================================================
WARNING: lock held when returning to user space!
4.16.0+ #2 Not tainted
------------------------------------------------
syz-executor0/20697 is leaving the kernel with locks still held!
1 lock held by syz-executor0/20697:
 #0: 00000000fdc832f3 (&lo->lo_ctl_mutex/1){+.+.}, at: lo_ioctl+0x8d/0x1ec0 drivers/block/loop.c:1363
==================================================================
BUG: KASAN: use-after-free in mutex_can_spin_on_owner kernel/locking/mutex.c:479 [inline]
BUG: KASAN: use-after-free in mutex_optimistic_spin kernel/locking/mutex.c:523 [inline]
BUG: KASAN: use-after-free in __mutex_lock_common kernel/locking/mutex.c:759 [inline]
BUG: KASAN: use-after-free in __mutex_lock+0x175f/0x17f0 kernel/locking/mutex.c:893
Read of size 4 at addr ffff8801ad554578 by task syz-executor0/4533

CPU: 1 PID: 4533 Comm: syz-executor0 Not tainted 4.16.0+ #2
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+0x1b9/0x294 lib/dump_stack.c:113
 print_address_description+0x6c/0x20b mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.7+0xac/0x2f5 mm/kasan/report.c:412
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432
 mutex_can_spin_on_owner kernel/locking/mutex.c:479 [inline]
 mutex_optimistic_spin kernel/locking/mutex.c:523 [inline]
 __mutex_lock_common kernel/locking/mutex.c:759 [inline]
 __mutex_lock+0x175f/0x17f0 kernel/locking/mutex.c:893
 mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:923
 lo_ioctl+0x8d/0x1ec0 drivers/block/loop.c:1363
 __blkdev_driver_ioctl block/ioctl.c:303 [inline]
 blkdev_ioctl+0x9b6/0x2020 block/ioctl.c:601
 block_ioctl+0xee/0x130 fs/block_dev.c:1877
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:500 [inline]
 do_vfs_ioctl+0x1cf/0x1650 fs/ioctl.c:684
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
 SYSC_ioctl fs/ioctl.c:708 [inline]
 SyS_ioctl+0x24/0x30 fs/ioctl.c:706
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x455187
RSP: 002b:0000000000a3eab8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000000000f6 RCX: 0000000000455187
RDX: 0000000000000000 RSI: 0000000000004c01 RDI: 0000000000000013
RBP: 0000000000000013 R08: 0000000000000000 R09: 000000000000000a
R10: 0000000000000075 R11: 0000000000000246 R12: 0000000000000013
R13: 0000000000000000 R14: 00000000006fe800 R15: 0000000000001380

Allocated by task 20687:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
 kmem_cache_alloc_node+0x144/0x780 mm/slab.c:3644
 alloc_task_struct_node kernel/fork.c:157 [inline]
 dup_task_struct kernel/fork.c:772 [inline]
 copy_process.part.38+0x16bf/0x6ee0 kernel/fork.c:1633
 copy_process kernel/fork.c:1608 [inline]
 _do_fork+0x291/0x12a0 kernel/fork.c:2089
 SYSC_clone kernel/fork.c:2196 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2190
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7

Freed by task 20744:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0x11a/0x170 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+0x86/0x2d0 mm/slab.c:3756
 free_task_struct kernel/fork.c:162 [inline]
 free_task+0x166/0x1d0 kernel/fork.c:391
 __put_task_struct+0x2d2/0x600 kernel/fork.c:659
 put_task_struct include/linux/sched/task.h:96 [inline]
 delayed_put_task_struct+0x367/0x470 kernel/exit.c:180
 __rcu_reclaim kernel/rcu/rcu.h:178 [inline]
 rcu_do_batch kernel/rcu/tree.c:2675 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2930 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2897 [inline]
 rcu_process_callbacks+0x941/0x15f0 kernel/rcu/tree.c:2914
 __do_softirq+0x2e0/0xaf5 kernel/softirq.c:285

The buggy address belongs to the object at ffff8801ad554540
 which belongs to the cache task_struct(76:syz0) of size 5952
The buggy address is located 56 bytes inside of
 5952-byte region [ffff8801ad554540, ffff8801ad555c80)
The buggy address belongs to the page:
page:ffffea0006b55500 count:1 mapcount:0 mapping:ffff8801ad554540 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffff8801ad554540 0000000000000000 0000000100000001
raw: ffffea000761aaa0 ffffea0007169ea0 ffff8801b2c8f300 ffff8801b29b80c0
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8801b29b80c0

Memory state around the buggy address:
 ffff8801ad554400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801ad554480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801ad554500: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
                                                                ^
 ffff8801ad554580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801ad554600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================