general protection fault in rdma_join_multicast

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
ce380619fab99036f5e745c7a865b21c59f005f6 (Tue Mar 6 04:31:14 2018 +0000)
Merge tag 'please-pull-ia64_misc' of
git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux

So far this crash happened 6 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+e6aba7...@syzkaller.appspotmail.com
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audit: type=1400 audit(1520377342.565:7): avc: denied { map } for
pid=4277 comm="syzkaller584356" path="/root/syzkaller584356328" dev="sda1"
ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
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: 4279 Comm: syzkaller584356 Not tainted 4.16.0-rc4+ #343
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:rdma_protocol_roce include/rdma/ib_verbs.h:2546 [inline]
RIP: 0010:rdma_join_multicast+0x46d/0x3bb0
drivers/infiniband/core/cma.c:4194
RSP: 0018:ffff8801d3bdf570 EFLAGS: 00010202
RAX: 0000000000000000 RBX: ffff8801d5b30000 RCX: 0000000000000029
RDX: dffffc0000000000 RSI: 0000000000000002 RDI: 0000000000000148
RBP: ffff8801d3bdf870 R08: ffff8801db227fc0 R09: 1ffff1003a77be8c
R10: ffff8801d3bdf120 R11: 0000000000000001 R12: ffff8801afd264c0
R13: ffff8801d5b300ad R14: 0000000000000000 R15: ffff8801afd266c0
FS: 00007fdb9d9e6700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055b03ff56470 CR3: 00000001afddc006 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
ucma_process_join+0x4da/0xa90 drivers/infiniband/core/ucma.c:1369
ucma_join_multicast+0xa5/0x110 drivers/infiniband/core/ucma.c:1429
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: 0033:0x445809
RSP: 002b:00007fdb9d9e5da8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000006dac3c RCX: 0000000000445809
RDX: 00000000000000a0 RSI: 00000000200001c0 RDI: 0000000000000005
RBP: 00000000006dac38 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 006d635f616d6472
R13: 2f646e6162696e69 R14: 666e692f7665642f R15: 0000000000000005
Code: 00 48 c1 ea 03 80 3c 02 00 0f 85 d7 34 00 00 49 8b 04 24 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 f5 35 00 00 49 c1 e6 04 4c 03 b0 48 01 00 00
RIP: rdma_protocol_roce include/rdma/ib_verbs.h:2546 [inline] RSP:
ffff8801d3bdf570
RIP: rdma_join_multicast+0x46d/0x3bb0 drivers/infiniband/core/cma.c:4194
RSP: ffff8801d3bdf570
---[ end trace be927aa3e5eed9d8 ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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