Re: [BUG] ALSA: usb: 6fire: KASAN slab-use-after-free in dummy_timer

[Shuangpeng]

> On Jul 24, 2026, at 03:45, Takashi Iwai <tiwai@xxxxxxx> wrote:
> 
> On Fri, 24 Jul 2026 05:07:50 +0200,
> Shuangpeng Bai wrote:
>> 
>> Hi Kernel Maintainers,
>> 
>> I hit the following report while testing current upstream kernel:
>> 
>> KASAN: slab-use-after-free in dummy_timer
>> 
>> on commit: fce2dfa773ced15f27dd27cd0b482a7473cdcf2a (2026-07-16)
>> 
>> The reproducer and .config files are here.
>> https://gist.github.com/shuangpengbai/a410bc05b4f22d1ba4ce7ef059043fea
>> 
>> I'm happy to test debug patches or provide additional information.
>> 
>> Reported-by: Shuangpeng Bai <shuangpeng.kernel@xxxxxxxxx>
>> 
>> [  400.891255][    C0] BUG: KASAN: slab-use-after-free in dummy_timer (drivers/usb/common/usb-otg-fsm.c:393)
>> [  400.891273][    C0] Read of size 4 at addr ffff8881789bc20c by task kworker/0:2/773
>> [  400.891276][    C0]
>> [  400.891291][    C0] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
>> [  400.891294][    C0] Workqueue: usb_hub_wq hub_event
>> [  400.891299][    C0] Call Trace:
>> [  400.891301][    C0]  <IRQ>
>> [  400.891302][    C0]  dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
>> [  400.891306][    C0]  print_report (mm/kasan/report.c:378 mm/kasan/report.c:482)
>> [  400.891322][    C0]  kasan_report (mm/kasan/report.c:595)
>> [  400.891330][    C0]  dummy_timer (drivers/usb/common/usb-otg-fsm.c:393)
>> [  400.891397][    C0]  __hrtimer_run_queues (kernel/time/hrtimer.c:2032 kernel/time/hrtimer.c:2096)
>> [  400.891403][    C0]  hrtimer_run_softirq (kernel/time/hrtimer.c:2113)
>> [  400.891414][    C0]  handle_softirqs (kernel/softirq.c:622)
>> [  400.891420][    C0]  __irq_exit_rcu (kernel/softirq.c:656 kernel/softirq.c:496 kernel/softirq.c:735)
>> [  400.891423][    C0]  sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1062 arch/x86/kernel/apic/apic.c:1062)
>> [  400.891427][    C0]  </IRQ>
>> [  400.891428][    C0]  <TASK>
>> [  400.891579][    C0]  really_probe (drivers/base/dd.c:644 drivers/base/dd.c:706)
>> [  400.891582][    C0]  __driver_probe_device (drivers/base/dd.c:868)
>> [  400.891585][    C0]  driver_probe_device (drivers/base/dd.c:898)
>> [  400.891588][    C0]  __device_attach_driver (drivers/base/dd.c:1026)
>> [  400.891593][    C0]  bus_for_each_drv (drivers/base/bus.c:500)
>> [  400.891615][    C0]  __device_attach (drivers/base/dd.c:1098)
>> [  400.891631][    C0]  device_initial_probe (drivers/base/dd.c:1153)
>> [  400.891634][    C0]  bus_probe_device (drivers/base/bus.c:620)
>> [  400.891637][    C0]  device_add (drivers/base/core.c:3772)
>> [  400.891641][    C0]  usb_set_configuration (drivers/usb/core/message.c:2268)
>> [  400.891647][    C0]  usb_generic_driver_probe (drivers/usb/core/generic.c:250)
>> [  400.891651][    C0]  usb_probe_device (drivers/usb/core/driver.c:291)
>> [  400.891653][    C0]  really_probe (drivers/base/dd.c:? drivers/base/dd.c:706)
>> [  400.891656][    C0]  __driver_probe_device (drivers/base/dd.c:868)
>> [  400.891663][    C0]  driver_probe_device (drivers/base/dd.c:898)
>> [  400.891665][    C0]  __device_attach_driver (drivers/base/dd.c:1026)
>> [  400.891671][    C0]  bus_for_each_drv (drivers/base/bus.c:500)
>> [  400.891685][    C0]  __device_attach (drivers/base/dd.c:1098)
>> [  400.891704][    C0]  device_initial_probe (drivers/base/dd.c:1153)
>> [  400.891707][    C0]  bus_probe_device (drivers/base/bus.c:620)
>> [  400.891710][    C0]  device_add (drivers/base/core.c:3772)
>> [  400.891714][    C0]  usb_new_device (drivers/usb/core/hub.c:2695)
>> [  400.891726][    C0]  hub_event (drivers/usb/core/hub.c:5567 drivers/usb/core/hub.c:5707 drivers/usb/core/hub.c:5871 drivers/usb/core/hub.c:5953)
>> [  400.891743][    C0]  process_scheduled_works (kernel/workqueue.c:3322 kernel/workqueue.c:3405)
>> [  400.891748][    C0]  worker_thread (kernel/workqueue.c:3486)
>> [  400.891756][    C0]  kthread (kernel/kthread.c:436)
>> [  400.891764][    C0]  ret_from_fork (arch/x86/kernel/process.c:158)
>> [  400.891790][    C0]  ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
>> [  400.891795][    C0]  </TASK>
>> [  400.891797][    C0] Freed by task 773 on cpu 0 at 400.890164s:
>> [  400.891805][    C0]  kasan_save_track (mm/kasan/common.c:57 mm/kasan/common.c:78)
>> [  400.891813][    C0]  kasan_save_free_info (mm/kasan/generic.c:584)
>> [  400.891821][    C0]  __kasan_slab_free (mm/kasan/common.c:253 mm/kasan/common.c:285)
>> [  400.891824][    C0]  kfree (./include/linux/kasan.h:235 mm/slub.c:2705 mm/slub.c:6405 mm/slub.c:6720)
>> [  400.891827][    C0]  usb6fire_comm_destroy (sound/usb/6fire/comm.c:197)
>> [  400.891830][    C0]  usb6fire_card_free (sound/usb/6fire/chip.c:65)
>> [  400.891832][    C0]  release_card_device (sound/core/init.c:594 sound/core/init.c:153)
>> [  400.891852][    C0]  kobject_put (lib/kobject.c:689 lib/kobject.c:720 ./include/linux/kref.h:65 lib/kobject.c:737)
>> [  400.891855][    C0]  snd_card_free (sound/core/init.c:626 sound/core/init.c:658)
>> [  400.891858][    C0]  usb6fire_chip_probe (sound/usb/6fire/chip.c:153)
>> [  400.891860][    C0]  usb_probe_interface (drivers/usb/core/driver.c:396)
> 
> Through a quick glance, this looks like a stale URB firing after the
> release.  Does the patch below work?
> 

I tested the patch. The reproducer does not trigger the bug on my side.
Thanks for your patch.


> thanks,
> 
> Takashi
> 
> -- 8< --
> --- a/sound/usb/6fire/chip.c
> +++ b/sound/usb/6fire/chip.c
> @@ -150,6 +150,10 @@ static int usb6fire_chip_probe(struct usb_interface *intf,
> return 0;
> 
> destroy_chip:
> + chip->shutdown = true;
> + if (card)
> + snd_card_disconnect(card);
> + usb6fire_chip_abort(chip);
> snd_card_free(card);
> return ret;
> }