Hello,

syzkaller hit the following crash on  
73005e1a35fd67c644b0645c9e4c1efabd0fe62c
git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


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Reported-by: syzbot+114b15f2be420a8886c3@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.

------------[ cut here ]------------
kernel BUG at net/l2tp/l2tp_ppp.c:176!
invalid opcode: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
    (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 3550 Comm: syz-executor3 Not tainted 4.15.0-rc6-next-20180103+  
#87
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:pppol2tp_sock_to_session net/l2tp/l2tp_ppp.c:176 [inline]
RIP: 0010:pppol2tp_sendmsg+0x4fd/0x660 net/l2tp/l2tp_ppp.c:304
RSP: 0018:ffff8801d007f9a0 EFLAGS: 00010293
RAX: ffff8801d0074180 RBX: ffff8801bf4a8ec0 RCX: ffffffff8473da1d
RDX: 0000000000000000 RSI: ffff8801d007fdb0 RDI: ffff8801bf4a92a0
RBP: ffff8801d007fa10 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000003 R11: ffffed003a00feff R12: ffff8801c0e4ab40
R13: 0000000000000000 R14: 00000000000000ec R15: ffff8801ba8fc680
FS:  00007f7a046ca700(0000) GS:ffff8801db500000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004d5878 CR3: 00000001bf7c8005 CR4: 00000000001606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  sock_sendmsg_nosec net/socket.c:628 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:638
  ___sys_sendmsg+0x2f4/0x8c0 net/socket.c:2018
  __sys_sendmmsg+0x159/0x3c0 net/socket.c:2108
  SYSC_sendmmsg net/socket.c:2139 [inline]
  SyS_sendmmsg+0x35/0x60 net/socket.c:2134
  entry_SYSCALL_64_fastpath+0x23/0x9a
RIP: 0033:0x452ac9
RSP: 002b:00007f7a046c9c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 000000000071c010 RCX: 0000000000452ac9
RDX: 0000000000000001 RSI: 0000000020003fc8 RDI: 0000000000000000
RBP: 0000000000000465 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4a18
R13: 00000000ffffffff R14: 00007f7a046ca6d4 R15: 0000000000000006
Code: 0a 35 ea fc 48 8b 7d d0 e8 b1 41 aa fd 84 c0 74 0d e8 f8 34 ea fc 48  
89 df e8 60 35 50 ff 41 bd f7 ff ff ff eb 86 e8 e3 34 ea fc <0f> 0b 41 bd  
95 ff ff ff e9 74 ff ff ff e8 61 16 16 fd e9 8c fb
RIP: pppol2tp_sock_to_session net/l2tp/l2tp_ppp.c:176 [inline] RSP:  
ffff8801d007f9a0
RIP: pppol2tp_sendmsg+0x4fd/0x660 net/l2tp/l2tp_ppp.c:304 RSP:  
ffff8801d007f9a0
---[ end trace 574e41d97d242295 ]---
Kernel panic - not syncing: Fatal exception
Dumping ftrace buffer:
    (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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