io_uring/sqpoll: work around a potential audit memory leak

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

io_uring/sqpoll: work around a potential audit memory leak

kmemleak complains that there's a memory leak related to connect

handling:

unreferenced object 0xffff0001093bdf00 (size 128):

comm "iou-sqp-455", pid 457, jiffies 4294894164

hex dump (first 32 bytes):

02 00 fa ea 7f 00 00 01 00 00 00 00 00 00 00 00 ................

00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

backtrace (crc 2e481b1a):

[<00000000c0a26af4>] kmemleak_alloc+0x30/0x38

[<000000009c30bb45>] kmalloc_trace+0x228/0x358

[<000000009da9d39f>] __audit_sockaddr+0xd0/0x138

[<0000000089a93e34>] move_addr_to_kernel+0x1a0/0x1f8

[<000000000b4e80e6>] io_connect_prep+0x1ec/0x2d4

[<00000000abfbcd99>] io_submit_sqes+0x588/0x1e48

[<00000000e7c25e07>] io_sq_thread+0x8a4/0x10e4

[<00000000d999b491>] ret_from_fork+0x10/0x20

which can can happen if:

1) The command type does something on the prep side that triggers an

audit call.

2) The thread hasn't done any operations before this that triggered

an audit call inside ->issue(), where we have audit_uring_entry()

and audit_uring_exit().

Work around this by issuing a blanket NOP operation before the SQPOLL

does anything.