KASAN: use-after-free Read in p54u_load_firmware_cb

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    43151d6c usb-fuzzer: main usb gadget fuzzer driver
git tree:       https://github.com/google/kasan.git usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=142b312ca00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4183eeef650d1234
dashboard link: https://syzkaller.appspot.com/bug?extid=200d4bb11b23d929335f
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+200d4bb11b23d929335f@xxxxxxxxxxxxxxxxxxxxxxxxx

usb 4-1: Direct firmware load for isl3887usb failed with error -2
usb 4-1: Firmware not found.
==================================================================
BUG: KASAN: use-after-free in p54u_load_firmware_cb.cold+0x97/0x13a  
drivers/net/wireless/intersil/p54/p54usb.c:936
Read of size 8 at addr ffff888098bf3588 by task kworker/0:1/12

CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.1.0-rc3-319004-g43151d6 #6
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: events request_firmware_work_func
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0xe8/0x16e lib/dump_stack.c:113
 print_address_description+0x6c/0x236 mm/kasan/report.c:187
 kasan_report.cold+0x1a/0x3c mm/kasan/report.c:317
 p54u_load_firmware_cb.cold+0x97/0x13a  
drivers/net/wireless/intersil/p54/p54usb.c:936
 request_firmware_work_func+0x12d/0x249  
drivers/base/firmware_loader/main.c:785
 process_one_work+0x90f/0x1580 kernel/workqueue.c:2269
 worker_thread+0x9b/0xe20 kernel/workqueue.c:2415
 kthread+0x313/0x420 kernel/kthread.c:253
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

The buggy address belongs to the page:
page:ffffea000262fcc0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0xfff00000000000()
raw: 00fff00000000000 0000000000000000 ffffffff02620101 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888098bf3480: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888098bf3500: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> ffff888098bf3580: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff888098bf3600: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888098bf3680: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.