KASAN: slab-out-of-bounds Read in chaoskey_disconnect

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: da06441b usb: gadget: add raw-gadget interface
git tree: https://github.com/google/kasan.git usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=10dd88eee00000
kernel config: https://syzkaller.appspot.com/x/.config?x=99c88c44660624e7
dashboard link: https://syzkaller.appspot.com/bug?extid=8632e5cd5a4e644e5745
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+8632e5...@syzkaller.appspotmail.com

usb 3-1: USB disconnect, device number 46
==================================================================
BUG: KASAN: slab-out-of-bounds in atomic_read
include/asm-generic/atomic-instrumented.h:26 [inline]
BUG: KASAN: slab-out-of-bounds in refcount_inc_not_zero_checked+0x72/0x1e0
lib/refcount.c:123
Read of size 4 at addr ffff8881d2771820 by task kworker/1:4/3303

CPU: 1 PID: 3303 Comm: kworker/1:4 Not tainted 5.4.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: usb_hub_wq hub_event
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0xca/0x13e lib/dump_stack.c:113
print_address_description.constprop.0+0x36/0x50 mm/kasan/report.c:374
__kasan_report.cold+0x1a/0x33 mm/kasan/report.c:506
kasan_report+0xe/0x20 mm/kasan/common.c:634
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x128/0x190 mm/kasan/generic.c:192
atomic_read include/asm-generic/atomic-instrumented.h:26 [inline]
refcount_inc_not_zero_checked+0x72/0x1e0 lib/refcount.c:123
refcount_inc_checked+0x12/0x60 lib/refcount.c:156
get_task_struct include/linux/sched/task.h:110 [inline]
kthread_stop+0x6c/0x610 kernel/kthread.c:554
hwrng_unregister+0x190/0x210 drivers/char/hw_random/core.c:538
chaoskey_disconnect+0x1b2/0x200 drivers/usb/misc/chaoskey.c:232
usb_unbind_interface+0x1bd/0x8a0 drivers/usb/core/driver.c:423
__device_release_driver drivers/base/dd.c:1134 [inline]
device_release_driver_internal+0x42f/0x500 drivers/base/dd.c:1165
bus_remove_device+0x2dc/0x4a0 drivers/base/bus.c:532
device_del+0x420/0xb20 drivers/base/core.c:2376
usb_disable_device+0x211/0x690 drivers/usb/core/message.c:1237
usb_disconnect+0x284/0x8d0 drivers/usb/core/hub.c:2200
hub_port_connect drivers/usb/core/hub.c:5035 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5324 [inline]
port_event drivers/usb/core/hub.c:5470 [inline]
hub_event+0x16f2/0x3800 drivers/usb/core/hub.c:5552
process_one_work+0x92b/0x1530 kernel/workqueue.c:2269
worker_thread+0x96/0xe20 kernel/workqueue.c:2415
kthread+0x318/0x420 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

Allocated by task 25070:
save_stack+0x1b/0x80 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
__kasan_kmalloc mm/kasan/common.c:510 [inline]
__kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:483
kmalloc_node include/linux/slab.h:599 [inline]
kvmalloc_node+0x61/0xf0 mm/util.c:564
kvmalloc include/linux/mm.h:670 [inline]
seq_buf_alloc fs/seq_file.c:32 [inline]
seq_read+0x805/0x10f0 fs/seq_file.c:204
kernfs_fop_read+0xe9/0x560 fs/kernfs/file.c:251
__vfs_read+0x76/0x100 fs/read_write.c:425
vfs_read+0x1ea/0x430 fs/read_write.c:461
ksys_read+0x127/0x250 fs/read_write.c:587
do_syscall_64+0xb7/0x580 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 25070:
save_stack+0x1b/0x80 mm/kasan/common.c:69
set_track mm/kasan/common.c:77 [inline]
kasan_set_free_info mm/kasan/common.c:332 [inline]
__kasan_slab_free+0x130/0x180 mm/kasan/common.c:471
slab_free_hook mm/slub.c:1424 [inline]
slab_free_freelist_hook mm/slub.c:1475 [inline]
slab_free mm/slub.c:3025 [inline]
kfree+0xe4/0x320 mm/slub.c:3977
kvfree+0x59/0x60 mm/util.c:593
seq_release+0x4f/0x80 fs/seq_file.c:360
kernfs_fop_release+0xf2/0x190 fs/kernfs/file.c:780
__fput+0x2d7/0x840 fs/file_table.c:280
task_work_run+0x13f/0x1c0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x1d2/0x200 arch/x86/entry/common.c:163
prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
syscall_return_slowpath arch/x86/entry/common.c:274 [inline]
do_syscall_64+0x45f/0x580 arch/x86/entry/common.c:300
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8881d2770000
which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 2080 bytes to the right of
4096-byte region [ffff8881d2770000, ffff8881d2771000)
The buggy address belongs to the page:
page:ffffea000749dc00 refcount:1 mapcount:0 mapping:ffff8881da00c280
index:0x0 compound_mapcount: 0
flags: 0x200000000010200(slab|head)
raw: 0200000000010200 dead000000000100 dead000000000122 ffff8881da00c280
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8881d2771700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881d2771780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8881d2771800: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff8881d2771880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881d2771900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
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[Andrey Konovalov]

Most likely:

#syz dup: KASAN: use-after-free Read in chaoskey_disconnect

https://syzkaller.appspot.com/bug?id=d39d574f73e4b96265c6af6deeaff32f9bbd5ede