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BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:764 [inline]
BUG: KASAN: use-after-free in detach_timer kernel/time/timer.c:824 [inline]
BUG: KASAN: use-after-free in detach_if_pending kernel/time/timer.c:841 [inline]
BUG: KASAN: use-after-free in try_to_del_timer_sync+0x2b1/0x460 kernel/time/timer.c:1238
Write of size 8 at addr ffff888199a371c8 by task syz-executor.2/2055

CPU: 1 PID: 2055 Comm: syz-executor.2 Not tainted 5.4.114-syzkaller-00371-gaa0556d71ff1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1d8/0x24e lib/dump_stack.c:118
 print_address_description+0x9b/0x650 mm/kasan/report.c:384
 __kasan_report+0x182/0x260 mm/kasan/report.c:516
 kasan_report+0x30/0x60 mm/kasan/common.c:641
 __hlist_del include/linux/list.h:764 [inline]
 detach_timer kernel/time/timer.c:824 [inline]
 detach_if_pending kernel/time/timer.c:841 [inline]
 try_to_del_timer_sync+0x2b1/0x460 kernel/time/timer.c:1238
 del_timer_sync+0x78/0xe0 kernel/time/timer.c:1377
 tun_flow_uninit drivers/net/tun.c:1382 [inline]
 tun_free_netdev+0x99/0x3b0 drivers/net/tun.c:2323
 netdev_run_todo+0xb31/0xda0 net/core/dev.c:9409
 tun_detach drivers/net/tun.c:751 [inline]
 tun_chr_close+0xc0/0xd0 drivers/net/tun.c:3517
 __fput+0x27d/0x6c0 fs/file_table.c:281
 task_work_run+0x186/0x1b0 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop arch/x86/entry/common.c:163 [inline]
 prepare_exit_to_usermode+0x2b0/0x310 arch/x86/entry/common.c:194
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4665f9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd9ce4ad188 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 000000000056bf60 RCX: 00000000004665f9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00000000004bfbb9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000056bf60
R13: 00007ffceead44bf R14: 00007fd9ce4ad300 R15: 0000000000022000

The buggy address belongs to the page:
page:ffffea0006668dc0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x8000000000000000()
raw: 8000000000000000 ffffea0007aaf608 ffffea0006668d88 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888199a37080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888199a37100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888199a37180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff888199a37200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888199a37280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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