Subscription rejected, illegal request
==================================================================
BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:188 [inline]
BUG: KASAN: use-after-free in atomic_read arch/x86/include/asm/atomic.h:27 [inline]
BUG: KASAN: use-after-free in refcount_inc_not_zero+0x16e/0x180 lib/refcount.c:120
Read of size 4 at addr ffff8801be79ae40 by task syz-executor4/9808

CPU: 0 PID: 9808 Comm: syz-executor4 Not tainted 4.15.0-rc4-mm1+ #49
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Subscription rejected, illegal request
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_address_description+0x73/0x250 mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:355 [inline]
 kasan_report+0x23b/0x360 mm/kasan/report.c:413
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:433
 __read_once_size include/linux/compiler.h:188 [inline]
 atomic_read arch/x86/include/asm/atomic.h:27 [inline]
 refcount_inc_not_zero+0x16e/0x180 lib/refcount.c:120
 refcount_inc+0x15/0x50 lib/refcount.c:153
 get_ipc_ns include/linux/ipc_namespace.h:129 [inline]
 __get_ns_from_inode ipc/mqueue.c:110 [inline]
 mqueue_create_attr+0xd8/0x400 ipc/mqueue.c:446
 mqueue_create+0x1e/0x30 ipc/mqueue.c:485
 lookup_open+0x1217/0x1970 fs/namei.c:3218
 do_last fs/namei.c:3309 [inline]
 path_openat+0xd76/0x3530 fs/namei.c:3537
 do_filp_open+0x25b/0x3b0 fs/namei.c:3572
 do_sys_open+0x502/0x6d0 fs/open.c:1059
 SYSC_open fs/open.c:1077 [inline]
 SyS_open fs/open.c:1072 [inline]
 SYSC_creat fs/open.c:1117 [inline]
 SyS_creat+0x27/0x30 fs/open.c:1115
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x452ac9
RSP: 002b:00007f7a744e5c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000055
RAX: ffffffffffffffda RBX: 000000000071bf58 RCX: 0000000000452ac9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020015ff4
RBP: 00000000000003f2 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f2f50
R13: 00000000ffffffff R14: 00007f7a744e66d4 R15: 0000000000000004

Allocated by task 9800:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
 kmem_cache_alloc_trace+0x136/0x750 mm/slab.c:3607
 kmalloc include/linux/slab.h:516 [inline]
 create_ipc_ns ipc/namespace.c:45 [inline]
 copy_ipcs+0x1b3/0x520 ipc/namespace.c:96
 create_new_namespaces+0x278/0x880 kernel/nsproxy.c:87
 unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:206
 SYSC_unshare kernel/fork.c:2421 [inline]
 SyS_unshare+0x653/0xfa0 kernel/fork.c:2371
 entry_SYSCALL_64_fastpath+0x1f/0x96

Freed by task 9800:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:447
 set_track mm/kasan/kasan.c:459 [inline]
 kasan_slab_free+0x71/0xc0 mm/kasan/kasan.c:524
 __cache_free mm/slab.c:3485 [inline]
 kfree+0xd6/0x260 mm/slab.c:3800
 free_ipc_ns ipc/namespace.c:139 [inline]
 put_ipc_ns+0x112/0x150 ipc/namespace.c:164
 free_nsproxy+0xc0/0x1f0 kernel/nsproxy.c:180
 switch_task_namespaces+0x9d/0xc0 kernel/nsproxy.c:229
 SYSC_unshare kernel/fork.c:2440 [inline]
 SyS_unshare+0x738/0xfa0 kernel/fork.c:2371
 entry_SYSCALL_64_fastpath+0x1f/0x96

The buggy address belongs to the object at ffff8801be79ae40
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 0 bytes inside of
 2048-byte region [ffff8801be79ae40, ffff8801be79b640)
The buggy address belongs to the page:
page:ffffea0006f9e680 count:1 mapcount:0 mapping:ffff8801be79a5c0 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801be79a5c0 0000000000000000 0000000100000003
raw: ffffea0006f97e20 ffffea0006f81120 ffff8801dac00c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801be79ad00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801be79ad80: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff8801be79ae00: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                           ^
 ffff8801be79ae80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801be79af00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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