Re: net/kcm: double free of kcm inode

[Dmitry Vyukov]

On Thu, Mar 23, 2017 at 7:07 PM, Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
> On Thu, Mar 23, 2017 at 5:09 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>> Hello,
>>
>> I've got the following report while running syzkaller fuzzer. Note the
>> preceding kmem_cache_alloc injected failure, it's most likely the root
>> cause.
>>
>> FAULT_INJECTION: forcing a failure.
>> name failslab, interval 1, probability 0, space 0, times 0
>> CPU: 1 PID: 21839 Comm: syz-executor4 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]
>>  kmem_cache_alloc+0x200/0x720 mm/slab.c:3570
>>  sk_prot_alloc+0x65/0x2a0 net/core/sock.c:1331
>>  sk_alloc+0x8c/0x710 net/core/sock.c:1393
>>  kcm_clone net/kcm/kcmsock.c:1655 [inline]
>>  kcm_ioctl+0xb65/0x17e0 net/kcm/kcmsock.c:1713
>>  sock_do_ioctl+0x65/0xb0 net/socket.c:895
>>  sock_ioctl+0x2c2/0x440 net/socket.c:993
>>  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
>
> I don't know if this patch could fix this bug or not:
> https://patchwork.ozlabs.org/patch/742860/
>
> This is why I don't add your Reported-by. But it could be related.
>
> Thanks.

That patch only handles copy_from_user failures in kcm_ioctl. This
issue is  kmem_cache_alloc failure in  sk_alloc called from kcm_clone.
I would expect that the patch does not fix it.


>> RIP: 0033:0x445b79
>> RSP: 002b:00007f05eb28e858 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 0000000000445b79
>> RDX: 0000000020001000 RSI: 00000000000089e2 RDI: 0000000000000005
>> RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000286 R12: 00000000004a7e31
>> R13: 0000000000000000 R14: 00007f05eb28e618 R15: 00007f05eb28e788
>> ==================================================================
>> BUG: KASAN: use-after-free in __fput+0x6b0/0x7f0 fs/file_table.c:211
>> at addr ffff880037a25670
>> Read of size 2 by task syz-executor4/21839
>> CPU: 1 PID: 21839 Comm: syz-executor4 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:335 [inline]
>>  __asan_report_load2_noabort+0x29/0x30 mm/kasan/report.c:335
>>  __fput+0x6b0/0x7f0 fs/file_table.c:211
>>  ____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:00007f05eb28e858 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
>> RAX: fffffffffffffff4 RBX: 0000000000708000 RCX: 0000000000445b79
>> RDX: 0000000020001000 RSI: 00000000000089e2 RDI: 0000000000000005
>> RBP: 0000000000002170 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000286 R12: 00000000006e0230
>> R13: 00000000000089e2 R14: 0000000020001000 R15: 0000000000000005
>> Object at ffff880037a25640, in cache sock_inode_cache size: 944
>> Allocated:
>> PID = 21839
>>  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
>>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:559
>>  kmem_cache_alloc+0x110/0x720 mm/slab.c:3572
>>  sock_alloc_inode+0x70/0x300 net/socket.c:250
>>  alloc_inode+0x65/0x180 fs/inode.c:207
>>  new_inode_pseudo+0x69/0x190 fs/inode.c:889
>>  sock_alloc+0x41/0x270 net/socket.c:565
>>  kcm_clone net/kcm/kcmsock.c:1634 [inline]
>>  kcm_ioctl+0x990/0x17e0 net/kcm/kcmsock.c:1713
>>  sock_do_ioctl+0x65/0xb0 net/socket.c:895
>>  sock_ioctl+0x2c2/0x440 net/socket.c:993
>>  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 = 21839
>>  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]
>>  kmem_cache_free+0x71/0x240 mm/slab.c:3774
>>  sock_destroy_inode+0x56/0x70 net/socket.c:280
>>  destroy_inode+0x15d/0x200 fs/inode.c:264
>>  evict+0x57e/0x920 fs/inode.c:570
>>  iput_final fs/inode.c:1515 [inline]
>>  iput+0x62b/0xa20 fs/inode.c:1542
>>  sock_release+0x168/0x1e0 net/socket.c:607
>>  sock_close+0x16/0x20 net/socket.c:1061
>>  __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:
>>  ffff880037a25500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>  ffff880037a25580: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
>>>ffff880037a25600: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
>>                                                              ^
>>  ffff880037a25680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>  ffff880037a25700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ==================================================================
>>
>> On commit 093b995e3b55a0ae0670226ddfcb05bfbf0099ae