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BUG: KASAN: use-after-free in atomic_dec_and_test include/asm-generic/atomic-instrumented.h:259 [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/0x1610 kernel/events/core.c:4446
Write of size 4 at addr ffff88018816e4a0 by task syz-executor5/1801
ip_tunnel: non-ECT from 0.0.0.0 with TOS=0x1

CPU: 1 PID: 1801 Comm: syz-executor5 Not tainted 4.19.0-rc5-next-20180925+ #80
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+0x1d3/0x2c4 lib/dump_stack.c:113
ip_tunnel: non-ECT from 0.0.0.0 with TOS=0x1
 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.9+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:259 [inline]
 put_task_struct include/linux/sched/task.h:95 [inline]
 _free_event+0x49a/0x1610 kernel/events/core.c:4446
 free_event+0xb4/0x180 kernel/events/core.c:4467
 perf_event_release_kernel+0x7d8/0xfa0 kernel/events/core.c:4628
 perf_release+0x37/0x50 kernel/events/core.c:4642
 __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
 tracehook_notify_resume include/linux/tracehook.h:188 [inline]
 exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
 prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
 syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
 do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x411051
Code: 75 14 b8 03 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 34 19 00 00 c3 48 83 ec 08 e8 0a fc ff ff 48 89 04 24 b8 03 00 00 00 0f 05 <48> 8b 3c 24 48 89 c2 e8 53 fc ff ff 48 89 d0 48 83 c4 08 48 3d 01
RSP: 002b:00007ffc83e5cdb0 EFLAGS: 00000293 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000006 RCX: 0000000000411051
RDX: 0000000000000000 RSI: 0000000000730a38 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 00007ffc83e5ccd0 R11: 0000000000000293 R12: 0000000000000000
R13: 0000000000000001 R14: 00000000000004a2 R15: 0000000000000005

Allocated by task 1803:
 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+0x1ff3/0x8780 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 1803:
 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:3756
 free_task_struct kernel/fork.c:163 [inline]
 free_task+0x16e/0x1f0 kernel/fork.c:457
 copy_process+0x1d99/0x8780 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 ffff88018816e480
 which belongs to the cache task_struct(97:syz5) of size 6080
The buggy address is located 32 bytes inside of
 6080-byte region [ffff88018816e480, ffff88018816fc40)
The buggy address belongs to the page:
page:ffffea0006205b80 count:1 mapcount:0 mapping:ffff8801cd09f900 index:0x0 compound_mapcount: 0
flags: 0x2fffc0000010200(slab|head)
raw: 02fffc0000010200 ffffea0006382508 ffff8801cc9d5e48 ffff8801cd09f900
raw: 0000000000000000 ffff88018816e480 0000000100000001 ffff88018a888680
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff88018a888680

Memory state around the buggy address:
 ffff88018816e380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88018816e400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88018816e480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff88018816e500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88018816e580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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