s390/qeth: fix use-after-free in hsci

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

s390/qeth: fix use-after-free in hsci

KASAN found that addr was dereferenced after br2dev_event_work was freed.

==================================================================
BUG: KASAN: use-after-free in qeth_l2_br2dev_worker+0x5ba/0x6b0
Read of size 1 at addr 00000000fdcea440 by task kworker/u760:4/540
CPU: 17 PID: 540 Comm: kworker/u760:4 Tainted: G E 6.1.0-20221128.rc7.git1.5aa3bed4ce83.300.fc36.s390x+kasan #1
Hardware name: IBM 8561 T01 703 (LPAR)
Workqueue: 0.0.8000_event qeth_l2_br2dev_worker
Call Trace:
[<000000016944d4ce>] dump_stack_lvl+0xc6/0xf8
[<000000016942cd9c>] print_address_description.constprop.0+0x34/0x2a0
[<000000016942d118>] print_report+0x110/0x1f8
[<0000000167a7bd04>] kasan_report+0xfc/0x128
[<000000016938d79a>] qeth_l2_br2dev_worker+0x5ba/0x6b0
[<00000001673edd1e>] process_one_work+0x76e/0x1128
[<00000001673ee85c>] worker_thread+0x184/0x1098
[<000000016740718a>] kthread+0x26a/0x310
[<00000001672c606a>] __ret_from_fork+0x8a/0xe8
[<00000001694711da>] ret_from_fork+0xa/0x40
Allocated by task 108338:
kasan_save_stack+0x40/0x68
kasan_set_track+0x36/0x48
__kasan_kmalloc+0xa0/0xc0
qeth_l2_switchdev_event+0x25a/0x738
atomic_notifier_call_chain+0x9c/0xf8
br_switchdev_fdb_notify+0xf4/0x110
fdb_notify+0x122/0x180
fdb_add_entry.constprop.0.isra.0+0x312/0x558
br_fdb_add+0x59e/0x858
rtnl_fdb_add+0x58a/0x928
rtnetlink_rcv_msg+0x5f8/0x8d8
netlink_rcv_skb+0x1f2/0x408
netlink_unicast+0x570/0x790
netlink_sendmsg+0x752/0xbe0
sock_sendmsg+0xca/0x110
____sys_sendmsg+0x510/0x6a8
___sys_sendmsg+0x12a/0x180
__sys_sendmsg+0xe6/0x168
__do_sys_socketcall+0x3c8/0x468
do_syscall+0x22c/0x328
__do_syscall+0x94/0xf0
system_call+0x82/0xb0
Freed by task 540:
kasan_save_stack+0x40/0x68
kasan_set_track+0x36/0x48
kasan_save_free_info+0x4c/0x68
____kasan_slab_free+0x14e/0x1a8
__kasan_slab_free+0x24/0x30
__kmem_cache_free+0x168/0x338
qeth_l2_br2dev_worker+0x154/0x6b0
process_one_work+0x76e/0x1128
worker_thread+0x184/0x1098
kthread+0x26a/0x310
__ret_from_fork+0x8a/0xe8
ret_from_fork+0xa/0x40
Last potentially related work creation:
kasan_save_stack+0x40/0x68
__kasan_record_aux_stack+0xbe/0xd0
insert_work+0x56/0x2e8
__queue_work+0x4ce/0xd10
queue_work_on+0xf4/0x100
qeth_l2_switchdev_event+0x520/0x738
atomic_notifier_call_chain+0x9c/0xf8
br_switchdev_fdb_notify+0xf4/0x110
fdb_notify+0x122/0x180
fdb_add_entry.constprop.0.isra.0+0x312/0x558
br_fdb_add+0x59e/0x858
rtnl_fdb_add+0x58a/0x928
rtnetlink_rcv_msg+0x5f8/0x8d8
netlink_rcv_skb+0x1f2/0x408
netlink_unicast+0x570/0x790
netlink_sendmsg+0x752/0xbe0
sock_sendmsg+0xca/0x110
____sys_sendmsg+0x510/0x6a8
___sys_sendmsg+0x12a/0x180
__sys_sendmsg+0xe6/0x168
__do_sys_socketcall+0x3c8/0x468
do_syscall+0x22c/0x328
__do_syscall+0x94/0xf0
system_call+0x82/0xb0
Second to last potentially related work creation:
kasan_save_stack+0x40/0x68
__kasan_record_aux_stack+0xbe/0xd0
kvfree_call_rcu+0xb2/0x760
kernfs_unlink_open_file+0x348/0x430
kernfs_fop_release+0xc2/0x320
__fput+0x1ae/0x768
task_work_run+0x1bc/0x298
exit_to_user_mode_prepare+0x1a0/0x1a8
__do_syscall+0x94/0xf0
system_call+0x82/0xb0
The buggy address belongs to the object at 00000000fdcea400
which belongs to the cache kmalloc-96 of size 96
The buggy address is located 64 bytes inside of
96-byte region [00000000fdcea400, 00000000fdcea460)
The buggy address belongs to the physical page:
page:000000005a9c26e8 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xfdcea
flags: 0x3ffff00000000200(slab|node=0|zone=1|lastcpupid=0x1ffff)
raw: 3ffff00000000200 0000000000000000 0000000100000122 000000008008cc00
raw: 0000000000000000 0020004100000000 ffffffff00000001 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
00000000fdcea300: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
00000000fdcea380: fb fb fb fb fb fb f
---truncated---