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Subject: Re: [PATCH] Bluetooth: Fix memory leak of hci device
From:   Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <20211012075634.8041-1-weiyongjun1@huawei.com>
Date:   Tue, 12 Oct 2021 17:54:32 +0200
Cc:     linux-bluetooth <linux-bluetooth@vger.kernel.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>
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Message-Id: <3EC78E44-6E60-4B99-B880-2F5CC468C424@holtmann.org>
References: <20211012075634.8041-1-weiyongjun1@huawei.com>
To:     Wei Yongjun <weiyongjun1@huawei.com>
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Hi Wei,

> Fault injection test reported memory leak of hci device as follows:
> 
> unreferenced object 0xffff88800b858000 (size 8192):
>  comm "kworker/0:2", pid 167, jiffies 4294955747 (age 557.148s)
>  hex dump (first 32 bytes):
>    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>    00 00 00 00 00 00 00 00 00 00 00 00 ad 4e ad de  .............N..
>  backtrace:
>    [<0000000070eb1059>] kmem_cache_alloc_trace mm/slub.c:3208
>    [<00000000015eb521>] hci_alloc_dev_priv include/linux/slab.h:591
>    [<00000000dcfc1e21>] bpa10x_probe include/net/bluetooth/hci_core.h:1240
>    [<000000005d3028c7>] usb_probe_interface drivers/usb/core/driver.c:397
>    [<00000000cbac9243>] really_probe drivers/base/dd.c:517
>    [<0000000024cab3f0>] __driver_probe_device drivers/base/dd.c:751
>    [<00000000202135cb>] driver_probe_device drivers/base/dd.c:782
>    [<000000000761f2bc>] __device_attach_driver drivers/base/dd.c:899
>    [<00000000f7d63134>] bus_for_each_drv drivers/base/bus.c:427
>    [<00000000c9551f0b>] __device_attach drivers/base/dd.c:971
>    [<000000007f79bd16>] bus_probe_device drivers/base/bus.c:487
>    [<000000007bb8b95a>] device_add drivers/base/core.c:3364
>    [<000000009564d9ea>] usb_set_configuration drivers/usb/core/message.c:2171
>    [<00000000e4657087>] usb_generic_driver_probe drivers/usb/core/generic.c:239
>    [<0000000071ede518>] usb_probe_device drivers/usb/core/driver.c:294
>    [<00000000cbac9243>] really_probe drivers/base/dd.c:517
> 
> hci_alloc_dev() do not init the device's flag. And hci_free_dev()
> using put_device() to free the memory allocated for this device,
> but it calls just kfree(dev) only in case of HCI_UNREGISTER flag
> is set. So any error handing before hci_register_dev() success
> will cause memory leak.
> 
> To avoid this behaviour we need to set hdev HCI_UNREGISTER flag
> in hci_alloc_dev_priv().
> 
> Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
> 
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index 8a47a3017d61..42410f568e90 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -3876,6 +3876,11 @@ struct hci_dev *hci_alloc_dev_priv(int sizeof_priv)
> 	INIT_DELAYED_WORK(&hdev->cmd_timer, hci_cmd_timeout);
> 	INIT_DELAYED_WORK(&hdev->ncmd_timer, hci_ncmd_timeout);
> 
> +	/* We need to set HCI_UNREGISTER flag to correctly release
> +	 * the device in hci_free_dev()
> +	 */
> +	hci_dev_set_flag(hdev, HCI_UNREGISTER);
> +

I can see the point in the bug report, but I don’t see that the fix is correct. Can you prove that this fix is correct when hci_register_dev is actually called.

Regards

Marcel