dbwrap_watch: Set rec->value_valid while returning nested share_mode_…

…do_locked()

As reported on samba-technical by Rouven WEILER <Rouven_Weiler@gmx.net>:
https://lists.samba.org/archive/samba-technical/2020-April/135116.html

Following backtrace was observed with vfs_fruit for time machine backup:

[2020/04/10 08:00:38.107917,  0] ../../lib/dbwrap/dbwrap.c:82(dbwrap_record_get_value)
  PANIC: assert failed at ../../lib/dbwrap/dbwrap.c(82): rec->value_valid
[2020/04/10 08:00:38.108499,  0] ../../source3/lib/util.c:830(smb_panic_s3)
  PANIC (pid 3427): assert failed: rec->value_valid
[2020/04/10 08:00:38.109541,  0] ../../lib/util/fault.c:265(log_stack_trace)
  BACKTRACE: 37 stack frames:
   #0 /usr/lib/samba/amd64/libsamba-util.so.0.0.1'log_stack_trace+0x26 [0xfffffd7fee51de66]
   #1 /usr/lib/samba/amd64/libsmbconf.so.0'smb_panic_s3+0x26 [0xfffffd7fedf5a596]
   #2 /usr/lib/samba/amd64/libsamba-util.so.0.0.1'smb_panic+0x1f [0xfffffd7fee51df3f]
   #3 /usr/lib/samba/private/amd64/libdbwrap-samba4.so'dbwrap_record_get_value+0x2a [0xfffffd7feccb627a]
   #4 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'get_share_mode_lock+0x109 [0xfffffd7fee7195c9]
   #5 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_contend_level2_oplocks_begin+0xa1 [0xfffffd7fee7f7761]
   #6 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'brl_lock+0x635 [0xfffffd7fee710f45]
   #7 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'do_lock_fn+0xa4 [0xfffffd7fee70d534]
   #8 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'share_mode_do_locked_fn+0x86 [0xfffffd7fee7174b6]
   #9 /usr/lib/samba/amd64/libsmbconf.so.0'dbwrap_watched_do_locked_fn+0xfa [0xfffffd7fedf622ca]
   #10 /usr/lib/samba/private/amd64/libdbwrap-samba4.so'db_tdb_do_locked+0x12f [0xfffffd7feccb95cf]
   #11 /usr/lib/samba/private/amd64/libdbwrap-samba4.so'dbwrap_do_locked+0x48 [0xfffffd7feccb69a8]
   #12 /usr/lib/samba/amd64/libsmbconf.so.0'dbwrap_watched_do_locked+0x6f [0xfffffd7fedf60d7f]
   #13 /usr/lib/samba/private/amd64/libdbwrap-samba4.so'dbwrap_do_locked+0x48 [0xfffffd7feccb69a8]
   #14 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'share_mode_do_locked+0xd2 [0xfffffd7fee719b82]
   #15 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'do_lock+0xf0 [0xfffffd7fee70dfe0]
   #16 /usr/lib/samba/amd64/vfs/fruit.so'fruit_create_file+0x7ba [0xfffffd7fe88855aa]
   #17 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_smb2_request_process_create+0xa07 [0xfffffd7fee7d3237]
   #18 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_smb2_request_dispatch+0xc8f [0xfffffd7fee7c985f]
   #19 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_smb2_connection_handler+0x621 [0xfffffd7fee7ca7e1]
   #20 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'tevent_common_invoke_fd_handler+0x80 [0xfffffd7fecd3a580]
   #21 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'epoll_event_loop_once+0x22c [0xfffffd7fecd4180c]
   #22 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'std_event_loop_once+0x40 [0xfffffd7fecd3f8f0]
   #23 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'_tevent_loop_once+0x95 [0xfffffd7fecd39bd5]
   #24 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'tevent_common_loop_wait+0x23 [0xfffffd7fecd39e43]
   #25 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'std_event_loop_wait+0x40 [0xfffffd7fecd3f870]
   #26 /usr/lib/samba/private/amd64/libsmbd-base-samba4.so'smbd_process+0x777 [0xfffffd7fee7b8677]
   #27 /usr/lib/samba/sbin/amd64/smbd'smbd_accept_connection+0x189 [0x40d5b9]
   #28 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'tevent_common_invoke_fd_handler+0x80 [0xfffffd7fecd3a580]
   #29 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'epoll_event_loop_once+0x22c [0xfffffd7fecd4180c]
   #30 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'std_event_loop_once+0x40 [0xfffffd7fecd3f8f0]
   #31 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'_tevent_loop_once+0x95 [0xfffffd7fecd39bd5]
   #32 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'tevent_common_loop_wait+0x23 [0xfffffd7fecd39e43]
   #33 /usr/lib/samba/private/amd64/libtevent.so.0.10.2'std_event_loop_wait+0x40 [0xfffffd7fecd3f870]
   #34 /usr/lib/samba/sbin/amd64/smbd'main+0x1a0f [0x40f9ff]
   #35 /usr/lib/samba/sbin/amd64/smbd'_start_crt+0x83 [0x408e73]
   #36 /usr/lib/samba/sbin/amd64/smbd'_start+0x18 [0x408dd8]

In this particular nested share_mode_do_locked() invocation, callback
comes through dbwrap_watched_do_locked_fn() where it fails to update
rec->value_valid which further gets assigned to static_share_mode_record
within share_mode_do_locked_fn().

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14352

Signed-off-by: Anoop C S <anoopcs@redhat.com>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>

Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Tue Apr 21 17:37:43 UTC 2020 on sn-devel-184

(cherry picked from commit 5651faf)

source3/lib/dbwrap/dbwrap_watch.c

@@ -333,6 +333,7 @@ static void dbwrap_watched_do_locked_fn(
 	struct db_record rec = {
 		.db = state->db,
 		.key = dbwrap_record_get_key(subrec),
+		.value_valid = true,
 		.storev = dbwrap_watched_do_locked_storev,
 		.delete_rec = dbwrap_watched_do_locked_delete,
 		.private_data = state