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SubjectRe: KASAN: use-after-free Read in vhost_work_queue
syzbot has found a reproducer for the following crash on:

HEAD commit: 46c163a036b4 Add linux-next specific files for 20180921
git tree: linux-next
console output:
kernel config:
dashboard link:
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:

IMPORTANT: if you fix the bug, please add the following tag to the commit:

IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
8021q: adding VLAN 0 to HW filter on device team0
BUG: KASAN: use-after-free in vhost_work_queue+0xc3/0xe0
Read of size 8 at addr ffff8801b05432a8 by task syz-executor0/9644

CPU: 1 PID: 9644 Comm: syz-executor0 Not tainted 4.19.0-rc4-next-20180921+
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+0x1d3/0x2c4 lib/dump_stack.c:113
print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
kasan_report_error mm/kasan/report.c:354 [inline]
kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
__asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
vhost_work_queue+0xc3/0xe0 drivers/vhost/vhost.c:258
vhost_transport_send_pkt+0x28a/0x380 drivers/vhost/vsock.c:227
vsock_stream_connect+0x4ed/0xe40 net/vmw_vsock/af_vsock.c:1200
__sys_connect+0x37d/0x4c0 net/socket.c:1665
__do_sys_connect net/socket.c:1676 [inline]
__se_sys_connect net/socket.c:1673 [inline]
__x64_sys_connect+0x73/0xb0 net/socket.c:1673
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
RIP: 0033:0x457679
Code: 1d 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 eb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f746bbf5c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f746bbf66d4 RCX: 0000000000457679
RDX: 0000000000000010 RSI: 0000000020000200 RDI: 0000000000000009
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004cc658 R14: 00000000004bdcb3 R15: 0000000000000000

Allocated by task 9654:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
kasan_kmalloc+0xc7/0xe0 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:589 [inline]
kvmalloc_node+0xb9/0xf0 mm/util.c:423
kvmalloc include/linux/mm.h:577 [inline]
vhost_vsock_dev_open+0xa2/0x5a0 drivers/vhost/vsock.c:511
misc_open+0x3ca/0x560 drivers/char/misc.c:141
chrdev_open+0x25a/0x710 fs/char_dev.c:417
do_dentry_open+0x499/0x1250 fs/open.c:771
vfs_open+0xa0/0xd0 fs/open.c:880
do_last fs/namei.c:3418 [inline]
path_openat+0x12bc/0x5160 fs/namei.c:3534
do_filp_open+0x255/0x380 fs/namei.c:3564
do_sys_open+0x568/0x700 fs/open.c:1063
__do_sys_openat fs/open.c:1090 [inline]
__se_sys_openat fs/open.c:1084 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1084
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290

Freed by task 9643:
save_stack+0x43/0xd0 mm/kasan/kasan.c:448
set_track mm/kasan/kasan.c:460 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/kasan.c:521
kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
__cache_free mm/slab.c:3498 [inline]
kfree+0xcf/0x230 mm/slab.c:3813
kvfree+0x61/0x70 mm/util.c:452
vhost_vsock_free drivers/vhost/vsock.c:499 [inline]
vhost_vsock_dev_release+0x4f4/0x720 drivers/vhost/vsock.c:604
__fput+0x3bc/0xa70 fs/file_table.c:279
____fput+0x15/0x20 fs/file_table.c:312
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:193 [inline]
exit_to_usermode_loop+0x318/0x380 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

The buggy address belongs to the object at ffff8801b0543200
which belongs to the cache kmalloc-64k of size 65536
The buggy address is located 168 bytes inside of
65536-byte region [ffff8801b0543200, ffff8801b0553200)
The buggy address belongs to the page:
page:ffffea0006c15000 count:1 mapcount:0 mapping:ffff8801da802500 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000010200(slab|head)
raw: 02fffc0000010200 ffffea0006c14808 ffffea0006c15808 ffff8801da802500
raw: 0000000000000000 ffff8801b0543200 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8801b0543180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801b0543200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff8801b0543280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801b0543300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801b0543380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

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