Re: KASAN: use-after-free Read in vhost_transport_send_pkt

[Dmitry Vyukov]

On Tue, Jul 31, 2018 at 5:43 PM, Stefan Hajnoczi <stefanha@xxxxxxxxx> wrote:
> On Mon, Jul 30, 2018 at 11:15:03AM -0700, syzbot wrote:
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    acb1872577b3 Linux 4.18-rc7
>> git tree:       upstream
>> console output: https://syzkaller.appspot.com/x/log.txt?x=14eb932c400000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=2dc0cd7c2eefb46f
>> dashboard link: https://syzkaller.appspot.com/bug?extid=bd391451452fb0b93039
>> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
>>
>> Unfortunately, I don't have any reproducer for this crash yet.
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+bd391451452fb0b93039@xxxxxxxxxxxxxxxxxxxxxxxxx
>>
>> netlink: 'syz-executor5': attribute type 2 has an invalid length.
>> binder: 28577:28588 transaction failed 29189/-22, size 0-0 line 2852
>> ==================================================================
>> BUG: KASAN: use-after-free in debug_spin_lock_before
>> kernel/locking/spinlock_debug.c:83 [inline]
>> BUG: KASAN: use-after-free in do_raw_spin_lock+0x1c0/0x200
>> kernel/locking/spinlock_debug.c:112
>> Read of size 4 at addr ffff880194d0ec6c by task syz-executor4/28583
>>
>> CPU: 1 PID: 28583 Comm: syz-executor4 Not tainted 4.18.0-rc7+ #169
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> Google 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:77 [inline]
>>  dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
>>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>>  kasan_report_error mm/kasan/report.c:354 [inline]
>>  kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
>>  __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
>>  debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline]
>>  do_raw_spin_lock+0x1c0/0x200 kernel/locking/spinlock_debug.c:112
>>  __raw_spin_lock_bh include/linux/spinlock_api_smp.h:136 [inline]
>>  _raw_spin_lock_bh+0x39/0x40 kernel/locking/spinlock.c:168
>>  spin_lock_bh include/linux/spinlock.h:315 [inline]
>>  vhost_transport_send_pkt+0x12e/0x380 drivers/vhost/vsock.c:223
>
> Thanks for the vsock fuzzing.  This is a useful bug report.

Thanks. But note that syzkaller descriptions for vsock were written by
people who have no idea what is vsock whatsoever:
https://github.com/google/syzkaller/blob/master/sys/linux/socket_vnet.txt
So most likely fuzzing is inefficient and does not test the most
interesting parts of vsock.


> It looks like vhost_vsock_get() needs to involve a reference count so
> that vhost_vsock instances cannot be freed while something is still
> using them.
>
> The reproducer probably involves racing close() with connect().
>
> I am looking into a fix.
>
> Stefan
>
>>  virtio_transport_send_pkt_info+0x31d/0x460
>> net/vmw_vsock/virtio_transport_common.c:190
>>  virtio_transport_connect+0x17c/0x220
>> net/vmw_vsock/virtio_transport_common.c:588
>>  vsock_stream_connect+0x4fb/0xfc0 net/vmw_vsock/af_vsock.c:1197
>>  __sys_connect+0x37d/0x4c0 net/socket.c:1673
>>  __do_sys_connect net/socket.c:1684 [inline]
>>  __se_sys_connect net/socket.c:1681 [inline]
>>  __x64_sys_connect+0x73/0xb0 net/socket.c:1681
>>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> RIP: 0033:0x456a09
>> Code: fd b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
>> 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff
>> 0f 83 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
>> RSP: 002b:00007fa4aee5bc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
>> RAX: ffffffffffffffda RBX: 00007fa4aee5c6d4 RCX: 0000000000456a09
>> RDX: 0000000000000010 RSI: 0000000020000200 RDI: 0000000000000016
>> RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
>> R13: 00000000004ca838 R14: 00000000004c25fb R15: 0000000000000000
>>
>> Allocated by task 28583:
>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>>  set_track mm/kasan/kasan.c:460 [inline]
>>  kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
>>  __do_kmalloc_node mm/slab.c:3682 [inline]
>>  __kmalloc_node+0x47/0x70 mm/slab.c:3689
>>  kmalloc_node include/linux/slab.h:555 [inline]
>>  kvmalloc_node+0xb9/0xf0 mm/util.c:423
>>  kvmalloc include/linux/mm.h:573 [inline]
>>  vhost_vsock_dev_open+0xa2/0x5a0 drivers/vhost/vsock.c:511
>>  misc_open+0x3ca/0x560 drivers/char/misc.c:141
>>  chrdev_open+0x25a/0x770 fs/char_dev.c:417
>>  do_dentry_open+0x818/0xe40 fs/open.c:794
>>  vfs_open+0x139/0x230 fs/open.c:908
>>  do_last fs/namei.c:3399 [inline]
>>  path_openat+0x174a/0x4e10 fs/namei.c:3540
>>  do_filp_open+0x255/0x380 fs/namei.c:3574
>>  do_sys_open+0x584/0x760 fs/open.c:1101
>>  __do_sys_openat fs/open.c:1128 [inline]
>>  __se_sys_openat fs/open.c:1122 [inline]
>>  __x64_sys_openat+0x9d/0x100 fs/open.c:1122
>>  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
>>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> Freed by task 28579:
>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>>  set_track mm/kasan/kasan.c:460 [inline]
>>  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
>>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>>  __cache_free mm/slab.c:3498 [inline]
>>  kfree+0xd9/0x260 mm/slab.c:3813
>>  kvfree+0x61/0x70 mm/util.c:442
>>  vhost_vsock_free drivers/vhost/vsock.c:499 [inline]
>>  vhost_vsock_dev_release+0x4fd/0x750 drivers/vhost/vsock.c:604
>>  __fput+0x355/0x8b0 fs/file_table.c:209
>>  ____fput+0x15/0x20 fs/file_table.c:243
>>  task_work_run+0x1ec/0x2a0 kernel/task_work.c:113
>>  tracehook_notify_resume include/linux/tracehook.h:192 [inline]
>>  exit_to_usermode_loop+0x313/0x370 arch/x86/entry/common.c:166
>>  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>>  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>>  do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
>>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>
>> The buggy address belongs to the object at ffff880194d05f80
>>  which belongs to the cache kmalloc-65536 of size 65536
>> The buggy address is located 36076 bytes inside of
>>  65536-byte region [ffff880194d05f80, ffff880194d15f80)
>> The buggy address belongs to the page:
>> page:ffffea0006534000 count:1 mapcount:0 mapping:ffff8801dac02500 index:0x0
>> compound_mapcount: 0
>> flags: 0x2fffc0000008100(slab|head)
>> raw: 02fffc0000008100 ffffea0006599808 ffff8801dac01e48 ffff8801dac02500
>> raw: 0000000000000000 ffff880194d05f80 0000000100000001 0000000000000000
>> page dumped because: kasan: bad access detected
>>
>> Memory state around the buggy address:
>>  ffff880194d0eb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>  ffff880194d0eb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> > ffff880194d0ec00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>                                                           ^
>>  ffff880194d0ec80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>  ffff880194d0ed00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ==================================================================
>>
>>
>> ---
>> This bug is generated by a bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for more information about syzbot.
>> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>>
>> syzbot will keep track of this bug report. See:
>> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
>> syzbot.
>
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