Subject: kernel BUG at drivers/vhost/vhost.c:LINE! (2)

From: syzbot <[email-masked]>
Date: Fri, 06 Apr 2018 12:02:01 -0700

Hello,

syzbot hit the following crash on upstream commit
38c23685b273cfb4ccf31a199feccce3bdcb5d83 (Fri Apr 6 04:29:35 2018 +0000)
Merge tag 'armsoc-drivers' of  
git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc
syzbot dashboard link:  
https://syzkaller.appspot.com/bug?extid=65a84dde0214b0387ccd

So far this crash happened 4 times on upstream.
C reproducer: https://syzkaller.appspot.com/x/repro.c?id=6586748079439872
syzkaller reproducer:  
https://syzkaller.appspot.com/x/repro.syz?id=5974272052822016
Raw console output:  
https://syzkaller.appspot.com/x/log.txt?id=6224632407392256
Kernel config:  
https://syzkaller.appspot.com/x/.config?id=-5813481738265533882
compiler: gcc (GCC) 8.0.1 20180301 (experimental)

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. See footer for  
details.
If you forward the report, please keep this part and the footer.

------------[ cut here ]------------
kernel BUG at drivers/vhost/vhost.c:1652!
invalid opcode: 0000 [#1] SMP KASAN
------------[ cut here ]------------
Dumping ftrace buffer:
kernel BUG at drivers/vhost/vhost.c:1652!
    (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 4461 Comm: syzkaller684218 Not tainted 4.16.0+ #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:set_bit_to_user drivers/vhost/vhost.c:1652 [inline]
RIP: 0010:log_write+0x42a/0x4d0 drivers/vhost/vhost.c:1676
RSP: 0018:ffff8801b256f920 EFLAGS: 00010293
RAX: ffff8801adc9e2c0 RBX: dffffc0000000000 RCX: ffffffff85924a0f
RDX: 0000000000000000 RSI: ffffffff85924cea RDI: 0000000000000005
RBP: ffff8801b256fa58 R08: ffff8801adc9e2c0 R09: ffffed003962412d
R10: ffff8801b256fad8 R11: ffff8801cb12096f R12: 0001ffffffffffff
R13: ffffed00364adf36 R14: 0000000000000000 R15: ffff8801b256fa30
FS:  00007fdf24b19700(0000) GS:ffff8801db100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020bf6000 CR3: 00000001ae6a7000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  vhost_update_used_flags+0x3af/0x4a0 drivers/vhost/vhost.c:1723
  vhost_vq_init_access+0x117/0x590 drivers/vhost/vhost.c:1763
  vhost_vsock_start drivers/vhost/vsock.c:446 [inline]
  vhost_vsock_dev_ioctl+0x751/0x920 drivers/vhost/vsock.c:678
  vfs_ioctl fs/ioctl.c:46 [inline]
  file_ioctl fs/ioctl.c:500 [inline]
  do_vfs_ioctl+0x1cf/0x1650 fs/ioctl.c:684
  ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
  SYSC_ioctl fs/ioctl.c:708 [inline]
  SyS_ioctl+0x24/0x30 fs/ioctl.c:706
  do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x4456c9
RSP: 002b:00007fdf24b18da8 EFLAGS: 00000297 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000006dac24 RCX: 00000000004456c9
RDX: 0000000020f82ffc RSI: 000000004004af61 RDI: 000000000000001b
RBP: 00000000006dac20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000297 R12: 6b636f73762d7473
R13: 6f68762f7665642f R14: fffffffffffffffc R15: 0000000000000007
Code: e8 7c 5e e4 fb 4c 89 ef e8 e4 16 06 fc 48 8d 85 58 ff ff ff 48 c1 e8  
03 c6 04 18 f8 e9 46 ff ff ff 45 31 f6 eb 91 e8 56 5e e4 fb <0f> 0b e8 4f  
5e e4 fb 48 c7 c6 a0 a3 24 88 4c 89 ef e8 60 b6 10
RIP: set_bit_to_user drivers/vhost/vhost.c:1652 [inline] RSP:  
ffff8801b256f920
RIP: log_write+0x42a/0x4d0 drivers/vhost/vhost.c:1676 RSP: ffff8801b256f920
invalid opcode: 0000 [#2] SMP KASAN
---[ end trace 0d0ff45aa44d8a23 ]---
Dumping ftrace buffer:
    (ftrace buffer empty)
Modules linked in:

---
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