* [Bug]KASAN: slab-use-after-free Read in iowarrior_release
@ 2026-06-18 8:02 Yue Sun
2026-06-18 10:31 ` Greg Kroah-Hartman
0 siblings, 1 reply; 2+ messages in thread
From: Yue Sun @ 2026-06-18 8:02 UTC (permalink / raw)
To: Greg Kroah-Hartman, Oliver Neukum
Cc: Kees Cook, linux-usb, linux-kernel, syzkaller
Hello,
I would like to report a use-after-free in the iowarrior USB misc
driver. The crash was found by local syzkaller testing with USB gadget
emulation. Although the crash was collected on an older kernel, I also
confirmed that the same issue is still present on the latest kernel
commit I checked, 6b5a2b7d9bc1 (v7.1-2765-g6b5a2b7d9bc1).
Observed kernel/configuration
=============================
Relevant config:
CONFIG_USB_IOWARRIOR=y
CONFIG_USB_RAW_GADGET=y
CONFIG_USB_DUMMY_HCD=y
CONFIG_KASAN=y
CONFIG_KASAN_GENERIC=y
CONFIG_PREEMPT=y
Test environment:
QEMU 6.2.0, x86_64, 2 CPUs, 4096 MB RAM
The following is the raw KASAN report excerpt from the syzkaller crash:
==================================================================
BUG: KASAN: slab-use-after-free in __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
BUG: KASAN: slab-use-after-free in _raw_spin_lock_irqsave+0x3d/0x60 kernel/locking/spinlock.c:166
Read of size 1 at addr ff110000238d3020 by task syz.0.924/37593
CPU: 0 UID: 0 PID: 37593 Comm: syz.0.924 Tainted: G L 7.1.0-rc3-00362-g6916d5703ddf-dirty #35 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x116/0x1b0 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xf1/0x5c0 mm/kasan/report.c:482
kasan_report+0xca/0x100 mm/kasan/report.c:595
__kasan_check_byte+0x3a/0x50 mm/kasan/common.c:574
kasan_check_byte include/linux/kasan.h:402 [inline]
lock_acquire kernel/locking/lockdep.c:5842 [inline]
lock_acquire+0x132/0x360 kernel/locking/lockdep.c:5825
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
_raw_spin_lock_irqsave+0x3d/0x60 kernel/locking/spinlock.c:166
__mutex_unlock_slowpath+0x182/0x880 kernel/locking/mutex.c:1015
iowarrior_release+0x231/0x2c0 drivers/usb/misc/iowarrior.c:678
__fput+0x402/0xb60 fs/file_table.c:510
task_work_run+0x16b/0x260 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
exit_to_user_mode_loop+0x121/0x570 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
do_syscall_64+0x737/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9eb63b561d
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f9eb8356f68 EFLAGS: 00000246 ORIG_RAX: 0000000000000128
RAX: ffffffffffffffb9 RBX: 00007f9eb76b0020 RCX: 00007f9eb63b561d
RDX: 0000000000000001 RSI: 0000200000000240 RDI: 0000000000000005
RBP: 0000000000000056 R08: 0000000000000004 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f9eb6351640 R15: 00007f9eb8337000
</TASK>
Allocated by task 10489:
kasan_save_stack+0x24/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
kmalloc_noprof include/linux/slab.h:950 [inline]
kzalloc_noprof include/linux/slab.h:1188 [inline]
iowarrior_probe+0x87/0x13a0 drivers/usb/misc/iowarrior.c:766
usb_probe_interface+0x30e/0xac0 drivers/usb/core/driver.c:396
call_driver_probe drivers/base/dd.c:631 [inline]
really_probe+0x252/0xb20 drivers/base/dd.c:709
__driver_probe_device+0x3d3/0x4f0 drivers/base/dd.c:871
driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:901
__device_attach_driver+0x1db/0x340 drivers/base/dd.c:1029
bus_for_each_drv+0x14b/0x1d0 drivers/base/bus.c:500
__device_attach+0x1ee/0x4f0 drivers/base/dd.c:1101
device_initial_probe+0xaa/0xc0 drivers/base/dd.c:1156
bus_probe_device+0x64/0x150 drivers/base/bus.c:613
device_add+0x1169/0x1930 drivers/base/core.c:3706
usb_set_configuration+0x1346/0x1e90 drivers/usb/core/message.c:2268
usb_generic_driver_probe+0xb7/0x110 drivers/usb/core/generic.c:250
usb_probe_device+0xed/0x400 drivers/usb/core/driver.c:291
call_driver_probe drivers/base/dd.c:631 [inline]
really_probe+0x252/0xb20 drivers/base/dd.c:709
__driver_probe_device+0x3d3/0x4f0 drivers/base/dd.c:871
driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:901
__device_attach_driver+0x1db/0x340 drivers/base/dd.c:1029
bus_for_each_drv+0x14b/0x1d0 drivers/base/bus.c:500
__device_attach+0x1ee/0x4f0 drivers/base/dd.c:1101
device_initial_probe+0xaa/0xc0 drivers/base/dd.c:1156
bus_probe_device+0x64/0x150 drivers/base/bus.c:613
device_add+0x1169/0x1930 drivers/base/core.c:3706
usb_new_device+0xd2c/0x1ac0 drivers/usb/core/hub.c:2695
hub_port_connect drivers/usb/core/hub.c:5567 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5707 [inline]
port_event drivers/usb/core/hub.c:5871 [inline]
hub_event+0x2eff/0x5030 drivers/usb/core/hub.c:5953
process_one_work+0xc57/0x2240 kernel/workqueue.c:3594
process_scheduled_works kernel/workqueue.c:3703 [inline]
worker_thread+0x693/0xeb0 kernel/workqueue.c:3784
kthread+0x38d/0x4a0 kernel/kthread.c:436
ret_from_fork+0xb09/0xdb0 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
Freed by task 48:
kasan_save_stack+0x24/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x61/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2689 [inline]
slab_free mm/slub.c:6250 [inline]
kfree+0x2d6/0x6d0 mm/slub.c:6565
iowarrior_delete drivers/usb/misc/iowarrior.c:249 [inline]
iowarrior_disconnect+0x210/0x270 drivers/usb/misc/iowarrior.c:921
usb_unbind_interface+0x1e8/0x9e0 drivers/usb/core/driver.c:458
device_remove drivers/base/dd.c:621 [inline]
device_remove+0x125/0x170 drivers/base/dd.c:613
__device_release_driver drivers/base/dd.c:1352 [inline]
device_release_driver_internal+0x45e/0x630 drivers/base/dd.c:1375
bus_remove_device+0x2ba/0x570 drivers/base/bus.c:657
device_del+0x396/0x9d0 drivers/base/core.c:3895
usb_disable_device+0x35c/0x810 drivers/usb/core/message.c:1478
usb_disconnect+0x2df/0xa00 drivers/usb/core/hub.c:2345
hub_port_connect drivers/usb/core/hub.c:5407 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5707 [inline]
port_event drivers/usb/core/hub.c:5871 [inline]
hub_event+0x1ece/0x5030 drivers/usb/core/hub.c:5953
process_one_work+0xc57/0x2240 kernel/workqueue.c:3594
process_scheduled_works kernel/workqueue.c:3703 [inline]
worker_thread+0x693/0xeb0 kernel/workqueue.c:3784
kthread+0x38d/0x4a0 kernel/kthread.c:436
ret_from_fork+0xb09/0xdb0 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
The buggy address belongs to the object at ff110000238d3000
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 32 bytes inside of
freed 1024-byte region [ff110000238d3000, ff110000238d3400)
Memory state around the buggy address:
ff110000238d2f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ff110000238d2f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ff110000238d3000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ff110000238d3080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ff110000238d3100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
Root cause analysis
===================
iowarrior_open() stores a raw struct iowarrior pointer in
file->private_data. The object lifetime is controlled only by the
dev->opened and dev->present state flags. These flags are not sufficient
to protect the object across the file release path and the USB disconnect
path.
In the observed crash, iowarrior_release() is still returning through
mutex_unlock(&dev->mutex) while iowarrior_disconnect(), running from the
USB hub worker, observes dev->opened == 0 and frees the same object via
iowarrior_delete(). KASAN then reports a use-after-free on dev->mutex
inside __mutex_unlock_slowpath().
This matches the mutex_unlock() lifetime rule documented in
kernel/locking/mutex.c:
The caller must ensure that the mutex stays alive until this function has
returned - mutex_unlock() can NOT directly be used to release an object such
that another concurrent task can free it.
Mutexes are different from spinlocks & refcounts in this aspect.
The iowarrior release/disconnect paths can violate this rule because
iowarrior_disconnect() can free dev while iowarrior_release() is still
inside mutex_unlock(&dev->mutex).
One interleaving matching the KASAN report is:
CPU 0: close()/__fput()/iowarrior_release()
CPU 1: USB hub workqueue/iowarrior_disconnect()
CPU 0 CPU 1
----- -----
dev = file->private_data
mutex_lock(&dev->mutex)
dev->opened = 0
if (dev->present) {
usb_kill_urb(dev->int_in_urb)
wake_up_interruptible(&dev->read_wait)
wake_up_interruptible(&dev->write_wait)
mutex_unlock(&dev->mutex)
enters __mutex_unlock_slowpath()
// while still releasing/waking a waiter
mutex_lock(&dev->mutex)
dev->present = 0
if (!dev->opened) {
mutex_unlock(&dev->mutex)
iowarrior_delete(dev)
kfree(dev)
}
// continues touching dev->mutex
KASAN reports UAF in _raw_spin_lock_irqsave()
from __mutex_unlock_slowpath()
The freed-by stack confirms that the object is freed from the asynchronous
USB disconnect path running as hub_event on a worker thread. Unfortunately,
I do not have a minimized standalone reproducer yet.
If you have any questions, please let me know.
Best regards,
Yue
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [Bug]KASAN: slab-use-after-free Read in iowarrior_release
2026-06-18 8:02 [Bug]KASAN: slab-use-after-free Read in iowarrior_release Yue Sun
@ 2026-06-18 10:31 ` Greg Kroah-Hartman
0 siblings, 0 replies; 2+ messages in thread
From: Greg Kroah-Hartman @ 2026-06-18 10:31 UTC (permalink / raw)
To: Yue Sun; +Cc: Oliver Neukum, Kees Cook, linux-usb, linux-kernel, syzkaller
On Thu, Jun 18, 2026 at 04:02:04PM +0800, Yue Sun wrote:
> Hello,
>
> I would like to report a use-after-free in the iowarrior USB misc
> driver. The crash was found by local syzkaller testing with USB gadget
> emulation. Although the crash was collected on an older kernel, I also
> confirmed that the same issue is still present on the latest kernel
> commit I checked, 6b5a2b7d9bc1 (v7.1-2765-g6b5a2b7d9bc1).
>
> Observed kernel/configuration
> =============================
>
> Relevant config:
>
> CONFIG_USB_IOWARRIOR=y
> CONFIG_USB_RAW_GADGET=y
> CONFIG_USB_DUMMY_HCD=y
> CONFIG_KASAN=y
> CONFIG_KASAN_GENERIC=y
> CONFIG_PREEMPT=y
>
> Test environment:
>
> QEMU 6.2.0, x86_64, 2 CPUs, 4096 MB RAM
>
> The following is the raw KASAN report excerpt from the syzkaller crash:
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
> BUG: KASAN: slab-use-after-free in _raw_spin_lock_irqsave+0x3d/0x60 kernel/locking/spinlock.c:166
> Read of size 1 at addr ff110000238d3020 by task syz.0.924/37593
>
> CPU: 0 UID: 0 PID: 37593 Comm: syz.0.924 Tainted: G L 7.1.0-rc3-00362-g6916d5703ddf-dirty #35 PREEMPT(full)
> Tainted: [L]=SOFTLOCKUP
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> Call Trace:
> <TASK>
> __dump_stack lib/dump_stack.c:94 [inline]
> dump_stack_lvl+0x116/0x1b0 lib/dump_stack.c:120
> print_address_description mm/kasan/report.c:378 [inline]
> print_report+0xf1/0x5c0 mm/kasan/report.c:482
> kasan_report+0xca/0x100 mm/kasan/report.c:595
> __kasan_check_byte+0x3a/0x50 mm/kasan/common.c:574
> kasan_check_byte include/linux/kasan.h:402 [inline]
> lock_acquire kernel/locking/lockdep.c:5842 [inline]
> lock_acquire+0x132/0x360 kernel/locking/lockdep.c:5825
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
> _raw_spin_lock_irqsave+0x3d/0x60 kernel/locking/spinlock.c:166
> __mutex_unlock_slowpath+0x182/0x880 kernel/locking/mutex.c:1015
> iowarrior_release+0x231/0x2c0 drivers/usb/misc/iowarrior.c:678
> __fput+0x402/0xb60 fs/file_table.c:510
> task_work_run+0x16b/0x260 kernel/task_work.c:233
> resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
> __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
> exit_to_user_mode_loop+0x121/0x570 kernel/entry/common.c:98
> __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
> syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
> syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
> do_syscall_64+0x737/0xf80 arch/x86/entry/syscall_64.c:100
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f9eb63b561d
> Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f9eb8356f68 EFLAGS: 00000246 ORIG_RAX: 0000000000000128
> RAX: ffffffffffffffb9 RBX: 00007f9eb76b0020 RCX: 00007f9eb63b561d
> RDX: 0000000000000001 RSI: 0000200000000240 RDI: 0000000000000005
> RBP: 0000000000000056 R08: 0000000000000004 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 0000000000000000 R14: 00007f9eb6351640 R15: 00007f9eb8337000
> </TASK>
>
> Allocated by task 10489:
> kasan_save_stack+0x24/0x50 mm/kasan/common.c:57
> kasan_save_track+0x14/0x30 mm/kasan/common.c:78
> poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
> __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
> kmalloc_noprof include/linux/slab.h:950 [inline]
> kzalloc_noprof include/linux/slab.h:1188 [inline]
> iowarrior_probe+0x87/0x13a0 drivers/usb/misc/iowarrior.c:766
> usb_probe_interface+0x30e/0xac0 drivers/usb/core/driver.c:396
> call_driver_probe drivers/base/dd.c:631 [inline]
> really_probe+0x252/0xb20 drivers/base/dd.c:709
> __driver_probe_device+0x3d3/0x4f0 drivers/base/dd.c:871
> driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:901
> __device_attach_driver+0x1db/0x340 drivers/base/dd.c:1029
> bus_for_each_drv+0x14b/0x1d0 drivers/base/bus.c:500
> __device_attach+0x1ee/0x4f0 drivers/base/dd.c:1101
> device_initial_probe+0xaa/0xc0 drivers/base/dd.c:1156
> bus_probe_device+0x64/0x150 drivers/base/bus.c:613
> device_add+0x1169/0x1930 drivers/base/core.c:3706
> usb_set_configuration+0x1346/0x1e90 drivers/usb/core/message.c:2268
> usb_generic_driver_probe+0xb7/0x110 drivers/usb/core/generic.c:250
> usb_probe_device+0xed/0x400 drivers/usb/core/driver.c:291
> call_driver_probe drivers/base/dd.c:631 [inline]
> really_probe+0x252/0xb20 drivers/base/dd.c:709
> __driver_probe_device+0x3d3/0x4f0 drivers/base/dd.c:871
> driver_probe_device+0x4c/0x1a0 drivers/base/dd.c:901
> __device_attach_driver+0x1db/0x340 drivers/base/dd.c:1029
> bus_for_each_drv+0x14b/0x1d0 drivers/base/bus.c:500
> __device_attach+0x1ee/0x4f0 drivers/base/dd.c:1101
> device_initial_probe+0xaa/0xc0 drivers/base/dd.c:1156
> bus_probe_device+0x64/0x150 drivers/base/bus.c:613
> device_add+0x1169/0x1930 drivers/base/core.c:3706
> usb_new_device+0xd2c/0x1ac0 drivers/usb/core/hub.c:2695
> hub_port_connect drivers/usb/core/hub.c:5567 [inline]
> hub_port_connect_change drivers/usb/core/hub.c:5707 [inline]
> port_event drivers/usb/core/hub.c:5871 [inline]
> hub_event+0x2eff/0x5030 drivers/usb/core/hub.c:5953
> process_one_work+0xc57/0x2240 kernel/workqueue.c:3594
> process_scheduled_works kernel/workqueue.c:3703 [inline]
> worker_thread+0x693/0xeb0 kernel/workqueue.c:3784
> kthread+0x38d/0x4a0 kernel/kthread.c:436
> ret_from_fork+0xb09/0xdb0 arch/x86/kernel/process.c:158
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>
> Freed by task 48:
> kasan_save_stack+0x24/0x50 mm/kasan/common.c:57
> kasan_save_track+0x14/0x30 mm/kasan/common.c:78
> kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:584
> poison_slab_object mm/kasan/common.c:253 [inline]
> __kasan_slab_free+0x61/0x80 mm/kasan/common.c:285
> kasan_slab_free include/linux/kasan.h:235 [inline]
> slab_free_hook mm/slub.c:2689 [inline]
> slab_free mm/slub.c:6250 [inline]
> kfree+0x2d6/0x6d0 mm/slub.c:6565
> iowarrior_delete drivers/usb/misc/iowarrior.c:249 [inline]
> iowarrior_disconnect+0x210/0x270 drivers/usb/misc/iowarrior.c:921
> usb_unbind_interface+0x1e8/0x9e0 drivers/usb/core/driver.c:458
> device_remove drivers/base/dd.c:621 [inline]
> device_remove+0x125/0x170 drivers/base/dd.c:613
> __device_release_driver drivers/base/dd.c:1352 [inline]
> device_release_driver_internal+0x45e/0x630 drivers/base/dd.c:1375
> bus_remove_device+0x2ba/0x570 drivers/base/bus.c:657
> device_del+0x396/0x9d0 drivers/base/core.c:3895
> usb_disable_device+0x35c/0x810 drivers/usb/core/message.c:1478
> usb_disconnect+0x2df/0xa00 drivers/usb/core/hub.c:2345
> hub_port_connect drivers/usb/core/hub.c:5407 [inline]
> hub_port_connect_change drivers/usb/core/hub.c:5707 [inline]
> port_event drivers/usb/core/hub.c:5871 [inline]
> hub_event+0x1ece/0x5030 drivers/usb/core/hub.c:5953
> process_one_work+0xc57/0x2240 kernel/workqueue.c:3594
> process_scheduled_works kernel/workqueue.c:3703 [inline]
> worker_thread+0x693/0xeb0 kernel/workqueue.c:3784
> kthread+0x38d/0x4a0 kernel/kthread.c:436
> ret_from_fork+0xb09/0xdb0 arch/x86/kernel/process.c:158
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>
> The buggy address belongs to the object at ff110000238d3000
> which belongs to the cache kmalloc-1k of size 1024
> The buggy address is located 32 bytes inside of
> freed 1024-byte region [ff110000238d3000, ff110000238d3400)
>
> Memory state around the buggy address:
> ff110000238d2f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ff110000238d2f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ff110000238d3000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ff110000238d3080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ff110000238d3100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> Root cause analysis
> ===================
>
> iowarrior_open() stores a raw struct iowarrior pointer in
> file->private_data. The object lifetime is controlled only by the
> dev->opened and dev->present state flags. These flags are not sufficient
> to protect the object across the file release path and the USB disconnect
> path.
>
> In the observed crash, iowarrior_release() is still returning through
> mutex_unlock(&dev->mutex) while iowarrior_disconnect(), running from the
> USB hub worker, observes dev->opened == 0 and frees the same object via
> iowarrior_delete(). KASAN then reports a use-after-free on dev->mutex
> inside __mutex_unlock_slowpath().
>
> This matches the mutex_unlock() lifetime rule documented in
> kernel/locking/mutex.c:
>
> The caller must ensure that the mutex stays alive until this function has
> returned - mutex_unlock() can NOT directly be used to release an object such
> that another concurrent task can free it.
> Mutexes are different from spinlocks & refcounts in this aspect.
>
> The iowarrior release/disconnect paths can violate this rule because
> iowarrior_disconnect() can free dev while iowarrior_release() is still
> inside mutex_unlock(&dev->mutex).
>
> One interleaving matching the KASAN report is:
>
> CPU 0: close()/__fput()/iowarrior_release()
> CPU 1: USB hub workqueue/iowarrior_disconnect()
>
> CPU 0 CPU 1
> ----- -----
> dev = file->private_data
> mutex_lock(&dev->mutex)
> dev->opened = 0
> if (dev->present) {
> usb_kill_urb(dev->int_in_urb)
> wake_up_interruptible(&dev->read_wait)
> wake_up_interruptible(&dev->write_wait)
> mutex_unlock(&dev->mutex)
> enters __mutex_unlock_slowpath()
> // while still releasing/waking a waiter
> mutex_lock(&dev->mutex)
> dev->present = 0
> if (!dev->opened) {
> mutex_unlock(&dev->mutex)
> iowarrior_delete(dev)
> kfree(dev)
> }
> // continues touching dev->mutex
> KASAN reports UAF in _raw_spin_lock_irqsave()
> from __mutex_unlock_slowpath()
>
> The freed-by stack confirms that the object is freed from the asynchronous
> USB disconnect path running as hub_event on a worker thread. Unfortunately,
> I do not have a minimized standalone reproducer yet.
>
> If you have any questions, please let me know.
Great, can you please submit a patch to fix this?
thanks,
greg k-h
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2026-06-18 8:02 [Bug]KASAN: slab-use-after-free Read in iowarrior_release Yue Sun
2026-06-18 10:31 ` Greg Kroah-Hartman
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