WARNING: kernel stack frame pointer at (ptrval) in syzkaller has bad value (ptrval)

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
5ec83b22a2dd13180762c89698e4e2c2881a423c (Sun Apr 22 19:13:04 2018 +0000)
Merge tag '4.17-rc1-SMB3-CIFS' of git://git.samba.org/sfrench/cifs-2.6
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=e81cee75d9f3fe72ec33

C reproducer: https://syzkaller.appspot.com/x/repro.c?id=4545675937185792
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=6597511200374784
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=4986591978192896
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=1808800213120130118
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e81cee75d9f3fe72ec33@xxxxxxxxxxxxxxxxxxxxxxxxx
It will help syzbot understand when the bug is fixed. See footer for  
details.
If you forward the report, please keep this part and the footer.

        (ptrval): 000000000043fe19 (0x43fe19)
        (ptrval): 0000000000000033 (0x33)
        (ptrval): 0000000000000216 (0x216)
        (ptrval): 00007ffd01ce4bd8 (0x7ffd01ce4bd8)
        (ptrval): 000000000000002b (0x2b)
WARNING: kernel stack frame pointer at         (ptrval) in  
syzkaller601944:4492 has bad value         (ptrval)
WARNING: kernel stack regs at         (ptrval) in syzkaller601944:4492 has  
bad 'bp' value         (ptrval)


---
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See https://goo.gl/tpsmEJ for details.
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