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BUG: KASAN: use-after-free in mqueue_get_tree+0x2ac/0x2e0 ipc/mqueue.c:362
Read of size 8 at addr ffff8801cac1bc28 by task syz-executor3/20647

CPU: 1 PID: 20647 Comm: syz-executor3 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
 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
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:00007f5f2cb23c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00007f5f2cb246d4 RCX: 00000000004572d9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000008020000
RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004d7c40 R14: 00000000004caa82 R15: 0000000000000000

Allocated by task 5623:
 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]
 alloc_vfsmnt+0xe9/0x990 fs/namespace.c:183
 vfs_create_mount+0xe7/0x610 fs/namespace.c:3210
 mq_create_mount+0x103/0x190 ipc/mqueue.c:419
 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
 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 9:
 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
 free_vfsmnt+0x6a/0x80 fs/namespace.c:560
 delayed_free_vfsmnt+0x16/0x20 fs/namespace.c:565
 __rcu_reclaim kernel/rcu/rcu.h:240 [inline]
 rcu_do_batch kernel/rcu/tree.c:2437 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2716 [inline]
 rcu_process_callbacks+0x100a/0x1ac0 kernel/rcu/tree.c:2697
 __do_softirq+0x30b/0xb03 kernel/softirq.c:292

The buggy address belongs to the object at ffff8801cac1bc00
 which belongs to the cache mnt_cache of size 432
The buggy address is located 40 bytes inside of
 432-byte region [ffff8801cac1bc00, ffff8801cac1bdb0)
The buggy address belongs to the page:
page:ffffea00072b06c0 count:1 mapcount:0 mapping:ffff8801da972780 index:0xffff8801cac1b600
flags: 0x2fffc0000000100(slab)
raw: 02fffc0000000100 ffffea00075fb848 ffffea000710bc48 ffff8801da972780
raw: ffff8801cac1b600 ffff8801cac1b000 0000000100000005 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801cac1bb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801cac1bb80: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
>ffff8801cac1bc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                  ^
 ffff8801cac1bc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801cac1bd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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