Message-ID: <CACT4Y+YiQ47gUDfJeo5A-YWaGE_a84nZY+dntr8sazEb=+bq5g@mail.gmail.com>
Date:   Fri, 2 Nov 2018 16:33:37 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+3ed2626dbfac197ce4d4@...kaller.appspotmail.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>, rafael@...nel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: WARNING: refcount bug in kobject_put

On Fri, Nov 2, 2018 at 4:31 PM, syzbot
<syzbot+3ed2626dbfac197ce4d4@...kaller.appspotmail.com> wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    e468f5c06b5e Merge tag 'compiler-attributes-for-linus-4.20..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17ad34b9400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=9384ecb1c973baed
> dashboard link: https://syzkaller.appspot.com/bug?extid=3ed2626dbfac197ce4d4
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16f6882b400000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1423f983400000

Looks the same as:

https://syzkaller.appspot.com/bug?id=b52dec65c1aaaec9b3893458b13a3304303de321

#syz dup: WARNING in kernfs_get


> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+3ed2626dbfac197ce4d4@...kaller.appspotmail.com
>
> ------------[ cut here ]------------
> refcount_t: underflow; use-after-free.
> WARNING: CPU: 1 PID: 7046 at lib/refcount.c:187
> refcount_sub_and_test_checked+0x2c9/0x310 lib/refcount.c:187
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 7046 Comm: syz-executor895 Not tainted 4.19.0+ #315
> 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
>  panic+0x2ad/0x55c kernel/panic.c:188
>  __warn.cold.8+0x20/0x45 kernel/panic.c:540
>  report_bug+0x254/0x2d0 lib/bug.c:186
>  fixup_bug arch/x86/kernel/traps.c:178 [inline]
>  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
>  do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
>  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
> RIP: 0010:refcount_sub_and_test_checked+0x2c9/0x310 lib/refcount.c:187
> Code: 89 de e8 0a 87 ed fd 84 db 74 07 31 db e9 4d ff ff ff e8 2a 86 ed fd
> 48 c7 c7 20 9d 60 88 c6 05 85 5e 7f 06 01 e8 c7 e6 b6 fd <0f> 0b 31 db e9 2c
> ff ff ff 48 89 cf e8 56 cd 30 fe e9 41 fe ff ff
> RSP: 0018:ffff8801bcdd76a8 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff8165d6c5 RDI: 0000000000000005
> RBP: ffff8801bcdd7790 R08: ffff8801bcb98700 R09: ffffed003b5e5020
> R10: ffffed003b5e5020 R11: ffff8801daf28107 R12: ffff8801d72459b8
> R13: 00000000ffffffff R14: ffff8801bcdd7768 R15: ffff8801bcdfa620
>  refcount_dec_and_test_checked+0x1a/0x20 lib/refcount.c:212
>  kref_put include/linux/kref.h:69 [inline]
>  kobject_put+0x6c/0xe0 lib/kobject.c:708
>  kset_put include/linux/kobject.h:218 [inline]
>  kobj_kset_leave+0x25b/0x3f0 lib/kobject.c:201
>  kobject_del.part.4+0x79/0xf0 lib/kobject.c:596
>  kobject_del+0x1f/0x30 lib/kobject.c:588
>  cleanup_glue_dir.part.19+0x1c2/0x210 drivers/base/core.c:1651
>  cleanup_glue_dir drivers/base/core.c:681 [inline]
>  device_del+0x813/0xb70 drivers/base/core.c:2094
>  hci_unregister_dev+0x3a2/0x990 net/bluetooth/hci_core.c:3355
>  vhci_release+0x76/0xf0 drivers/bluetooth/hci_vhci.c:354
>  __fput+0x385/0xa30 fs/file_table.c:278
>  ____fput+0x15/0x20 fs/file_table.c:309
>  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: 0033:0x400dd0
> Code: 01 f0 ff ff 0f 83 b0 0a 00 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f
> 44 00 00 83 3d fd 18 2d 00 00 75 14 b8 03 00 00 00 0f 05 <48> 3d 01 f0 ff ff
> 0f 83 84 0a 00 00 c3 48 83 ec 08 e8 3a 01 00 00
> RSP: 002b:00007ffc5caf19d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
> RAX: 0000000000000000 RBX: 0000000000000003 RCX: 0000000000400dd0
> RDX: 0000000000000002 RSI: 00000000200000c0 RDI: 0000000000000003
> RBP: 0000000000000000 R08: 00000000004002c8 R09: 00000000004002c8
> R10: 0000000000b0c880 R11: 0000000000000246 R12: 000000000000b95f
> R13: 0000000000401d70 R14: 0000000000000000 R15: 0000000000000000
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>
>
> ---
> 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@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>
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