general protection fault in ucma_set_ib_path (2)

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
642e7fd23353e22290e3d51719fcb658dc252342 (Tue Apr 3 04:22:12 2018 +0000)
Merge branch 'syscalls-next' of  
git://git.kernel.org/pub/scm/linux/kernel/git/brodo/linux
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=a67bc93e14682d92fc2f

So far this crash happened 3 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5952837750095872
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=6196262000918528
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=4604792739463168
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-6874493495260513980
compiler: gcc (GCC) 7.1.1 20170620

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Reported-by: syzbot+a67bc93e14682d92fc2f@xxxxxxxxxxxxxxxxxxxxxxxxx
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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: 1 PID: 4443 Comm: syzkaller826180 Not tainted 4.16.0+ #377
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:rdma_cap_opa_ah include/rdma/ib_verbs.h:2773 [inline]
RIP: 0010:ucma_set_ib_path.isra.14+0x26a/0x850  
drivers/infiniband/core/ucma.c:1249
RSP: 0018:ffff8801da4cf7f0 EFLAGS: 00010202
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000029
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: 0000000000000148
RBP: ffff8801da4cf9f0 R08: ffffed003b499f18 R09: ffffffff87b6c65c
R10: 0000000000000002 R11: ffffed003b499f17 R12: ffff8801da4cf8a0
R13: 1ffff1003b499f00 R14: ffff8801d91a11b0 R15: ffff8801d95cadc0
FS:  0000000001ef1880(0000) GS:ffff8801db100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000140 CR3: 00000001d956e001 CR4: 00000000001606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 ucma_set_option_ib drivers/infiniband/core/ucma.c:1272 [inline]
 ucma_set_option_level drivers/infiniband/core/ucma.c:1291 [inline]
 ucma_set_option+0x234/0x520 drivers/infiniband/core/ucma.c:1325
 ucma_write+0x2d6/0x3d0 drivers/infiniband/core/ucma.c:1656
 __vfs_write+0xef/0x970 fs/read_write.c:485
 vfs_write+0x189/0x510 fs/read_write.c:549
 ksys_write+0xef/0x220 fs/read_write.c:598
 SYSC_write fs/read_write.c:610 [inline]
 SyS_write+0x24/0x30 fs/read_write.c:607
 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x440039
RSP: 002b:00007ffdc2f973a8 EFLAGS: 00000217 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440039
RDX: 0000000000000020 RSI: 0000000020001500 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 00000000004002c8 R11: 0000000000000217 R12: 0000000000401960
R13: 00000000004019f0 R14: 0000000000000000 R15: 0000000000000000
Code: 00 00 48 c1 ea 03 80 3c 02 00 0f 85 0d 05 00 00 49 8b 07 48 ba 00 00  
00 00 00 fc ff df 48 8d b8 48 01 00 00 48 89 f9 48 c1 e9 03 <80> 3c 11 00  
0f 85 54 05 00 00 48 c1 e3 04 48 03 98 48 01 00 00
RIP: rdma_cap_opa_ah include/rdma/ib_verbs.h:2773 [inline] RSP:  
ffff8801da4cf7f0
RIP: ucma_set_ib_path.isra.14+0x26a/0x850  
drivers/infiniband/core/ucma.c:1249 RSP: ffff8801da4cf7f0
---[ end trace 96ad186dbb9ca6d0 ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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