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

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    28157b8c USB: Better name for __check_usb_generic()
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
console output: https://syzkaller.appspot.com/x/log.txt?x=1064697a900000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ccafc70ac3d5f49c
dashboard link: https://syzkaller.appspot.com/bug?extid=ff4b26b0bfbff2dc7960
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10f0a00e900000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=162bc289900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ff4b26b0bfbff2dc7960@xxxxxxxxxxxxxxxxxxxxxxxxx

usb 6-1: Direct firmware load for rtlwifi/rtl8192cufw_TMSC.bin failed with error -2
usb 6-1: Direct firmware load for rtlwifi/rtl8192cufw.bin failed with error -2
==================================================================
BUG: KASAN: use-after-free in rtl_fw_do_work+0x407/0x430 drivers/net/wireless/realtek/rtlwifi/core.c:87
Read of size 8 at addr ffff8881ca9aff38 by task kworker/0:1/328

CPU: 0 PID: 328 Comm: kworker/0:1 Not tainted 5.9.0-rc1-syzkaller #0
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+0xf6/0x16e lib/dump_stack.c:118
 print_address_description.constprop.0+0x1c/0x210 mm/kasan/report.c:383
 __kasan_report mm/kasan/report.c:513 [inline]
 kasan_report.cold+0x37/0x7c mm/kasan/report.c:530
 rtl_fw_do_work+0x407/0x430 drivers/net/wireless/realtek/rtlwifi/core.c:87
 request_firmware_work_func+0x126/0x250 drivers/base/firmware_loader/main.c:1001
 process_one_work+0x94c/0x15f0 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x392/0x470 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

The buggy address belongs to the page:
page:00000000fcdef481 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1ca9af
flags: 0x200000000000000()
raw: 0200000000000000 0000000000000000 ffffea00072a6bc8 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881ca9afe00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881ca9afe80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8881ca9aff00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                        ^
 ffff8881ca9aff80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881ca9b0000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================