==================================================================
BUG: KASAN: use-after-free in atomic_dec_and_test include/asm-generic/atomic-instrumented.h:747 [inline]
BUG: KASAN: use-after-free in put_task_struct include/linux/sched/task.h:95 [inline]
BUG: KASAN: use-after-free in _free_event+0x49a/0x1660 kernel/events/core.c:4452
Write of size 4 at addr ffff8801b7fa26a0 by task syz-executor1/11496

CPU: 1 PID: 11496 Comm: syz-executor1 Not tainted 4.20.0-rc1-next-20181109+ #110
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+0x244/0x39d lib/dump_stack.c:113
 print_address_description.cold.7+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.8+0x242/0x309 mm/kasan/report.c:412
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
 kasan_check_write+0x14/0x20 mm/kasan/kasan.c:278
 atomic_dec_and_test include/asm-generic/atomic-instrumented.h:747 [inline]
 put_task_struct include/linux/sched/task.h:95 [inline]
 _free_event+0x49a/0x1660 kernel/events/core.c:4452
 free_event+0xb4/0x180 kernel/events/core.c:4473
 perf_event_release_kernel+0x7d4/0x10e0 kernel/events/core.c:4634
 perf_release+0x37/0x50 kernel/events/core.c:4648
 __fput+0x3bc/0xa70 fs/file_table.c:279
 ____fput+0x15/0x20 fs/file_table.c:312
 task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0x1a48/0x2620 kernel/exit.c:867
 do_group_exit+0x177/0x440 kernel/exit.c:970
 get_signal+0x8a8/0x1970 kernel/signal.c:2517
 do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816
 exit_to_usermode_loop+0x2e5/0x380 arch/x86/entry/common.c:162
 prepare_exit_to_usermode+0x342/0x3b0 arch/x86/entry/common.c:197
 retint_user+0x8/0x18
RIP: 0033:0x457575
Code: 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 48 3d 01 f0 ff ff 0f 83 cb b3 fb ff <c3> 66 2e 0f 1f 84 00 00 00 00 00 48 85 ff 41 57 4d 89 cf 41 56 41
RSP: 002b:0000000020000300 EFLAGS: 00010217
RAX: 0000000000000000 RBX: 0000000000000005 RCX: 0000000000457569
RDX: 0000000020000040 RSI: 0000000020000300 RDI: 0000000000000000
RBP: 000000000072bf00 R08: 0000000020000180 R09: 0000000000000000
R10: 0000000020000280 R11: 0000000000000246 R12: 00007f97549db6d4
R13: 00000000004bdaa6 R14: 00000000004cce30 R15: 00000000ffffffff

Allocated by task 11490:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 kasan_kmalloc+0xc7/0xe0 mm/kasan/kasan.c:553
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
 kmem_cache_alloc_node+0x144/0x730 mm/slab.c:3644
 alloc_task_struct_node kernel/fork.c:158 [inline]
 dup_task_struct kernel/fork.c:843 [inline]
 copy_process+0x2027/0x8790 kernel/fork.c:1751
 _do_fork+0x1cb/0x11c0 kernel/fork.c:2216
 __do_sys_clone kernel/fork.c:2323 [inline]
 __se_sys_clone kernel/fork.c:2317 [inline]
 __x64_sys_clone+0xbf/0x150 kernel/fork.c:2317
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 11490:
 save_stack+0x43/0xd0 mm/kasan/kasan.c:448
 set_track mm/kasan/kasan.c:460 [inline]
 __kasan_slab_free+0x102/0x150 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+0x83/0x290 mm/slab.c:3760
 free_task_struct kernel/fork.c:163 [inline]
 free_task+0x16e/0x1f0 kernel/fork.c:457
 copy_process+0x1dcd/0x8790 kernel/fork.c:2148
 _do_fork+0x1cb/0x11c0 kernel/fork.c:2216
 __do_sys_clone kernel/fork.c:2323 [inline]
 __se_sys_clone kernel/fork.c:2317 [inline]
 __x64_sys_clone+0xbf/0x150 kernel/fork.c:2317
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8801b7fa2680
 which belongs to the cache task_struct(33:syz1) of size 6080
The buggy address is located 32 bytes inside of
 6080-byte region [ffff8801b7fa2680, ffff8801b7fa3e40)
The buggy address belongs to the page:
page:ffffea0006dfe880 count:1 mapcount:0 mapping:ffff8801bc791a80 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000010200(slab|head)
raw: 02fffc0000010200 ffffea00070aab08 ffffea000633e608 ffff8801bc791a80
raw: 0000000000000000 ffff8801b7fa2680 0000000100000001 ffff8801be3186c0
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8801be3186c0

Memory state around the buggy address:
 ffff8801b7fa2580: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8801b7fa2600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8801b7fa2680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff8801b7fa2700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8801b7fa2780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
binder: undelivered TRANSACTION_ERROR: 29189