smb: client: let smbd_destroy() call disable_work_sync(&info->post_send_credits_work)

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

smb: client: let smbd_destroy() call disable_work_sync(&info->post_send_credits_work)

In smbd_destroy() we may destroy the memory so we better
wait until post_send_credits_work is no longer pending
and will never be started again.

I actually just hit the case using rxe:

WARNING: CPU: 0 PID: 138 at drivers/infiniband/sw/rxe/rxe_verbs.c:1032 rxe_post_recv+0x1ee/0x480 [rdma_rxe]
...
[ 5305.686979] [ T138] smbd_post_recv+0x445/0xc10 [cifs]
[ 5305.687135] [ T138] ? srso_alias_return_thunk+0x5/0xfbef5
[ 5305.687149] [ T138] ? __kasan_check_write+0x14/0x30
[ 5305.687185] [ T138] ? __pfx_smbd_post_recv+0x10/0x10 [cifs]
[ 5305.687329] [ T138] ? __pfx__raw_spin_lock_irqsave+0x10/0x10
[ 5305.687356] [ T138] ? srso_alias_return_thunk+0x5/0xfbef5
[ 5305.687368] [ T138] ? srso_alias_return_thunk+0x5/0xfbef5
[ 5305.687378] [ T138] ? _raw_spin_unlock_irqrestore+0x11/0x60
[ 5305.687389] [ T138] ? srso_alias_return_thunk+0x5/0xfbef5
[ 5305.687399] [ T138] ? get_receive_buffer+0x168/0x210 [cifs]
[ 5305.687555] [ T138] smbd_post_send_credits+0x382/0x4b0 [cifs]
[ 5305.687701] [ T138] ? __pfx_smbd_post_send_credits+0x10/0x10 [cifs]
[ 5305.687855] [ T138] ? __pfx___schedule+0x10/0x10
[ 5305.687865] [ T138] ? __pfx__raw_spin_lock_irq+0x10/0x10
[ 5305.687875] [ T138] ? queue_delayed_work_on+0x8e/0xa0
[ 5305.687889] [ T138] process_one_work+0x629/0xf80
[ 5305.687908] [ T138] ? srso_alias_return_thunk+0x5/0xfbef5
[ 5305.687917] [ T138] ? __kasan_check_write+0x14/0x30
[ 5305.687933] [ T138] worker_thread+0x87f/0x1570
...

It means rxe_post_recv was called after rdma_destroy_qp().
This happened because put_receive_buffer() was triggered
by ib_drain_qp() and called:
queue_work(info->workqueue, &info->post_send_credits_work);