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BUG: KASAN: use-after-free in hlist_add_head include/linux/list.h:787 [inline]
BUG: KASAN: use-after-free in enqueue_timer kernel/time/timer.c:540 [inline]
BUG: KASAN: use-after-free in __internal_add_timer+0x28d/0x490 kernel/time/timer.c:553
Write of size 8 at addr ffff8881c83fb188 by task syz-executor.5/7994

CPU: 1 PID: 7994 Comm: syz-executor.5 Not tainted 5.4.50-syzkaller-00011-g07da2129a868 #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+0x14a/0x1ce lib/dump_stack.c:118
 print_address_description+0x93/0x620 mm/kasan/report.c:374
 __kasan_report+0x16d/0x1e0 mm/kasan/report.c:506
 kasan_report+0x36/0x60 mm/kasan/common.c:634
 hlist_add_head include/linux/list.h:787 [inline]
 enqueue_timer kernel/time/timer.c:540 [inline]
 __internal_add_timer+0x28d/0x490 kernel/time/timer.c:553
 internal_add_timer kernel/time/timer.c:595 [inline]
 __mod_timer+0xbf4/0x1af0 kernel/time/timer.c:1053
 tun_flow_init drivers/net/tun.c:1368 [inline]
 tun_set_iff drivers/net/tun.c:2832 [inline]
 __tun_chr_ioctl+0x35c7/0x4bc0 drivers/net/tun.c:3088
 do_vfs_ioctl+0x770/0x1750 fs/ioctl.c:47
 ksys_ioctl fs/ioctl.c:714 [inline]
 __do_sys_ioctl fs/ioctl.c:721 [inline]
 __se_sys_ioctl fs/ioctl.c:719 [inline]
 __x64_sys_ioctl+0xd4/0x110 fs/ioctl.c:719
 do_syscall_64+0xcb/0x150 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45cba9
Code: 8d b6 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 5b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f762205fc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004f05e0 RCX: 000000000045cba9
RDX: 0000000020000300 RSI: 00000000400454ca RDI: 0000000000000003
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000005b8 R14: 00000000004c88dd R15: 00007f76220606d4

The buggy address belongs to the page:
page:ffffea000720fec0 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x8000000000000000()
raw: 8000000000000000 0000000000000000 ffffea000709ab08 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881c83fb080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881c83fb100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8881c83fb180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff8881c83fb200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff8881c83fb280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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