BUG: KASAN: out-of-bounds in __list_del_entry_valid+0x10b/0x150 lib/list_debug.c:51
Read of size 8 at addr ffff8800391efa80 by task syz-executor3/5431

CPU: 3 PID: 5431 Comm: syz-executor3 Not tainted 4.13.0-next-20170904+ #14
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:52
 print_address_description+0x73/0x250 mm/kasan/report.c:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x24e/0x340 mm/kasan/report.c:409
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
 __list_del_entry_valid+0x10b/0x150 lib/list_debug.c:51
 __list_del_entry include/linux/list.h:116 [inline]
 list_del include/linux/list.h:124 [inline]
 __remove_wait_queue include/linux/wait.h:182 [inline]
 userfaultfd_event_wait_completion+0x519/0x910 fs/userfaultfd.c:591
 dup_fctx fs/userfaultfd.c:687 [inline]
 dup_userfaultfd_complete+0x2de/0x480 fs/userfaultfd.c:695
 dup_mmap kernel/fork.c:726 [inline]
 dup_mm kernel/fork.c:1179 [inline]
 copy_mm+0xe9b/0x1310 kernel/fork.c:1233
 copy_process.part.36+0x1eae/0x4af0 kernel/fork.c:1735
 copy_process kernel/fork.c:1548 [inline]
 _do_fork+0x1ef/0xfe0 kernel/fork.c:2027
 SYSC_clone kernel/fork.c:2137 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2131
 do_syscall_64+0x26c/0x8c0 arch/x86/entry/common.c:287
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x447299
RSP: 002b:00007f78ab587c08 EFLAGS: 00000282 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000447299
RDX: 0000000020d6f000 RSI: 0000000020d42fff RDI: 0000000000000000
RBP: 0000000000708160 R08: 0000000020497000 R09: 0000000000000000
R10: 0000000020a6bffc R11: 0000000000000282 R12: 00000000ffffffff
R13: 0000000000000450 R14: 00000000006e3510 R15: 0000000020d42fff

The buggy address belongs to the page:
page:ffffea0000e47bc0 count:0 mapcount:0 mapping:          (null) index:0x0
flags: 0x100000000000000()
raw: 0100000000000000 0000000000000000 0000000000000000 00000000ffffffff
raw: 0000000000000000 0000000100000001 0000000000000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8800391ef980: 00 00 00 f1 f1 f1 f1 00 f2 f2 f2 f2 f2 f2 f2 00
 ffff8800391efa00: f2 f2 f2 f2 f2 f2 f2 00 f2 f2 f2 f3 f3 f3 f3 00
>ffff8800391efa80: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
                      ^
 ffff8800391efb00: 00 f2 f2 f2 f2 f2 f2 f2 f8 f2 f2 f2 f2 f2 f2 f2
 ffff8800391efb80: 00 f2 f2 f2 f3 f3 f3 f3 00 00 00 00 00 00 00 00
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