Re: kvm: use-after-free function call in kvm_io_bus_destroy

[David Hildenbrand]

On 23.03.2017 13:33, Dmitry Vyukov wrote:
> Hello,
> 
> I've got the following report while running syzkaller fuzzer on
> 093b995e3b55a0ae0670226ddfcb05bfbf0099ae. Note the preceding injected
> kmalloc failure, most likely it's the root cause.
> 
> 
> FAULT_INJECTION: forcing a failure.
> name failslab, interval 1, probability 0, space 0, times 0
> CPU: 0 PID: 14650 Comm: syz-executor2 Not tainted 4.11.0-rc3+ #364
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:16 [inline]
>  dump_stack+0x1b8/0x28d lib/dump_stack.c:52
>  fail_dump lib/fault-inject.c:45 [inline]
>  should_fail+0x78a/0x870 lib/fault-inject.c:154
>  should_failslab+0xec/0x120 mm/failslab.c:31
>  slab_pre_alloc_hook mm/slab.h:434 [inline]
>  slab_alloc mm/slab.c:3394 [inline]
>  __do_kmalloc mm/slab.c:3734 [inline]
>  __kmalloc+0x220/0x730 mm/slab.c:3745
>  kmalloc include/linux/slab.h:495 [inline]
>  kvm_io_bus_unregister_dev+0x1a2/0x300
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:3594
>  kvm_free_pit+0x58/0x110 arch/x86/kvm/i8254.c:727
>  kvm_arch_sync_events+0x35/0x40 arch/x86/kvm/x86.c:8078
>  kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:727 [inline]
>  kvm_put_kvm+0x27f/0xa70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:761
>  kvm_vm_release+0x42/0x50 arch/x86/kvm/../../../virt/kvm/kvm_main.c:772
>  __fput+0x327/0x7f0 fs/file_table.c:209
>  ____fput+0x15/0x20 fs/file_table.c:245
>  task_work_run+0x1a4/0x270 kernel/task_work.c:116
>  tracehook_notify_resume include/linux/tracehook.h:191 [inline]
>  exit_to_usermode_loop+0x24d/0x2d0 arch/x86/entry/common.c:161
>  prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
>  syscall_return_slowpath+0x3bd/0x460 arch/x86/entry/common.c:260
>  entry_SYSCALL_64_fastpath+0xc0/0xc2
> RIP: 0033:0x445b79
> RSP: 002b:00007f6e094bc858 EFLAGS: 00000292 ORIG_RAX: 0000000000000021
> RAX: 000000000000001c RBX: 0000000000708000 RCX: 0000000000445b79
> RDX: 0000000000000000 RSI: 000000000000001c RDI: 000000000000001b
> RBP: 0000000000000430 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000292 R12: 00000000006de4f0
> R13: 000000000000001c R14: 0000000000000000 R15: 000000000000001b
> ==================================================================
> BUG: KASAN: use-after-free in kvm_io_bus_destroy
> include/kvm/iodev.h:72 [inline] at addr ffff88003bfb7d40
> BUG: KASAN: use-after-free in kvm_destroy_vm
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:733 [inline] at addr
> ffff88003bfb7d40
> BUG: KASAN: use-after-free in kvm_put_kvm+0x932/0xa70
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:761 at addr ffff88003bfb7d40
> Read of size 8 by task syz-executor2/14650
> CPU: 0 PID: 14650 Comm: syz-executor2 Not tainted 4.11.0-rc3+ #364
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:16 [inline]
>  dump_stack+0x1b8/0x28d lib/dump_stack.c:52
>  kasan_object_err+0x1c/0x70 mm/kasan/report.c:166
>  print_address_description mm/kasan/report.c:210 [inline]
>  kasan_report_error mm/kasan/report.c:294 [inline]
>  kasan_report.part.2+0x1be/0x480 mm/kasan/report.c:316
>  kasan_report mm/kasan/report.c:337 [inline]
>  __asan_report_load8_noabort+0x29/0x30 mm/kasan/report.c:337
>  kvm_io_bus_destroy include/kvm/iodev.h:72 [inline]
>  kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:733 [inline]
>  kvm_put_kvm+0x932/0xa70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:761
>  kvm_vm_release+0x42/0x50 arch/x86/kvm/../../../virt/kvm/kvm_main.c:772
>  __fput+0x327/0x7f0 fs/file_table.c:209
>  ____fput+0x15/0x20 fs/file_table.c:245
>  task_work_run+0x1a4/0x270 kernel/task_work.c:116
>  tracehook_notify_resume include/linux/tracehook.h:191 [inline]
>  exit_to_usermode_loop+0x24d/0x2d0 arch/x86/entry/common.c:161
>  prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
>  syscall_return_slowpath+0x3bd/0x460 arch/x86/entry/common.c:260
>  entry_SYSCALL_64_fastpath+0xc0/0xc2
> RIP: 0033:0x445b79
> RSP: 002b:00007f6e094bc858 EFLAGS: 00000292 ORIG_RAX: 0000000000000021
> RAX: 000000000000001c RBX: 0000000000708000 RCX: 0000000000445b79
> RDX: 0000000000000000 RSI: 000000000000001c RDI: 000000000000001b
> RBP: 0000000000000430 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000292 R12: 00000000006de4f0
> R13: 000000000000001c R14: 0000000000000000 R15: 000000000000001b
> Object at ffff88003bfb7d40, in cache kmalloc-512 size: 512
> Allocated:
> PID = 14650
>  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:517
>  set_track mm/kasan/kasan.c:529 [inline]
>  kasan_kmalloc+0xbc/0xf0 mm/kasan/kasan.c:620
>  kmem_cache_alloc_trace+0x11a/0x720 mm/slab.c:3638
>  kmalloc include/linux/slab.h:490 [inline]
>  kzalloc include/linux/slab.h:663 [inline]
>  kvm_create_pit+0xc2/0x8b0 arch/x86/kvm/i8254.c:656
>  kvm_arch_vm_ioctl+0x1339/0x2190 arch/x86/kvm/x86.c:4058
>  kvm_vm_ioctl+0x20f/0x1c60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3113
>  vfs_ioctl fs/ioctl.c:45 [inline]
>  do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
>  SYSC_ioctl fs/ioctl.c:700 [inline]
>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>  entry_SYSCALL_64_fastpath+0x1f/0xc2
> Freed:
> PID = 14650
>  save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:517
>  set_track mm/kasan/kasan.c:529 [inline]
>  kasan_slab_free+0x81/0xc0 mm/kasan/kasan.c:593
>  __cache_free mm/slab.c:3514 [inline]
>  kfree+0xd7/0x250 mm/slab.c:3831
>  kvm_free_pit+0xe0/0x110 arch/x86/kvm/i8254.c:733
>  kvm_arch_sync_events+0x35/0x40 arch/x86/kvm/x86.c:8078
>  kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:727 [inline]
>  kvm_put_kvm+0x27f/0xa70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:761
>  kvm_vm_release+0x42/0x50 arch/x86/kvm/../../../virt/kvm/kvm_main.c:772
>  __fput+0x327/0x7f0 fs/file_table.c:209
>  ____fput+0x15/0x20 fs/file_table.c:245
>  task_work_run+0x1a4/0x270 kernel/task_work.c:116
>  tracehook_notify_resume include/linux/tracehook.h:191 [inline]
>  exit_to_usermode_loop+0x24d/0x2d0 arch/x86/entry/common.c:161
>  prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
>  syscall_return_slowpath+0x3bd/0x460 arch/x86/entry/common.c:260
>  entry_SYSCALL_64_fastpath+0xc0/0xc2
> Memory state around the buggy address:
>  ffff88003bfb7c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>  ffff88003bfb7c80: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc
>> ffff88003bfb7d00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>                                            ^
>  ffff88003bfb7d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>  ffff88003bfb7e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
> 


Looks like nobody is prepared to see kvm_io_bus_unregister_dev() fail.

kvm_free_pit() silently goes ahead and and zappes itself. Actually, I
think nobody even takes care if kvm_io_bus_unregister_dev() fails, so
this is a more general problem. It should never fail. No caller can
handle it.

Will look into this! zyzkaller is magic, thanks Dimitry.

-- 

Thanks,

David