general protection fault in encode_rpcb_string

[syzbot <syzbot+4b98281f2401ab849f4b@syzkaller.appspotmail.com>]

Hello,

syzbot hit the following crash on bpf-next commit
5d1365940a68dd57b031b6e3c07d7d451cd69daf (Thu Apr 12 18:09:05 2018 +0000)
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=4b98281f2401ab849f4b

So far this crash happened 2 times on bpf-next.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=6433835633868800
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=6407311794896896
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5861511176126464
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-5947642240294114534
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

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Reported-by: syzbot+4b98281f2401ab849f4b@syzkaller.appspotmail.com
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.

RBP: 00000000006dbc50 R08: 000000002000a000 R09: 0000000000003437
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fe464ffed80
R13: 0030656c69662f2e R14: ffffffffffffffff R15: 0000000000000006
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: 1861 Comm: kworker/u4:4 Not tainted 4.16.0+ #2
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: rpciod rpc_async_schedule
RIP: 0010:strlen+0x1f/0xa0 lib/string.c:479
RSP: 0018:ffff8801cf75f318 EFLAGS: 00010296
RAX: dffffc0000000000 RBX: ffff8801cf68f200 RCX: ffffffff86a8c407
RDX: 0000000000000000 RSI: ffffffff86a84d7b RDI: 0000000000000000
RBP: ffff8801cf75f330 R08: ffff8801cf7de080 R09: ffffed0039ea3d43
R10: ffffed0039ea3d43 R11: ffff8801cf51ea1f R12: 0000000000000000
R13: 0000000002000000 R14: 0000000000000000 R15: ffff8801cf75f3e0
FS:  0000000000000000(0000) GS:ffff8801db000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f64808a4000 CR3: 00000001b566a000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  strlen include/linux/string.h:267 [inline]
  encode_rpcb_string+0x23/0x70 net/sunrpc/rpcb_clnt.c:914
  rpcb_enc_getaddr+0x146/0x1f0 net/sunrpc/rpcb_clnt.c:940
  rpcauth_wrap_req_encode net/sunrpc/auth.c:777 [inline]
  rpcauth_wrap_req+0x1a8/0x230 net/sunrpc/auth.c:791
  rpc_xdr_encode net/sunrpc/clnt.c:1754 [inline]
  call_transmit+0x8a9/0xfe0 net/sunrpc/clnt.c:1949
  __rpc_execute+0x28a/0xfe0 net/sunrpc/sched.c:784
  rpc_async_schedule+0x16/0x20 net/sunrpc/sched.c:857
  process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
  worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
  kthread+0x345/0x410 kernel/kthread.c:238
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:411
Code: 37 ff ff ff 0f 1f 84 00 00 00 00 00 48 b8 00 00 00 00 00 fc ff df 55  
48 89 fa 48 c1 ea 03 48 89 e5 41 54 49 89 fc 53 48 83 ec 08 <0f> b6 04 02  
48 89 fa 83 e2 07 38 d0 7f 04 84 c0 75 4d 41 80 3c
RIP: strlen+0x1f/0xa0 lib/string.c:479 RSP: ffff8801cf75f318
---[ end trace bd76ed0378a56845 ]---


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