Date:   Tue, 31 Jul 2018 16:43:51 +0100
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     syzbot <syzbot+bd391451452fb0b93039@...kaller.appspotmail.com>
Cc:     jasowang@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, mst@...hat.com,
        netdev@...r.kernel.org, stefanha@...hat.com,
        syzkaller-bugs@...glegroups.com,
        virtualization@...ts.linux-foundation.org
Subject: Re: KASAN: use-after-free Read in vhost_transport_send_pkt

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@...kaller.appspotmail.com
> 
> 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.

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@...glegroups.com.
> 
> 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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