ksmbd: fix out-of-bound read in parse_lease_state()

ksmbd: fix out-of-bound read in parse_lease_state()

This bug is in parse_lease_state, and it is caused by the missing check
of `struct create_context`. When the ksmbd traverses the create_contexts,
it doesn't check if the field of `NameOffset` and `Next` is valid,
The KASAN message is following:

[    6.664323] BUG: KASAN: slab-out-of-bounds in parse_lease_state+0x7d/0x280
[    6.664738] Read of size 2 at addr ffff888005c08988 by task kworker/0:3/103
...
[    6.666644] Call Trace:
[    6.666796]  <TASK>
[    6.666933]  dump_stack_lvl+0x33/0x50
[    6.667167]  print_report+0xcc/0x620
[    6.667903]  kasan_report+0xae/0xe0
[    6.668374]  kasan_check_range+0x35/0x1b0
[    6.668621]  parse_lease_state+0x7d/0x280
[    6.668868]  smb2_open+0xbe8/0x4420
[    6.675137]  handle_ksmbd_work+0x282/0x820

Use smb2_find_context_vals() to find smb2 create request lease context.
smb2_find_context_vals validate create context fields.

Cc: stable@vger.kernel.org
Reported-by: Chih-Yen Chang <cc85nod@gmail.com>
Tested-by: Chih-Yen Chang <cc85nod@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>