general protection fault in mount_fs

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
3e968c9f1401088abc9a19ae6ff571644d37a355 (Wed Apr 4 21:19:24 2018 +0000)
Merge tag 'ext4_for_linus' of  
git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=01ffaf5d9568dd1609f7

C reproducer: https://syzkaller.appspot.com/x/repro.c?id=6269272955289600
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=5190169938362368
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5077254979715072
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=9118669095563550941
compiler: gcc (GCC) 7.1.1 20170620

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Reported-by: syzbot+01ffaf5d9568dd1609f7@xxxxxxxxxxxxxxxxxxxxxxxxx
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hfsplus: failed to load root directory
hfsplus: failed to load root directory
hfsplus: failed to load root directory
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 5704 Comm: syzkaller335224 Not tainted 4.16.0+ #15
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:mount_fs+0x92/0x2d0 fs/super.c:1227
RSP: 0018:ffff8801acc9fad0 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81b2ddaa
RDX: 0000000000000019 RSI: 0000000000000000 RDI: 00000000000000c8
RBP: ffff8801acc9fb00 R08: 1ffff10035993e87 R09: ffffed0035993efc
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff886b29c0
R13: ffff8801c6243000 R14: ffff8801ac942ac0 R15: 0000000000000000
FS:  00007f8ca5272700(0000) GS:ffff8801db100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004c5198 CR3: 00000001af14e000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 vfs_kern_mount.part.26+0xc6/0x4a0 fs/namespace.c:1037
 vfs_kern_mount fs/namespace.c:2514 [inline]
 do_new_mount fs/namespace.c:2517 [inline]
 do_mount+0xea4/0x2b90 fs/namespace.c:2847
 ksys_mount+0xab/0x120 fs/namespace.c:3063
 SYSC_mount fs/namespace.c:3077 [inline]
 SyS_mount+0x39/0x50 fs/namespace.c:3074
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x44a34a
RSP: 002b:00007f8ca5271d38 EFLAGS: 00000297 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000020000318 RCX: 000000000044a34a
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f8ca5271d50
RBP: 00000000006e39c4 R08: 0000000020000140 R09: 000000000000000a
R10: 0000000000000000 R11: 0000000000000297 R12: 0000000000000003
R13: 0000000000000004 R14: 00000000006e39c0 R15: 0073756c70736668
Code: 3d 00 f0 ff ff 48 89 c3 0f 87 eb 01 00 00 e8 66 c6 be ff 48 8d bb c8  
00 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00  
0f 85 08 02 00 00 4c 8b b3 c8 00 00 00 4d 85 f6 0f
RIP: mount_fs+0x92/0x2d0 fs/super.c:1227 RSP: ffff8801acc9fad0
---[ end trace 81f30bb7bca06fe8 ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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