (tevent_req.c:135)
==26053==    by 0x40B2309: _tc_free_internal (talloc.c:1158)
==26053==    by 0x40B3539: _tc_free_children_internal (talloc.c:1669)
==26053==    by 0x40B24C4: _tc_free_internal (talloc.c:1184)
==26053==    by 0x40B2685: _talloc_free_internal (talloc.c:1248)
==26053==    by 0x40B3963: _talloc_free (talloc.c:1792)
==26053==    by 0x1384EF: cups_pcap_load_async (print_cups.c:507)
==26053==    by 0x13894B: cups_cache_reload (print_cups.c:602)
==26053==    by 0x1373AE: pcap_cache_reload (pcap.c:140)
==26053==    by 0x1369D2: register_printing_bq_handlers (queue_process.c:323)
==26053==    by 0x122AD6: main (samba-bgqd.c:316)
==26053==  Address 0xed64d48 is 120 bytes inside a block of size 128 free'd
==26053==    at 0x4C370EB: free (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==26053==    by 0x40B25E1: _tc_free_internal (talloc.c:1222)
==26053==    by 0x40B2685: _talloc_free_internal (talloc.c:1248)
==26053==    by 0x40B3963: _talloc_free (talloc.c:1792)
==26053==    by 0x71691F6: messaging_ctdb_destroy (messages_ctdb.c:141)
==26053==    by 0x7169C21: msg_ctdb_ref_destructor (messages_ctdb_ref.c:142)
==26053==    by 0x40B2309: _tc_free_internal (talloc.c:1158)
==26053==    by 0x40B3539: _tc_free_children_internal (talloc.c:1669)
==26053==    by 0x40B24C4: _tc_free_internal (talloc.c:1184)
==26053==    by 0x40B2685: _talloc_free_internal (talloc.c:1248)
==26053==    by 0x40B3963: _talloc_free (talloc.c:1792)
==26053==    by 0x4157380: messaging_reinit (messages.c:646)
==26053==    by 0x416C01E: reinit_after_fork (util.c:488)
==26053==    by 0x13844C: cups_pcap_load_async (print_cups.c:498)
==26053==    by 0x13894B: cups_cache_reload (print_cups.c:602)
==26053==    by 0x1373AE: pcap_cache_reload (pcap.c:140)
==26053==    by 0x1369D2: register_printing_bq_handlers (queue_process.c:323)
==26053==    by 0x122AD6: main (samba-bgqd.c:316)
==26053==  Block was alloc'd at
==26053==    at 0x4C346A4: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==26053==    by 0x40B1989: __talloc_with_prefix (talloc.c:783)
==26053==    by 0x40B1B23: __talloc (talloc.c:825)
==26053==    by 0x40B1ECC: _talloc_named_const (talloc.c:982)
==26053==    by 0x40B49C3: _talloc_zero (talloc.c:2421)
==26053==    by 0x7168E68: messaging_ctdb_init (messages_ctdb.c:93)
==26053==    by 0x716979D: messaging_ctdb_ref (messages_ctdb_ref.c:75)
==26053==    by 0x415702A: messaging_init_internal (messages.c:563)
==26053==    by 0x41572FD: messaging_init (messages.c:622)
==26053==    by 0x4163ED3: global_messaging_context (global_contexts.c:62)
==26053==    by 0x12273B: main (samba-bgqd.c:271)
==26053==

Bug: https://bugzilla.samba.org/show_bug.cgi?id=15293

Signed-off-by: Noel Power <npower@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
(cherry picked from commit 7a880ef52dfc85ed2f674250b5baf5109f8d4691)

Autobuild-User(v4-17-test): Jule Anger <janger@samba.org>
Autobuild-Date(v4-17-test): Fri Jan 27 09:45:10 UTC 2023 on sn-devel-184