KMSAN: uninit-value in pppol2tp_connect

KMSAN: uninit-value in pppol2tp_connect

[syzbot]

Hello,

syzbot hit the following crash on  
https://github.com/google/kmsan.git/master commit
a7f95e9c8a95e9fbb388c3999b61a17667cd3bbe (Sat Apr 21 13:50:22 2018 +0000)
kmsan: disable assembly checksums
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=a70ac890b23b1bf29f5c

So far this crash happened 3 times on  
https://github.com/google/kmsan.git/master.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=4946656566968320
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=5395971013869568
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=5936570024591360
Kernel config: https://syzkaller.appspot.com/x/.config?id=328654897048964367
compiler: clang version 7.0.0 (trunk 329391)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a70ac890b23b1bf29f5c@syzkaller.appspotmail.com
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details.
If you forward the report, please keep this part and the footer.

==================================================================
BUG: KMSAN: uninit-value in pppol2tp_connect+0x258/0x1c50  
net/l2tp/l2tp_ppp.c:622
CPU: 1 PID: 4524 Comm: syzkaller735385 Not tainted 4.16.0+ #85
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x185/0x1d0 lib/dump_stack.c:53
  kmsan_report+0x142/0x240 mm/kmsan/kmsan.c:1067
  __msan_warning_32+0x6c/0xb0 mm/kmsan/kmsan_instr.c:683
  pppol2tp_connect+0x258/0x1c50 net/l2tp/l2tp_ppp.c:622
  SYSC_connect+0x41a/0x510 net/socket.c:1639
  SyS_connect+0x54/0x80 net/socket.c:1620
  do_syscall_64+0x309/0x430 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x3d/0xa2
RIP: 0033:0x445559
RSP: 002b:00007f0b96f0ddb8 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00000000006dac24 RCX: 0000000000445559
RDX: 0000000000000000 RSI: 0000000020000200 RDI: 0000000000000003
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffec2b0929f R14: 00007f0b96f0e9c0 R15: 0000000000000001

Local variable description: ----address@SYSC_connect
Variable was created at:
  SYSC_connect+0x6f/0x510 net/socket.c:1622
  SyS_connect+0x54/0x80 net/socket.c:1620
==================================================================


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