KASAN: slab-use-after-free Read in dummy_timer

Status: upstream: reported on 2026/08/22 02:22
Subsystems: usb
Labels: prio:normal
[Documentation on labels]
Reported-by: syzbot+ba7702afee9d7d1375f0@syzkaller.appspotmail.com
First crash: 17d, last: 2d05h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
f96ea831 repro-c 💥 KASAN: slab-use-after-free Read in dummy_timer 2026/09/04 08:27 2026/09/04 09:41 2026/09/04 11:41 801f0966
7b4f7c87 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-use-after-free Read in dummy_timer 2026/08/20 00:01 2026/08/20 00:01 2026/08/20 01:08 1e72964b
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [usb?] KASAN: slab-use-after-free Read in dummy_timer 0 (1) 2026/08/22 02:22
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream general protection fault in dummy_timer (2) prio:high usb 19 syz, C 97 18d 649d 29/29 fixed on 2026/08/17 15:57
linux-6.6 KASAN: slab-use-after-free Read in dummy_timer origin:upstream 19 syz, C error 11 12d 428d 0/2 upstream: reported C repro on 2025/07/02 21:23
linux-5.15 KASAN: use-after-free Read in dummy_timer 19 2 376d 466d 0/3 auto-obsoleted due to no activity on 2025/12/02 15:39
upstream general protection fault in dummy_timer usb 2 2 1023d 1069d 0/29 auto-obsoleted due to no activity on 2024/02/14 16:35
linux-5.15 KASAN: use-after-free Read in dummy_timer (2) 19 2 210d 214d 0/3 auto-obsoleted due to no activity on 2026/05/16 23:24

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in find_endpoint drivers/usb/gadget/udc/dummy_hcd.c:1618 [inline]
BUG: KASAN: slab-use-after-free in handle_control_request drivers/usb/gadget/udc/dummy_hcd.c:1761 [inline]
BUG: KASAN: slab-use-after-free in dummy_timer+0x33f2/0x4cf0 drivers/usb/gadget/udc/dummy_hcd.c:1942
Read of size 1 at addr ffff88801eeac0e8 by task syz-executor/18063

CPU: 1 UID: 0 PID: 18063 Comm: syz-executor Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 find_endpoint drivers/usb/gadget/udc/dummy_hcd.c:1618 [inline]
 handle_control_request drivers/usb/gadget/udc/dummy_hcd.c:1761 [inline]
 dummy_timer+0x33f2/0x4cf0 drivers/usb/gadget/udc/dummy_hcd.c:1942
 __run_hrtimer kernel/time/hrtimer.c:2067 [inline]
 __hrtimer_run_queues+0x3bc/0xa10 kernel/time/hrtimer.c:2124
 hrtimer_run_softirq+0x1e3/0x2e0 kernel/time/hrtimer.c:2141
 handle_softirqs+0x226/0x860 kernel/softirq.c:645
 __do_softirq kernel/softirq.c:679 [inline]
 invoke_softirq kernel/softirq.c:519 [inline]
 __irq_exit_rcu+0xcb/0x220 kernel/softirq.c:767
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:784
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1062
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:finish_task_switch+0x413/0xc60 kernel/sched/core.c:5371
Code: 04 00 00 41 c7 84 24 20 0e 00 00 00 00 00 00 0f 1f 44 00 00 49 83 c4 48 4c 89 e7 e8 f7 9d 50 0a e8 d2 00 3a 00 fb 4c 8b 65 c8 <49> 8d bc 24 10 17 00 00 48 89 f8 48 c1 e8 03 42 0f b6 04 30 84 c0
RSP: 0018:ffffc900000f7020 EFLAGS: 00000206
RAX: 00000000001c237b RBX: ffff8880b873c8e0 RCX: 8000000000000001
RDX: 0000000000000006 RSI: ffffffff8e474257 RDI: ffffffff8c6d9480
RBP: ffffc900000f7070 R08: ffffffff907a137f R09: 1ffffffff20f426f
R10: dffffc0000000000 R11: fffffbfff20f4270 R12: ffff88802fd83e80
R13: ffff8880b873c8a8 R14: dffffc0000000000 R15: 1ffff110170e791c
 context_switch kernel/sched/core.c:5523 [inline]
 __schedule+0x17e3/0x58f0 kernel/sched/core.c:7270
 preempt_schedule_common+0x7f/0xd0 kernel/sched/core.c:7449
 preempt_schedule_thunk+0x16/0x40 arch/x86/entry/thunk.S:12
 __raw_spin_unlock include/linux/spinlock_api_smp.h:201 [inline]
 _raw_spin_unlock+0x41/0x50 kernel/locking/spinlock.c:213
 spin_unlock include/linux/spinlock.h:401 [inline]
 copy_pte_range mm/memory.c:1429 [inline]
 copy_pmd_range+0x5176/0x5c10 mm/memory.c:1490
 copy_pud_range mm/memory.c:1527 [inline]
 copy_p4d_range mm/memory.c:1551 [inline]
 copy_page_range+0xc82/0x1290 mm/memory.c:1637
 dup_mmap+0xf17/0x1dc0 mm/mmap.c:1819
 dup_mm kernel/fork.c:1543 [inline]
 copy_mm+0x11a/0x480 kernel/fork.c:1595
 copy_process+0x1e75/0x43e0 kernel/fork.c:2307
 kernel_clone+0x2d7/0x940 kernel/fork.c:2766
 __do_sys_clone kernel/fork.c:2908 [inline]
 __se_sys_clone kernel/fork.c:2892 [inline]
 __x64_sys_clone+0x1b6/0x230 kernel/fork.c:2892
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbe14fc6bd2
Code: 89 e7 e8 71 8b f7 ff 45 31 c0 31 d2 31 f6 64 48 8b 04 25 10 00 00 00 bf 11 00 20 01 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 66 89 c5 85 c0 75 3b 64 48 8b 04 25 10 00 00
RSP: 002b:00007fff5847dc50 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007fff5847dc50 RCX: 00007fbe14fc6bd2
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011
RBP: 00007fff5847dddc R08: 0000000000000000 R09: 0000000000000001
R10: 00005555702187d0 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000000927c0 R14: 0000000000189153 R15: 00007fff5847de30
 </TASK>

Allocated by task 9420:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5414 [inline]
 __kmalloc_noprof+0x36b/0x720 mm/slub.c:5439
 _kmalloc_noprof include/linux/slab.h:995 [inline]
 usb_copy_descriptors+0xf7/0x320 drivers/usb/gadget/config.c:82
 f_midi2_bind+0x2736/0x2c40 drivers/usb/gadget/function/f_midi2.c:2026
 usb_add_function+0x2e1/0x9f0 drivers/usb/gadget/composite.c:333
 configfs_composite_bind+0xde0/0x1410 drivers/usb/gadget/configfs.c:1802
 gadget_bind_driver+0x2ca/0x9e0 drivers/usb/gadget/udc/core.c:1662
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x254/0xae0 drivers/base/dd.c:706
 __driver_probe_device+0x1e8/0x360 drivers/base/dd.c:868
 driver_probe_device+0x4f/0x240 drivers/base/dd.c:898
 __driver_attach+0x339/0x600 drivers/base/dd.c:1292
 bus_for_each_dev+0x23b/0x2c0 drivers/base/bus.c:383
 bus_add_driver+0x345/0x670 drivers/base/bus.c:763
 driver_register+0x23a/0x320 drivers/base/driver.c:174
 usb_gadget_register_driver_owner+0xf9/0x270 drivers/usb/gadget/udc/core.c:1752
 gadget_dev_desc_UDC_store+0x1c9/0x2f0 drivers/usb/gadget/configfs.c:300
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x337/0x430 fs/configfs/file.c:229
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x612/0xba0 fs/read_write.c:687
 ksys_write+0x150/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 22260:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2748 [inline]
 slab_free mm/slub.c:6499 [inline]
 kfree+0x1c5/0x650 mm/slub.c:6792
 usb_free_descriptors include/linux/usb/gadget.h:903 [inline]
 usb_free_all_descriptors+0x78/0x110 drivers/usb/gadget/config.c:151
 purge_configs_funcs+0x248/0x3d0 drivers/usb/gadget/configfs.c:1600
 configfs_composite_unbind+0xa4/0x1c0 drivers/usb/gadget/configfs.c:1846
 gadget_unbind_driver+0x1cb/0x410 drivers/usb/gadget/udc/core.c:1724
 device_remove drivers/base/dd.c:616 [inline]
 __device_release_driver drivers/base/dd.c:1349 [inline]
 device_release_driver_internal+0x48b/0x880 drivers/base/dd.c:1372
 driver_detach+0x1f3/0x2d0 drivers/base/dd.c:1435
 bus_remove_driver+0x226/0x320 drivers/base/bus.c:832
 usb_gadget_unregister_driver+0x4e/0x70 drivers/usb/gadget/udc/core.c:1784
 unregister_gadget drivers/usb/gadget/configfs.c:263 [inline]
 gadget_dev_desc_UDC_store+0x17a/0x2f0 drivers/usb/gadget/configfs.c:290
 flush_write_buffer fs/configfs/file.c:207 [inline]
 configfs_write_iter+0x337/0x430 fs/configfs/file.c:229
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x612/0xba0 fs/read_write.c:687
 ksys_write+0x150/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88801eeac000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 232 bytes inside of
 freed 512-byte region [ffff88801eeac000, ffff88801eeac200)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1eeac
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801b041c80 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801b041c80 dead000000000100 dead000000000122
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000002 ffffffffffffff01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000004
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 1882718254
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1871
 prep_new_page mm/page_alloc.c:1879 [inline]
 get_page_from_freelist+0x2209/0x2280 mm/page_alloc.c:3943
 __alloc_frozen_pages_noprof+0x217/0x5a0 mm/page_alloc.c:5436
 alloc_slab_page mm/slub.c:3347 [inline]
 allocate_slab+0x7d/0x620 mm/slub.c:3462
 new_slab mm/slub.c:3513 [inline]
 refill_objects+0x2d5/0x350 mm/slub.c:7410
 refill_sheaf mm/slub.c:2885 [inline]
 __pcs_replace_empty_main+0x2c8/0x6c0 mm/slub.c:4774
 alloc_from_pcs mm/slub.c:4850 [inline]
 slab_alloc_node mm/slub.c:4984 [inline]
 __do_kmalloc_node mm/slub.c:5413 [inline]
 __kmalloc_flags_noprof+0x5c6/0x7a0 mm/slub.c:5602
 _kmalloc_flags_noprof mm/slab.h:55 [inline]
 __alloc_empty_sheaf mm/slub.c:2822 [inline]
 alloc_empty_sheaf mm/slub.c:2842 [inline]
 init_percpu_sheaves mm/slub.c:7733 [inline]
 do_kmem_cache_create+0x877/0x970 mm/slub.c:8783
 create_cache mm/slab_common.c:252 [inline]
 __kmem_cache_create_args+0x322/0x460 mm/slab_common.c:387
 fsnotify_init_connector_caches+0xb9/0x140 fs/notify/mark.c:1189
 fsnotify_init+0x27/0x40 fs/notify/fsnotify.c:729
 do_one_initcall+0x250/0x870 init/main.c:1357
 do_initcall_level+0x10a/0x1a0 init/main.c:1419
 do_initcalls+0x59/0xa0 init/main.c:1435
 kernel_init_freeable+0x29d/0x3e0 init/main.c:1670
 kernel_init+0x22/0x1d0 init/main.c:1560
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88801eeabf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff88801eeac000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88801eeac080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                          ^
 ffff88801eeac100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88801eeac180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess), 1 bytes skipped:
   0:	00 00                	add    %al,(%rax)
   2:	41 c7 84 24 20 0e 00 	movl   $0x0,0xe20(%r12)
   9:	00 00 00 00 00
   e:	0f 1f 44 00 00       	nopl   0x0(%rax,%rax,1)
  13:	49 83 c4 48          	add    $0x48,%r12
  17:	4c 89 e7             	mov    %r12,%rdi
  1a:	e8 f7 9d 50 0a       	call   0xa509e16
  1f:	e8 d2 00 3a 00       	call   0x3a00f6
  24:	fb                   	sti
  25:	4c 8b 65 c8          	mov    -0x38(%rbp),%r12
* 29:	49 8d bc 24 10 17 00 	lea    0x1710(%r12),%rdi <-- trapping instruction
  30:	00
  31:	48 89 f8             	mov    %rdi,%rax
  34:	48 c1 e8 03          	shr    $0x3,%rax
  38:	42 0f b6 04 30       	movzbl (%rax,%r14,1),%eax
  3d:	84 c0                	test   %al,%al

Crashes (24):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/02 14:26 upstream 89a312991dc6 85995287 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/09/01 22:49 upstream 786262be6048 587f6b29 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/31 14:16 upstream cee9395acd80 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/31 13:42 upstream cee9395acd80 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/30 20:04 upstream 08dbfad3f504 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/28 09:20 upstream 1b78070aaef6 e2fa417d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/28 08:58 upstream 1b78070aaef6 e2fa417d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/27 12:34 upstream 73e3f0710014 a2b77b9e .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/31 10:29 linux-next e30626823a40 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/31 10:28 linux-next e30626823a40 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/31 02:30 linux-next e30626823a40 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/31 00:06 linux-next e30626823a40 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/21 14:22 linux-next 7079a12d7506 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/20 23:56 linux-next 7079a12d7506 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/20 21:05 linux-next 7079a12d7506 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/20 18:28 linux-next 7079a12d7506 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/20 17:53 linux-next 7079a12d7506 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/20 17:47 linux-next 7079a12d7506 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/20 17:38 linux-next 7079a12d7506 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/20 17:37 linux-next 7079a12d7506 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/20 17:37 linux-next 7079a12d7506 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce KASAN: slab-use-after-free Read in dummy_timer
2026/08/18 02:14 linux-next e6664f2b33db 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-use-after-free Read in dummy_timer
2026/08/25 13:23 upstream 66498c75b4f8 614e416a .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root KASAN: use-after-free Read in dummy_timer
2026/08/23 09:39 linux-next 903c1cf6dff9 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root KASAN: slab-out-of-bounds Read in dummy_timer
* Struck through repros no longer work on HEAD.