linux-kernel - Re: [PATCH v4] bluetooth: hci_h5: fix memory leak in h5

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Date:   Fri, 16 Oct 2020 13:28:23 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Anant Thazhemadam <anant.thazhemadam@...il.com>
Cc:     linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+6ce141c55b2f7aafd1c4@...kaller.appspotmail.com,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] bluetooth: hci_h5: fix memory leak in h5_close

Hi,

On 10/7/20 5:48 AM, Anant Thazhemadam wrote:
> If h5_close is called when !hu->serdev, h5 is directly freed.
> However, h5->rx_skb is not freed, which causes a memory leak.
> 
> Freeing h5->rx_skb fixes this memory leak.
> 
> In case hu->serdev exists, h5->rx_skb is then set to NULL,
> since we do not want to risk a potential NULL pointer 
> dereference.
> 
> Fixes: ce945552fde4 ("Bluetooth: hci_h5: Add support for serdev enumerated devices")
> Reported-by: syzbot+6ce141c55b2f7aafd1c4@...kaller.appspotmail.com
> Tested-by: syzbot+6ce141c55b2f7aafd1c4@...kaller.appspotmail.com
> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@...il.com>h5_close v4
> ---
> Changes in v4:
> 	* Free h5->rx_skb even when hu->serdev
> 	(Suggested by Hans de Goede <hdegoede@...hat.com>)
> 	* If hu->serdev, then assign h5->rx_skb = NULL
> 
> Changes in v3:
> 	* Free h5->rx_skb when !hu->serdev, and fix the memory leak
> 	* Do not incorrectly and unnecessarily call serdev_device_close()
> 
> Changes in v2:
> 	* Fixed the Fixes tag
> 
>  drivers/bluetooth/hci_h5.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/bluetooth/hci_h5.c b/drivers/bluetooth/hci_h5.c
> index e41854e0d79a..39f9553caa5c 100644
> --- a/drivers/bluetooth/hci_h5.c
> +++ b/drivers/bluetooth/hci_h5.c
> @@ -245,11 +245,15 @@ static int h5_close(struct hci_uart *hu)
>  	skb_queue_purge(&h5->rel);
>  	skb_queue_purge(&h5->unrel);
>  
> +	kfree_skb(h5->rx_skb);
> +
>  	if (h5->vnd && h5->vnd->close)
>  		h5->vnd->close(h5);
>  
>  	if (!hu->serdev)
>  		kfree(h5);
> +	else
> +		h5->rx_skb = NULL;

Please just do this unconditionally directly after
the kfree_skb()

So after this comment has been addressed the end result should
look like this:

	skb_queue_purge(&h5->rel);
	skb_queue_purge(&h5->unrel);
	kfree_skb(h5->rx_skb);
	h5->rx_skb = NULL;

	if (h5->vnd && h5->vnd->close)
		h5->vnd->close(h5);

	if (!hu->serdev)
		kfree(h5);
 
 	return 0;

Regards,

Hans