linux-kernel - Re: [syzbot] [usb?] WARNING: refcount bug in hdm

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Message-ID: <684e16ec.050a0220.be214.02b7.GAE@google.com>
Date: Sat, 14 Jun 2025 17:42:20 -0700
From: syzbot <syzbot+d175ca7205b4f18390b1@...kaller.appspotmail.com>
To: dakr@...nel.org, gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org, 
	linux-usb@...r.kernel.org, rafael@...nel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [usb?] WARNING: refcount bug in hdm_disconnect

syzbot has found a reproducer for the following issue on:

HEAD commit:    4774cfe3543a Merge tag 'scsi-fixes' of git://git.kernel.or..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14cf25d4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=706b535f9c369932
dashboard link: https://syzkaller.appspot.com/bug?extid=d175ca7205b4f18390b1
compiler:       arm-linux-gnueabi-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14bb3d70580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1448f10c580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/98a89b9f34e4/non_bootable_disk-4774cfe3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/cae525065b5b/vmlinux-4774cfe3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ce14ef6ecfe2/zImage-4774cfe3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d175ca7205b4f18390b1@...kaller.appspotmail.com

usb 1-1: USB disconnect, device number 2
------------[ cut here ]------------
WARNING: CPU: 0 PID: 97 at lib/refcount.c:28 refcount_warn_saturate+0x13c/0x174 lib/refcount.c:28
refcount_t: underflow; use-after-free.
Modules linked in:
Kernel panic - not syncing: kernel: panic_on_warn set ...
CPU: 0 UID: 0 PID: 97 Comm: kworker/0:2 Not tainted 6.16.0-rc1-syzkaller #0 PREEMPT 
Hardware name: ARM-Versatile Express
Workqueue: usb_hub_wq hub_event
Call trace: 
[<80201a00>] (dump_backtrace) from [<80201afc>] (show_stack+0x18/0x1c arch/arm/kernel/traps.c:257)
 r7:00000000 r6:8282083c r5:00000000 r4:82259bd0
[<80201ae4>] (show_stack) from [<8021fd94>] (__dump_stack lib/dump_stack.c:94 [inline])
[<80201ae4>] (show_stack) from [<8021fd94>] (dump_stack_lvl+0x54/0x7c lib/dump_stack.c:120)
[<8021fd40>] (dump_stack_lvl) from [<8021fdd4>] (dump_stack+0x18/0x1c lib/dump_stack.c:129)
 r5:00000000 r4:82a6dd18
[<8021fdbc>] (dump_stack) from [<80202614>] (panic+0x120/0x374 kernel/panic.c:382)
[<802024f4>] (panic) from [<802585b8>] (check_panic_on_warn kernel/panic.c:273 [inline])
[<802024f4>] (panic) from [<802585b8>] (get_taint+0x0/0x1c kernel/panic.c:268)
 r3:8280c684 r2:00000001 r1:822406fc r0:822480ac
 r7:808c00f4
[<80258544>] (check_panic_on_warn) from [<8025871c>] (__warn+0x80/0x188 kernel/panic.c:777)
[<8025869c>] (__warn) from [<80258a0c>] (warn_slowpath_fmt+0x1e8/0x1f4 kernel/panic.c:812)
 r8:00000009 r7:822b1be4 r6:df9b5bfc r5:833a1800 r4:00000000
[<80258828>] (warn_slowpath_fmt) from [<808c00f4>] (refcount_warn_saturate+0x13c/0x174 lib/refcount.c:28)
 r10:00000001 r9:829ca3e8 r8:844d4c88 r7:844d6474 r6:8419ffb4 r5:844d6400
 r4:84571800
[<808bffb8>] (refcount_warn_saturate) from [<819fce88>] (__refcount_sub_and_test include/linux/refcount.h:400 [inline])
[<808bffb8>] (refcount_warn_saturate) from [<819fce88>] (__refcount_dec_and_test include/linux/refcount.h:432 [inline])
[<808bffb8>] (refcount_warn_saturate) from [<819fce88>] (refcount_dec_and_test include/linux/refcount.h:450 [inline])
[<808bffb8>] (refcount_warn_saturate) from [<819fce88>] (kref_put include/linux/kref.h:64 [inline])
[<808bffb8>] (refcount_warn_saturate) from [<819fce88>] (kobject_put+0x158/0x1f4 lib/kobject.c:737)
[<819fcd30>] (kobject_put) from [<80b307e8>] (put_device+0x18/0x1c drivers/base/core.c:3800)
 r7:844d6474 r6:8419ffb4 r5:844d6400 r4:8419f800
[<80b307d0>] (put_device) from [<81418e74>] (hdm_disconnect+0x90/0x9c drivers/most/most_usb.c:1129)
[<81418de4>] (hdm_disconnect) from [<80e8cd04>] (usb_unbind_interface+0x84/0x2b4 drivers/usb/core/driver.c:458)
 r7:844d6474 r6:844d6430 r5:00000000 r4:844d4c00
[<80e8cc80>] (usb_unbind_interface) from [<80b38870>] (device_remove drivers/base/dd.c:569 [inline])
[<80e8cc80>] (usb_unbind_interface) from [<80b38870>] (device_remove+0x64/0x6c drivers/base/dd.c:561)
 r10:00000001 r9:844d4c88 r8:00000044 r7:844d6474 r6:829ca3e8 r5:00000000
 r4:844d6430
[<80b3880c>] (device_remove) from [<80b39d60>] (__device_release_driver drivers/base/dd.c:1272 [inline])
[<80b3880c>] (device_remove) from [<80b39d60>] (device_release_driver_internal+0x18c/0x200 drivers/base/dd.c:1295)
 r5:00000000 r4:844d6430
[<80b39bd4>] (device_release_driver_internal) from [<80b39dec>] (device_release_driver+0x18/0x1c drivers/base/dd.c:1318)
 r9:844d4c88 r8:832d5d40 r7:832d5d38 r6:832d5d0c r5:844d6430 r4:832d5d30
[<80b39dd4>] (device_release_driver) from [<80b37ec4>] (bus_remove_device+0xcc/0x120 drivers/base/bus.c:579)
[<80b37df8>] (bus_remove_device) from [<80b32220>] (device_del+0x148/0x38c drivers/base/core.c:3881)
 r9:844d4c88 r8:833a1800 r7:04208060 r6:00000000 r5:844d6430 r4:844d6474
[<80b320d8>] (device_del) from [<80e8a754>] (usb_disable_device+0xd4/0x1e8 drivers/usb/core/message.c:1418)
 r10:00000001 r9:00000000 r8:00000000 r7:844d6400 r6:844d4c00 r5:84791288
 r4:60000013
[<80e8a680>] (usb_disable_device) from [<80e7f4d0>] (usb_disconnect+0xec/0x29c drivers/usb/core/hub.c:2316)
 r9:84571c00 r8:844d4ccc r7:83b56400 r6:844d4c88 r5:844d4c00 r4:60000013
[<80e7f3e4>] (usb_disconnect) from [<80e82190>] (hub_port_connect drivers/usb/core/hub.c:5375 [inline])
[<80e7f3e4>] (usb_disconnect) from [<80e82190>] (hub_port_connect_change drivers/usb/core/hub.c:5675 [inline])
[<80e7f3e4>] (usb_disconnect) from [<80e82190>] (port_event drivers/usb/core/hub.c:5835 [inline])
[<80e7f3e4>] (usb_disconnect) from [<80e82190>] (hub_event+0xe78/0x194c drivers/usb/core/hub.c:5917)
 r10:00000001 r9:00000100 r8:83caed00 r7:844d4c00 r6:83b55c00 r5:83b56610
 r4:00000001
[<80e81318>] (hub_event) from [<8027e2e8>] (process_one_work+0x1b4/0x4f4 kernel/workqueue.c:3238)
 r10:832d5f70 r9:8380e205 r8:833a1800 r7:dddced40 r6:8380e200 r5:83caed00
 r4:83338e80
[<8027e134>] (process_one_work) from [<8027ef30>] (process_scheduled_works kernel/workqueue.c:3321 [inline])
[<8027e134>] (process_one_work) from [<8027ef30>] (worker_thread+0x1fc/0x3d8 kernel/workqueue.c:3402)
 r10:61c88647 r9:833a1800 r8:83338eac r7:82804d40 r6:dddced40 r5:dddced60
 r4:83338e80
[<8027ed34>] (worker_thread) from [<80285f5c>] (kthread+0x12c/0x280 kernel/kthread.c:464)
 r10:00000000 r9:83338e80 r8:8027ed34 r7:df841e60 r6:83338f00 r5:833a1800
 r4:00000001
[<80285e30>] (kthread) from [<80200114>] (ret_from_fork+0x14/0x20 arch/arm/kernel/entry-common.S:137)
Exception stack(0xdf9b5fb0 to 0xdf9b5ff8)
5fa0:                                     00000000 00000000 00000000 00000000
5fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
5fe0: 00000000 00000000 00000000 00000000 00000013 00000000
 r10:00000000 r9:00000000 r8:00000000 r7:00000000 r6:00000000 r5:80285e30
 r4:83335080
Rebooting in 86400 seconds..


---
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#syz test: git://repo/address.git branch-or-commit-hash
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