Re: KASAN: use-after-free Read in p54u_load_firmware_cb

[syzbot]

syzbot has found a reproducer for 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=16b64110a00000
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)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1634c900a00000

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

usb 1-1: config 0 descriptor??
usb 1-1: reset high-speed USB device number 2 using dummy_hcd
usb 1-1: device descriptor read/64, error -71
usb 1-1: Using ep0 maxpacket: 8
usb 1-1: Loading firmware file isl3887usb
usb 1-1: Direct firmware load for isl3887usb failed with error -2
usb 1-1: 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 ffff88809803f588 by task kworker/1:0/17

CPU: 1 PID: 17 Comm: kworker/1:0 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

Allocated by task 0:
(stack is not available)

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff88809803f180
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 8 bytes to the right of
 1024-byte region [ffff88809803f180, ffff88809803f580)
The buggy address belongs to the page:
page:ffffea0002600f00 count:1 mapcount:0 mapping:ffff88812c3f4a00 index:0x0  
compound_mapcount: 0
flags: 0xfff00000010200(slab|head)
raw: 00fff00000010200 dead000000000100 dead000000000200 ffff88812c3f4a00
raw: 0000000000000000 00000000800e000e 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809803f480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88809803f500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff88809803f580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                      ^
 ffff88809803f600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88809803f680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================