syzbot


KASAN: use-after-free Read in dummy_timer (2)

Status: upstream: reported on 2026/02/02 03:00
Reported-by: syzbot+10598bf6994d7b70b1a4@syzkaller.appspotmail.com
First crash: 22d, last: 19d
Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 KASAN: use-after-free Read in dummy_timer 19 2 184d 275d 0/3 auto-obsoleted due to no activity on 2025/12/02 15:39
upstream general protection fault in dummy_timer (2) usb 2 syz 70 6d23h 457d 0/29 upstream: reported syz repro on 2024/11/24 05:03
linux-6.6 KASAN: slab-use-after-free Read in dummy_timer origin:upstream 19 C error 5 1d03h 237d 0/2 upstream: reported C repro on 2025/07/02 21:23
upstream general protection fault in dummy_timer usb 2 2 831d 877d 0/29 auto-obsoleted due to no activity on 2024/02/14 16:35

Sample crash report:
smsusb:smsusb_onresponse: error, urb status -71, 0 bytes
smsusb:smsusb_onresponse: error, urb status -71, 0 bytes
smsusb:smsusb_onresponse: error, urb status -71, 0 bytes
smsusb:smsusb_onresponse: error, urb status -71, 0 bytes
==================================================================
BUG: KASAN: use-after-free in dummy_timer+0x29cb/0x31e0 drivers/usb/gadget/udc/dummy_hcd.c:1844
Read of size 4 at addr ffff88801f404034 by task syz.1.1508/8063

CPU: 0 PID: 8063 Comm: syz.1.1508 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 dummy_timer+0x29cb/0x31e0 drivers/usb/gadget/udc/dummy_hcd.c:1844
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1451
 expire_timers kernel/time/timer.c:1496 [inline]
 __run_timers+0x53a/0x7f0 kernel/time/timer.c:1767
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:preempt_schedule_irq+0xb6/0x160 kernel/sched/core.c:6799
Code: 00 00 43 c6 44 37 04 f8 74 0b 0f 0b 48 f7 03 08 00 00 00 74 7f bf 01 00 00 00 e8 e5 2f 8e f7 e8 70 19 bb f7 fb bf 01 00 00 00 <e8> 65 b5 ff ff 43 c6 44 37 08 00 48 c7 44 24 40 00 00 00 00 9c 8f
RSP: 0018:ffffc9000334f840 EFLAGS: 00000286
RAX: 28bd9ef10a42fd00 RBX: 0000000000000000 RCX: 28bd9ef10a42fd00
RDX: dffffc0000000000 RSI: ffffffff8a2b2780 RDI: 0000000000000001
RBP: ffffc9000334f8e0 R08: ffffffff901d10c7 R09: 1ffffffff203a218
R10: dffffc0000000000 R11: fffffbfff203a219 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff92000669f08
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_reschedule_ipi+0x16/0x20 arch/x86/include/asm/idtentry.h:681
RIP: 0010:console_unlock+0xcad/0x1120 kernel/printk/printk.c:2749
Code: 75 11 e8 76 d6 18 00 4d 85 ff 75 16 e8 6c d6 18 00 eb 15 e8 65 d6 18 00 e8 90 9f 5b 08 4d 85 ff 74 ea e8 56 d6 18 00 fb 31 ff <89> de e8 ac d9 18 00 85 db 0f 94 c0 22 44 24 17 3c 01 75 1f e8 3a
RSP: 0018:ffffc9000334f9a0 EFLAGS: 00000246
RAX: ffffffff8160494a RBX: 0000000000000000 RCX: 0000000000080000
RDX: ffffc900056a9000 RSI: 000000000007ffff RDI: 0000000000000000
RBP: ffffc9000334fc10 R08: ffffffff901d10c7 R09: 1ffffffff203a218
R10: dffffc0000000000 R11: fffffbfff203a219 R12: 1ffffffff198d6ad
R13: 00000000000000a2 R14: 0000000000000000 R15: 0000000000000200
 do_fb_ioctl+0x813/0x850 drivers/video/fbdev/core/fbmem.c:1133
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f62af5abeb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f62ad807028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f62af826fa0 RCX: 00007f62af5abeb9
RDX: 0000200000000100 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 00007f62af619c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f62af827038 R14: 00007f62af826fa0 R15: 00007ffd1e044bc8
 </TASK>

Allocated by task 4293:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0xb5/0xf0 mm/kasan/common.c:522
 kmalloc include/linux/slab.h:607 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 smsusb_init_device drivers/media/usb/siano/smsusb.c:397 [inline]
 smsusb_probe+0x8a1/0x1de0 drivers/media/usb/siano/smsusb.c:569
 usb_probe_interface+0x5c5/0xb20 drivers/usb/core/driver.c:396
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x284/0xc80 drivers/base/dd.c:595
 __driver_probe_device+0x18c/0x330 drivers/base/dd.c:755
 driver_probe_device+0x4f/0x420 drivers/base/dd.c:785
 __device_attach_driver+0x2b0/0x500 drivers/base/dd.c:907
 bus_for_each_drv+0x184/0x210 drivers/base/bus.c:429
 __device_attach+0x2a8/0x480 drivers/base/dd.c:979
 bus_probe_device+0xbc/0x1e0 drivers/base/bus.c:489
 device_add+0xa00/0xfb0 drivers/base/core.c:3412
 usb_set_configuration+0x1991/0x1fd0 drivers/usb/core/message.c:2165
 usb_generic_driver_probe+0x89/0x150 drivers/usb/core/generic.c:238
 usb_probe_device+0x139/0x270 drivers/usb/core/driver.c:293
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x284/0xc80 drivers/base/dd.c:595
 __driver_probe_device+0x18c/0x330 drivers/base/dd.c:755
 driver_probe_device+0x4f/0x420 drivers/base/dd.c:785
 __device_attach_driver+0x2b0/0x500 drivers/base/dd.c:907
 bus_for_each_drv+0x184/0x210 drivers/base/bus.c:429
 __device_attach+0x2a8/0x480 drivers/base/dd.c:979
 bus_probe_device+0xbc/0x1e0 drivers/base/bus.c:489
 device_add+0xa00/0xfb0 drivers/base/core.c:3412
 usb_new_device+0xd65/0x1660 drivers/usb/core/hub.c:2632
 hub_port_connect drivers/usb/core/hub.c:5497 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5637 [inline]
 port_event drivers/usb/core/hub.c:5799 [inline]
 hub_event+0x2e4a/0x55e0 drivers/usb/core/hub.c:5881
 process_one_work+0x85f/0x1010 kernel/workqueue.c:2310
 worker_thread+0xaa6/0x1290 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

Freed by task 4293:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xea/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 smsusb_term_device+0x1ac/0x220 drivers/media/usb/siano/smsusb.c:352
 smsusb_init_device drivers/media/usb/siano/smsusb.c:491 [inline]
 smsusb_probe+0x1746/0x1de0 drivers/media/usb/siano/smsusb.c:569
 usb_probe_interface+0x5c5/0xb20 drivers/usb/core/driver.c:396
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x284/0xc80 drivers/base/dd.c:595
 __driver_probe_device+0x18c/0x330 drivers/base/dd.c:755
 driver_probe_device+0x4f/0x420 drivers/base/dd.c:785
 __device_attach_driver+0x2b0/0x500 drivers/base/dd.c:907
 bus_for_each_drv+0x184/0x210 drivers/base/bus.c:429
 __device_attach+0x2a8/0x480 drivers/base/dd.c:979
 bus_probe_device+0xbc/0x1e0 drivers/base/bus.c:489
 device_add+0xa00/0xfb0 drivers/base/core.c:3412
 usb_set_configuration+0x1991/0x1fd0 drivers/usb/core/message.c:2165
 usb_generic_driver_probe+0x89/0x150 drivers/usb/core/generic.c:238
 usb_probe_device+0x139/0x270 drivers/usb/core/driver.c:293
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x284/0xc80 drivers/base/dd.c:595
 __driver_probe_device+0x18c/0x330 drivers/base/dd.c:755
 driver_probe_device+0x4f/0x420 drivers/base/dd.c:785
 __device_attach_driver+0x2b0/0x500 drivers/base/dd.c:907
 bus_for_each_drv+0x184/0x210 drivers/base/bus.c:429
 __device_attach+0x2a8/0x480 drivers/base/dd.c:979
 bus_probe_device+0xbc/0x1e0 drivers/base/bus.c:489
 device_add+0xa00/0xfb0 drivers/base/core.c:3412
 usb_new_device+0xd65/0x1660 drivers/usb/core/hub.c:2632
 hub_port_connect drivers/usb/core/hub.c:5497 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5637 [inline]
 port_event drivers/usb/core/hub.c:5799 [inline]
 hub_event+0x2e4a/0x55e0 drivers/usb/core/hub.c:5881
 process_one_work+0x85f/0x1010 kernel/workqueue.c:2310
 worker_thread+0xaa6/0x1290 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

Last potentially related work creation:
 kasan_save_stack+0x35/0x60 mm/kasan/common.c:38
 kasan_record_aux_stack+0xb8/0x100 mm/kasan/generic.c:348
 insert_work+0x54/0x3d0 kernel/workqueue.c:1366
 __queue_work+0x9c5/0xd50 kernel/workqueue.c:1532
 queue_work_on+0x124/0x1f0 kernel/workqueue.c:1559
 __usb_hcd_giveback_urb+0x35f/0x520 drivers/usb/core/hcd.c:1674
 dummy_timer+0x8a8/0x31e0 drivers/usb/gadget/udc/dummy_hcd.c:1988
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1451
 expire_timers kernel/time/timer.c:1496 [inline]
 __run_timers+0x53a/0x7f0 kernel/time/timer.c:1767
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676

Second to last potentially related work creation:
 kasan_save_stack+0x35/0x60 mm/kasan/common.c:38
 kasan_record_aux_stack+0xb8/0x100 mm/kasan/generic.c:348
 insert_work+0x54/0x3d0 kernel/workqueue.c:1366
 __queue_work+0x9c5/0xd50 kernel/workqueue.c:1532
 queue_work_on+0x124/0x1f0 kernel/workqueue.c:1559
 __usb_hcd_giveback_urb+0x35f/0x520 drivers/usb/core/hcd.c:1674
 dummy_timer+0x8a8/0x31e0 drivers/usb/gadget/udc/dummy_hcd.c:1988
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1451
 expire_timers kernel/time/timer.c:1496 [inline]
 __run_timers+0x53a/0x7f0 kernel/time/timer.c:1767
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676

The buggy address belongs to the object at ffff88801f404000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 52 bytes inside of
 4096-byte region [ffff88801f404000, ffff88801f405000)
The buggy address belongs to the page:
page:ffffea00007d0000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1f400
head:ffffea00007d0000 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 0000000300000001 ffff888016c42140
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 4193, ts 56489510909, free_ts 56420529317
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x1bbd/0x1ca0 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5487
 alloc_slab_page mm/slub.c:1780 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xc0/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x80a/0xdd0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc_trace+0x1a5/0x2a0 mm/slub.c:3250
 kmalloc include/linux/slab.h:607 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 kobject_uevent_env+0x27a/0x890 lib/kobject_uevent.c:539
 rx_queue_add_kobject net/core/net-sysfs.c:1070 [inline]
 net_rx_queue_update_kobjects+0x221/0x490 net/core/net-sysfs.c:1110
 register_queue_kobjects net/core/net-sysfs.c:1767 [inline]
 netdev_register_kobject+0x231/0x320 net/core/net-sysfs.c:2018
 register_netdevice+0x1039/0x16f0 net/core/dev.c:10397
 hsr_dev_finalize+0x5f6/0x870 net/hsr/hsr_device.c:689
 hsr_newlink+0x637/0x6f0 net/hsr/hsr_netlink.c:102
 __rtnl_newlink net/core/rtnetlink.c:3526 [inline]
 rtnl_newlink+0x1359/0x1a50 net/core/rtnetlink.c:3574
 rtnetlink_rcv_msg+0x844/0xf30 net/core/rtnetlink.c:5684
 netlink_rcv_skb+0x1f5/0x440 net/netlink/af_netlink.c:2507
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x774/0x920 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x8ba/0xbe0 net/netlink/af_netlink.c:1918
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1340 [inline]
 free_pcp_prepare mm/page_alloc.c:1391 [inline]
 free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
 free_unref_page+0x8f/0x2a0 mm/page_alloc.c:3396
 qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xd0 mm/kasan/common.c:444
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc_trace+0x103/0x2a0 mm/slub.c:3250
 kmalloc include/linux/slab.h:607 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 kset_create lib/kobject.c:982 [inline]
 kset_create_and_add+0x56/0x160 lib/kobject.c:1025
 register_queue_kobjects net/core/net-sysfs.c:1759 [inline]
 netdev_register_kobject+0x1ae/0x320 net/core/net-sysfs.c:2018
 register_netdevice+0x1039/0x16f0 net/core/dev.c:10397
 veth_newlink+0x8d7/0xe30 drivers/net/veth.c:1714
 __rtnl_newlink net/core/rtnetlink.c:3526 [inline]
 rtnl_newlink+0x1359/0x1a50 net/core/rtnetlink.c:3574
 rtnetlink_rcv_msg+0x844/0xf30 net/core/rtnetlink.c:5684
 netlink_rcv_skb+0x1f5/0x440 net/netlink/af_netlink.c:2507
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x774/0x920 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x8ba/0xbe0 net/netlink/af_netlink.c:1918

Memory state around the buggy address:
 ffff88801f403f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88801f403f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801f404000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                     ^
 ffff88801f404080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88801f404100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess):
   0:	00 00                	add    %al,(%rax)
   2:	43 c6 44 37 04 f8    	movb   $0xf8,0x4(%r15,%r14,1)
   8:	74 0b                	je     0x15
   a:	0f 0b                	ud2
   c:	48 f7 03 08 00 00 00 	testq  $0x8,(%rbx)
  13:	74 7f                	je     0x94
  15:	bf 01 00 00 00       	mov    $0x1,%edi
  1a:	e8 e5 2f 8e f7       	call   0xf78e3004
  1f:	e8 70 19 bb f7       	call   0xf7bb1994
  24:	fb                   	sti
  25:	bf 01 00 00 00       	mov    $0x1,%edi
* 2a:	e8 65 b5 ff ff       	call   0xffffb594 <-- trapping instruction
  2f:	43 c6 44 37 08 00    	movb   $0x0,0x8(%r15,%r14,1)
  35:	48 c7 44 24 40 00 00 	movq   $0x0,0x40(%rsp)
  3c:	00 00
  3e:	9c                   	pushf
  3f:	8f                   	.byte 0x8f

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/05 23:23 linux-5.15.y 9eec9a14ee10 f03c4191 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in dummy_timer
2026/02/02 02:59 linux-5.15.y 9eec9a14ee10 6b8752f2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in dummy_timer
* Struck through repros no longer work on HEAD.