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BUG: KASAN: use-after-free in __write_once_size include/linux/compiler.h:226 [inline]
BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:762 [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+0x3bd/0x480 kernel/time/timer.c:1238
Write of size 8 at addr ffff8881ad40b1c0 by task syz-executor.4/22351

CPU: 0 PID: 22351 Comm: syz-executor.4 Tainted: G        W         5.4.65-syzkaller-00172-g48ad97696bbb #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+0x1b0/0x21e lib/dump_stack.c:118
 print_address_description+0x96/0x5d0 mm/kasan/report.c:374
 __kasan_report+0x14b/0x1c0 mm/kasan/report.c:506
 kasan_report+0x27/0x50 mm/kasan/common.c:634
 __write_once_size include/linux/compiler.h:226 [inline]
 __hlist_del include/linux/list.h:762 [inline]
 detach_timer kernel/time/timer.c:824 [inline]
 detach_if_pending kernel/time/timer.c:841 [inline]
 try_to_del_timer_sync+0x3bd/0x480 kernel/time/timer.c:1238
 del_timer_sync+0x74/0xe0 kernel/time/timer.c:1377
 tun_flow_uninit drivers/net/tun.c:1374 [inline]
 tun_free_netdev+0x99/0x3a0 drivers/net/tun.c:2307
 netdev_run_todo+0xb6f/0xe00 net/core/dev.c:9360
 tun_detach drivers/net/tun.c:743 [inline]
 tun_chr_close+0xc0/0xd0 drivers/net/tun.c:3461
 __fput+0x27d/0x6c0 fs/file_table.c:280
 task_work_run+0x176/0x1a0 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+0x286/0x2e0 arch/x86/entry/common.c:194
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d5f9
Code: 5d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f679817bc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000002040 RCX: 000000000045d5f9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 000000000118cf70 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007ffc723af39f R14: 00007f679817c9c0 R15: 000000000118cf4c

The buggy address belongs to the page:
page:ffffea0006b502c0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x8000000000000000()
raw: 8000000000000000 0000000000000000 ffffea0006b50288 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881ad40b080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881ad40b100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8881ad40b180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                           ^
 ffff8881ad40b200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881ad40b280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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