ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()

In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()

smb_grant_oplock() has two issues in the oplock publication sequence:

1) opinfo is linked into ci->m_op_list (via opinfo_add) before

add_lease_global_list() is called. If add_lease_global_list()

fails (kmalloc returns NULL), the error path frees the opinfo

via __free_opinfo() while it is still linked in ci->m_op_list.

Concurrent m_op_list readers (opinfo_get_list, or direct iteration

in smb_break_all_levII_oplock) dereference the freed node.

2) opinfo->o_fp is assigned after add_lease_global_list() publishes

the opinfo on the global lease list. A concurrent

find_same_lease_key() can walk the lease list and dereference

opinfo->o_fp->f_ci while o_fp is still NULL.

Fix by restructuring the publication sequence to eliminate post-publish

failure:

- Set opinfo->o_fp before any list publication (fixes NULL deref).

- Preallocate lease_table via alloc_lease_table() before opinfo_add()

so add_lease_global_list() becomes infallible after publication.

- Keep the original m_op_list publication order (opinfo_add before

lease list) so concurrent opens via same_client_has_lease() and

opinfo_get_list() still see the in-flight grant.

- Use opinfo_put() instead of __free_opinfo() on err_out so that

the RCU-deferred free path is used.

This also requires splitting add_lease_global_list() to take a

preallocated lease_table and changing its return type from int to void,

since it can no longer fail.