==================================================================
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 ffff8881a55a71c8 by task syz-executor.4/9877

CPU: 0 PID: 9877 Comm: syz-executor.4 Not tainted 5.4.125-syzkaller-00001-g306607c78507 #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:653
 __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:9428
 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: 0033:0x4193fb
Code: 0f 05 48 3d 00 f0 ff ff 77 45 c3 0f 1f 40 00 48 83 ec 18 89 7c 24 0c e8 63 fc ff ff 8b 7c 24 0c 41 89 c0 b8 03 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 89 44 24 0c e8 a1 fc ff ff 8b 44
RSP: 002b:00007ffe92f31090 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000009 RCX: 00000000004193fb
RDX: 00000000005724f8 RSI: 00007f521e294490 RDI: 0000000000000008
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000001b31526f98
R10: 0000000000000564 R11: 0000000000000293 R12: 000000000005e315
R13: 00000000000003e8 R14: 000000000056bf80 R15: 000000000005e2fb

The buggy address belongs to the page:
page:ffffea00069569c0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x8000000000000000()
raw: 8000000000000000 0000000000000000 ffffea0006956988 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x46dc0(GFP_KERNEL|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP|__GFP_ZERO)
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook mm/page_alloc.c:2165 [inline]
 prep_new_page+0x19a/0x380 mm/page_alloc.c:2171
 get_page_from_freelist+0x550/0x8b0 mm/page_alloc.c:3794
 __alloc_pages_nodemask+0x3a2/0x880 mm/page_alloc.c:4855
 __alloc_pages include/linux/gfp.h:503 [inline]
 __alloc_pages_node include/linux/gfp.h:516 [inline]
 alloc_pages_node include/linux/gfp.h:530 [inline]
 kmalloc_order mm/slab_common.c:1341 [inline]
 kmalloc_order_trace+0x2a/0xf0 mm/slab_common.c:1357
 kmalloc_large include/linux/slab.h:485 [inline]
 __kmalloc+0x1ae/0x2f0 mm/slub.c:3892
 __kmalloc_node include/linux/slab.h:422 [inline]
 kmalloc_node include/linux/slab.h:599 [inline]
 kvmalloc_node+0x7e/0xf0 mm/util.c:564
 kvmalloc include/linux/mm.h:758 [inline]
 kvzalloc include/linux/mm.h:766 [inline]
 alloc_netdev_mqs+0x85/0xc60 net/core/dev.c:9580
 tun_set_iff drivers/net/tun.c:2808 [inline]
 __tun_chr_ioctl+0x20c6/0x4d20 drivers/net/tun.c:3143
 do_vfs_ioctl+0x76a/0x1720 fs/ioctl.c:47
 ksys_ioctl fs/ioctl.c:742 [inline]
 __do_sys_ioctl fs/ioctl.c:749 [inline]
 __se_sys_ioctl fs/ioctl.c:747 [inline]
 __x64_sys_ioctl+0xd4/0x110 fs/ioctl.c:747
 do_syscall_64+0xcb/0x1e0 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1176 [inline]
 __free_pages_ok+0xc60/0xd80 mm/page_alloc.c:1438
 free_the_page mm/page_alloc.c:4917 [inline]
 __free_pages+0x8f/0x250 mm/page_alloc.c:4923
 kfree+0x1ee/0x660 mm/slub.c:4058
 device_release+0x70/0x1a0 drivers/base/core.c:1776
 kobject_cleanup+0x1de/0x3c0 lib/kobject.c:708
 netdev_run_todo+0xc0b/0xda0 net/core/dev.c:9439
 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

Memory state around the buggy address:
 ffff8881a55a7080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881a55a7100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8881a55a7180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                                              ^
 ffff8881a55a7200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881a55a7280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================