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BUG: KASAN: use-after-free in __read_once_size include/linux/compiler.h:183 [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 ffff8801ce63ea00 by task syz-executor2/3401

CPU: 1 PID: 3401 Comm: syz-executor2 Not tainted 4.15.0-rc4-next-20171221+ #78
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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:252
 kasan_report_error mm/kasan/report.c:351 [inline]
 kasan_report+0x25b/0x340 mm/kasan/report.c:409
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:429
 __read_once_size include/linux/compiler.h:183 [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]
 get_ns_from_inode ipc/mqueue.c:118 [inline]
 mqueue_evict_inode+0x137/0x9c0 ipc/mqueue.c:402
 evict+0x481/0x920 fs/inode.c:552
 iput_final fs/inode.c:1514 [inline]
 iput+0x7b9/0xaf0 fs/inode.c:1541
 do_unlinkat+0x54b/0x940 fs/namei.c:4065
 SYSC_unlink fs/namei.c:4106 [inline]
 SyS_unlink+0x26/0x30 fs/namei.c:4104
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x452837
RSP: 002b:0000000000a2d888 EFLAGS: 00000206 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 00000000006f65c0 RCX: 0000000000452837
RDX: 0000000000a2d890 RSI: 0000000000a2d920 RDI: 0000000000a2d920
RBP: 0000000000008041 R08: 0000000000000000 R09: 0000000000000012
R10: 0000000000000005 R11: 0000000000000206 R12: 00000000006f6618
R13: 00000000006f6618 R14: 0000000000035a10 R15: 0000000000002710

Allocated by task 7153:
 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:3611
 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:2414 [inline]
 SyS_unshare+0x653/0xfa0 kernel/fork.c:2364
 entry_SYSCALL_64_fastpath+0x1f/0x96

Freed by task 7157:
 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:3489 [inline]
 kfree+0xd6/0x260 mm/slab.c:3804
 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
 exit_task_namespaces+0x17/0x20 kernel/nsproxy.c:234
 do_exit+0x9b6/0x1ad0 kernel/exit.c:868
 do_group_exit+0x149/0x400 kernel/exit.c:972
 SYSC_exit_group kernel/exit.c:983 [inline]
 SyS_exit_group+0x1d/0x20 kernel/exit.c:981
 entry_SYSCALL_64_fastpath+0x1f/0x96

The buggy address belongs to the object at ffff8801ce63ea00
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 0 bytes inside of
 2048-byte region [ffff8801ce63ea00, ffff8801ce63f200)
The buggy address belongs to the page:
page:0000000080d3951a count:1 mapcount:0 mapping:0000000028bdb01f index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801ce63e180 0000000000000000 0000000100000003
raw: ffffea000732e920 ffffea00073783a0 ffff8801dac00c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801ce63e900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801ce63e980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801ce63ea00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8801ce63ea80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801ce63eb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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