Subject: BUG: unable to handle kernel NULL pointer dereference in neigh_fill_info

From: syzbot <[email-masked]>
Date: Tue, 19 Dec 2017 10:41:00 -0800

Hello,

syzkaller hit the following crash on  
6084b576dca2e898f5c101baef151f7bfdbb606d
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.

Unfortunately, I don't have any reproducer for this bug yet.

netlink: 3 bytes leftover after parsing attributes in process  
`syz-executor5'.
netlink: 3 bytes leftover after parsing attributes in process  
`syz-executor5'.
BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
sock: process `syz-executor4' is using obsolete getsockopt SO_BSDCOMPAT
IP: neigh_fill_info+0xe6/0x460 net/core/neighbour.c:2218
PGD 1dece0067 P4D 1dece0067 PUD 1dc5b9067 PMD 0
Oops: 0000 [#1] SMP
Dumping ftrace buffer:
    (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 25561 Comm: syz-executor5 Not tainted 4.15.0-rc3-next-20171214+  
#67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:neigh_fill_info+0xe6/0x460 net/core/neighbour.c:2218
RSP: 0018:ffffc90000eaf9d0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88021568b000 RCX: ffff88021568b288
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff880215753800
RBP: ffffc90000eafa40 R08: 000000000000000c R09: ffff88020ff500b4
R10: ffffc90000eaf9d8 R11: 0000000000000002 R12: ffff88020ff50098
R13: 0000000093fffff7 R14: 000000000000001c R15: ffff880215753800
FS:  00007f91a7086700(0000) GS:ffff88021fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000008 CR3: 00000001df751000 CR4: 00000000001426f0
DR0: 0000000020000008 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000030602
Call Trace:
  neigh_dump_table net/core/neighbour.c:2350 [inline]
  neigh_dump_info+0x532/0x9d0 net/core/neighbour.c:2438
  netlink_dump+0x14e/0x360 net/netlink/af_netlink.c:2222
  __netlink_dump_start+0x1bb/0x210 net/netlink/af_netlink.c:2319
  netlink_dump_start include/linux/netlink.h:214 [inline]
  rtnetlink_rcv_msg+0x44f/0x5d0 net/core/rtnetlink.c:4485
  netlink_rcv_skb+0x92/0x160 net/netlink/af_netlink.c:2441
  rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4540
  netlink_unicast_kernel net/netlink/af_netlink.c:1308 [inline]
  netlink_unicast+0x1d4/0x290 net/netlink/af_netlink.c:1334
  netlink_sendmsg+0x345/0x470 net/netlink/af_netlink.c:1897
  sock_sendmsg_nosec net/socket.c:636 [inline]
  sock_sendmsg+0x51/0x70 net/socket.c:646
  sock_write_iter+0xa4/0x100 net/socket.c:915
  call_write_iter include/linux/fs.h:1776 [inline]
  new_sync_write fs/read_write.c:469 [inline]
  __vfs_write+0x15b/0x1e0 fs/read_write.c:482
  vfs_write+0xf0/0x230 fs/read_write.c:544
  SYSC_write fs/read_write.c:589 [inline]
  SyS_write+0x57/0xd0 fs/read_write.c:581
  entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x452a39
RSP: 002b:00007f91a7085c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f91a7086700 RCX: 0000000000452a39
RDX: 000000000000001f RSI: 000000002083a000 RDI: 0000000000000017
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 0000000000000000
R13: 0000000000a6f7ff R14: 00007f91a70869c0 R15: 0000000000000000
Code: 14 01 00 00 41 88 44 24 1a 0f b6 83 16 01 00 00 41 88 44 24 1b 48 8b  
83 80 02 00 00 8b 80 08 01 00 00 41 89 44 24 14 48 8b 43 08 <8b> 50 08 e8  
c2 e3 68 ff 85 c0 0f 85 5d 02 00 00 4c 8d 73 28 e8
RIP: neigh_fill_info+0xe6/0x460 net/core/neighbour.c:2218 RSP:  
ffffc90000eaf9d0
CR2: 0000000000000008
---[ end trace fd0910621fa1f590 ]---

---
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