libcli/smb: make sure we have a body size of 0x31 before dereferencing an ioctl response

libcli/smb: make sure we have a body size of 0x31 before dereferencing an ioctl response

Found by valgrind, reported by Noel Power <nopower@suse.com>:

==7913== Invalid read of size 1
==7913==    at 0xC4F23EE: smb2cli_ioctl_done (smb2cli_ioctl.c:245)
==7913==    by 0x747A744: _tevent_req_notify_callback (tevent_req.c:112)
==7913==    by 0x747A817: tevent_req_finish (tevent_req.c:149)
==7913==    by 0x747A93C: tevent_req_trigger (tevent_req.c:206)
==7913==    by 0x7479B2B: tevent_common_loop_immediate
(tevent_immediate.c:135)
==7913==    by 0xA9CB4BE: run_events_poll (events.c:192)
==7913==    by 0xA9CBB32: s3_event_loop_once (events.c:303)
==7913==    by 0x7478C72: _tevent_loop_once (tevent.c:533)
==7913==    by 0x747AACD: tevent_req_poll (tevent_req.c:256)
==7913==    by 0x505315D: tevent_req_poll_ntstatus (tevent_ntstatus.c:109)
==7913==    by 0xA7201F2: cli_tree_connect (cliconnect.c:2764)
==7913==    by 0x165FF7: cm_prepare_connection (winbindd_cm.c:1276)
==7913==  Address 0x16ce24ec is 764 bytes inside a block of size 813 alloc'd
==7913==    at 0x4C29110: malloc (in
/usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==7913==    by 0x768A0C1: __talloc_with_prefix (talloc.c:668)
==7913==    by 0x768A27E: _talloc_pool (talloc.c:721)
==7913==    by 0x768A41E: _talloc_pooled_object (talloc.c:790)
==7913==    by 0x747A594: _tevent_req_create (tevent_req.c:66)
==7913==    by 0xCF6E2FA: read_packet_send (async_sock.c:414)
==7913==    by 0xCF6EB54: read_smb_send (read_smb.c:54)
==7913==    by 0xC4DA146: smbXcli_conn_receive_next (smbXcli_base.c:1027)
==7913==    by 0xC4DA02D: smbXcli_req_set_pending (smbXcli_base.c:978)
==7913==    by 0xC4DF776: smb2cli_req_compound_submit (smbXcli_base.c:3166)
==7913==    by 0xC4DFC1D: smb2cli_req_send (smbXcli_base.c:3268)
==7913==    by 0xC4F2210: smb2cli_ioctl_send (smb2cli_ioctl.c:149)
==7913==

BUG: https://bugzilla.samba.org/show_bug.cgi?id=11622

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>