syzbot


KASAN: use-after-free Write in detach_timer

Status: upstream: reported C repro on 2025/12/11 21:59
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+66c971bd055d6950cf56@syzkaller.appspotmail.com
First crash: 223d, last: 190d
Fix bisection: the issue occurs on the latest tested release (bisect log)
Crash: WARNING: ODEBUG bug in snd_rawmidi_free (log)
Repro: C syz .config
  
Bug presence (2)
Date Name Commit Repro Result
2025/12/12 linux-5.15.y (ToT) 68efe5a6c16a C [report] KASAN: use-after-free Write in __run_timers
2025/12/12 upstream (ToT) 187d0801404f C Didn't crash
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream general protection fault in detach_timer (2) kernel 22 16 144d 153d 0/29 auto-obsoleted due to no activity on 2026/05/09 18:57
upstream general protection fault in detach_timer mm tomoyo batman 22 4 1174d 1179d 0/29 auto-obsoleted due to no activity on 2023/08/03 11:53
Last patch testing requests (5)
Created Duration User Patch Repo Result
2026/06/23 06:20 21m retest repro linux-5.15.y OK log
2026/05/16 17:30 15m retest repro linux-5.15.y report log
2026/03/25 18:24 10m retest repro linux-5.15.y report log
2026/03/06 16:48 22m retest repro linux-5.15.y report log
2025/12/26 14:19 13m retest repro linux-5.15.y report log
Fix bisection attempts (5)
Created Duration User Patch Repo Result
2026/05/26 06:19 18m fix candidate upstream error job log
2026/03/25 13:52 1m fix candidate upstream error job log
2026/02/21 14:32 1m fix candidate upstream error job log
2026/01/22 11:18 6m fix candidate upstream error job log
2026/01/14 05:48 1h58m bisect fix linux-5.15.y OK (0) job log log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:858 [inline]
BUG: KASAN: use-after-free in detach_timer+0x12e/0x2b0 kernel/time/timer.c:827
Write of size 8 at addr ffff8880792a0848 by task udevd/4412

CPU: 0 PID: 4412 Comm: udevd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0x168/0x230 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
 __hlist_del include/linux/list.h:858 [inline]
 detach_timer+0x12e/0x2b0 kernel/time/timer.c:827
 expire_timers kernel/time/timer.c:1485 [inline]
 __run_timers+0x4ab/0x7c0 kernel/time/timer.c:1767
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
 handle_softirqs+0x328/0x820 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x12f/0x220 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:stack_trace_consume_entry+0x52/0x270 kernel/stacktrace.c:89
Code: 84 c0 0f 85 04 01 00 00 44 8b 4f 10 4c 8d 77 08 4d 89 f5 49 c1 ed 03 41 0f b6 44 15 00 84 c0 0f 85 1d 01 00 00 45 3b 0e 73 3a <48> 8d 5f 0c 49 89 df 49 c1 ef 03 41 0f b6 04 17 84 c0 0f 85 42 01
RSP: 0018:ffffc9000387f3f8 EFLAGS: 00000287
RAX: 0000000000000000 RBX: ffffc9000387f500 RCX: 0000000080000001
RDX: dffffc0000000000 RSI: ffffffff81c97c13 RDI: ffffc9000387f500
RBP: 1ffff9200070fea2 R08: ffffc9000387f510 R09: 0000000000000006
R10: fffff5200070fe95 R11: 1ffff9200070fe93 R12: ffff888020643b80
R13: 1ffff9200070fea1 R14: ffffc9000387f508 R15: ffffc9000387f448
 arch_stack_walk+0x100/0x140 arch/x86/kernel/stacktrace.c:27
 stack_trace_save+0x98/0xe0 kernel/stacktrace.c:122
 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_slab_alloc+0x9c/0xd0 mm/kasan/common.c:467
 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+0x100/0x290 mm/slub.c:3238
 __d_alloc+0x2a/0x6f0 fs/dcache.c:1749
 d_alloc fs/dcache.c:1828 [inline]
 d_alloc_parallel+0x7b/0x1330 fs/dcache.c:2584
 lookup_open fs/namei.c:3395 [inline]
 open_last_lookups fs/namei.c:3540 [inline]
 path_openat+0x935/0x2f30 fs/namei.c:3747
 do_filp_open+0x1b3/0x3e0 fs/namei.c:3777
 do_sys_openat2+0x142/0x4a0 fs/open.c:1255
 do_sys_open fs/open.c:1271 [inline]
 __do_sys_openat fs/open.c:1287 [inline]
 __se_sys_openat fs/open.c:1282 [inline]
 __x64_sys_openat+0x135/0x160 fs/open.c:1282
 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: 0033:0x7fce2564f407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffe23313660 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007fce25561880 RCX: 00007fce2564f407
RDX: 0000000000080000 RSI: 00007ffe233137d0 RDI: ffffffffffffff9c
RBP: 0000000000000008 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 000055dbe92297f5
R13: 000055dbe92297f5 R14: 0000000000000001 R15: 000055dbe9244140
 </TASK>

Allocated by task 4299:
 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]
 __snd_usbmidi_create+0xda/0x2f90 sound/usb/midi.c:2539
 snd_usb_create_quirk sound/usb/quirks.c:577 [inline]
 create_composite_quirk+0x1ec/0x4e0 sound/usb/quirks.c:48
 usb_audio_probe+0xb72/0x1d50 sound/usb/card.c:885
 usb_probe_interface+0x5a0/0xaf0 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+0x175/0x200 drivers/base/bus.c:429
 __device_attach+0x29b/0x460 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+0x175/0x200 drivers/base/bus.c:429
 __device_attach+0x29b/0x460 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+0xd53/0x1640 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+0x2dd9/0x5560 drivers/usb/core/hub.c:5881
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 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 4299:
 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
 snd_rawmidi_free+0x3b7/0x3e0 sound/core/rawmidi.c:1844
 snd_rawmidi_dev_free+0x34/0x40 sound/core/rawmidi.c:1853
 __snd_device_free+0x1cd/0x2e0 sound/core/device.c:76
 snd_device_free_all+0xcb/0x180 sound/core/device.c:233
 snd_card_do_free sound/core/init.c:588 [inline]
 release_card_device+0x6d/0x1f0 sound/core/init.c:145
 device_release+0x92/0x1c0 drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:713 [inline]
 kobject_release lib/kobject.c:744 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x21d/0x460 lib/kobject.c:761
 snd_card_free_when_closed sound/core/init.c:620 [inline]
 snd_card_free+0x123/0x190 sound/core/init.c:653
 usb_audio_probe+0x187f/0x1d50 sound/usb/card.c:939
 usb_probe_interface+0x5a0/0xaf0 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+0x175/0x200 drivers/base/bus.c:429
 __device_attach+0x29b/0x460 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+0x175/0x200 drivers/base/bus.c:429
 __device_attach+0x29b/0x460 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+0xd53/0x1640 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+0x2dd9/0x5560 drivers/usb/core/hub.c:5881
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

The buggy address belongs to the object at ffff8880792a0800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 72 bytes inside of
 1024-byte region [ffff8880792a0800, ffff8880792a0c00)
The buggy address belongs to the page:
page:ffffea0001e4a800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x792a0
head:ffffea0001e4a800 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 ffffea0001f0d200 0000000200000002 ffff888016841dc0
raw: 0000000000000000 0000000000100010 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 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 154, ts 83151802343, free_ts 83108711250
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x1b77/0x1c60 mm/page_alloc.c:4192
 __alloc_pages+0x1e1/0x470 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+0x81e/0xdf0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 __kmalloc_node_track_caller+0x1fc/0x3a0 mm/slub.c:4963
 kmalloc_reserve net/core/skbuff.c:356 [inline]
 __alloc_skb+0x22c/0x750 net/core/skbuff.c:427
 alloc_skb include/linux/skbuff.h:1162 [inline]
 nlmsg_new include/net/netlink.h:953 [inline]
 inet6_rt_notify+0xdd/0x290 net/ipv6/route.c:6181
 fib6_add_rt2node net/ipv6/ip6_fib.c:1255 [inline]
 fib6_add+0x1d3b/0x3d30 net/ipv6/ip6_fib.c:1484
 __ip6_ins_rt net/ipv6/route.c:1305 [inline]
 ip6_route_add+0x86/0x130 net/ipv6/route.c:3869
 addrconf_add_mroute net/ipv6/addrconf.c:2510 [inline]
 addrconf_add_dev+0x250/0x350 net/ipv6/addrconf.c:2528
 addrconf_dev_config net/ipv6/addrconf.c:3405 [inline]
 addrconf_init_auto_addrs+0x5f8/0xa80 net/ipv6/addrconf.c:3493
 addrconf_notify+0xa6b/0xf00 net/ipv6/addrconf.c:3662
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:391
 netdev_state_change+0xd2/0x140 net/core/dev.c:1440
 linkwatch_do_dev+0x10d/0x160 net/core/link_watch.c:167
 __linkwatch_run_queue+0x4a9/0x7b0 net/core/link_watch.c:213
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+0x94/0x280 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]
 netdevice_queue_work drivers/infiniband/core/roce_gid_mgmt.c:643 [inline]
 netdevice_event+0x324/0x900 drivers/infiniband/core/roce_gid_mgmt.c:802
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:391
 call_netdevice_notifiers_extack net/core/dev.c:2061 [inline]
 call_netdevice_notifiers net/core/dev.c:2075 [inline]
 __dev_notify_flags+0x178/0x2d0 net/core/dev.c:-1
 dev_change_flags+0xe3/0x1a0 net/core/dev.c:8929
 do_setlink+0xc01/0x3980 net/core/rtnetlink.c:2781
 __rtnl_newlink net/core/rtnetlink.c:3452 [inline]
 rtnl_newlink+0x1419/0x17d0 net/core/rtnetlink.c:3574
 rtnetlink_rcv_msg+0x7ff/0xe90 net/core/rtnetlink.c:5684
 netlink_rcv_skb+0x1e0/0x430 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

Memory state around the buggy address:
 ffff8880792a0700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880792a0780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880792a0800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff8880792a0880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880792a0900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
----------------
Code disassembly (best guess):
   0:	84 c0                	test   %al,%al
   2:	0f 85 04 01 00 00    	jne    0x10c
   8:	44 8b 4f 10          	mov    0x10(%rdi),%r9d
   c:	4c 8d 77 08          	lea    0x8(%rdi),%r14
  10:	4d 89 f5             	mov    %r14,%r13
  13:	49 c1 ed 03          	shr    $0x3,%r13
  17:	41 0f b6 44 15 00    	movzbl 0x0(%r13,%rdx,1),%eax
  1d:	84 c0                	test   %al,%al
  1f:	0f 85 1d 01 00 00    	jne    0x142
  25:	45 3b 0e             	cmp    (%r14),%r9d
  28:	73 3a                	jae    0x64
* 2a:	48 8d 5f 0c          	lea    0xc(%rdi),%rbx <-- trapping instruction
  2e:	49 89 df             	mov    %rbx,%r15
  31:	49 c1 ef 03          	shr    $0x3,%r15
  35:	41 0f b6 04 17       	movzbl (%r15,%rdx,1),%eax
  3a:	84 c0                	test   %al,%al
  3c:	0f                   	.byte 0xf
  3d:	85 42 01             	test   %eax,0x1(%rdx)

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/12/11 21:58 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in detach_timer
2025/12/12 01:39 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in detach_timer
* Struck through repros no longer work on HEAD.