Hello,

syzkaller hit the following crash on  
aae4e7a8bc44722fe70d58920a36916b1043195e
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.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


BUG: KASAN: use-after-free in irq_bypass_register_consumer+0x4f0/0x500  
virt/lib/irqbypass.c:198
Read of size 8 at addr ffff8801cf1d9178 by task syzkaller948360/3420

CPU: 1 PID: 3420 Comm: syzkaller948360 Not tainted 4.13.0-rc4+ #23
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:16 [inline]
  dump_stack+0x194/0x257 lib/dump_stack.c:52
  print_address_description+0x7f/0x260 mm/kasan/report.c:252
  kasan_report_error mm/kasan/report.c:351 [inline]
  kasan_report+0x24e/0x340 mm/kasan/report.c:409
  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
  irq_bypass_register_consumer+0x4f0/0x500 virt/lib/irqbypass.c:198
  kvm_irqfd_assign arch/x86/kvm/../../../virt/kvm/eventfd.c:417 [inline]
  kvm_irqfd+0x137a/0x1d50 arch/x86/kvm/../../../virt/kvm/eventfd.c:572
  kvm_vm_ioctl+0x1079/0x1c40 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3029
  vfs_ioctl fs/ioctl.c:45 [inline]
  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685
  SYSC_ioctl fs/ioctl.c:700 [inline]
  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
  entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x4460d9
RSP: 002b:00007f24ae19adc8 EFLAGS: 00000202 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004460d9
RDX: 000000002000d000 RSI: 000000004020ae76 RDI: 000000000000002b
RBP: 0000000000000086 R08: 00007f24ae19b700 R09: 00007f24ae19b700
R10: 00007f24ae19b700 R11: 0000000000000202 R12: 0000000000000000
R13: 00007ffe1847ef3f R14: 00007f24ae19b9c0 R15: 0000000000000000

Allocated by task 3420:
  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
  set_track mm/kasan/kasan.c:459 [inline]
  kasan_kmalloc+0xaa/0xd0 mm/kasan/kasan.c:551
  kmem_cache_alloc_trace+0x101/0x6f0 mm/slab.c:3627
  kmalloc include/linux/slab.h:493 [inline]
  kzalloc include/linux/slab.h:666 [inline]
  kvm_irqfd_assign arch/x86/kvm/../../../virt/kvm/eventfd.c:296 [inline]
  kvm_irqfd+0x16c/0x1d50 arch/x86/kvm/../../../virt/kvm/eventfd.c:572
  kvm_vm_ioctl+0x1079/0x1c40 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3029
  vfs_ioctl fs/ioctl.c:45 [inline]
  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685
  SYSC_ioctl fs/ioctl.c:700 [inline]
  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
  entry_SYSCALL_64_fastpath+0x1f/0xbe

Freed by task 24:
  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
  set_track mm/kasan/kasan.c:459 [inline]
  kasan_slab_free+0x6e/0xc0 mm/kasan/kasan.c:524
  __cache_free mm/slab.c:3503 [inline]
  kfree+0xd3/0x260 mm/slab.c:3820
  irqfd_shutdown+0x13c/0x1a0 arch/x86/kvm/../../../virt/kvm/eventfd.c:148
  process_one_work+0xbf3/0x1bc0 kernel/workqueue.c:2097
  worker_thread+0x223/0x1860 kernel/workqueue.c:2231
  kthread+0x35e/0x430 kernel/kthread.c:231
  ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:425

The buggy address belongs to the object at ffff8801cf1d9000
  which belongs to the cache kmalloc-512 of size 512
The buggy address is located 376 bytes inside of
  512-byte region [ffff8801cf1d9000, ffff8801cf1d9200)
The buggy address belongs to the page:
page:ffffea000654e778 count:1 mapcount:0 mapping:ffff8801cf1d9000 index:0x0
flags: 0x200000000000100(slab)
raw: 0200000000000100 ffff8801cf1d9000 0000000000000000 0000000100000006
raw: ffffea000654e648 ffffea0006560c48 ffff8801dbc00600
page dumped because: kasan: bad access detected

Memory state around the buggy address:
  ffff8801cf1d9000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801cf1d9080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801cf1d9100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                                 ^
  ffff8801cf1d9180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff8801cf1d9200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
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