Subject: kernel BUG at net/core/skbuff.c:LINE! (2)

From: syzbot <[email-masked]>
Date: Mon, 15 Jan 2018 12:22:01 -0800

syzkaller has found reproducer for the following crash on  
b625c1ff82272e26c76570d3c7123419ec345b20
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.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by:  
[email-masked]
It will help syzbot understand when the bug is fixed.

skbuff: skb_under_panic: text:000000001d390b3a len:31 put:24  
head:00000000d8ed776f data:000000008150e823 tail:0x7 end:0xc0 dev:gre0
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:104!
invalid opcode: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
    (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 3670 Comm: syzkaller801466 Not tainted  
4.15.0-rc7-next-20180115+ #97
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:skb_panic+0x162/0x1f0 net/core/skbuff.c:100
RSP: 0018:ffff8801d9bd7840 EFLAGS: 00010282
RAX: 0000000000000083 RBX: ffff8801d4f083c0 RCX: 0000000000000000
RDX: 0000000000000083 RSI: 1ffff1003b37ae92 RDI: ffffed003b37aefc
RBP: ffff8801d9bd78a8 R08: 1ffff1003b37ae8a R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff86200de0
R13: ffffffff84a981ad R14: 0000000000000018 R15: ffff8801d2d34180
FS:  00000000019c4880(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000208bc000 CR3: 00000001d9111001 CR4: 00000000001606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  skb_under_panic net/core/skbuff.c:114 [inline]
  skb_push+0xce/0xf0 net/core/skbuff.c:1714
  ipgre_header+0x6d/0x4e0 net/ipv4/ip_gre.c:879
  dev_hard_header include/linux/netdevice.h:2723 [inline]
  pppoe_sendmsg+0x58e/0x8b0 drivers/net/ppp/pppoe.c:890
  sock_sendmsg_nosec net/socket.c:630 [inline]
  sock_sendmsg+0xca/0x110 net/socket.c:640
  sock_write_iter+0x31a/0x5d0 net/socket.c:909
  call_write_iter include/linux/fs.h:1775 [inline]
  do_iter_readv_writev+0x525/0x7f0 fs/read_write.c:653
  do_iter_write+0x154/0x540 fs/read_write.c:932
  vfs_writev+0x18a/0x340 fs/read_write.c:977
  do_writev+0xfc/0x2a0 fs/read_write.c:1012
  SYSC_writev fs/read_write.c:1085 [inline]
  SyS_writev+0x27/0x30 fs/read_write.c:1082
  entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x445009
RSP: 002b:00007ffcab0aa648 EFLAGS: 00000217 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000445009
RDX: 0000000000000001 RSI: 0000000020211f90 RDI: 0000000000000004
RBP: 00007ffcab0aa748 R08: 0000000020adffb2 R09: 0000000020adffb2
R10: 0000000020adffb2 R11: 0000000000000217 R12: 00007ffcab0aa748
R13: 0000000000402510 R14: 0000000000000000 R15: 0000000000000000
Code: 04 01 84 c0 74 04 3c 03 7e 23 8b 8b 80 00 00 00 41 57 48 c7 c7 a0 06  
20 86 52 56 4c 89 ea 41 50 4c 89 e6 45 89 f0 e8 b6 c9 23 fd <0f> 0b 4c 89  
4d b8 4c 89 45 c0 48 89 75 c8 48 89 55 d0 e8 37 42
RIP: skb_panic+0x162/0x1f0 net/core/skbuff.c:100 RSP: ffff8801d9bd7840
---[ end trace 1478d06428a41d88 ]---