WARNING in dummy_free_request (2)

Status: upstream: reported C repro on 2026/07/29 00:10
Subsystems: usb
Labels: prio:normal
[Documentation on labels]
Reported-by: syzbot+c73e1942197af9f54ca3@syzkaller.appspotmail.com
First crash: 8d15h, last: 11h09m
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
a52d103a assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ WARNING in dummy_free_request (2) 2026/07/26 00:00 2026/07/26 00:00 2026/07/26 00:51 492bab15 

			
				
	

	
	



			

		

	

	
	

		

			▶
			▼
			Discussions (1)
		

		

			
			
			



	
	

		Title
		Replies (including bot)
		Last reply
	

	
	
	
		

			[syzbot] [usb?] WARNING in dummy_free_request (2)
			0 (2)
			2026/08/02 00:10
		

	
	




			
			
		

	

	
	

		

			▶
			▼
			Similar bugs (2)
		

		

			




	
	

		
			Kernel
		
		Title
		
			Rank
			
🛈

		
		Repro
		Cause bisect
		Fix bisect
		Count
		Last
		Reported
		
		
		
			Patched
		
		
			Status
		
		
	

	
	
	
		

			upstream
			
				WARNING in dummy_free_request
					usb
			
			-1
			
			
			
			1
			2360d
			
				
					2353d
				
			
			
			
			
				0/29
			
			
				
					
						closed as invalid on 2020/02/24 16:14
					
				
			
			
		

	
		

			linux-6.1
			
				WARNING in dummy_free_request
			
			-1
			syz, C
			
			
			2
			17m
			
				
					1d14h
				
			
			
			
			
				0/3
			
			
				
					
						upstream: reported C repro on 2026/07/31 20:31
					
				
			
			
		

	
	





			
			
			
			
		

	

	

	
	
Sample crash report:

	
gadgetfs: suspended from state 3
gadgetfs: disconnected
------------[ cut here ]------------
WARNING: drivers/usb/gadget/udc/dummy_hcd.c:710 at dummy_free_request+0x7c/0x84 drivers/usb/gadget/udc/dummy_hcd.c:710, CPU#0: syz.0.32/4939
Modules linked in:
CPU: 0 UID: 0 PID: 4939 Comm: syz.0.32 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : dummy_free_request+0x7c/0x84 drivers/usb/gadget/udc/dummy_hcd.c:710
lr : dummy_free_request+0x7c/0x84 drivers/usb/gadget/udc/dummy_hcd.c:710
sp : ffff8000962579d0
x29: ffff8000962579d0 x28: 1fffe000195c4a01 x27: ffff0000cae25008
x26: 1fffe0001a0e2408 x25: 1fffe0001952998b x24: 1fffe000195299aa
x23: dfff800000000000 x22: ffff800088b07eb8 x21: ffff800087332200
x20: ffff0000ca94c068 x19: ffff0000d866f900 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
x14: 00000000868e5610 x13: 0000000000000001 x12: 0000000000000000
x11: ffff800080156ee8 x10: 0000000000000003 x9 : 0000000000000000
x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000
x5 : 0000000000000001 x4 : 0000000000000008 x3 : ffff8000835a7208
x2 : 0000000000000001 x1 : ffff0000c82cba80 x0 : 0000000000000000
Call trace:
 dummy_free_request+0x7c/0x84 drivers/usb/gadget/udc/dummy_hcd.c:710 (P)
 usb_ep_free_request+0x108/0x3fc drivers/usb/gadget/udc/core.c:221
 gadgetfs_unbind+0x19c/0x1f0 drivers/usb/gadget/legacy/inode.c:1661
 gadget_unbind_driver+0x188/0x790 drivers/usb/gadget/udc/core.c:1724
 device_remove+0xc4/0x134 drivers/base/dd.c:616
 __device_release_driver drivers/base/dd.c:1349 [inline]
 device_release_driver_internal+0x124/0x20c drivers/base/dd.c:1372
 driver_detach+0x124/0x1b4 drivers/base/dd.c:1435
 bus_remove_driver+0x124/0x22c drivers/base/bus.c:832
 driver_unregister+0x78/0xac drivers/base/driver.c:202
 usb_gadget_unregister_driver+0x50/0x78 drivers/usb/gadget/udc/core.c:1784
 dev_release+0x8c/0x15c drivers/usb/gadget/legacy/inode.c:1198
 __fput+0x338/0x74c fs/file_table.c:512
 ____fput+0x20/0x30 fs/file_table.c:540
 task_work_run+0x1cc/0x25c 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:70 [inline]
 exit_to_user_mode_loop+0x10c/0x17c kernel/entry/common.c:101
 __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:230 [inline]
 arm64_syscall_exit_to_user_mode arch/arm64/kernel/entry-common.c:88 [inline]
 el0_svc+0x18c/0x260 arch/arm64/kernel/entry-common.c:737
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
irq event stamp: 2192
hardirqs last  enabled at (2191): [<ffff80008690a7dc>] __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:187 [inline]
hardirqs last  enabled at (2191): [<ffff80008690a7dc>] _raw_spin_unlock_irq+0x30/0x80 kernel/locking/spinlock.c:206
hardirqs last disabled at (2192): [<ffff8000868e5428>] el1_brk64+0x20/0x54 arch/arm64/kernel/entry-common.c:425
softirqs last  enabled at (1170): [<ffff80008030ff18>] softirq_handle_end kernel/softirq.c:468 [inline]
softirqs last  enabled at (1170): [<ffff80008030ff18>] handle_softirqs+0xc28/0xd98 kernel/softirq.c:650
softirqs last disabled at (1161): [<ffff8000800204c0>] __do_softirq+0x14/0x20 kernel/softirq.c:656
---[ end trace 0000000000000000 ]---
==================================================================
BUG: KASAN: slab-use-after-free in __list_del_entry_valid_or_report+0x3c/0x1b8 lib/list_debug.c:49
Read of size 8 at addr ffff0000d866f908 by task syz.0.32/4939

CPU: 1 UID: 0 PID: 4939 Comm: syz.0.32 Tainted: G        W           syzkaller #0 PREEMPT 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 print_address_description+0xb0/0x238 mm/kasan/report.c:378
 print_report+0x68/0x84 mm/kasan/report.c:482
 kasan_report+0x8c/0xc4 mm/kasan/report.c:595
 __asan_report_load8_noabort+0x20/0x2c mm/kasan/report_generic.c:381
 __list_del_entry_valid_or_report+0x3c/0x1b8 lib/list_debug.c:49
 __list_del_entry_valid include/linux/list.h:132 [inline]
 __list_del_entry include/linux/list.h:246 [inline]
 list_del_init include/linux/list.h:318 [inline]
 nuke+0x60/0x194 drivers/usb/gadget/udc/dummy_hcd.c:360
 stop_activity drivers/usb/gadget/udc/dummy_hcd.c:379 [inline]
 dummy_udc_stop+0xe4/0x180 drivers/usb/gadget/udc/dummy_hcd.c:1057
 usb_gadget_udc_stop_locked drivers/usb/gadget/udc/core.c:1265 [inline]
 gadget_unbind_driver+0x204/0x790 drivers/usb/gadget/udc/core.c:1727
 device_remove+0xc4/0x134 drivers/base/dd.c:616
 __device_release_driver drivers/base/dd.c:1349 [inline]
 device_release_driver_internal+0x124/0x20c drivers/base/dd.c:1372
 driver_detach+0x124/0x1b4 drivers/base/dd.c:1435
 bus_remove_driver+0x124/0x22c drivers/base/bus.c:832
 driver_unregister+0x78/0xac drivers/base/driver.c:202
 usb_gadget_unregister_driver+0x50/0x78 drivers/usb/gadget/udc/core.c:1784
 dev_release+0x8c/0x15c drivers/usb/gadget/legacy/inode.c:1198
 __fput+0x338/0x74c fs/file_table.c:512
 ____fput+0x20/0x30 fs/file_table.c:540
 task_work_run+0x1cc/0x25c 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:70 [inline]
 exit_to_user_mode_loop+0x10c/0x17c kernel/entry/common.c:101
 __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:230 [inline]
 arm64_syscall_exit_to_user_mode arch/arm64/kernel/entry-common.c:88 [inline]
 el0_svc+0x18c/0x260 arch/arm64/kernel/entry-common.c:737
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

Allocated by task 4939:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:78
 kasan_save_alloc_info+0x44/0x54 mm/kasan/generic.c:570
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x9c/0xb4 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x2e8/0x5ec mm/slub.c:5489
 _kmalloc_noprof include/linux/slab.h:988 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 dummy_alloc_request+0x88/0x128 drivers/usb/gadget/udc/dummy_hcd.c:693
 usb_ep_alloc_request+0x74/0x480 drivers/usb/gadget/udc/core.c:197
 gadgetfs_bind+0x104/0x75c drivers/usb/gadget/legacy/inode.c:1686
 gadget_bind_driver+0x274/0x834 drivers/usb/gadget/udc/core.c:1662
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x29c/0x800 drivers/base/dd.c:706
 __driver_probe_device+0x1e0/0x350 drivers/base/dd.c:868
 driver_probe_device+0x6c/0x19c drivers/base/dd.c:898
 __driver_attach+0x168/0x384 drivers/base/dd.c:1292
 bus_for_each_dev+0x128/0x1b4 drivers/base/bus.c:383
 driver_attach+0x50/0x60 drivers/base/dd.c:1310
 bus_add_driver+0x208/0x500 drivers/base/bus.c:763
 driver_register+0x220/0x310 drivers/base/driver.c:174
 usb_gadget_register_driver_owner+0xf0/0x25c drivers/usb/gadget/udc/core.c:1752
 dev_config+0x91c/0xcc0 drivers/usb/gadget/legacy/inode.c:1883
 vfs_write+0x2a4/0xa0c fs/read_write.c:685
 ksys_write+0x12c/0x228 fs/read_write.c:739
 __do_sys_write fs/read_write.c:750 [inline]
 __se_sys_write fs/read_write.c:747 [inline]
 __arm64_sys_write+0x7c/0x90 fs/read_write.c:747
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

Freed by task 4939:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:78
 kasan_save_free_info+0x58/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x74/0xa4 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2677 [inline]
 slab_free mm/slub.c:6377 [inline]
 kfree+0x188/0x690 mm/slub.c:6692
 dummy_free_request+0x5c/0x84 drivers/usb/gadget/udc/dummy_hcd.c:711
 usb_ep_free_request+0x108/0x3fc drivers/usb/gadget/udc/core.c:221
 gadgetfs_unbind+0x19c/0x1f0 drivers/usb/gadget/legacy/inode.c:1661
 gadget_unbind_driver+0x188/0x790 drivers/usb/gadget/udc/core.c:1724
 device_remove+0xc4/0x134 drivers/base/dd.c:616
 __device_release_driver drivers/base/dd.c:1349 [inline]
 device_release_driver_internal+0x124/0x20c drivers/base/dd.c:1372
 driver_detach+0x124/0x1b4 drivers/base/dd.c:1435
 bus_remove_driver+0x124/0x22c drivers/base/bus.c:832
 driver_unregister+0x78/0xac drivers/base/driver.c:202
 usb_gadget_unregister_driver+0x50/0x78 drivers/usb/gadget/udc/core.c:1784
 dev_release+0x8c/0x15c drivers/usb/gadget/legacy/inode.c:1198
 __fput+0x338/0x74c fs/file_table.c:512
 ____fput+0x20/0x30 fs/file_table.c:540
 task_work_run+0x1cc/0x25c 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:70 [inline]
 exit_to_user_mode_loop+0x10c/0x17c kernel/entry/common.c:101
 __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:230 [inline]
 arm64_syscall_exit_to_user_mode arch/arm64/kernel/entry-common.c:88 [inline]
 el0_svc+0x18c/0x260 arch/arm64/kernel/entry-common.c:737
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594

The buggy address belongs to the object at ffff0000d866f900
 which belongs to the cache kmalloc-128 of size 128
The buggy address is located 8 bytes inside of
 freed 128-byte region [ffff0000d866f900, ffff0000d866f980)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11866f
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 05ffc00000000000 ffff0000c0001a00 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000d866f800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff0000d866f880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff0000d866f900: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff0000d866f980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff0000d866fa00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
list_del corruption, ffff0000d866f900->next is NULL
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:53!
Internal error: Oops - BUG: 00000000f2000800 [#1]  SMP
Modules linked in:
CPU: 1 UID: 0 PID: 4939 Comm: syz.0.32 Tainted: G    B   W           syzkaller #0 PREEMPT 
Tainted: [B]=BAD_PAGE, [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026
pstate: 634000c5 (nZCv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : __list_del_entry_valid_or_report+0xec/0x1b8 lib/list_debug.c:52
lr : __list_del_entry_valid_or_report+0xec/0x1b8 lib/list_debug.c:52
sp : ffff8000962579c0
x29: ffff8000962579c0 x28: 1fffe000195c4a01 x27: ffff0000cae25008
x26: 1fffe000195c4a00 x25: 00000000ffffff94 x24: 1fffe00019529808
x23: dfff800000000000 x22: dfff800000000000 x21: 0338032e0000134b
x20: 0000000000000000 x19: ffff0000d866f900 x18: 0000000000000000
x17: 3d3d3d3d3d3d3d3d x16: 3d3d3d3d3d3d3d3d x15: 3d3d3d3d3d3d3d3d
x14: 3d3d3d3d3d3d3d3d x13: 0000000000000001 x12: 0000000000000000
x11: 0000000000000000 x10: 0000000000000002 x9 : bfb6b4227df68700
x8 : bfb6b4227df68700 x7 : 0000000000000001 x6 : ffff80008048de94
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff800080498bc8
x2 : 0000000100000001 x1 : ffff0000c82cba80 x0 : 0000000000000033
Call trace:
 __list_del_entry_valid_or_report+0xec/0x1b8 lib/list_debug.c:52 (P)
 __list_del_entry_valid include/linux/list.h:132 [inline]
 __list_del_entry include/linux/list.h:246 [inline]
 list_del_init include/linux/list.h:318 [inline]
 nuke+0x60/0x194 drivers/usb/gadget/udc/dummy_hcd.c:360
 stop_activity drivers/usb/gadget/udc/dummy_hcd.c:379 [inline]
 dummy_udc_stop+0xe4/0x180 drivers/usb/gadget/udc/dummy_hcd.c:1057
 usb_gadget_udc_stop_locked drivers/usb/gadget/udc/core.c:1265 [inline]
 gadget_unbind_driver+0x204/0x790 drivers/usb/gadget/udc/core.c:1727
 device_remove+0xc4/0x134 drivers/base/dd.c:616
 __device_release_driver drivers/base/dd.c:1349 [inline]
 device_release_driver_internal+0x124/0x20c drivers/base/dd.c:1372
 driver_detach+0x124/0x1b4 drivers/base/dd.c:1435
 bus_remove_driver+0x124/0x22c drivers/base/bus.c:832
 driver_unregister+0x78/0xac drivers/base/driver.c:202
 usb_gadget_unregister_driver+0x50/0x78 drivers/usb/gadget/udc/core.c:1784
 dev_release+0x8c/0x15c drivers/usb/gadget/legacy/inode.c:1198
 __fput+0x338/0x74c fs/file_table.c:512
 ____fput+0x20/0x30 fs/file_table.c:540
 task_work_run+0x1cc/0x25c 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:70 [inline]
 exit_to_user_mode_loop+0x10c/0x17c kernel/entry/common.c:101
 __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:230 [inline]
 arm64_syscall_exit_to_user_mode arch/arm64/kernel/entry-common.c:88 [inline]
 el0_svc+0x18c/0x260 arch/arm64/kernel/entry-common.c:737
 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594
Code: f0029ac0 91328000 aa1303e1 979c21eb (d4210000) 
---[ end trace 0000000000000000 ]---



	

	



	Crashes (5):
		
		

			Time
			Kernel
			Commit
			Syzkaller
			Config
			Log
			Report
			Syz repro
			C repro
			VM info
			Assets (help?)
			Manager
			Title
		

		
		
		
		

			2026/08/02 00:09
			git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
			e2d5e23967d0
			e611ffe1
			.config
			console log
			report
			syz / log
			C
			
			
				[disk image]
			
				[vmlinux]
			
				[kernel image]
			
			ci-upstream-gce-arm64
			WARNING in dummy_free_request
		

		
		

			2026/08/01 15:32
			upstream
			02dc699f83d0
			e611ffe1
			.config
			console log
			report
			
			
			info
			
				[disk image (non-bootable)]
			
				[vmlinux]
			
				[kernel image]
			
			ci-qemu-upstream-386
			WARNING in dummy_free_request
		

		
		

			2026/07/24 20:10
			linux-next
			cc2b5f627e8c
			05b26a28
			.config
			console log
			report
			
			
			info
			
				[disk image]
			
				[vmlinux]
			
				[kernel image]
			
			ci-upstream-rust-kasan-gce
			WARNING in dummy_free_request
		

		
		

			2026/08/01 23:15
			git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
			e2d5e23967d0
			e611ffe1
			.config
			console log
			report
			
			
			info
			
				[disk image]
			
				[vmlinux]
			
				[kernel image]
			
			ci-upstream-gce-arm64
			WARNING in dummy_free_request
		

		
		

			2026/08/01 23:15
			git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
			e2d5e23967d0
			e611ffe1
			.config
			console log
			report
			
			
			info
			
				[disk image]
			
				[vmlinux]
			
				[kernel image]
			
			ci-upstream-gce-arm64
			WARNING in dummy_free_request
		

		
		


* Struck through repros no longer work on HEAD.