s3: smbd: Fix a read after free if a chained SMB1 call goes async.

s3: smbd: Fix a read after free if a chained SMB1 call goes async.

Reported to the Samba Team by Yihan Lian <lianyihan@360.cn>, a security
researcher of Qihoo 360 GearTeam. Thanks a lot!

smb1_parse_chain() incorrectly used talloc_tos() for the memory
context of the chained smb1 requests. This gets freed between
requests so if a chained request goes async, the saved request
array also is freed, which causes a crash on resume.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12836

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
(cherry picked from commit 5fe76a5474823ed7602938a07c9c43226a7882a3)

Autobuild-User(v4-6-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-6-test): Tue Jul 25 06:16:37 CEST 2017 on sn-devel-144