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From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Hillf Danton <hdanton@sina.com>,
	Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc: johan.hedberg@gmail.com, linux-bluetooth@vger.kernel.org,
	linux-kernel@vger.kernel.org, luiz.von.dentz@intel.com,
	marcel@holtmann.org, netdev@vger.kernel.org,
	syzkaller-bugs@googlegroups.com,
	syzbot <syzbot+47c6d0efbb7fe2f7a5b8@syzkaller.appspotmail.com>
Subject: Re: [syzbot] general protection fault in hci_release_dev
Date: Mon, 2 Aug 2021 20:02:24 +0900	[thread overview]
Message-ID: <92ae9eb0-0a9c-f73a-57f3-20059d9e4c21@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20210802095403.2100-1-hdanton@sina.com>

Hello.

On 2021/08/02 18:54, Hillf Danton wrote:
> To fix what was addressed in e305509e678b3a4a, defer putting hdev until
> sock is released with sock locked.
> 
> Now only for thoughts.

Thanks for your analysis.

hci_alloc_dev() is called from hci_uart_register_dev() from  hci_uart_set_proto()
 from hci_uart_tty_ioctl(HCIUARTSETPROTO) via ld->ops->ioctl() from tty_ioctl(),
and bt_host_release() is called from device_release() from kobject_put() from
hci_uart_tty_close() from tty_ldisc_kill() from tty_ldisc_release() from
tty_release_struct() from tty_release() from __fput().

The problem is that bt_host_release() is expecting that hci_register_dev()
was called if "struct hci_dev" was allocated by hci_alloc_dev(). In other
words, hci_register_dev() might not be called before bt_host_release().

Then, the fix I think is not to call hci_release_dev() when hci_unregister_dev()
was not called. That is,

 static void bt_host_release(struct device *dev)
 {
        struct hci_dev *hdev = to_hci_dev(dev);
+
+       if (hci_dev_test_flag(hdev, HCI_UNREGISTER))
+               hci_release_dev(hdev);
        kfree(hdev);
        module_put(THIS_MODULE);
 }

and remove kfree(hdev) from hci_release_dev(), for HCI_UNREGISTER flag is
set if hci_unregister_dev() was called before bt_host_release() is called.

  parent reply	other threads:[~2021-08-02 11:03 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-02  4:07 syzbot
     [not found] ` <20210802095403.2100-1-hdanton@sina.com>
2021-08-02 11:02   ` Tetsuo Handa [this message]
2021-08-02 11:38     ` Marcel Holtmann

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