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SubjectKASAN: use-after-free Write in _free_event
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Hello,

syzbot found the following crash on:

HEAD commit: b2d44d145d2a Merge tag '4.18-rc3-smb3fixes' of git://git.s..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=178cf50c400000
kernel config: https://syzkaller.appspot.com/x/.config?x=2ca6c7a31d407f86
dashboard link: https://syzkaller.appspot.com/bug?extid=a24c397a29ad22d86c98
compiler: gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a24c397a29ad22d86c98@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in atomic_dec_and_test
include/asm-generic/atomic-instrumented.h:222 [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+0x48d/0x1440
kernel/events/core.c:4451
Write of size 4 at addr ffff8801999ee2a0 by task syz-executor2/19286

CPU: 1 PID: 19286 Comm: syz-executor2 Not tainted 4.18.0-rc3+ #136
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+0x1c9/0x2b4 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+0x242/0x2fe 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:222 [inline]
put_task_struct include/linux/sched/task.h:95 [inline]
_free_event+0x48d/0x1440 kernel/events/core.c:4451
free_event+0xb4/0x180 kernel/events/core.c:4472
perf_event_release_kernel+0x7d5/0x1050 kernel/events/core.c:4633
perf_release+0x37/0x50 kernel/events/core.c:4647
__fput+0x355/0x8b0 fs/file_table.c:209
____fput+0x15/0x20 fs/file_table.c:243
task_work_run+0x1ec/0x2a0 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0x1b08/0x2750 kernel/exit.c:865
do_group_exit+0x177/0x440 kernel/exit.c:968
get_signal+0x88e/0x1970 kernel/signal.c:2468
do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816
exit_to_usermode_loop+0x2e0/0x370 arch/x86/entry/common.c:162
prepare_exit_to_usermode+0x342/0x3b0 arch/x86/entry/common.c:197
retint_user+0x8/0x18
RIP: 0033: (null)
Code: Bad RIP value.
RSP: 002b:0000000020000048 EFLAGS: 00010217
RAX: 0000000000000000 RBX: 00007f62934726d4 RCX: 0000000000455e29
RDX: 0000000020000100 RSI: 0000000020000040 RDI: 0000000000000000
RBP: 000000000072bea0 R08: 0000000020000080 R09: 0000000000000000
R10: 0000000020000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004bbc2c R14: 00000000004c8f48 R15: 0000000000000000

Allocated by task 19280:
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:779 [inline]
copy_process.part.39+0x16b5/0x7220 kernel/fork.c:1641
copy_process kernel/fork.c:1616 [inline]
_do_fork+0x291/0x12a0 kernel/fork.c:2099
__do_sys_clone kernel/fork.c:2206 [inline]
__se_sys_clone kernel/fork.c:2200 [inline]
__x64_sys_clone+0xbf/0x150 kernel/fork.c:2200
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 19280:
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+0x16e/0x1f0 kernel/fork.c:390
copy_process.part.39+0x15c9/0x7220 kernel/fork.c:2034
copy_process kernel/fork.c:1616 [inline]
_do_fork+0x291/0x12a0 kernel/fork.c:2099
__do_sys_clone kernel/fork.c:2206 [inline]
__se_sys_clone kernel/fork.c:2200 [inline]
__x64_sys_clone+0xbf/0x150 kernel/fork.c:2200
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 ffff8801999ee280
which belongs to the cache task_struct(81:syz2) of size 5952
The buggy address is located 32 bytes inside of
5952-byte region [ffff8801999ee280, ffff8801999ef9c0)
The buggy address belongs to the page:
page:ffffea0006667b80 count:1 mapcount:0 mapping:ffff8801b0bb6300 index:0x0
compound_mapcount: 0
flags: 0x2fffc0000008100(slab|head)
raw: 02fffc0000008100 ffffea00071a0888 ffff8801ab65ce48 ffff8801b0bb6300
raw: 0000000000000000 ffff8801999ee280 0000000100000001 ffff8801acaa4000
page dumped because: kasan: bad access detected
page->mem_cgroup:ffff8801acaa4000

Memory state around the buggy address:
ffff8801999ee180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8801999ee200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff8801999ee280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8801999ee300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8801999ee380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
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syzbot.

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