Hello,

syzbot hit the following crash on upstream commit
1b88accf6a659c46d5c8e68912896f112bf882bb (Thu Mar 8 01:49:33 2018 +0000)
Merge tag 'for_linus' of  
git://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost

So far this crash happened 2 times on upstream.
C reproducer is attached.
syzkaller reproducer is attached.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

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Reported-by: syzbot+b9336dcb3661363ee088@syzkaller.appspotmail.com
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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: 0 PID: 6876 Comm: syzkaller888997 Not tainted 4.16.0-rc4+ #346
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:rdma_reject+0x37/0x220 drivers/infiniband/core/cma.c:3851
RSP: 0018:ffff8801b50bf8f8 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 1ffff10036a17f29 RCX: ffffffff841bb25f
RDX: 0000000000000078 RSI: ffff8801b50bf970 RDI: 00000000000003c0
RBP: ffff8801b50bf928 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff88613380 R11: 0000000000000000 R12: 0000000000000000
R13: ffff8801b50bfaa8 R14: ffff8801b50bf970 R15: 0000000000000000
FS:  00007f7d987bc700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000006de0f8 CR3: 00000001bf0e0006 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  ucma_reject+0x149/0x220 drivers/infiniband/core/ucma.c:1112
  ucma_write+0x2d6/0x3d0 drivers/infiniband/core/ucma.c:1627
  __vfs_write+0xef/0x970 fs/read_write.c:480
  vfs_write+0x189/0x510 fs/read_write.c:544
  SYSC_write fs/read_write.c:589 [inline]
  SyS_write+0xef/0x220 fs/read_write.c:581
  do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4489a9
RSP: 002b:00007f7d987bbda8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000700024 RCX: 00000000004489a9
RDX: 0000000000000008 RSI: 00000000200003c0 RDI: 0000000000000003
RBP: 0000000000700020 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 006d635f616d6472
R13: 2f646e6162696e69 R14: 666e692f7665642f R15: 0000000000000001
Code: 49 89 ff 53 41 89 d4 49 89 f6 48 83 ec 08 e8 b1 53 55 fd 49 8d bf c0  
03 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 a0 01 00 00 4d 8b af c0 03 00 00 4d 85 ed 0f
RIP: rdma_reject+0x37/0x220 drivers/infiniband/core/cma.c:3851 RSP:  
ffff8801b50bf8f8
---[ end trace edcac9dcf5a05d54 ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
    (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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