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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 ffff8801d925c100 by task syz-executor3/3390

CPU: 1 PID: 3390 Comm: syz-executor3 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
 dentry_unlink_inode+0x4b0/0x5e0 fs/dcache.c:375
 __dentry_kill+0x3b7/0x6d0 fs/dcache.c:572
 shrink_dentry_list+0x3c5/0xcf0 fs/dcache.c:1019
 shrink_dcache_parent+0xba/0x230 fs/dcache.c:1453
 do_one_tree+0x15/0x50 fs/dcache.c:1484
 shrink_dcache_for_umount+0xbb/0x290 fs/dcache.c:1501
 generic_shutdown_super+0xcd/0x540 fs/super.c:424
 kill_anon_super fs/super.c:991 [inline]
 kill_litter_super+0x72/0x90 fs/super.c:1001
 deactivate_locked_super+0x88/0xd0 fs/super.c:312
 deactivate_super+0x141/0x1b0 fs/super.c:343
 cleanup_mnt+0xb2/0x150 fs/namespace.c:1173
 __cleanup_mnt+0x16/0x20 fs/namespace.c:1180
 task_work_run+0x199/0x270 kernel/task_work.c:113
 tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 exit_to_usermode_loop+0x275/0x2f0 arch/x86/entry/common.c:165
 prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
 syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264
 entry_SYSCALL_64_fastpath+0x94/0x96
RIP: 0033:0x4554d7
RSP: 002b:0000000000a2d888 EFLAGS: 00000206 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000063 RCX: 00000000004554d7
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000a2e9f0
RBP: 0000000000a2e9f0 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000009 R11: 0000000000000206 R12: 0000000000b0cce0
R13: 0000000000000000 R14: 000000000004b1de R15: 0000000000000010

Allocated by task 25554:
 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 25554:
 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
 SYSC_unshare kernel/fork.c:2433 [inline]
 SyS_unshare+0x738/0xfa0 kernel/fork.c:2364
 entry_SYSCALL_64_fastpath+0x1f/0x96

The buggy address belongs to the object at ffff8801d925c100
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 0 bytes inside of
 2048-byte region [ffff8801d925c100, ffff8801d925c900)
The buggy address belongs to the page:
page:000000001922f7b6 count:1 mapcount:0 mapping:00000000ad7e8968 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801d925c100 0000000000000000 0000000100000003
raw: ffffea00076414a0 ffffea0006f56420 ffff8801dac00c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801d925c000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801d925c080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801d925c100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff8801d925c180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801d925c200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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