==================================================================
BUG: KASAN: use-after-free in mqueue_get_tree+0x2ac/0x2e0 ipc/mqueue.c:362
Read of size 8 at addr ffff8801d7ae1394 by task syz-executor2/8611

CPU: 1 PID: 8611 Comm: syz-executor2 Not tainted 4.19.0-rc3-next-20180912+ #72
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
 mqueue_get_tree+0x2ac/0x2e0 ipc/mqueue.c:362
 vfs_get_tree+0x1cb/0x5c0 fs/super.c:1787
 mq_create_mount+0xe3/0x190 ipc/mqueue.c:415
 mq_init_ns+0x15a/0x210 ipc/mqueue.c:1621
 create_ipc_ns ipc/namespace.c:58 [inline]
 copy_ipcs+0x3d2/0x580 ipc/namespace.c:84
 create_new_namespaces+0x376/0x900 kernel/nsproxy.c:87
 copy_namespaces+0x3ff/0x4d0 kernel/nsproxy.c:165
 copy_process+0x4e06/0x8780 kernel/fork.c:1916
 _do_fork+0x1cb/0x11d0 kernel/fork.c:2212
 __do_sys_clone kernel/fork.c:2319 [inline]
 __se_sys_clone kernel/fork.c:2313 [inline]
 __x64_sys_clone+0xbf/0x150 kernel/fork.c:2313
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4572d9
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:00007f2ce339cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007f2ce339d6d4 RCX: 00000000004572d9
RDX: 00000000200001c0 RSI: 0000000020000080 RDI: 000000000e828900
RBP: 00000000009300a0 R08: 0000000020000040 R09: 0000000000000000
R10: 0000000020000140 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004cbe68 R14: 00000000004c36da R15: 0000000000000000

Allocated by task 7240:
 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
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
 kmem_cache_alloc+0x12e/0x730 mm/slab.c:3554
 kmem_cache_zalloc include/linux/slab.h:697 [inline]
 net_alloc net/core/net_namespace.c:384 [inline]
 copy_net_ns+0x15b/0x4a0 net/core/net_namespace.c:424
 create_new_namespaces+0x6ad/0x900 kernel/nsproxy.c:107
 unshare_nsproxy_namespaces+0xc3/0x1f0 kernel/nsproxy.c:206
 ksys_unshare+0x79c/0x10b0 kernel/fork.c:2535
 __do_sys_unshare kernel/fork.c:2603 [inline]
 __se_sys_unshare kernel/fork.c:2601 [inline]
 __x64_sys_unshare+0x31/0x40 kernel/fork.c:2601
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 5896:
 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]
 kmem_cache_free+0x83/0x290 mm/slab.c:3756
 net_free net/core/net_namespace.c:400 [inline]
 net_drop_ns.part.14+0x129/0x150 net/core/net_namespace.c:407
 net_drop_ns net/core/net_namespace.c:406 [inline]
 cleanup_net+0x849/0xb10 net/core/net_namespace.c:569
 process_one_work+0xc90/0x1b90 kernel/workqueue.c:2153
 worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
 kthread+0x35a/0x420 kernel/kthread.c:246
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

The buggy address belongs to the object at ffff8801d7ae0080
 which belongs to the cache net_namespace(81:syz1) of size 8576
The buggy address is located 4884 bytes inside of
 8576-byte region [ffff8801d7ae0080, ffff8801d7ae2200)
The buggy address belongs to the page:
page:ffffea00075eb800 count:1 mapcount:0 mapping:ffff8801c8572200 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffffea0005819808 ffffea00057b5908 ffff8801c8572200
raw: 0000000000000000 ffff8801d7ae0080 0000000100000001 ffff8801be134840
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8801be134840

Memory state around the buggy address:
 ffff8801d7ae1280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d7ae1300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8801d7ae1380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff8801d7ae1400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d7ae1480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================