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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 ffff8801be1292c0 by task syz-executor4/3542

CPU: 1 PID: 3542 Comm: syz-executor4 Not tainted 4.15.0-rc2-mm1+ #39
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:376
 __dentry_kill+0x3b7/0x6d0 fs/dcache.c:573
 shrink_dentry_list+0x3c5/0xcf0 fs/dcache.c:1020
 shrink_dcache_parent+0xba/0x230 fs/dcache.c:1454
 do_one_tree+0x15/0x50 fs/dcache.c:1485
 shrink_dcache_for_umount+0xbb/0x290 fs/dcache.c:1502
 generic_shutdown_super+0xcd/0x540 fs/super.c:424
 kill_anon_super fs/super.c:987 [inline]
 kill_litter_super+0x72/0x90 fs/super.c:997
 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
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0x9bb/0x1ae0 kernel/exit.c:869
 do_group_exit+0x149/0x400 kernel/exit.c:972
 get_signal+0x73f/0x16c0 kernel/signal.c:2337
 do_signal+0x94/0x1ee0 arch/x86/kernel/signal.c:809
 exit_to_usermode_loop+0x258/0x2f0 arch/x86/entry/common.c:161
 prepare_exit_to_usermode+0x2e1/0x340 arch/x86/entry/common.c:195
 retint_user+0x8/0x18
RIP: 0033:0x4087a2
RSP: 002b:0000000000a6f7b0 EFLAGS: 00000216 ORIG_RAX: ffffffffffffff02
RAX: 00007f5e44b55868 RBX: 00007f5e44b55680 RCX: ffffffff818f864a
RDX: 00007f5e44b55868 RSI: 00007f5e44b558c0 RDI: 00007f5e44b55690
RBP: 00007f5e44b55628 R08: ffffffff818f864a R09: 00007f5e44b55688
R10: 0000000000a6f910 R11: 0000000000000206 R12: 00007f5e44b55680
R13: 0000000000000012 R14: 00007f5e44b55628 R15: 0000000000000000

Allocated by task 3383:
 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:3614
 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 3542:
 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:3492 [inline]
 kfree+0xca/0x250 mm/slab.c:3807
 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+0x9b6/0x1ae0 kernel/exit.c:868
 do_group_exit+0x149/0x400 kernel/exit.c:972
 get_signal+0x73f/0x16c0 kernel/signal.c:2337
 do_signal+0x94/0x1ee0 arch/x86/kernel/signal.c:809
 exit_to_usermode_loop+0x258/0x2f0 arch/x86/entry/common.c:161
 prepare_exit_to_usermode+0x2e1/0x340 arch/x86/entry/common.c:195
 retint_user+0x8/0x18

The buggy address belongs to the object at ffff8801be1292c0
 which belongs to the cache kmalloc-2048 of size 2048
The buggy address is located 0 bytes inside of
 2048-byte region [ffff8801be1292c0, ffff8801be129ac0)
The buggy address belongs to the page:
page:0000000045a0da78 count:1 mapcount:0 mapping:00000000e8c9c21f index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801be1281c0 0000000000000000 0000000100000003
raw: ffffea0007092520 ffffea0006f82f20 ffff8801dac00c40 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8801be129180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801be129200: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff8801be129280: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                           ^
 ffff8801be129300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801be129380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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