syzbot

BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff836bfee0>] sock_hold include/net/sock.h:584 [inline]
IP: [<ffffffff836bfee0>] l2tp_session_create+0xc60/0x16f0 net/l2tp/l2tp_core.c:1911
PGD 1d4f5b067 [   45.640137] PUD 1c3da1067 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 8875 Comm: syz-executor892 Not tainted 4.9.111-g03c70fe #5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d0728000 task.stack: ffff8801cf210000
RIP: 0010:[<ffffffff836bfee0>]  [<ffffffff836bfee0>] sock_hold include/net/sock.h:584 [inline]
RIP: 0010:[<ffffffff836bfee0>]  [<ffffffff836bfee0>] l2tp_session_create+0xc60/0x16f0 net/l2tp/l2tp_core.c:1911
RSP: 0018:ffff8801cf217ac0  EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8801cfc70780 RCX: 1ffff1003a0e511d
RDX: 1ffff10039ed60d0 RSI: ffff8801d07288c8 RDI: ffff8801cf6b0680
RBP: ffff8801cf217b60 R08: ffff8801d07288e8 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801cf6b0558
R13: 0000000000000000 R14: ffff8801cf6b0500 R15: 0000000000000000
FS:  00007fc0eb908700(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001da0f2000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff836c0157 ffffffff836c11f1 ffff8801cdfa0848 0000000000000000
 ffff8801cf6b0500 ffff8801cfc708d8 ffff8801cf6b0558 ffff8801cfc708d0
 ffff8801cfc70830 ffff8801cf6b0520 ffff8801cdfa0000 0000000000000000
Call Trace:
 [<ffffffff836c5097>] pppol2tp_connect+0x10d7/0x18f0 net/l2tp/l2tp_ppp.c:718
 [<ffffffff83016958>] SYSC_connect+0x1b8/0x300 net/socket.c:1562
 [<ffffffff83019224>] SyS_connect+0x24/0x30 net/socket.c:1543
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f8cd3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 00 00 49 8d be 80 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 7b 09 00 00 49 8b 86 80 01 00 00 <f0> ff 80 80 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 55 d0 
RIP  [<ffffffff836bfee0>] sock_hold include/net/sock.h:584 [inline]
RIP  [<ffffffff836bfee0>] l2tp_session_create+0xc60/0x16f0 net/l2tp/l2tp_core.c:1911
 RSP <ffff8801cf217ac0>
CR2: 0000000000000080
---[ end trace 7cd0db5a47ff901b ]---